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Diffstat (limited to 'llvm/lib/Transforms/Utils/SimplifyCFG.cpp')
| -rw-r--r-- | llvm/lib/Transforms/Utils/SimplifyCFG.cpp | 6136 |
1 files changed, 6136 insertions, 0 deletions
diff --git a/llvm/lib/Transforms/Utils/SimplifyCFG.cpp b/llvm/lib/Transforms/Utils/SimplifyCFG.cpp new file mode 100644 index 000000000000..3a5e3293ed4f --- /dev/null +++ b/llvm/lib/Transforms/Utils/SimplifyCFG.cpp @@ -0,0 +1,6136 @@ +//===- SimplifyCFG.cpp - Code to perform CFG simplification ---------------===// +// +// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions. +// See https://llvm.org/LICENSE.txt for license information. +// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception +// +//===----------------------------------------------------------------------===// +// +// Peephole optimize the CFG. +// +//===----------------------------------------------------------------------===// + +#include "llvm/ADT/APInt.h" +#include "llvm/ADT/ArrayRef.h" +#include "llvm/ADT/DenseMap.h" +#include "llvm/ADT/Optional.h" +#include "llvm/ADT/STLExtras.h" +#include "llvm/ADT/SetOperations.h" +#include "llvm/ADT/SetVector.h" +#include "llvm/ADT/SmallPtrSet.h" +#include "llvm/ADT/SmallVector.h" +#include "llvm/ADT/Statistic.h" +#include "llvm/ADT/StringRef.h" +#include "llvm/Analysis/AssumptionCache.h" +#include "llvm/Analysis/ConstantFolding.h" +#include "llvm/Analysis/EHPersonalities.h" +#include "llvm/Analysis/InstructionSimplify.h" +#include "llvm/Analysis/MemorySSA.h" +#include "llvm/Analysis/MemorySSAUpdater.h" +#include "llvm/Analysis/TargetTransformInfo.h" +#include "llvm/Analysis/ValueTracking.h" +#include "llvm/IR/Attributes.h" +#include "llvm/IR/BasicBlock.h" +#include "llvm/IR/CFG.h" +#include "llvm/IR/CallSite.h" +#include "llvm/IR/Constant.h" +#include "llvm/IR/ConstantRange.h" +#include "llvm/IR/Constants.h" +#include "llvm/IR/DataLayout.h" +#include "llvm/IR/DerivedTypes.h" +#include "llvm/IR/Function.h" +#include "llvm/IR/GlobalValue.h" +#include "llvm/IR/GlobalVariable.h" +#include "llvm/IR/IRBuilder.h" +#include "llvm/IR/InstrTypes.h" +#include "llvm/IR/Instruction.h" +#include "llvm/IR/Instructions.h" +#include "llvm/IR/IntrinsicInst.h" +#include "llvm/IR/Intrinsics.h" +#include "llvm/IR/LLVMContext.h" +#include "llvm/IR/MDBuilder.h" +#include "llvm/IR/Metadata.h" +#include "llvm/IR/Module.h" +#include "llvm/IR/NoFolder.h" +#include "llvm/IR/Operator.h" +#include "llvm/IR/PatternMatch.h" +#include "llvm/IR/Type.h" +#include "llvm/IR/Use.h" +#include "llvm/IR/User.h" +#include "llvm/IR/Value.h" +#include "llvm/Support/Casting.h" +#include "llvm/Support/CommandLine.h" +#include "llvm/Support/Debug.h" +#include "llvm/Support/ErrorHandling.h" +#include "llvm/Support/KnownBits.h" +#include "llvm/Support/MathExtras.h" +#include "llvm/Support/raw_ostream.h" +#include "llvm/Transforms/Utils/BasicBlockUtils.h" +#include "llvm/Transforms/Utils/Local.h" +#include "llvm/Transforms/Utils/ValueMapper.h" +#include <algorithm> +#include <cassert> +#include <climits> +#include <cstddef> +#include <cstdint> +#include <iterator> +#include <map> +#include <set> +#include <tuple> +#include <utility> +#include <vector> + +using namespace llvm; +using namespace PatternMatch; + +#define DEBUG_TYPE "simplifycfg" + +// Chosen as 2 so as to be cheap, but still to have enough power to fold +// a select, so the "clamp" idiom (of a min followed by a max) will be caught. +// To catch this, we need to fold a compare and a select, hence '2' being the +// minimum reasonable default. +static cl::opt<unsigned> PHINodeFoldingThreshold( + "phi-node-folding-threshold", cl::Hidden, cl::init(2), + cl::desc( + "Control the amount of phi node folding to perform (default = 2)")); + +static cl::opt<unsigned> TwoEntryPHINodeFoldingThreshold( + "two-entry-phi-node-folding-threshold", cl::Hidden, cl::init(4), + cl::desc("Control the maximal total instruction cost that we are willing " + "to speculatively execute to fold a 2-entry PHI node into a " + "select (default = 4)")); + +static cl::opt<bool> DupRet( + "simplifycfg-dup-ret", cl::Hidden, cl::init(false), + cl::desc("Duplicate return instructions into unconditional branches")); + +static cl::opt<bool> + SinkCommon("simplifycfg-sink-common", cl::Hidden, cl::init(true), + cl::desc("Sink common instructions down to the end block")); + +static cl::opt<bool> HoistCondStores( + "simplifycfg-hoist-cond-stores", cl::Hidden, cl::init(true), + cl::desc("Hoist conditional stores if an unconditional store precedes")); + +static cl::opt<bool> MergeCondStores( + "simplifycfg-merge-cond-stores", cl::Hidden, cl::init(true), + cl::desc("Hoist conditional stores even if an unconditional store does not " + "precede - hoist multiple conditional stores into a single " + "predicated store")); + +static cl::opt<bool> MergeCondStoresAggressively( + "simplifycfg-merge-cond-stores-aggressively", cl::Hidden, cl::init(false), + cl::desc("When merging conditional stores, do so even if the resultant " + "basic blocks are unlikely to be if-converted as a result")); + +static cl::opt<bool> SpeculateOneExpensiveInst( + "speculate-one-expensive-inst", cl::Hidden, cl::init(true), + cl::desc("Allow exactly one expensive instruction to be speculatively " + "executed")); + +static cl::opt<unsigned> MaxSpeculationDepth( + "max-speculation-depth", cl::Hidden, cl::init(10), + cl::desc("Limit maximum recursion depth when calculating costs of " + "speculatively executed instructions")); + +STATISTIC(NumBitMaps, "Number of switch instructions turned into bitmaps"); +STATISTIC(NumLinearMaps, + "Number of switch instructions turned into linear mapping"); +STATISTIC(NumLookupTables, + "Number of switch instructions turned into lookup tables"); +STATISTIC( + NumLookupTablesHoles, + "Number of switch instructions turned into lookup tables (holes checked)"); +STATISTIC(NumTableCmpReuses, "Number of reused switch table lookup compares"); +STATISTIC(NumSinkCommons, + "Number of common instructions sunk down to the end block"); +STATISTIC(NumSpeculations, "Number of speculative executed instructions"); + +namespace { + +// The first field contains the value that the switch produces when a certain +// case group is selected, and the second field is a vector containing the +// cases composing the case group. +using SwitchCaseResultVectorTy = + SmallVector<std::pair<Constant *, SmallVector<ConstantInt *, 4>>, 2>; + +// The first field contains the phi node that generates a result of the switch +// and the second field contains the value generated for a certain case in the +// switch for that PHI. +using SwitchCaseResultsTy = SmallVector<std::pair<PHINode *, Constant *>, 4>; + +/// ValueEqualityComparisonCase - Represents a case of a switch. +struct ValueEqualityComparisonCase { + ConstantInt *Value; + BasicBlock *Dest; + + ValueEqualityComparisonCase(ConstantInt *Value, BasicBlock *Dest) + : Value(Value), Dest(Dest) {} + + bool operator<(ValueEqualityComparisonCase RHS) const { + // Comparing pointers is ok as we only rely on the order for uniquing. + return Value < RHS.Value; + } + + bool operator==(BasicBlock *RHSDest) const { return Dest == RHSDest; } +}; + +class SimplifyCFGOpt { + const TargetTransformInfo &TTI; + const DataLayout &DL; + SmallPtrSetImpl<BasicBlock *> *LoopHeaders; + const SimplifyCFGOptions &Options; + bool Resimplify; + + Value *isValueEqualityComparison(Instruction *TI); + BasicBlock *GetValueEqualityComparisonCases( + Instruction *TI, std::vector<ValueEqualityComparisonCase> &Cases); + bool SimplifyEqualityComparisonWithOnlyPredecessor(Instruction *TI, + BasicBlock *Pred, + IRBuilder<> &Builder); + bool FoldValueComparisonIntoPredecessors(Instruction *TI, + IRBuilder<> &Builder); + + bool SimplifyReturn(ReturnInst *RI, IRBuilder<> &Builder); + bool SimplifyResume(ResumeInst *RI, IRBuilder<> &Builder); + bool SimplifySingleResume(ResumeInst *RI); + bool SimplifyCommonResume(ResumeInst *RI); + bool SimplifyCleanupReturn(CleanupReturnInst *RI); + bool SimplifyUnreachable(UnreachableInst *UI); + bool SimplifySwitch(SwitchInst *SI, IRBuilder<> &Builder); + bool SimplifyIndirectBr(IndirectBrInst *IBI); + bool SimplifyUncondBranch(BranchInst *BI, IRBuilder<> &Builder); + bool SimplifyCondBranch(BranchInst *BI, IRBuilder<> &Builder); + + bool tryToSimplifyUncondBranchWithICmpInIt(ICmpInst *ICI, + IRBuilder<> &Builder); + +public: + SimplifyCFGOpt(const TargetTransformInfo &TTI, const DataLayout &DL, + SmallPtrSetImpl<BasicBlock *> *LoopHeaders, + const SimplifyCFGOptions &Opts) + : TTI(TTI), DL(DL), LoopHeaders(LoopHeaders), Options(Opts) {} + + bool run(BasicBlock *BB); + bool simplifyOnce(BasicBlock *BB); + + // Helper to set Resimplify and return change indication. + bool requestResimplify() { + Resimplify = true; + return true; + } +}; + +} // end anonymous namespace + +/// Return true if it is safe to merge these two +/// terminator instructions together. +static bool +SafeToMergeTerminators(Instruction *SI1, Instruction *SI2, + SmallSetVector<BasicBlock *, 4> *FailBlocks = nullptr) { + if (SI1 == SI2) + return false; // Can't merge with self! + + // It is not safe to merge these two switch instructions if they have a common + // successor, and if that successor has a PHI node, and if *that* PHI node has + // conflicting incoming values from the two switch blocks. + BasicBlock *SI1BB = SI1->getParent(); + BasicBlock *SI2BB = SI2->getParent(); + + SmallPtrSet<BasicBlock *, 16> SI1Succs(succ_begin(SI1BB), succ_end(SI1BB)); + bool Fail = false; + for (BasicBlock *Succ : successors(SI2BB)) + if (SI1Succs.count(Succ)) + for (BasicBlock::iterator BBI = Succ->begin(); isa<PHINode>(BBI); ++BBI) { + PHINode *PN = cast<PHINode>(BBI); + if (PN->getIncomingValueForBlock(SI1BB) != + PN->getIncomingValueForBlock(SI2BB)) { + if (FailBlocks) + FailBlocks->insert(Succ); + Fail = true; + } + } + + return !Fail; +} + +/// Return true if it is safe and profitable to merge these two terminator +/// instructions together, where SI1 is an unconditional branch. PhiNodes will +/// store all PHI nodes in common successors. +static bool +isProfitableToFoldUnconditional(BranchInst *SI1, BranchInst *SI2, + Instruction *Cond, + SmallVectorImpl<PHINode *> &PhiNodes) { + if (SI1 == SI2) + return false; // Can't merge with self! + assert(SI1->isUnconditional() && SI2->isConditional()); + + // We fold the unconditional branch if we can easily update all PHI nodes in + // common successors: + // 1> We have a constant incoming value for the conditional branch; + // 2> We have "Cond" as the incoming value for the unconditional branch; + // 3> SI2->getCondition() and Cond have same operands. + CmpInst *Ci2 = dyn_cast<CmpInst>(SI2->getCondition()); + if (!Ci2) + return false; + if (!(Cond->getOperand(0) == Ci2->getOperand(0) && + Cond->getOperand(1) == Ci2->getOperand(1)) && + !(Cond->getOperand(0) == Ci2->getOperand(1) && + Cond->getOperand(1) == Ci2->getOperand(0))) + return false; + + BasicBlock *SI1BB = SI1->getParent(); + BasicBlock *SI2BB = SI2->getParent(); + SmallPtrSet<BasicBlock *, 16> SI1Succs(succ_begin(SI1BB), succ_end(SI1BB)); + for (BasicBlock *Succ : successors(SI2BB)) + if (SI1Succs.count(Succ)) + for (BasicBlock::iterator BBI = Succ->begin(); isa<PHINode>(BBI); ++BBI) { + PHINode *PN = cast<PHINode>(BBI); + if (PN->getIncomingValueForBlock(SI1BB) != Cond || + !isa<ConstantInt>(PN->getIncomingValueForBlock(SI2BB))) + return false; + PhiNodes.push_back(PN); + } + return true; +} + +/// Update PHI nodes in Succ to indicate that there will now be entries in it +/// from the 'NewPred' block. The values that will be flowing into the PHI nodes +/// will be the same as those coming in from ExistPred, an existing predecessor +/// of Succ. +static void AddPredecessorToBlock(BasicBlock *Succ, BasicBlock *NewPred, + BasicBlock *ExistPred, + MemorySSAUpdater *MSSAU = nullptr) { + for (PHINode &PN : Succ->phis()) + PN.addIncoming(PN.getIncomingValueForBlock(ExistPred), NewPred); + if (MSSAU) + if (auto *MPhi = MSSAU->getMemorySSA()->getMemoryAccess(Succ)) + MPhi->addIncoming(MPhi->getIncomingValueForBlock(ExistPred), NewPred); +} + +/// Compute an abstract "cost" of speculating the given instruction, +/// which is assumed to be safe to speculate. TCC_Free means cheap, +/// TCC_Basic means less cheap, and TCC_Expensive means prohibitively +/// expensive. +static unsigned ComputeSpeculationCost(const User *I, + const TargetTransformInfo &TTI) { + assert(isSafeToSpeculativelyExecute(I) && + "Instruction is not safe to speculatively execute!"); + return TTI.getUserCost(I); +} + +/// If we have a merge point of an "if condition" as accepted above, +/// return true if the specified value dominates the block. We +/// don't handle the true generality of domination here, just a special case +/// which works well enough for us. +/// +/// If AggressiveInsts is non-null, and if V does not dominate BB, we check to +/// see if V (which must be an instruction) and its recursive operands +/// that do not dominate BB have a combined cost lower than CostRemaining and +/// are non-trapping. If both are true, the instruction is inserted into the +/// set and true is returned. +/// +/// The cost for most non-trapping instructions is defined as 1 except for +/// Select whose cost is 2. +/// +/// After this function returns, CostRemaining is decreased by the cost of +/// V plus its non-dominating operands. If that cost is greater than +/// CostRemaining, false is returned and CostRemaining is undefined. +static bool DominatesMergePoint(Value *V, BasicBlock *BB, + SmallPtrSetImpl<Instruction *> &AggressiveInsts, + int &BudgetRemaining, + const TargetTransformInfo &TTI, + unsigned Depth = 0) { + // It is possible to hit a zero-cost cycle (phi/gep instructions for example), + // so limit the recursion depth. + // TODO: While this recursion limit does prevent pathological behavior, it + // would be better to track visited instructions to avoid cycles. + if (Depth == MaxSpeculationDepth) + return false; + + Instruction *I = dyn_cast<Instruction>(V); + if (!I) { + // Non-instructions all dominate instructions, but not all constantexprs + // can be executed unconditionally. + if (ConstantExpr *C = dyn_cast<ConstantExpr>(V)) + if (C->canTrap()) + return false; + return true; + } + BasicBlock *PBB = I->getParent(); + + // We don't want to allow weird loops that might have the "if condition" in + // the bottom of this block. + if (PBB == BB) + return false; + + // If this instruction is defined in a block that contains an unconditional + // branch to BB, then it must be in the 'conditional' part of the "if + // statement". If not, it definitely dominates the region. + BranchInst *BI = dyn_cast<BranchInst>(PBB->getTerminator()); + if (!BI || BI->isConditional() || BI->getSuccessor(0) != BB) + return true; + + // If we have seen this instruction before, don't count it again. + if (AggressiveInsts.count(I)) + return true; + + // Okay, it looks like the instruction IS in the "condition". Check to + // see if it's a cheap instruction to unconditionally compute, and if it + // only uses stuff defined outside of the condition. If so, hoist it out. + if (!isSafeToSpeculativelyExecute(I)) + return false; + + BudgetRemaining -= ComputeSpeculationCost(I, TTI); + + // Allow exactly one instruction to be speculated regardless of its cost + // (as long as it is safe to do so). + // This is intended to flatten the CFG even if the instruction is a division + // or other expensive operation. The speculation of an expensive instruction + // is expected to be undone in CodeGenPrepare if the speculation has not + // enabled further IR optimizations. + if (BudgetRemaining < 0 && + (!SpeculateOneExpensiveInst || !AggressiveInsts.empty() || Depth > 0)) + return false; + + // Okay, we can only really hoist these out if their operands do + // not take us over the cost threshold. + for (User::op_iterator i = I->op_begin(), e = I->op_end(); i != e; ++i) + if (!DominatesMergePoint(*i, BB, AggressiveInsts, BudgetRemaining, TTI, + Depth + 1)) + return false; + // Okay, it's safe to do this! Remember this instruction. + AggressiveInsts.insert(I); + return true; +} + +/// Extract ConstantInt from value, looking through IntToPtr +/// and PointerNullValue. Return NULL if value is not a constant int. +static ConstantInt *GetConstantInt(Value *V, const DataLayout &DL) { + // Normal constant int. + ConstantInt *CI = dyn_cast<ConstantInt>(V); + if (CI || !isa<Constant>(V) || !V->getType()->isPointerTy()) + return CI; + + // This is some kind of pointer constant. Turn it into a pointer-sized + // ConstantInt if possible. + IntegerType *PtrTy = cast<IntegerType>(DL.getIntPtrType(V->getType())); + + // Null pointer means 0, see SelectionDAGBuilder::getValue(const Value*). + if (isa<ConstantPointerNull>(V)) + return ConstantInt::get(PtrTy, 0); + + // IntToPtr const int. + if (ConstantExpr *CE = dyn_cast<ConstantExpr>(V)) + if (CE->getOpcode() == Instruction::IntToPtr) + if (ConstantInt *CI = dyn_cast<ConstantInt>(CE->getOperand(0))) { + // The constant is very likely to have the right type already. + if (CI->getType() == PtrTy) + return CI; + else + return cast<ConstantInt>( + ConstantExpr::getIntegerCast(CI, PtrTy, /*isSigned=*/false)); + } + return nullptr; +} + +namespace { + +/// Given a chain of or (||) or and (&&) comparison of a value against a +/// constant, this will try to recover the information required for a switch +/// structure. +/// It will depth-first traverse the chain of comparison, seeking for patterns +/// like %a == 12 or %a < 4 and combine them to produce a set of integer +/// representing the different cases for the switch. +/// Note that if the chain is composed of '||' it will build the set of elements +/// that matches the comparisons (i.e. any of this value validate the chain) +/// while for a chain of '&&' it will build the set elements that make the test +/// fail. +struct ConstantComparesGatherer { + const DataLayout &DL; + + /// Value found for the switch comparison + Value *CompValue = nullptr; + + /// Extra clause to be checked before the switch + Value *Extra = nullptr; + + /// Set of integers to match in switch + SmallVector<ConstantInt *, 8> Vals; + + /// Number of comparisons matched in the and/or chain + unsigned UsedICmps = 0; + + /// Construct and compute the result for the comparison instruction Cond + ConstantComparesGatherer(Instruction *Cond, const DataLayout &DL) : DL(DL) { + gather(Cond); + } + + ConstantComparesGatherer(const ConstantComparesGatherer &) = delete; + ConstantComparesGatherer & + operator=(const ConstantComparesGatherer &) = delete; + +private: + /// Try to set the current value used for the comparison, it succeeds only if + /// it wasn't set before or if the new value is the same as the old one + bool setValueOnce(Value *NewVal) { + if (CompValue && CompValue != NewVal) + return false; + CompValue = NewVal; + return (CompValue != nullptr); + } + + /// Try to match Instruction "I" as a comparison against a constant and + /// populates the array Vals with the set of values that match (or do not + /// match depending on isEQ). + /// Return false on failure. On success, the Value the comparison matched + /// against is placed in CompValue. + /// If CompValue is already set, the function is expected to fail if a match + /// is found but the value compared to is different. + bool matchInstruction(Instruction *I, bool isEQ) { + // If this is an icmp against a constant, handle this as one of the cases. + ICmpInst *ICI; + ConstantInt *C; + if (!((ICI = dyn_cast<ICmpInst>(I)) && + (C = GetConstantInt(I->getOperand(1), DL)))) { + return false; + } + + Value *RHSVal; + const APInt *RHSC; + + // Pattern match a special case + // (x & ~2^z) == y --> x == y || x == y|2^z + // This undoes a transformation done by instcombine to fuse 2 compares. + if (ICI->getPredicate() == (isEQ ? ICmpInst::ICMP_EQ : ICmpInst::ICMP_NE)) { + // It's a little bit hard to see why the following transformations are + // correct. Here is a CVC3 program to verify them for 64-bit values: + + /* + ONE : BITVECTOR(64) = BVZEROEXTEND(0bin1, 63); + x : BITVECTOR(64); + y : BITVECTOR(64); + z : BITVECTOR(64); + mask : BITVECTOR(64) = BVSHL(ONE, z); + QUERY( (y & ~mask = y) => + ((x & ~mask = y) <=> (x = y OR x = (y | mask))) + ); + QUERY( (y | mask = y) => + ((x | mask = y) <=> (x = y OR x = (y & ~mask))) + ); + */ + + // Please note that each pattern must be a dual implication (<--> or + // iff). One directional implication can create spurious matches. If the + // implication is only one-way, an unsatisfiable condition on the left + // side can imply a satisfiable condition on the right side. Dual + // implication ensures that satisfiable conditions are transformed to + // other satisfiable conditions and unsatisfiable conditions are + // transformed to other unsatisfiable conditions. + + // Here is a concrete example of a unsatisfiable condition on the left + // implying a satisfiable condition on the right: + // + // mask = (1 << z) + // (x & ~mask) == y --> (x == y || x == (y | mask)) + // + // Substituting y = 3, z = 0 yields: + // (x & -2) == 3 --> (x == 3 || x == 2) + + // Pattern match a special case: + /* + QUERY( (y & ~mask = y) => + ((x & ~mask = y) <=> (x = y OR x = (y | mask))) + ); + */ + if (match(ICI->getOperand(0), + m_And(m_Value(RHSVal), m_APInt(RHSC)))) { + APInt Mask = ~*RHSC; + if (Mask.isPowerOf2() && (C->getValue() & ~Mask) == C->getValue()) { + // If we already have a value for the switch, it has to match! + if (!setValueOnce(RHSVal)) + return false; + + Vals.push_back(C); + Vals.push_back( + ConstantInt::get(C->getContext(), + C->getValue() | Mask)); + UsedICmps++; + return true; + } + } + + // Pattern match a special case: + /* + QUERY( (y | mask = y) => + ((x | mask = y) <=> (x = y OR x = (y & ~mask))) + ); + */ + if (match(ICI->getOperand(0), + m_Or(m_Value(RHSVal), m_APInt(RHSC)))) { + APInt Mask = *RHSC; + if (Mask.isPowerOf2() && (C->getValue() | Mask) == C->getValue()) { + // If we already have a value for the switch, it has to match! + if (!setValueOnce(RHSVal)) + return false; + + Vals.push_back(C); + Vals.push_back(ConstantInt::get(C->getContext(), + C->getValue() & ~Mask)); + UsedICmps++; + return true; + } + } + + // If we already have a value for the switch, it has to match! + if (!setValueOnce(ICI->getOperand(0))) + return false; + + UsedICmps++; + Vals.push_back(C); + return ICI->getOperand(0); + } + + // If we have "x ult 3", for example, then we can add 0,1,2 to the set. + ConstantRange Span = ConstantRange::makeAllowedICmpRegion( + ICI->getPredicate(), C->getValue()); + + // Shift the range if the compare is fed by an add. This is the range + // compare idiom as emitted by instcombine. + Value *CandidateVal = I->getOperand(0); + if (match(I->getOperand(0), m_Add(m_Value(RHSVal), m_APInt(RHSC)))) { + Span = Span.subtract(*RHSC); + CandidateVal = RHSVal; + } + + // If this is an and/!= check, then we are looking to build the set of + // value that *don't* pass the and chain. I.e. to turn "x ugt 2" into + // x != 0 && x != 1. + if (!isEQ) + Span = Span.inverse(); + + // If there are a ton of values, we don't want to make a ginormous switch. + if (Span.isSizeLargerThan(8) || Span.isEmptySet()) { + return false; + } + + // If we already have a value for the switch, it has to match! + if (!setValueOnce(CandidateVal)) + return false; + + // Add all values from the range to the set + for (APInt Tmp = Span.getLower(); Tmp != Span.getUpper(); ++Tmp) + Vals.push_back(ConstantInt::get(I->getContext(), Tmp)); + + UsedICmps++; + return true; + } + + /// Given a potentially 'or'd or 'and'd together collection of icmp + /// eq/ne/lt/gt instructions that compare a value against a constant, extract + /// the value being compared, and stick the list constants into the Vals + /// vector. + /// One "Extra" case is allowed to differ from the other. + void gather(Value *V) { + bool isEQ = (cast<Instruction>(V)->getOpcode() == Instruction::Or); + + // Keep a stack (SmallVector for efficiency) for depth-first traversal + SmallVector<Value *, 8> DFT; + SmallPtrSet<Value *, 8> Visited; + + // Initialize + Visited.insert(V); + DFT.push_back(V); + + while (!DFT.empty()) { + V = DFT.pop_back_val(); + + if (Instruction *I = dyn_cast<Instruction>(V)) { + // If it is a || (or && depending on isEQ), process the operands. + if (I->getOpcode() == (isEQ ? Instruction::Or : Instruction::And)) { + if (Visited.insert(I->getOperand(1)).second) + DFT.push_back(I->getOperand(1)); + if (Visited.insert(I->getOperand(0)).second) + DFT.push_back(I->getOperand(0)); + continue; + } + + // Try to match the current instruction + if (matchInstruction(I, isEQ)) + // Match succeed, continue the loop + continue; + } + + // One element of the sequence of || (or &&) could not be match as a + // comparison against the same value as the others. + // We allow only one "Extra" case to be checked before the switch + if (!Extra) { + Extra = V; + continue; + } + // Failed to parse a proper sequence, abort now + CompValue = nullptr; + break; + } + } +}; + +} // end anonymous namespace + +static void EraseTerminatorAndDCECond(Instruction *TI, + MemorySSAUpdater *MSSAU = nullptr) { + Instruction *Cond = nullptr; + if (SwitchInst *SI = dyn_cast<SwitchInst>(TI)) { + Cond = dyn_cast<Instruction>(SI->getCondition()); + } else if (BranchInst *BI = dyn_cast<BranchInst>(TI)) { + if (BI->isConditional()) + Cond = dyn_cast<Instruction>(BI->getCondition()); + } else if (IndirectBrInst *IBI = dyn_cast<IndirectBrInst>(TI)) { + Cond = dyn_cast<Instruction>(IBI->getAddress()); + } + + TI->eraseFromParent(); + if (Cond) + RecursivelyDeleteTriviallyDeadInstructions(Cond, nullptr, MSSAU); +} + +/// Return true if the specified terminator checks +/// to see if a value is equal to constant integer value. +Value *SimplifyCFGOpt::isValueEqualityComparison(Instruction *TI) { + Value *CV = nullptr; + if (SwitchInst *SI = dyn_cast<SwitchInst>(TI)) { + // Do not permit merging of large switch instructions into their + // predecessors unless there is only one predecessor. + if (!SI->getParent()->hasNPredecessorsOrMore(128 / SI->getNumSuccessors())) + CV = SI->getCondition(); + } else if (BranchInst *BI = dyn_cast<BranchInst>(TI)) + if (BI->isConditional() && BI->getCondition()->hasOneUse()) + if (ICmpInst *ICI = dyn_cast<ICmpInst>(BI->getCondition())) { + if (ICI->isEquality() && GetConstantInt(ICI->getOperand(1), DL)) + CV = ICI->getOperand(0); + } + + // Unwrap any lossless ptrtoint cast. + if (CV) { + if (PtrToIntInst *PTII = dyn_cast<PtrToIntInst>(CV)) { + Value *Ptr = PTII->getPointerOperand(); + if (PTII->getType() == DL.getIntPtrType(Ptr->getType())) + CV = Ptr; + } + } + return CV; +} + +/// Given a value comparison instruction, +/// decode all of the 'cases' that it represents and return the 'default' block. +BasicBlock *SimplifyCFGOpt::GetValueEqualityComparisonCases( + Instruction *TI, std::vector<ValueEqualityComparisonCase> &Cases) { + if (SwitchInst *SI = dyn_cast<SwitchInst>(TI)) { + Cases.reserve(SI->getNumCases()); + for (auto Case : SI->cases()) + Cases.push_back(ValueEqualityComparisonCase(Case.getCaseValue(), + Case.getCaseSuccessor())); + return SI->getDefaultDest(); + } + + BranchInst *BI = cast<BranchInst>(TI); + ICmpInst *ICI = cast<ICmpInst>(BI->getCondition()); + BasicBlock *Succ = BI->getSuccessor(ICI->getPredicate() == ICmpInst::ICMP_NE); + Cases.push_back(ValueEqualityComparisonCase( + GetConstantInt(ICI->getOperand(1), DL), Succ)); + return BI->getSuccessor(ICI->getPredicate() == ICmpInst::ICMP_EQ); +} + +/// Given a vector of bb/value pairs, remove any entries +/// in the list that match the specified block. +static void +EliminateBlockCases(BasicBlock *BB, + std::vector<ValueEqualityComparisonCase> &Cases) { + Cases.erase(std::remove(Cases.begin(), Cases.end(), BB), Cases.end()); +} + +/// Return true if there are any keys in C1 that exist in C2 as well. +static bool ValuesOverlap(std::vector<ValueEqualityComparisonCase> &C1, + std::vector<ValueEqualityComparisonCase> &C2) { + std::vector<ValueEqualityComparisonCase> *V1 = &C1, *V2 = &C2; + + // Make V1 be smaller than V2. + if (V1->size() > V2->size()) + std::swap(V1, V2); + + if (V1->empty()) + return false; + if (V1->size() == 1) { + // Just scan V2. + ConstantInt *TheVal = (*V1)[0].Value; + for (unsigned i = 0, e = V2->size(); i != e; ++i) + if (TheVal == (*V2)[i].Value) + return true; + } + + // Otherwise, just sort both lists and compare element by element. + array_pod_sort(V1->begin(), V1->end()); + array_pod_sort(V2->begin(), V2->end()); + unsigned i1 = 0, i2 = 0, e1 = V1->size(), e2 = V2->size(); + while (i1 != e1 && i2 != e2) { + if ((*V1)[i1].Value == (*V2)[i2].Value) + return true; + if ((*V1)[i1].Value < (*V2)[i2].Value) + ++i1; + else + ++i2; + } + return false; +} + +// Set branch weights on SwitchInst. This sets the metadata if there is at +// least one non-zero weight. +static void setBranchWeights(SwitchInst *SI, ArrayRef<uint32_t> Weights) { + // Check that there is at least one non-zero weight. Otherwise, pass + // nullptr to setMetadata which will erase the existing metadata. + MDNode *N = nullptr; + if (llvm::any_of(Weights, [](uint32_t W) { return W != 0; })) + N = MDBuilder(SI->getParent()->getContext()).createBranchWeights(Weights); + SI->setMetadata(LLVMContext::MD_prof, N); +} + +// Similar to the above, but for branch and select instructions that take +// exactly 2 weights. +static void setBranchWeights(Instruction *I, uint32_t TrueWeight, + uint32_t FalseWeight) { + assert(isa<BranchInst>(I) || isa<SelectInst>(I)); + // Check that there is at least one non-zero weight. Otherwise, pass + // nullptr to setMetadata which will erase the existing metadata. + MDNode *N = nullptr; + if (TrueWeight || FalseWeight) + N = MDBuilder(I->getParent()->getContext()) + .createBranchWeights(TrueWeight, FalseWeight); + I->setMetadata(LLVMContext::MD_prof, N); +} + +/// If TI is known to be a terminator instruction and its block is known to +/// only have a single predecessor block, check to see if that predecessor is +/// also a value comparison with the same value, and if that comparison +/// determines the outcome of this comparison. If so, simplify TI. This does a +/// very limited form of jump threading. +bool SimplifyCFGOpt::SimplifyEqualityComparisonWithOnlyPredecessor( + Instruction *TI, BasicBlock *Pred, IRBuilder<> &Builder) { + Value *PredVal = isValueEqualityComparison(Pred->getTerminator()); + if (!PredVal) + return false; // Not a value comparison in predecessor. + + Value *ThisVal = isValueEqualityComparison(TI); + assert(ThisVal && "This isn't a value comparison!!"); + if (ThisVal != PredVal) + return false; // Different predicates. + + // TODO: Preserve branch weight metadata, similarly to how + // FoldValueComparisonIntoPredecessors preserves it. + + // Find out information about when control will move from Pred to TI's block. + std::vector<ValueEqualityComparisonCase> PredCases; + BasicBlock *PredDef = + GetValueEqualityComparisonCases(Pred->getTerminator(), PredCases); + EliminateBlockCases(PredDef, PredCases); // Remove default from cases. + + // Find information about how control leaves this block. + std::vector<ValueEqualityComparisonCase> ThisCases; + BasicBlock *ThisDef = GetValueEqualityComparisonCases(TI, ThisCases); + EliminateBlockCases(ThisDef, ThisCases); // Remove default from cases. + + // If TI's block is the default block from Pred's comparison, potentially + // simplify TI based on this knowledge. + if (PredDef == TI->getParent()) { + // If we are here, we know that the value is none of those cases listed in + // PredCases. If there are any cases in ThisCases that are in PredCases, we + // can simplify TI. + if (!ValuesOverlap(PredCases, ThisCases)) + return false; + + if (isa<BranchInst>(TI)) { + // Okay, one of the successors of this condbr is dead. Convert it to a + // uncond br. + assert(ThisCases.size() == 1 && "Branch can only have one case!"); + // Insert the new branch. + Instruction *NI = Builder.CreateBr(ThisDef); + (void)NI; + + // Remove PHI node entries for the dead edge. + ThisCases[0].Dest->removePredecessor(TI->getParent()); + + LLVM_DEBUG(dbgs() << "Threading pred instr: " << *Pred->getTerminator() + << "Through successor TI: " << *TI << "Leaving: " << *NI + << "\n"); + + EraseTerminatorAndDCECond(TI); + return true; + } + + SwitchInstProfUpdateWrapper SI = *cast<SwitchInst>(TI); + // Okay, TI has cases that are statically dead, prune them away. + SmallPtrSet<Constant *, 16> DeadCases; + for (unsigned i = 0, e = PredCases.size(); i != e; ++i) + DeadCases.insert(PredCases[i].Value); + + LLVM_DEBUG(dbgs() << "Threading pred instr: " << *Pred->getTerminator() + << "Through successor TI: " << *TI); + + for (SwitchInst::CaseIt i = SI->case_end(), e = SI->case_begin(); i != e;) { + --i; + if (DeadCases.count(i->getCaseValue())) { + i->getCaseSuccessor()->removePredecessor(TI->getParent()); + SI.removeCase(i); + } + } + LLVM_DEBUG(dbgs() << "Leaving: " << *TI << "\n"); + return true; + } + + // Otherwise, TI's block must correspond to some matched value. Find out + // which value (or set of values) this is. + ConstantInt *TIV = nullptr; + BasicBlock *TIBB = TI->getParent(); + for (unsigned i = 0, e = PredCases.size(); i != e; ++i) + if (PredCases[i].Dest == TIBB) { + if (TIV) + return false; // Cannot handle multiple values coming to this block. + TIV = PredCases[i].Value; + } + assert(TIV && "No edge from pred to succ?"); + + // Okay, we found the one constant that our value can be if we get into TI's + // BB. Find out which successor will unconditionally be branched to. + BasicBlock *TheRealDest = nullptr; + for (unsigned i = 0, e = ThisCases.size(); i != e; ++i) + if (ThisCases[i].Value == TIV) { + TheRealDest = ThisCases[i].Dest; + break; + } + + // If not handled by any explicit cases, it is handled by the default case. + if (!TheRealDest) + TheRealDest = ThisDef; + + // Remove PHI node entries for dead edges. + BasicBlock *CheckEdge = TheRealDest; + for (BasicBlock *Succ : successors(TIBB)) + if (Succ != CheckEdge) + Succ->removePredecessor(TIBB); + else + CheckEdge = nullptr; + + // Insert the new branch. + Instruction *NI = Builder.CreateBr(TheRealDest); + (void)NI; + + LLVM_DEBUG(dbgs() << "Threading pred instr: " << *Pred->getTerminator() + << "Through successor TI: " << *TI << "Leaving: " << *NI + << "\n"); + + EraseTerminatorAndDCECond(TI); + return true; +} + +namespace { + +/// This class implements a stable ordering of constant +/// integers that does not depend on their address. This is important for +/// applications that sort ConstantInt's to ensure uniqueness. +struct ConstantIntOrdering { + bool operator()(const ConstantInt *LHS, const ConstantInt *RHS) const { + return LHS->getValue().ult(RHS->getValue()); + } +}; + +} // end anonymous namespace + +static int ConstantIntSortPredicate(ConstantInt *const *P1, + ConstantInt *const *P2) { + const ConstantInt *LHS = *P1; + const ConstantInt *RHS = *P2; + if (LHS == RHS) + return 0; + return LHS->getValue().ult(RHS->getValue()) ? 1 : -1; +} + +static inline bool HasBranchWeights(const Instruction *I) { + MDNode *ProfMD = I->getMetadata(LLVMContext::MD_prof); + if (ProfMD && ProfMD->getOperand(0)) + if (MDString *MDS = dyn_cast<MDString>(ProfMD->getOperand(0))) + return MDS->getString().equals("branch_weights"); + + return false; +} + +/// Get Weights of a given terminator, the default weight is at the front +/// of the vector. If TI is a conditional eq, we need to swap the branch-weight +/// metadata. +static void GetBranchWeights(Instruction *TI, + SmallVectorImpl<uint64_t> &Weights) { + MDNode *MD = TI->getMetadata(LLVMContext::MD_prof); + assert(MD); + for (unsigned i = 1, e = MD->getNumOperands(); i < e; ++i) { + ConstantInt *CI = mdconst::extract<ConstantInt>(MD->getOperand(i)); + Weights.push_back(CI->getValue().getZExtValue()); + } + + // If TI is a conditional eq, the default case is the false case, + // and the corresponding branch-weight data is at index 2. We swap the + // default weight to be the first entry. + if (BranchInst *BI = dyn_cast<BranchInst>(TI)) { + assert(Weights.size() == 2); + ICmpInst *ICI = cast<ICmpInst>(BI->getCondition()); + if (ICI->getPredicate() == ICmpInst::ICMP_EQ) + std::swap(Weights.front(), Weights.back()); + } +} + +/// Keep halving the weights until all can fit in uint32_t. +static void FitWeights(MutableArrayRef<uint64_t> Weights) { + uint64_t Max = *std::max_element(Weights.begin(), Weights.end()); + if (Max > UINT_MAX) { + unsigned Offset = 32 - countLeadingZeros(Max); + for (uint64_t &I : Weights) + I >>= Offset; + } +} + +/// The specified terminator is a value equality comparison instruction +/// (either a switch or a branch on "X == c"). +/// See if any of the predecessors of the terminator block are value comparisons +/// on the same value. If so, and if safe to do so, fold them together. +bool SimplifyCFGOpt::FoldValueComparisonIntoPredecessors(Instruction *TI, + IRBuilder<> &Builder) { + BasicBlock *BB = TI->getParent(); + Value *CV = isValueEqualityComparison(TI); // CondVal + assert(CV && "Not a comparison?"); + bool Changed = false; + + SmallVector<BasicBlock *, 16> Preds(pred_begin(BB), pred_end(BB)); + while (!Preds.empty()) { + BasicBlock *Pred = Preds.pop_back_val(); + + // See if the predecessor is a comparison with the same value. + Instruction *PTI = Pred->getTerminator(); + Value *PCV = isValueEqualityComparison(PTI); // PredCondVal + + if (PCV == CV && TI != PTI) { + SmallSetVector<BasicBlock*, 4> FailBlocks; + if (!SafeToMergeTerminators(TI, PTI, &FailBlocks)) { + for (auto *Succ : FailBlocks) { + if (!SplitBlockPredecessors(Succ, TI->getParent(), ".fold.split")) + return false; + } + } + + // Figure out which 'cases' to copy from SI to PSI. + std::vector<ValueEqualityComparisonCase> BBCases; + BasicBlock *BBDefault = GetValueEqualityComparisonCases(TI, BBCases); + + std::vector<ValueEqualityComparisonCase> PredCases; + BasicBlock *PredDefault = GetValueEqualityComparisonCases(PTI, PredCases); + + // Based on whether the default edge from PTI goes to BB or not, fill in + // PredCases and PredDefault with the new switch cases we would like to + // build. + SmallVector<BasicBlock *, 8> NewSuccessors; + + // Update the branch weight metadata along the way + SmallVector<uint64_t, 8> Weights; + bool PredHasWeights = HasBranchWeights(PTI); + bool SuccHasWeights = HasBranchWeights(TI); + + if (PredHasWeights) { + GetBranchWeights(PTI, Weights); + // branch-weight metadata is inconsistent here. + if (Weights.size() != 1 + PredCases.size()) + PredHasWeights = SuccHasWeights = false; + } else if (SuccHasWeights) + // If there are no predecessor weights but there are successor weights, + // populate Weights with 1, which will later be scaled to the sum of + // successor's weights + Weights.assign(1 + PredCases.size(), 1); + + SmallVector<uint64_t, 8> SuccWeights; + if (SuccHasWeights) { + GetBranchWeights(TI, SuccWeights); + // branch-weight metadata is inconsistent here. + if (SuccWeights.size() != 1 + BBCases.size()) + PredHasWeights = SuccHasWeights = false; + } else if (PredHasWeights) + SuccWeights.assign(1 + BBCases.size(), 1); + + if (PredDefault == BB) { + // If this is the default destination from PTI, only the edges in TI + // that don't occur in PTI, or that branch to BB will be activated. + std::set<ConstantInt *, ConstantIntOrdering> PTIHandled; + for (unsigned i = 0, e = PredCases.size(); i != e; ++i) + if (PredCases[i].Dest != BB) + PTIHandled.insert(PredCases[i].Value); + else { + // The default destination is BB, we don't need explicit targets. + std::swap(PredCases[i], PredCases.back()); + + if (PredHasWeights || SuccHasWeights) { + // Increase weight for the default case. + Weights[0] += Weights[i + 1]; + std::swap(Weights[i + 1], Weights.back()); + Weights.pop_back(); + } + + PredCases.pop_back(); + --i; + --e; + } + + // Reconstruct the new switch statement we will be building. + if (PredDefault != BBDefault) { + PredDefault->removePredecessor(Pred); + PredDefault = BBDefault; + NewSuccessors.push_back(BBDefault); + } + + unsigned CasesFromPred = Weights.size(); + uint64_t ValidTotalSuccWeight = 0; + for (unsigned i = 0, e = BBCases.size(); i != e; ++i) + if (!PTIHandled.count(BBCases[i].Value) && + BBCases[i].Dest != BBDefault) { + PredCases.push_back(BBCases[i]); + NewSuccessors.push_back(BBCases[i].Dest); + if (SuccHasWeights || PredHasWeights) { + // The default weight is at index 0, so weight for the ith case + // should be at index i+1. Scale the cases from successor by + // PredDefaultWeight (Weights[0]). + Weights.push_back(Weights[0] * SuccWeights[i + 1]); + ValidTotalSuccWeight += SuccWeights[i + 1]; + } + } + + if (SuccHasWeights || PredHasWeights) { + ValidTotalSuccWeight += SuccWeights[0]; + // Scale the cases from predecessor by ValidTotalSuccWeight. + for (unsigned i = 1; i < CasesFromPred; ++i) + Weights[i] *= ValidTotalSuccWeight; + // Scale the default weight by SuccDefaultWeight (SuccWeights[0]). + Weights[0] *= SuccWeights[0]; + } + } else { + // If this is not the default destination from PSI, only the edges + // in SI that occur in PSI with a destination of BB will be + // activated. + std::set<ConstantInt *, ConstantIntOrdering> PTIHandled; + std::map<ConstantInt *, uint64_t> WeightsForHandled; + for (unsigned i = 0, e = PredCases.size(); i != e; ++i) + if (PredCases[i].Dest == BB) { + PTIHandled.insert(PredCases[i].Value); + + if (PredHasWeights || SuccHasWeights) { + WeightsForHandled[PredCases[i].Value] = Weights[i + 1]; + std::swap(Weights[i + 1], Weights.back()); + Weights.pop_back(); + } + + std::swap(PredCases[i], PredCases.back()); + PredCases.pop_back(); + --i; + --e; + } + + // Okay, now we know which constants were sent to BB from the + // predecessor. Figure out where they will all go now. + for (unsigned i = 0, e = BBCases.size(); i != e; ++i) + if (PTIHandled.count(BBCases[i].Value)) { + // If this is one we are capable of getting... + if (PredHasWeights || SuccHasWeights) + Weights.push_back(WeightsForHandled[BBCases[i].Value]); + PredCases.push_back(BBCases[i]); + NewSuccessors.push_back(BBCases[i].Dest); + PTIHandled.erase( + BBCases[i].Value); // This constant is taken care of + } + + // If there are any constants vectored to BB that TI doesn't handle, + // they must go to the default destination of TI. + for (ConstantInt *I : PTIHandled) { + if (PredHasWeights || SuccHasWeights) + Weights.push_back(WeightsForHandled[I]); + PredCases.push_back(ValueEqualityComparisonCase(I, BBDefault)); + NewSuccessors.push_back(BBDefault); + } + } + + // Okay, at this point, we know which new successor Pred will get. Make + // sure we update the number of entries in the PHI nodes for these + // successors. + for (BasicBlock *NewSuccessor : NewSuccessors) + AddPredecessorToBlock(NewSuccessor, Pred, BB); + + Builder.SetInsertPoint(PTI); + // Convert pointer to int before we switch. + if (CV->getType()->isPointerTy()) { + CV = Builder.CreatePtrToInt(CV, DL.getIntPtrType(CV->getType()), + "magicptr"); + } + + // Now that the successors are updated, create the new Switch instruction. + SwitchInst *NewSI = + Builder.CreateSwitch(CV, PredDefault, PredCases.size()); + NewSI->setDebugLoc(PTI->getDebugLoc()); + for (ValueEqualityComparisonCase &V : PredCases) + NewSI->addCase(V.Value, V.Dest); + + if (PredHasWeights || SuccHasWeights) { + // Halve the weights if any of them cannot fit in an uint32_t + FitWeights(Weights); + + SmallVector<uint32_t, 8> MDWeights(Weights.begin(), Weights.end()); + + setBranchWeights(NewSI, MDWeights); + } + + EraseTerminatorAndDCECond(PTI); + + // Okay, last check. If BB is still a successor of PSI, then we must + // have an infinite loop case. If so, add an infinitely looping block + // to handle the case to preserve the behavior of the code. + BasicBlock *InfLoopBlock = nullptr; + for (unsigned i = 0, e = NewSI->getNumSuccessors(); i != e; ++i) + if (NewSI->getSuccessor(i) == BB) { + if (!InfLoopBlock) { + // Insert it at the end of the function, because it's either code, + // or it won't matter if it's hot. :) + InfLoopBlock = BasicBlock::Create(BB->getContext(), "infloop", + BB->getParent()); + BranchInst::Create(InfLoopBlock, InfLoopBlock); + } + NewSI->setSuccessor(i, InfLoopBlock); + } + + Changed = true; + } + } + return Changed; +} + +// If we would need to insert a select that uses the value of this invoke +// (comments in HoistThenElseCodeToIf explain why we would need to do this), we +// can't hoist the invoke, as there is nowhere to put the select in this case. +static bool isSafeToHoistInvoke(BasicBlock *BB1, BasicBlock *BB2, + Instruction *I1, Instruction *I2) { + for (BasicBlock *Succ : successors(BB1)) { + for (const PHINode &PN : Succ->phis()) { + Value *BB1V = PN.getIncomingValueForBlock(BB1); + Value *BB2V = PN.getIncomingValueForBlock(BB2); + if (BB1V != BB2V && (BB1V == I1 || BB2V == I2)) { + return false; + } + } + } + return true; +} + +static bool passingValueIsAlwaysUndefined(Value *V, Instruction *I); + +/// Given a conditional branch that goes to BB1 and BB2, hoist any common code +/// in the two blocks up into the branch block. The caller of this function +/// guarantees that BI's block dominates BB1 and BB2. +static bool HoistThenElseCodeToIf(BranchInst *BI, + const TargetTransformInfo &TTI) { + // This does very trivial matching, with limited scanning, to find identical + // instructions in the two blocks. In particular, we don't want to get into + // O(M*N) situations here where M and N are the sizes of BB1 and BB2. As + // such, we currently just scan for obviously identical instructions in an + // identical order. + BasicBlock *BB1 = BI->getSuccessor(0); // The true destination. + BasicBlock *BB2 = BI->getSuccessor(1); // The false destination + + BasicBlock::iterator BB1_Itr = BB1->begin(); + BasicBlock::iterator BB2_Itr = BB2->begin(); + + Instruction *I1 = &*BB1_Itr++, *I2 = &*BB2_Itr++; + // Skip debug info if it is not identical. + DbgInfoIntrinsic *DBI1 = dyn_cast<DbgInfoIntrinsic>(I1); + DbgInfoIntrinsic *DBI2 = dyn_cast<DbgInfoIntrinsic>(I2); + if (!DBI1 || !DBI2 || !DBI1->isIdenticalToWhenDefined(DBI2)) { + while (isa<DbgInfoIntrinsic>(I1)) + I1 = &*BB1_Itr++; + while (isa<DbgInfoIntrinsic>(I2)) + I2 = &*BB2_Itr++; + } + // FIXME: Can we define a safety predicate for CallBr? + if (isa<PHINode>(I1) || !I1->isIdenticalToWhenDefined(I2) || + (isa<InvokeInst>(I1) && !isSafeToHoistInvoke(BB1, BB2, I1, I2)) || + isa<CallBrInst>(I1)) + return false; + + BasicBlock *BIParent = BI->getParent(); + + bool Changed = false; + do { + // If we are hoisting the terminator instruction, don't move one (making a + // broken BB), instead clone it, and remove BI. + if (I1->isTerminator()) + goto HoistTerminator; + + // If we're going to hoist a call, make sure that the two instructions we're + // commoning/hoisting are both marked with musttail, or neither of them is + // marked as such. Otherwise, we might end up in a situation where we hoist + // from a block where the terminator is a `ret` to a block where the terminator + // is a `br`, and `musttail` calls expect to be followed by a return. + auto *C1 = dyn_cast<CallInst>(I1); + auto *C2 = dyn_cast<CallInst>(I2); + if (C1 && C2) + if (C1->isMustTailCall() != C2->isMustTailCall()) + return Changed; + + if (!TTI.isProfitableToHoist(I1) || !TTI.isProfitableToHoist(I2)) + return Changed; + + if (isa<DbgInfoIntrinsic>(I1) || isa<DbgInfoIntrinsic>(I2)) { + assert (isa<DbgInfoIntrinsic>(I1) && isa<DbgInfoIntrinsic>(I2)); + // The debug location is an integral part of a debug info intrinsic + // and can't be separated from it or replaced. Instead of attempting + // to merge locations, simply hoist both copies of the intrinsic. + BIParent->getInstList().splice(BI->getIterator(), + BB1->getInstList(), I1); + BIParent->getInstList().splice(BI->getIterator(), + BB2->getInstList(), I2); + Changed = true; + } else { + // For a normal instruction, we just move one to right before the branch, + // then replace all uses of the other with the first. Finally, we remove + // the now redundant second instruction. + BIParent->getInstList().splice(BI->getIterator(), + BB1->getInstList(), I1); + if (!I2->use_empty()) + I2->replaceAllUsesWith(I1); + I1->andIRFlags(I2); + unsigned KnownIDs[] = {LLVMContext::MD_tbaa, + LLVMContext::MD_range, + LLVMContext::MD_fpmath, + LLVMContext::MD_invariant_load, + LLVMContext::MD_nonnull, + LLVMContext::MD_invariant_group, + LLVMContext::MD_align, + LLVMContext::MD_dereferenceable, + LLVMContext::MD_dereferenceable_or_null, + LLVMContext::MD_mem_parallel_loop_access, + LLVMContext::MD_access_group, + LLVMContext::MD_preserve_access_index}; + combineMetadata(I1, I2, KnownIDs, true); + + // I1 and I2 are being combined into a single instruction. Its debug + // location is the merged locations of the original instructions. + I1->applyMergedLocation(I1->getDebugLoc(), I2->getDebugLoc()); + + I2->eraseFromParent(); + Changed = true; + } + + I1 = &*BB1_Itr++; + I2 = &*BB2_Itr++; + // Skip debug info if it is not identical. + DbgInfoIntrinsic *DBI1 = dyn_cast<DbgInfoIntrinsic>(I1); + DbgInfoIntrinsic *DBI2 = dyn_cast<DbgInfoIntrinsic>(I2); + if (!DBI1 || !DBI2 || !DBI1->isIdenticalToWhenDefined(DBI2)) { + while (isa<DbgInfoIntrinsic>(I1)) + I1 = &*BB1_Itr++; + while (isa<DbgInfoIntrinsic>(I2)) + I2 = &*BB2_Itr++; + } + } while (I1->isIdenticalToWhenDefined(I2)); + + return true; + +HoistTerminator: + // It may not be possible to hoist an invoke. + // FIXME: Can we define a safety predicate for CallBr? + if (isa<InvokeInst>(I1) && !isSafeToHoistInvoke(BB1, BB2, I1, I2)) + return Changed; + + // TODO: callbr hoisting currently disabled pending further study. + if (isa<CallBrInst>(I1)) + return Changed; + + for (BasicBlock *Succ : successors(BB1)) { + for (PHINode &PN : Succ->phis()) { + Value *BB1V = PN.getIncomingValueForBlock(BB1); + Value *BB2V = PN.getIncomingValueForBlock(BB2); + if (BB1V == BB2V) + continue; + + // Check for passingValueIsAlwaysUndefined here because we would rather + // eliminate undefined control flow then converting it to a select. + if (passingValueIsAlwaysUndefined(BB1V, &PN) || + passingValueIsAlwaysUndefined(BB2V, &PN)) + return Changed; + + if (isa<ConstantExpr>(BB1V) && !isSafeToSpeculativelyExecute(BB1V)) + return Changed; + if (isa<ConstantExpr>(BB2V) && !isSafeToSpeculativelyExecute(BB2V)) + return Changed; + } + } + + // Okay, it is safe to hoist the terminator. + Instruction *NT = I1->clone(); + BIParent->getInstList().insert(BI->getIterator(), NT); + if (!NT->getType()->isVoidTy()) { + I1->replaceAllUsesWith(NT); + I2->replaceAllUsesWith(NT); + NT->takeName(I1); + } + + // Ensure terminator gets a debug location, even an unknown one, in case + // it involves inlinable calls. + NT->applyMergedLocation(I1->getDebugLoc(), I2->getDebugLoc()); + + // PHIs created below will adopt NT's merged DebugLoc. + IRBuilder<NoFolder> Builder(NT); + + // Hoisting one of the terminators from our successor is a great thing. + // Unfortunately, the successors of the if/else blocks may have PHI nodes in + // them. If they do, all PHI entries for BB1/BB2 must agree for all PHI + // nodes, so we insert select instruction to compute the final result. + std::map<std::pair<Value *, Value *>, SelectInst *> InsertedSelects; + for (BasicBlock *Succ : successors(BB1)) { + for (PHINode &PN : Succ->phis()) { + Value *BB1V = PN.getIncomingValueForBlock(BB1); + Value *BB2V = PN.getIncomingValueForBlock(BB2); + if (BB1V == BB2V) + continue; + + // These values do not agree. Insert a select instruction before NT + // that determines the right value. + SelectInst *&SI = InsertedSelects[std::make_pair(BB1V, BB2V)]; + if (!SI) + SI = cast<SelectInst>( + Builder.CreateSelect(BI->getCondition(), BB1V, BB2V, + BB1V->getName() + "." + BB2V->getName(), BI)); + + // Make the PHI node use the select for all incoming values for BB1/BB2 + for (unsigned i = 0, e = PN.getNumIncomingValues(); i != e; ++i) + if (PN.getIncomingBlock(i) == BB1 || PN.getIncomingBlock(i) == BB2) + PN.setIncomingValue(i, SI); + } + } + + // Update any PHI nodes in our new successors. + for (BasicBlock *Succ : successors(BB1)) + AddPredecessorToBlock(Succ, BIParent, BB1); + + EraseTerminatorAndDCECond(BI); + return true; +} + +// Check lifetime markers. +static bool isLifeTimeMarker(const Instruction *I) { + if (auto II = dyn_cast<IntrinsicInst>(I)) { + switch (II->getIntrinsicID()) { + default: + break; + case Intrinsic::lifetime_start: + case Intrinsic::lifetime_end: + return true; + } + } + return false; +} + +// All instructions in Insts belong to different blocks that all unconditionally +// branch to a common successor. Analyze each instruction and return true if it +// would be possible to sink them into their successor, creating one common +// instruction instead. For every value that would be required to be provided by +// PHI node (because an operand varies in each input block), add to PHIOperands. +static bool canSinkInstructions( + ArrayRef<Instruction *> Insts, + DenseMap<Instruction *, SmallVector<Value *, 4>> &PHIOperands) { + // Prune out obviously bad instructions to move. Each instruction must have + // exactly zero or one use, and we check later that use is by a single, common + // PHI instruction in the successor. + bool HasUse = !Insts.front()->user_empty(); + for (auto *I : Insts) { + // These instructions may change or break semantics if moved. + if (isa<PHINode>(I) || I->isEHPad() || isa<AllocaInst>(I) || + I->getType()->isTokenTy()) + return false; + + // Conservatively return false if I is an inline-asm instruction. Sinking + // and merging inline-asm instructions can potentially create arguments + // that cannot satisfy the inline-asm constraints. + if (const auto *C = dyn_cast<CallBase>(I)) + if (C->isInlineAsm()) + return false; + + // Each instruction must have zero or one use. + if (HasUse && !I->hasOneUse()) + return false; + if (!HasUse && !I->user_empty()) + return false; + } + + const Instruction *I0 = Insts.front(); + for (auto *I : Insts) + if (!I->isSameOperationAs(I0)) + return false; + + // All instructions in Insts are known to be the same opcode. If they have a + // use, check that the only user is a PHI or in the same block as the + // instruction, because if a user is in the same block as an instruction we're + // contemplating sinking, it must already be determined to be sinkable. + if (HasUse) { + auto *PNUse = dyn_cast<PHINode>(*I0->user_begin()); + auto *Succ = I0->getParent()->getTerminator()->getSuccessor(0); + if (!all_of(Insts, [&PNUse,&Succ](const Instruction *I) -> bool { + auto *U = cast<Instruction>(*I->user_begin()); + return (PNUse && + PNUse->getParent() == Succ && + PNUse->getIncomingValueForBlock(I->getParent()) == I) || + U->getParent() == I->getParent(); + })) + return false; + } + + // Because SROA can't handle speculating stores of selects, try not to sink + // loads, stores or lifetime markers of allocas when we'd have to create a + // PHI for the address operand. Also, because it is likely that loads or + // stores of allocas will disappear when Mem2Reg/SROA is run, don't sink + // them. + // This can cause code churn which can have unintended consequences down + // the line - see https://llvm.org/bugs/show_bug.cgi?id=30244. + // FIXME: This is a workaround for a deficiency in SROA - see + // https://llvm.org/bugs/show_bug.cgi?id=30188 + if (isa<StoreInst>(I0) && any_of(Insts, [](const Instruction *I) { + return isa<AllocaInst>(I->getOperand(1)->stripPointerCasts()); + })) + return false; + if (isa<LoadInst>(I0) && any_of(Insts, [](const Instruction *I) { + return isa<AllocaInst>(I->getOperand(0)->stripPointerCasts()); + })) + return false; + if (isLifeTimeMarker(I0) && any_of(Insts, [](const Instruction *I) { + return isa<AllocaInst>(I->getOperand(1)->stripPointerCasts()); + })) + return false; + + for (unsigned OI = 0, OE = I0->getNumOperands(); OI != OE; ++OI) { + if (I0->getOperand(OI)->getType()->isTokenTy()) + // Don't touch any operand of token type. + return false; + + auto SameAsI0 = [&I0, OI](const Instruction *I) { + assert(I->getNumOperands() == I0->getNumOperands()); + return I->getOperand(OI) == I0->getOperand(OI); + }; + if (!all_of(Insts, SameAsI0)) { + if (!canReplaceOperandWithVariable(I0, OI)) + // We can't create a PHI from this GEP. + return false; + // Don't create indirect calls! The called value is the final operand. + if (isa<CallBase>(I0) && OI == OE - 1) { + // FIXME: if the call was *already* indirect, we should do this. + return false; + } + for (auto *I : Insts) + PHIOperands[I].push_back(I->getOperand(OI)); + } + } + return true; +} + +// Assuming canSinkLastInstruction(Blocks) has returned true, sink the last +// instruction of every block in Blocks to their common successor, commoning +// into one instruction. +static bool sinkLastInstruction(ArrayRef<BasicBlock*> Blocks) { + auto *BBEnd = Blocks[0]->getTerminator()->getSuccessor(0); + + // canSinkLastInstruction returning true guarantees that every block has at + // least one non-terminator instruction. + SmallVector<Instruction*,4> Insts; + for (auto *BB : Blocks) { + Instruction *I = BB->getTerminator(); + do { + I = I->getPrevNode(); + } while (isa<DbgInfoIntrinsic>(I) && I != &BB->front()); + if (!isa<DbgInfoIntrinsic>(I)) + Insts.push_back(I); + } + + // The only checking we need to do now is that all users of all instructions + // are the same PHI node. canSinkLastInstruction should have checked this but + // it is slightly over-aggressive - it gets confused by commutative instructions + // so double-check it here. + Instruction *I0 = Insts.front(); + if (!I0->user_empty()) { + auto *PNUse = dyn_cast<PHINode>(*I0->user_begin()); + if (!all_of(Insts, [&PNUse](const Instruction *I) -> bool { + auto *U = cast<Instruction>(*I->user_begin()); + return U == PNUse; + })) + return false; + } + + // We don't need to do any more checking here; canSinkLastInstruction should + // have done it all for us. + SmallVector<Value*, 4> NewOperands; + for (unsigned O = 0, E = I0->getNumOperands(); O != E; ++O) { + // This check is different to that in canSinkLastInstruction. There, we + // cared about the global view once simplifycfg (and instcombine) have + // completed - it takes into account PHIs that become trivially + // simplifiable. However here we need a more local view; if an operand + // differs we create a PHI and rely on instcombine to clean up the very + // small mess we may make. + bool NeedPHI = any_of(Insts, [&I0, O](const Instruction *I) { + return I->getOperand(O) != I0->getOperand(O); + }); + if (!NeedPHI) { + NewOperands.push_back(I0->getOperand(O)); + continue; + } + + // Create a new PHI in the successor block and populate it. + auto *Op = I0->getOperand(O); + assert(!Op->getType()->isTokenTy() && "Can't PHI tokens!"); + auto *PN = PHINode::Create(Op->getType(), Insts.size(), + Op->getName() + ".sink", &BBEnd->front()); + for (auto *I : Insts) + PN->addIncoming(I->getOperand(O), I->getParent()); + NewOperands.push_back(PN); + } + + // Arbitrarily use I0 as the new "common" instruction; remap its operands + // and move it to the start of the successor block. + for (unsigned O = 0, E = I0->getNumOperands(); O != E; ++O) + I0->getOperandUse(O).set(NewOperands[O]); + I0->moveBefore(&*BBEnd->getFirstInsertionPt()); + + // Update metadata and IR flags, and merge debug locations. + for (auto *I : Insts) + if (I != I0) { + // The debug location for the "common" instruction is the merged locations + // of all the commoned instructions. We start with the original location + // of the "common" instruction and iteratively merge each location in the + // loop below. + // This is an N-way merge, which will be inefficient if I0 is a CallInst. + // However, as N-way merge for CallInst is rare, so we use simplified API + // instead of using complex API for N-way merge. + I0->applyMergedLocation(I0->getDebugLoc(), I->getDebugLoc()); + combineMetadataForCSE(I0, I, true); + I0->andIRFlags(I); + } + + if (!I0->user_empty()) { + // canSinkLastInstruction checked that all instructions were used by + // one and only one PHI node. Find that now, RAUW it to our common + // instruction and nuke it. + auto *PN = cast<PHINode>(*I0->user_begin()); + PN->replaceAllUsesWith(I0); + PN->eraseFromParent(); + } + + // Finally nuke all instructions apart from the common instruction. + for (auto *I : Insts) + if (I != I0) + I->eraseFromParent(); + + return true; +} + +namespace { + + // LockstepReverseIterator - Iterates through instructions + // in a set of blocks in reverse order from the first non-terminator. + // For example (assume all blocks have size n): + // LockstepReverseIterator I([B1, B2, B3]); + // *I-- = [B1[n], B2[n], B3[n]]; + // *I-- = [B1[n-1], B2[n-1], B3[n-1]]; + // *I-- = [B1[n-2], B2[n-2], B3[n-2]]; + // ... + class LockstepReverseIterator { + ArrayRef<BasicBlock*> Blocks; + SmallVector<Instruction*,4> Insts; + bool Fail; + + public: + LockstepReverseIterator(ArrayRef<BasicBlock*> Blocks) : Blocks(Blocks) { + reset(); + } + + void reset() { + Fail = false; + Insts.clear(); + for (auto *BB : Blocks) { + Instruction *Inst = BB->getTerminator(); + for (Inst = Inst->getPrevNode(); Inst && isa<DbgInfoIntrinsic>(Inst);) + Inst = Inst->getPrevNode(); + if (!Inst) { + // Block wasn't big enough. + Fail = true; + return; + } + Insts.push_back(Inst); + } + } + + bool isValid() const { + return !Fail; + } + + void operator--() { + if (Fail) + return; + for (auto *&Inst : Insts) { + for (Inst = Inst->getPrevNode(); Inst && isa<DbgInfoIntrinsic>(Inst);) + Inst = Inst->getPrevNode(); + // Already at beginning of block. + if (!Inst) { + Fail = true; + return; + } + } + } + + ArrayRef<Instruction*> operator * () const { + return Insts; + } + }; + +} // end anonymous namespace + +/// Check whether BB's predecessors end with unconditional branches. If it is +/// true, sink any common code from the predecessors to BB. +/// We also allow one predecessor to end with conditional branch (but no more +/// than one). +static bool SinkCommonCodeFromPredecessors(BasicBlock *BB) { + // We support two situations: + // (1) all incoming arcs are unconditional + // (2) one incoming arc is conditional + // + // (2) is very common in switch defaults and + // else-if patterns; + // + // if (a) f(1); + // else if (b) f(2); + // + // produces: + // + // [if] + // / \ + // [f(1)] [if] + // | | \ + // | | | + // | [f(2)]| + // \ | / + // [ end ] + // + // [end] has two unconditional predecessor arcs and one conditional. The + // conditional refers to the implicit empty 'else' arc. This conditional + // arc can also be caused by an empty default block in a switch. + // + // In this case, we attempt to sink code from all *unconditional* arcs. + // If we can sink instructions from these arcs (determined during the scan + // phase below) we insert a common successor for all unconditional arcs and + // connect that to [end], to enable sinking: + // + // [if] + // / \ + // [x(1)] [if] + // | | \ + // | | \ + // | [x(2)] | + // \ / | + // [sink.split] | + // \ / + // [ end ] + // + SmallVector<BasicBlock*,4> UnconditionalPreds; + Instruction *Cond = nullptr; + for (auto *B : predecessors(BB)) { + auto *T = B->getTerminator(); + if (isa<BranchInst>(T) && cast<BranchInst>(T)->isUnconditional()) + UnconditionalPreds.push_back(B); + else if ((isa<BranchInst>(T) || isa<SwitchInst>(T)) && !Cond) + Cond = T; + else + return false; + } + if (UnconditionalPreds.size() < 2) + return false; + + bool Changed = false; + // We take a two-step approach to tail sinking. First we scan from the end of + // each block upwards in lockstep. If the n'th instruction from the end of each + // block can be sunk, those instructions are added to ValuesToSink and we + // carry on. If we can sink an instruction but need to PHI-merge some operands + // (because they're not identical in each instruction) we add these to + // PHIOperands. + unsigned ScanIdx = 0; + SmallPtrSet<Value*,4> InstructionsToSink; + DenseMap<Instruction*, SmallVector<Value*,4>> PHIOperands; + LockstepReverseIterator LRI(UnconditionalPreds); + while (LRI.isValid() && + canSinkInstructions(*LRI, PHIOperands)) { + LLVM_DEBUG(dbgs() << "SINK: instruction can be sunk: " << *(*LRI)[0] + << "\n"); + InstructionsToSink.insert((*LRI).begin(), (*LRI).end()); + ++ScanIdx; + --LRI; + } + + auto ProfitableToSinkInstruction = [&](LockstepReverseIterator &LRI) { + unsigned NumPHIdValues = 0; + for (auto *I : *LRI) + for (auto *V : PHIOperands[I]) + if (InstructionsToSink.count(V) == 0) + ++NumPHIdValues; + LLVM_DEBUG(dbgs() << "SINK: #phid values: " << NumPHIdValues << "\n"); + unsigned NumPHIInsts = NumPHIdValues / UnconditionalPreds.size(); + if ((NumPHIdValues % UnconditionalPreds.size()) != 0) + NumPHIInsts++; + + return NumPHIInsts <= 1; + }; + + if (ScanIdx > 0 && Cond) { + // Check if we would actually sink anything first! This mutates the CFG and + // adds an extra block. The goal in doing this is to allow instructions that + // couldn't be sunk before to be sunk - obviously, speculatable instructions + // (such as trunc, add) can be sunk and predicated already. So we check that + // we're going to sink at least one non-speculatable instruction. + LRI.reset(); + unsigned Idx = 0; + bool Profitable = false; + while (ProfitableToSinkInstruction(LRI) && Idx < ScanIdx) { + if (!isSafeToSpeculativelyExecute((*LRI)[0])) { + Profitable = true; + break; + } + --LRI; + ++Idx; + } + if (!Profitable) + return false; + + LLVM_DEBUG(dbgs() << "SINK: Splitting edge\n"); + // We have a conditional edge and we're going to sink some instructions. + // Insert a new block postdominating all blocks we're going to sink from. + if (!SplitBlockPredecessors(BB, UnconditionalPreds, ".sink.split")) + // Edges couldn't be split. + return false; + Changed = true; + } + + // Now that we've analyzed all potential sinking candidates, perform the + // actual sink. We iteratively sink the last non-terminator of the source + // blocks into their common successor unless doing so would require too + // many PHI instructions to be generated (currently only one PHI is allowed + // per sunk instruction). + // + // We can use InstructionsToSink to discount values needing PHI-merging that will + // actually be sunk in a later iteration. This allows us to be more + // aggressive in what we sink. This does allow a false positive where we + // sink presuming a later value will also be sunk, but stop half way through + // and never actually sink it which means we produce more PHIs than intended. + // This is unlikely in practice though. + for (unsigned SinkIdx = 0; SinkIdx != ScanIdx; ++SinkIdx) { + LLVM_DEBUG(dbgs() << "SINK: Sink: " + << *UnconditionalPreds[0]->getTerminator()->getPrevNode() + << "\n"); + + // Because we've sunk every instruction in turn, the current instruction to + // sink is always at index 0. + LRI.reset(); + if (!ProfitableToSinkInstruction(LRI)) { + // Too many PHIs would be created. + LLVM_DEBUG( + dbgs() << "SINK: stopping here, too many PHIs would be created!\n"); + break; + } + + if (!sinkLastInstruction(UnconditionalPreds)) + return Changed; + NumSinkCommons++; + Changed = true; + } + return Changed; +} + +/// Determine if we can hoist sink a sole store instruction out of a +/// conditional block. +/// +/// We are looking for code like the following: +/// BrBB: +/// store i32 %add, i32* %arrayidx2 +/// ... // No other stores or function calls (we could be calling a memory +/// ... // function). +/// %cmp = icmp ult %x, %y +/// br i1 %cmp, label %EndBB, label %ThenBB +/// ThenBB: +/// store i32 %add5, i32* %arrayidx2 +/// br label EndBB +/// EndBB: +/// ... +/// We are going to transform this into: +/// BrBB: +/// store i32 %add, i32* %arrayidx2 +/// ... // +/// %cmp = icmp ult %x, %y +/// %add.add5 = select i1 %cmp, i32 %add, %add5 +/// store i32 %add.add5, i32* %arrayidx2 +/// ... +/// +/// \return The pointer to the value of the previous store if the store can be +/// hoisted into the predecessor block. 0 otherwise. +static Value *isSafeToSpeculateStore(Instruction *I, BasicBlock *BrBB, + BasicBlock *StoreBB, BasicBlock *EndBB) { + StoreInst *StoreToHoist = dyn_cast<StoreInst>(I); + if (!StoreToHoist) + return nullptr; + + // Volatile or atomic. + if (!StoreToHoist->isSimple()) + return nullptr; + + Value *StorePtr = StoreToHoist->getPointerOperand(); + + // Look for a store to the same pointer in BrBB. + unsigned MaxNumInstToLookAt = 9; + for (Instruction &CurI : reverse(BrBB->instructionsWithoutDebug())) { + if (!MaxNumInstToLookAt) + break; + --MaxNumInstToLookAt; + + // Could be calling an instruction that affects memory like free(). + if (CurI.mayHaveSideEffects() && !isa<StoreInst>(CurI)) + return nullptr; + + if (auto *SI = dyn_cast<StoreInst>(&CurI)) { + // Found the previous store make sure it stores to the same location. + if (SI->getPointerOperand() == StorePtr) + // Found the previous store, return its value operand. + return SI->getValueOperand(); + return nullptr; // Unknown store. + } + } + + return nullptr; +} + +/// Speculate a conditional basic block flattening the CFG. +/// +/// Note that this is a very risky transform currently. Speculating +/// instructions like this is most often not desirable. Instead, there is an MI +/// pass which can do it with full awareness of the resource constraints. +/// However, some cases are "obvious" and we should do directly. An example of +/// this is speculating a single, reasonably cheap instruction. +/// +/// There is only one distinct advantage to flattening the CFG at the IR level: +/// it makes very common but simplistic optimizations such as are common in +/// instcombine and the DAG combiner more powerful by removing CFG edges and +/// modeling their effects with easier to reason about SSA value graphs. +/// +/// +/// An illustration of this transform is turning this IR: +/// \code +/// BB: +/// %cmp = icmp ult %x, %y +/// br i1 %cmp, label %EndBB, label %ThenBB +/// ThenBB: +/// %sub = sub %x, %y +/// br label BB2 +/// EndBB: +/// %phi = phi [ %sub, %ThenBB ], [ 0, %EndBB ] +/// ... +/// \endcode +/// +/// Into this IR: +/// \code +/// BB: +/// %cmp = icmp ult %x, %y +/// %sub = sub %x, %y +/// %cond = select i1 %cmp, 0, %sub +/// ... +/// \endcode +/// +/// \returns true if the conditional block is removed. +static bool SpeculativelyExecuteBB(BranchInst *BI, BasicBlock *ThenBB, + const TargetTransformInfo &TTI) { + // Be conservative for now. FP select instruction can often be expensive. + Value *BrCond = BI->getCondition(); + if (isa<FCmpInst>(BrCond)) + return false; + + BasicBlock *BB = BI->getParent(); + BasicBlock *EndBB = ThenBB->getTerminator()->getSuccessor(0); + + // If ThenBB is actually on the false edge of the conditional branch, remember + // to swap the select operands later. + bool Invert = false; + if (ThenBB != BI->getSuccessor(0)) { + assert(ThenBB == BI->getSuccessor(1) && "No edge from 'if' block?"); + Invert = true; + } + assert(EndBB == BI->getSuccessor(!Invert) && "No edge from to end block"); + + // Keep a count of how many times instructions are used within ThenBB when + // they are candidates for sinking into ThenBB. Specifically: + // - They are defined in BB, and + // - They have no side effects, and + // - All of their uses are in ThenBB. + SmallDenseMap<Instruction *, unsigned, 4> SinkCandidateUseCounts; + + SmallVector<Instruction *, 4> SpeculatedDbgIntrinsics; + + unsigned SpeculatedInstructions = 0; + Value *SpeculatedStoreValue = nullptr; + StoreInst *SpeculatedStore = nullptr; + for (BasicBlock::iterator BBI = ThenBB->begin(), + BBE = std::prev(ThenBB->end()); + BBI != BBE; ++BBI) { + Instruction *I = &*BBI; + // Skip debug info. + if (isa<DbgInfoIntrinsic>(I)) { + SpeculatedDbgIntrinsics.push_back(I); + continue; + } + + // Only speculatively execute a single instruction (not counting the + // terminator) for now. + ++SpeculatedInstructions; + if (SpeculatedInstructions > 1) + return false; + + // Don't hoist the instruction if it's unsafe or expensive. + if (!isSafeToSpeculativelyExecute(I) && + !(HoistCondStores && (SpeculatedStoreValue = isSafeToSpeculateStore( + I, BB, ThenBB, EndBB)))) + return false; + if (!SpeculatedStoreValue && + ComputeSpeculationCost(I, TTI) > + PHINodeFoldingThreshold * TargetTransformInfo::TCC_Basic) + return false; + + // Store the store speculation candidate. + if (SpeculatedStoreValue) + SpeculatedStore = cast<StoreInst>(I); + + // Do not hoist the instruction if any of its operands are defined but not + // used in BB. The transformation will prevent the operand from + // being sunk into the use block. + for (User::op_iterator i = I->op_begin(), e = I->op_end(); i != e; ++i) { + Instruction *OpI = dyn_cast<Instruction>(*i); + if (!OpI || OpI->getParent() != BB || OpI->mayHaveSideEffects()) + continue; // Not a candidate for sinking. + + ++SinkCandidateUseCounts[OpI]; + } + } + + // Consider any sink candidates which are only used in ThenBB as costs for + // speculation. Note, while we iterate over a DenseMap here, we are summing + // and so iteration order isn't significant. + for (SmallDenseMap<Instruction *, unsigned, 4>::iterator + I = SinkCandidateUseCounts.begin(), + E = SinkCandidateUseCounts.end(); + I != E; ++I) + if (I->first->hasNUses(I->second)) { + ++SpeculatedInstructions; + if (SpeculatedInstructions > 1) + return false; + } + + // Check that the PHI nodes can be converted to selects. + bool HaveRewritablePHIs = false; + for (PHINode &PN : EndBB->phis()) { + Value *OrigV = PN.getIncomingValueForBlock(BB); + Value *ThenV = PN.getIncomingValueForBlock(ThenBB); + + // FIXME: Try to remove some of the duplication with HoistThenElseCodeToIf. + // Skip PHIs which are trivial. + if (ThenV == OrigV) + continue; + + // Don't convert to selects if we could remove undefined behavior instead. + if (passingValueIsAlwaysUndefined(OrigV, &PN) || + passingValueIsAlwaysUndefined(ThenV, &PN)) + return false; + + HaveRewritablePHIs = true; + ConstantExpr *OrigCE = dyn_cast<ConstantExpr>(OrigV); + ConstantExpr *ThenCE = dyn_cast<ConstantExpr>(ThenV); + if (!OrigCE && !ThenCE) + continue; // Known safe and cheap. + + if ((ThenCE && !isSafeToSpeculativelyExecute(ThenCE)) || + (OrigCE && !isSafeToSpeculativelyExecute(OrigCE))) + return false; + unsigned OrigCost = OrigCE ? ComputeSpeculationCost(OrigCE, TTI) : 0; + unsigned ThenCost = ThenCE ? ComputeSpeculationCost(ThenCE, TTI) : 0; + unsigned MaxCost = + 2 * PHINodeFoldingThreshold * TargetTransformInfo::TCC_Basic; + if (OrigCost + ThenCost > MaxCost) + return false; + + // Account for the cost of an unfolded ConstantExpr which could end up + // getting expanded into Instructions. + // FIXME: This doesn't account for how many operations are combined in the + // constant expression. + ++SpeculatedInstructions; + if (SpeculatedInstructions > 1) + return false; + } + + // If there are no PHIs to process, bail early. This helps ensure idempotence + // as well. + if (!HaveRewritablePHIs && !(HoistCondStores && SpeculatedStoreValue)) + return false; + + // If we get here, we can hoist the instruction and if-convert. + LLVM_DEBUG(dbgs() << "SPECULATIVELY EXECUTING BB" << *ThenBB << "\n";); + + // Insert a select of the value of the speculated store. + if (SpeculatedStoreValue) { + IRBuilder<NoFolder> Builder(BI); + Value *TrueV = SpeculatedStore->getValueOperand(); + Value *FalseV = SpeculatedStoreValue; + if (Invert) + std::swap(TrueV, FalseV); + Value *S = Builder.CreateSelect( + BrCond, TrueV, FalseV, "spec.store.select", BI); + SpeculatedStore->setOperand(0, S); + SpeculatedStore->applyMergedLocation(BI->getDebugLoc(), + SpeculatedStore->getDebugLoc()); + } + + // Metadata can be dependent on the condition we are hoisting above. + // Conservatively strip all metadata on the instruction. + for (auto &I : *ThenBB) + I.dropUnknownNonDebugMetadata(); + + // Hoist the instructions. + BB->getInstList().splice(BI->getIterator(), ThenBB->getInstList(), + ThenBB->begin(), std::prev(ThenBB->end())); + + // Insert selects and rewrite the PHI operands. + IRBuilder<NoFolder> Builder(BI); + for (PHINode &PN : EndBB->phis()) { + unsigned OrigI = PN.getBasicBlockIndex(BB); + unsigned ThenI = PN.getBasicBlockIndex(ThenBB); + Value *OrigV = PN.getIncomingValue(OrigI); + Value *ThenV = PN.getIncomingValue(ThenI); + + // Skip PHIs which are trivial. + if (OrigV == ThenV) + continue; + + // Create a select whose true value is the speculatively executed value and + // false value is the preexisting value. Swap them if the branch + // destinations were inverted. + Value *TrueV = ThenV, *FalseV = OrigV; + if (Invert) + std::swap(TrueV, FalseV); + Value *V = Builder.CreateSelect( + BrCond, TrueV, FalseV, "spec.select", BI); + PN.setIncomingValue(OrigI, V); + PN.setIncomingValue(ThenI, V); + } + + // Remove speculated dbg intrinsics. + // FIXME: Is it possible to do this in a more elegant way? Moving/merging the + // dbg value for the different flows and inserting it after the select. + for (Instruction *I : SpeculatedDbgIntrinsics) + I->eraseFromParent(); + + ++NumSpeculations; + return true; +} + +/// Return true if we can thread a branch across this block. +static bool BlockIsSimpleEnoughToThreadThrough(BasicBlock *BB) { + unsigned Size = 0; + + for (Instruction &I : BB->instructionsWithoutDebug()) { + if (Size > 10) + return false; // Don't clone large BB's. + ++Size; + + // We can only support instructions that do not define values that are + // live outside of the current basic block. + for (User *U : I.users()) { + Instruction *UI = cast<Instruction>(U); + if (UI->getParent() != BB || isa<PHINode>(UI)) + return false; + } + + // Looks ok, continue checking. + } + + return true; +} + +/// If we have a conditional branch on a PHI node value that is defined in the +/// same block as the branch and if any PHI entries are constants, thread edges +/// corresponding to that entry to be branches to their ultimate destination. +static bool FoldCondBranchOnPHI(BranchInst *BI, const DataLayout &DL, + AssumptionCache *AC) { + BasicBlock *BB = BI->getParent(); + PHINode *PN = dyn_cast<PHINode>(BI->getCondition()); + // NOTE: we currently cannot transform this case if the PHI node is used + // outside of the block. + if (!PN || PN->getParent() != BB || !PN->hasOneUse()) + return false; + + // Degenerate case of a single entry PHI. + if (PN->getNumIncomingValues() == 1) { + FoldSingleEntryPHINodes(PN->getParent()); + return true; + } + + // Now we know that this block has multiple preds and two succs. + if (!BlockIsSimpleEnoughToThreadThrough(BB)) + return false; + + // Can't fold blocks that contain noduplicate or convergent calls. + if (any_of(*BB, [](const Instruction &I) { + const CallInst *CI = dyn_cast<CallInst>(&I); + return CI && (CI->cannotDuplicate() || CI->isConvergent()); + })) + return false; + + // Okay, this is a simple enough basic block. See if any phi values are + // constants. + for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i) { + ConstantInt *CB = dyn_cast<ConstantInt>(PN->getIncomingValue(i)); + if (!CB || !CB->getType()->isIntegerTy(1)) + continue; + + // Okay, we now know that all edges from PredBB should be revectored to + // branch to RealDest. + BasicBlock *PredBB = PN->getIncomingBlock(i); + BasicBlock *RealDest = BI->getSuccessor(!CB->getZExtValue()); + + if (RealDest == BB) + continue; // Skip self loops. + // Skip if the predecessor's terminator is an indirect branch. + if (isa<IndirectBrInst>(PredBB->getTerminator())) + continue; + + // The dest block might have PHI nodes, other predecessors and other + // difficult cases. Instead of being smart about this, just insert a new + // block that jumps to the destination block, effectively splitting + // the edge we are about to create. + BasicBlock *EdgeBB = + BasicBlock::Create(BB->getContext(), RealDest->getName() + ".critedge", + RealDest->getParent(), RealDest); + BranchInst *CritEdgeBranch = BranchInst::Create(RealDest, EdgeBB); + CritEdgeBranch->setDebugLoc(BI->getDebugLoc()); + + // Update PHI nodes. + AddPredecessorToBlock(RealDest, EdgeBB, BB); + + // BB may have instructions that are being threaded over. Clone these + // instructions into EdgeBB. We know that there will be no uses of the + // cloned instructions outside of EdgeBB. + BasicBlock::iterator InsertPt = EdgeBB->begin(); + DenseMap<Value *, Value *> TranslateMap; // Track translated values. + for (BasicBlock::iterator BBI = BB->begin(); &*BBI != BI; ++BBI) { + if (PHINode *PN = dyn_cast<PHINode>(BBI)) { + TranslateMap[PN] = PN->getIncomingValueForBlock(PredBB); + continue; + } + // Clone the instruction. + Instruction *N = BBI->clone(); + if (BBI->hasName()) + N->setName(BBI->getName() + ".c"); + + // Update operands due to translation. + for (User::op_iterator i = N->op_begin(), e = N->op_end(); i != e; ++i) { + DenseMap<Value *, Value *>::iterator PI = TranslateMap.find(*i); + if (PI != TranslateMap.end()) + *i = PI->second; + } + + // Check for trivial simplification. + if (Value *V = SimplifyInstruction(N, {DL, nullptr, nullptr, AC})) { + if (!BBI->use_empty()) + TranslateMap[&*BBI] = V; + if (!N->mayHaveSideEffects()) { + N->deleteValue(); // Instruction folded away, don't need actual inst + N = nullptr; + } + } else { + if (!BBI->use_empty()) + TranslateMap[&*BBI] = N; + } + // Insert the new instruction into its new home. + if (N) + EdgeBB->getInstList().insert(InsertPt, N); + + // Register the new instruction with the assumption cache if necessary. + if (auto *II = dyn_cast_or_null<IntrinsicInst>(N)) + if (II->getIntrinsicID() == Intrinsic::assume) + AC->registerAssumption(II); + } + + // Loop over all of the edges from PredBB to BB, changing them to branch + // to EdgeBB instead. + Instruction *PredBBTI = PredBB->getTerminator(); + for (unsigned i = 0, e = PredBBTI->getNumSuccessors(); i != e; ++i) + if (PredBBTI->getSuccessor(i) == BB) { + BB->removePredecessor(PredBB); + PredBBTI->setSuccessor(i, EdgeBB); + } + + // Recurse, simplifying any other constants. + return FoldCondBranchOnPHI(BI, DL, AC) || true; + } + + return false; +} + +/// Given a BB that starts with the specified two-entry PHI node, +/// see if we can eliminate it. +static bool FoldTwoEntryPHINode(PHINode *PN, const TargetTransformInfo &TTI, + const DataLayout &DL) { + // Ok, this is a two entry PHI node. Check to see if this is a simple "if + // statement", which has a very simple dominance structure. Basically, we + // are trying to find the condition that is being branched on, which + // subsequently causes this merge to happen. We really want control + // dependence information for this check, but simplifycfg can't keep it up + // to date, and this catches most of the cases we care about anyway. + BasicBlock *BB = PN->getParent(); + const Function *Fn = BB->getParent(); + if (Fn && Fn->hasFnAttribute(Attribute::OptForFuzzing)) + return false; + + BasicBlock *IfTrue, *IfFalse; + Value *IfCond = GetIfCondition(BB, IfTrue, IfFalse); + if (!IfCond || + // Don't bother if the branch will be constant folded trivially. + isa<ConstantInt>(IfCond)) + return false; + + // Okay, we found that we can merge this two-entry phi node into a select. + // Doing so would require us to fold *all* two entry phi nodes in this block. + // At some point this becomes non-profitable (particularly if the target + // doesn't support cmov's). Only do this transformation if there are two or + // fewer PHI nodes in this block. + unsigned NumPhis = 0; + for (BasicBlock::iterator I = BB->begin(); isa<PHINode>(I); ++NumPhis, ++I) + if (NumPhis > 2) + return false; + + // Loop over the PHI's seeing if we can promote them all to select + // instructions. While we are at it, keep track of the instructions + // that need to be moved to the dominating block. + SmallPtrSet<Instruction *, 4> AggressiveInsts; + int BudgetRemaining = + TwoEntryPHINodeFoldingThreshold * TargetTransformInfo::TCC_Basic; + + for (BasicBlock::iterator II = BB->begin(); isa<PHINode>(II);) { + PHINode *PN = cast<PHINode>(II++); + if (Value *V = SimplifyInstruction(PN, {DL, PN})) { + PN->replaceAllUsesWith(V); + PN->eraseFromParent(); + continue; + } + + if (!DominatesMergePoint(PN->getIncomingValue(0), BB, AggressiveInsts, + BudgetRemaining, TTI) || + !DominatesMergePoint(PN->getIncomingValue(1), BB, AggressiveInsts, + BudgetRemaining, TTI)) + return false; + } + + // If we folded the first phi, PN dangles at this point. Refresh it. If + // we ran out of PHIs then we simplified them all. + PN = dyn_cast<PHINode>(BB->begin()); + if (!PN) + return true; + + // Return true if at least one of these is a 'not', and another is either + // a 'not' too, or a constant. + auto CanHoistNotFromBothValues = [](Value *V0, Value *V1) { + if (!match(V0, m_Not(m_Value()))) + std::swap(V0, V1); + auto Invertible = m_CombineOr(m_Not(m_Value()), m_AnyIntegralConstant()); + return match(V0, m_Not(m_Value())) && match(V1, Invertible); + }; + + // Don't fold i1 branches on PHIs which contain binary operators, unless one + // of the incoming values is an 'not' and another one is freely invertible. + // These can often be turned into switches and other things. + if (PN->getType()->isIntegerTy(1) && + (isa<BinaryOperator>(PN->getIncomingValue(0)) || + isa<BinaryOperator>(PN->getIncomingValue(1)) || + isa<BinaryOperator>(IfCond)) && + !CanHoistNotFromBothValues(PN->getIncomingValue(0), + PN->getIncomingValue(1))) + return false; + + // If all PHI nodes are promotable, check to make sure that all instructions + // in the predecessor blocks can be promoted as well. If not, we won't be able + // to get rid of the control flow, so it's not worth promoting to select + // instructions. + BasicBlock *DomBlock = nullptr; + BasicBlock *IfBlock1 = PN->getIncomingBlock(0); + BasicBlock *IfBlock2 = PN->getIncomingBlock(1); + if (cast<BranchInst>(IfBlock1->getTerminator())->isConditional()) { + IfBlock1 = nullptr; + } else { + DomBlock = *pred_begin(IfBlock1); + for (BasicBlock::iterator I = IfBlock1->begin(); !I->isTerminator(); ++I) + if (!AggressiveInsts.count(&*I) && !isa<DbgInfoIntrinsic>(I)) { + // This is not an aggressive instruction that we can promote. + // Because of this, we won't be able to get rid of the control flow, so + // the xform is not worth it. + return false; + } + } + + if (cast<BranchInst>(IfBlock2->getTerminator())->isConditional()) { + IfBlock2 = nullptr; + } else { + DomBlock = *pred_begin(IfBlock2); + for (BasicBlock::iterator I = IfBlock2->begin(); !I->isTerminator(); ++I) + if (!AggressiveInsts.count(&*I) && !isa<DbgInfoIntrinsic>(I)) { + // This is not an aggressive instruction that we can promote. + // Because of this, we won't be able to get rid of the control flow, so + // the xform is not worth it. + return false; + } + } + assert(DomBlock && "Failed to find root DomBlock"); + + LLVM_DEBUG(dbgs() << "FOUND IF CONDITION! " << *IfCond + << " T: " << IfTrue->getName() + << " F: " << IfFalse->getName() << "\n"); + + // If we can still promote the PHI nodes after this gauntlet of tests, + // do all of the PHI's now. + Instruction *InsertPt = DomBlock->getTerminator(); + IRBuilder<NoFolder> Builder(InsertPt); + + // Move all 'aggressive' instructions, which are defined in the + // conditional parts of the if's up to the dominating block. + if (IfBlock1) + hoistAllInstructionsInto(DomBlock, InsertPt, IfBlock1); + if (IfBlock2) + hoistAllInstructionsInto(DomBlock, InsertPt, IfBlock2); + + while (PHINode *PN = dyn_cast<PHINode>(BB->begin())) { + // Change the PHI node into a select instruction. + Value *TrueVal = PN->getIncomingValue(PN->getIncomingBlock(0) == IfFalse); + Value *FalseVal = PN->getIncomingValue(PN->getIncomingBlock(0) == IfTrue); + + Value *Sel = Builder.CreateSelect(IfCond, TrueVal, FalseVal, "", InsertPt); + PN->replaceAllUsesWith(Sel); + Sel->takeName(PN); + PN->eraseFromParent(); + } + + // At this point, IfBlock1 and IfBlock2 are both empty, so our if statement + // has been flattened. Change DomBlock to jump directly to our new block to + // avoid other simplifycfg's kicking in on the diamond. + Instruction *OldTI = DomBlock->getTerminator(); + Builder.SetInsertPoint(OldTI); + Builder.CreateBr(BB); + OldTI->eraseFromParent(); + return true; +} + +/// If we found a conditional branch that goes to two returning blocks, +/// try to merge them together into one return, +/// introducing a select if the return values disagree. +static bool SimplifyCondBranchToTwoReturns(BranchInst *BI, + IRBuilder<> &Builder) { + assert(BI->isConditional() && "Must be a conditional branch"); + BasicBlock *TrueSucc = BI->getSuccessor(0); + BasicBlock *FalseSucc = BI->getSuccessor(1); + ReturnInst *TrueRet = cast<ReturnInst>(TrueSucc->getTerminator()); + ReturnInst *FalseRet = cast<ReturnInst>(FalseSucc->getTerminator()); + + // Check to ensure both blocks are empty (just a return) or optionally empty + // with PHI nodes. If there are other instructions, merging would cause extra + // computation on one path or the other. + if (!TrueSucc->getFirstNonPHIOrDbg()->isTerminator()) + return false; + if (!FalseSucc->getFirstNonPHIOrDbg()->isTerminator()) + return false; + + Builder.SetInsertPoint(BI); + // Okay, we found a branch that is going to two return nodes. If + // there is no return value for this function, just change the + // branch into a return. + if (FalseRet->getNumOperands() == 0) { + TrueSucc->removePredecessor(BI->getParent()); + FalseSucc->removePredecessor(BI->getParent()); + Builder.CreateRetVoid(); + EraseTerminatorAndDCECond(BI); + return true; + } + + // Otherwise, figure out what the true and false return values are + // so we can insert a new select instruction. + Value *TrueValue = TrueRet->getReturnValue(); + Value *FalseValue = FalseRet->getReturnValue(); + + // Unwrap any PHI nodes in the return blocks. + if (PHINode *TVPN = dyn_cast_or_null<PHINode>(TrueValue)) + if (TVPN->getParent() == TrueSucc) + TrueValue = TVPN->getIncomingValueForBlock(BI->getParent()); + if (PHINode *FVPN = dyn_cast_or_null<PHINode>(FalseValue)) + if (FVPN->getParent() == FalseSucc) + FalseValue = FVPN->getIncomingValueForBlock(BI->getParent()); + + // In order for this transformation to be safe, we must be able to + // unconditionally execute both operands to the return. This is + // normally the case, but we could have a potentially-trapping + // constant expression that prevents this transformation from being + // safe. + if (ConstantExpr *TCV = dyn_cast_or_null<ConstantExpr>(TrueValue)) + if (TCV->canTrap()) + return false; + if (ConstantExpr *FCV = dyn_cast_or_null<ConstantExpr>(FalseValue)) + if (FCV->canTrap()) + return false; + + // Okay, we collected all the mapped values and checked them for sanity, and + // defined to really do this transformation. First, update the CFG. + TrueSucc->removePredecessor(BI->getParent()); + FalseSucc->removePredecessor(BI->getParent()); + + // Insert select instructions where needed. + Value *BrCond = BI->getCondition(); + if (TrueValue) { + // Insert a select if the results differ. + if (TrueValue == FalseValue || isa<UndefValue>(FalseValue)) { + } else if (isa<UndefValue>(TrueValue)) { + TrueValue = FalseValue; + } else { + TrueValue = + Builder.CreateSelect(BrCond, TrueValue, FalseValue, "retval", BI); + } + } + + Value *RI = + !TrueValue ? Builder.CreateRetVoid() : Builder.CreateRet(TrueValue); + + (void)RI; + + LLVM_DEBUG(dbgs() << "\nCHANGING BRANCH TO TWO RETURNS INTO SELECT:" + << "\n " << *BI << "NewRet = " << *RI << "TRUEBLOCK: " + << *TrueSucc << "FALSEBLOCK: " << *FalseSucc); + + EraseTerminatorAndDCECond(BI); + + return true; +} + +/// Return true if the given instruction is available +/// in its predecessor block. If yes, the instruction will be removed. +static bool tryCSEWithPredecessor(Instruction *Inst, BasicBlock *PB) { + if (!isa<BinaryOperator>(Inst) && !isa<CmpInst>(Inst)) + return false; + for (Instruction &I : *PB) { + Instruction *PBI = &I; + // Check whether Inst and PBI generate the same value. + if (Inst->isIdenticalTo(PBI)) { + Inst->replaceAllUsesWith(PBI); + Inst->eraseFromParent(); + return true; + } + } + return false; +} + +/// Return true if either PBI or BI has branch weight available, and store +/// the weights in {Pred|Succ}{True|False}Weight. If one of PBI and BI does +/// not have branch weight, use 1:1 as its weight. +static bool extractPredSuccWeights(BranchInst *PBI, BranchInst *BI, + uint64_t &PredTrueWeight, + uint64_t &PredFalseWeight, + uint64_t &SuccTrueWeight, + uint64_t &SuccFalseWeight) { + bool PredHasWeights = + PBI->extractProfMetadata(PredTrueWeight, PredFalseWeight); + bool SuccHasWeights = + BI->extractProfMetadata(SuccTrueWeight, SuccFalseWeight); + if (PredHasWeights || SuccHasWeights) { + if (!PredHasWeights) + PredTrueWeight = PredFalseWeight = 1; + if (!SuccHasWeights) + SuccTrueWeight = SuccFalseWeight = 1; + return true; + } else { + return false; + } +} + +/// If this basic block is simple enough, and if a predecessor branches to us +/// and one of our successors, fold the block into the predecessor and use +/// logical operations to pick the right destination. +bool llvm::FoldBranchToCommonDest(BranchInst *BI, MemorySSAUpdater *MSSAU, + unsigned BonusInstThreshold) { + BasicBlock *BB = BI->getParent(); + + const unsigned PredCount = pred_size(BB); + + Instruction *Cond = nullptr; + if (BI->isConditional()) + Cond = dyn_cast<Instruction>(BI->getCondition()); + else { + // For unconditional branch, check for a simple CFG pattern, where + // BB has a single predecessor and BB's successor is also its predecessor's + // successor. If such pattern exists, check for CSE between BB and its + // predecessor. + if (BasicBlock *PB = BB->getSinglePredecessor()) + if (BranchInst *PBI = dyn_cast<BranchInst>(PB->getTerminator())) + if (PBI->isConditional() && + (BI->getSuccessor(0) == PBI->getSuccessor(0) || + BI->getSuccessor(0) == PBI->getSuccessor(1))) { + for (auto I = BB->instructionsWithoutDebug().begin(), + E = BB->instructionsWithoutDebug().end(); + I != E;) { + Instruction *Curr = &*I++; + if (isa<CmpInst>(Curr)) { + Cond = Curr; + break; + } + // Quit if we can't remove this instruction. + if (!tryCSEWithPredecessor(Curr, PB)) + return false; + } + } + + if (!Cond) + return false; + } + + if (!Cond || (!isa<CmpInst>(Cond) && !isa<BinaryOperator>(Cond)) || + Cond->getParent() != BB || !Cond->hasOneUse()) + return false; + + // Make sure the instruction after the condition is the cond branch. + BasicBlock::iterator CondIt = ++Cond->getIterator(); + + // Ignore dbg intrinsics. + while (isa<DbgInfoIntrinsic>(CondIt)) + ++CondIt; + + if (&*CondIt != BI) + return false; + + // Only allow this transformation if computing the condition doesn't involve + // too many instructions and these involved instructions can be executed + // unconditionally. We denote all involved instructions except the condition + // as "bonus instructions", and only allow this transformation when the + // number of the bonus instructions we'll need to create when cloning into + // each predecessor does not exceed a certain threshold. + unsigned NumBonusInsts = 0; + for (auto I = BB->begin(); Cond != &*I; ++I) { + // Ignore dbg intrinsics. + if (isa<DbgInfoIntrinsic>(I)) + continue; + if (!I->hasOneUse() || !isSafeToSpeculativelyExecute(&*I)) + return false; + // I has only one use and can be executed unconditionally. + Instruction *User = dyn_cast<Instruction>(I->user_back()); + if (User == nullptr || User->getParent() != BB) + return false; + // I is used in the same BB. Since BI uses Cond and doesn't have more slots + // to use any other instruction, User must be an instruction between next(I) + // and Cond. + + // Account for the cost of duplicating this instruction into each + // predecessor. + NumBonusInsts += PredCount; + // Early exits once we reach the limit. + if (NumBonusInsts > BonusInstThreshold) + return false; + } + + // Cond is known to be a compare or binary operator. Check to make sure that + // neither operand is a potentially-trapping constant expression. + if (ConstantExpr *CE = dyn_cast<ConstantExpr>(Cond->getOperand(0))) + if (CE->canTrap()) + return false; + if (ConstantExpr *CE = dyn_cast<ConstantExpr>(Cond->getOperand(1))) + if (CE->canTrap()) + return false; + + // Finally, don't infinitely unroll conditional loops. + BasicBlock *TrueDest = BI->getSuccessor(0); + BasicBlock *FalseDest = (BI->isConditional()) ? BI->getSuccessor(1) : nullptr; + if (TrueDest == BB || FalseDest == BB) + return false; + + for (pred_iterator PI = pred_begin(BB), E = pred_end(BB); PI != E; ++PI) { + BasicBlock *PredBlock = *PI; + BranchInst *PBI = dyn_cast<BranchInst>(PredBlock->getTerminator()); + + // Check that we have two conditional branches. If there is a PHI node in + // the common successor, verify that the same value flows in from both + // blocks. + SmallVector<PHINode *, 4> PHIs; + if (!PBI || PBI->isUnconditional() || + (BI->isConditional() && !SafeToMergeTerminators(BI, PBI)) || + (!BI->isConditional() && + !isProfitableToFoldUnconditional(BI, PBI, Cond, PHIs))) + continue; + + // Determine if the two branches share a common destination. + Instruction::BinaryOps Opc = Instruction::BinaryOpsEnd; + bool InvertPredCond = false; + + if (BI->isConditional()) { + if (PBI->getSuccessor(0) == TrueDest) { + Opc = Instruction::Or; + } else if (PBI->getSuccessor(1) == FalseDest) { + Opc = Instruction::And; + } else if (PBI->getSuccessor(0) == FalseDest) { + Opc = Instruction::And; + InvertPredCond = true; + } else if (PBI->getSuccessor(1) == TrueDest) { + Opc = Instruction::Or; + InvertPredCond = true; + } else { + continue; + } + } else { + if (PBI->getSuccessor(0) != TrueDest && PBI->getSuccessor(1) != TrueDest) + continue; + } + + LLVM_DEBUG(dbgs() << "FOLDING BRANCH TO COMMON DEST:\n" << *PBI << *BB); + IRBuilder<> Builder(PBI); + + // If we need to invert the condition in the pred block to match, do so now. + if (InvertPredCond) { + Value *NewCond = PBI->getCondition(); + + if (NewCond->hasOneUse() && isa<CmpInst>(NewCond)) { + CmpInst *CI = cast<CmpInst>(NewCond); + CI->setPredicate(CI->getInversePredicate()); + } else { + NewCond = + Builder.CreateNot(NewCond, PBI->getCondition()->getName() + ".not"); + } + + PBI->setCondition(NewCond); + PBI->swapSuccessors(); + } + + // If we have bonus instructions, clone them into the predecessor block. + // Note that there may be multiple predecessor blocks, so we cannot move + // bonus instructions to a predecessor block. + ValueToValueMapTy VMap; // maps original values to cloned values + // We already make sure Cond is the last instruction before BI. Therefore, + // all instructions before Cond other than DbgInfoIntrinsic are bonus + // instructions. + for (auto BonusInst = BB->begin(); Cond != &*BonusInst; ++BonusInst) { + if (isa<DbgInfoIntrinsic>(BonusInst)) + continue; + Instruction *NewBonusInst = BonusInst->clone(); + RemapInstruction(NewBonusInst, VMap, + RF_NoModuleLevelChanges | RF_IgnoreMissingLocals); + VMap[&*BonusInst] = NewBonusInst; + + // If we moved a load, we cannot any longer claim any knowledge about + // its potential value. The previous information might have been valid + // only given the branch precondition. + // For an analogous reason, we must also drop all the metadata whose + // semantics we don't understand. + NewBonusInst->dropUnknownNonDebugMetadata(); + + PredBlock->getInstList().insert(PBI->getIterator(), NewBonusInst); + NewBonusInst->takeName(&*BonusInst); + BonusInst->setName(BonusInst->getName() + ".old"); + } + + // Clone Cond into the predecessor basic block, and or/and the + // two conditions together. + Instruction *CondInPred = Cond->clone(); + RemapInstruction(CondInPred, VMap, + RF_NoModuleLevelChanges | RF_IgnoreMissingLocals); + PredBlock->getInstList().insert(PBI->getIterator(), CondInPred); + CondInPred->takeName(Cond); + Cond->setName(CondInPred->getName() + ".old"); + + if (BI->isConditional()) { + Instruction *NewCond = cast<Instruction>( + Builder.CreateBinOp(Opc, PBI->getCondition(), CondInPred, "or.cond")); + PBI->setCondition(NewCond); + + uint64_t PredTrueWeight, PredFalseWeight, SuccTrueWeight, SuccFalseWeight; + bool HasWeights = + extractPredSuccWeights(PBI, BI, PredTrueWeight, PredFalseWeight, + SuccTrueWeight, SuccFalseWeight); + SmallVector<uint64_t, 8> NewWeights; + + if (PBI->getSuccessor(0) == BB) { + if (HasWeights) { + // PBI: br i1 %x, BB, FalseDest + // BI: br i1 %y, TrueDest, FalseDest + // TrueWeight is TrueWeight for PBI * TrueWeight for BI. + NewWeights.push_back(PredTrueWeight * SuccTrueWeight); + // FalseWeight is FalseWeight for PBI * TotalWeight for BI + + // TrueWeight for PBI * FalseWeight for BI. + // We assume that total weights of a BranchInst can fit into 32 bits. + // Therefore, we will not have overflow using 64-bit arithmetic. + NewWeights.push_back(PredFalseWeight * + (SuccFalseWeight + SuccTrueWeight) + + PredTrueWeight * SuccFalseWeight); + } + AddPredecessorToBlock(TrueDest, PredBlock, BB, MSSAU); + PBI->setSuccessor(0, TrueDest); + } + if (PBI->getSuccessor(1) == BB) { + if (HasWeights) { + // PBI: br i1 %x, TrueDest, BB + // BI: br i1 %y, TrueDest, FalseDest + // TrueWeight is TrueWeight for PBI * TotalWeight for BI + + // FalseWeight for PBI * TrueWeight for BI. + NewWeights.push_back(PredTrueWeight * + (SuccFalseWeight + SuccTrueWeight) + + PredFalseWeight * SuccTrueWeight); + // FalseWeight is FalseWeight for PBI * FalseWeight for BI. + NewWeights.push_back(PredFalseWeight * SuccFalseWeight); + } + AddPredecessorToBlock(FalseDest, PredBlock, BB, MSSAU); + PBI->setSuccessor(1, FalseDest); + } + if (NewWeights.size() == 2) { + // Halve the weights if any of them cannot fit in an uint32_t + FitWeights(NewWeights); + + SmallVector<uint32_t, 8> MDWeights(NewWeights.begin(), + NewWeights.end()); + setBranchWeights(PBI, MDWeights[0], MDWeights[1]); + } else + PBI->setMetadata(LLVMContext::MD_prof, nullptr); + } else { + // Update PHI nodes in the common successors. + for (unsigned i = 0, e = PHIs.size(); i != e; ++i) { + ConstantInt *PBI_C = cast<ConstantInt>( + PHIs[i]->getIncomingValueForBlock(PBI->getParent())); + assert(PBI_C->getType()->isIntegerTy(1)); + Instruction *MergedCond = nullptr; + if (PBI->getSuccessor(0) == TrueDest) { + // Create (PBI_Cond and PBI_C) or (!PBI_Cond and BI_Value) + // PBI_C is true: PBI_Cond or (!PBI_Cond and BI_Value) + // is false: !PBI_Cond and BI_Value + Instruction *NotCond = cast<Instruction>( + Builder.CreateNot(PBI->getCondition(), "not.cond")); + MergedCond = cast<Instruction>( + Builder.CreateBinOp(Instruction::And, NotCond, CondInPred, + "and.cond")); + if (PBI_C->isOne()) + MergedCond = cast<Instruction>(Builder.CreateBinOp( + Instruction::Or, PBI->getCondition(), MergedCond, "or.cond")); + } else { + // Create (PBI_Cond and BI_Value) or (!PBI_Cond and PBI_C) + // PBI_C is true: (PBI_Cond and BI_Value) or (!PBI_Cond) + // is false: PBI_Cond and BI_Value + MergedCond = cast<Instruction>(Builder.CreateBinOp( + Instruction::And, PBI->getCondition(), CondInPred, "and.cond")); + if (PBI_C->isOne()) { + Instruction *NotCond = cast<Instruction>( + Builder.CreateNot(PBI->getCondition(), "not.cond")); + MergedCond = cast<Instruction>(Builder.CreateBinOp( + Instruction::Or, NotCond, MergedCond, "or.cond")); + } + } + // Update PHI Node. + PHIs[i]->setIncomingValueForBlock(PBI->getParent(), MergedCond); + } + + // PBI is changed to branch to TrueDest below. Remove itself from + // potential phis from all other successors. + if (MSSAU) + MSSAU->changeCondBranchToUnconditionalTo(PBI, TrueDest); + + // Change PBI from Conditional to Unconditional. + BranchInst *New_PBI = BranchInst::Create(TrueDest, PBI); + EraseTerminatorAndDCECond(PBI, MSSAU); + PBI = New_PBI; + } + + // If BI was a loop latch, it may have had associated loop metadata. + // We need to copy it to the new latch, that is, PBI. + if (MDNode *LoopMD = BI->getMetadata(LLVMContext::MD_loop)) + PBI->setMetadata(LLVMContext::MD_loop, LoopMD); + + // TODO: If BB is reachable from all paths through PredBlock, then we + // could replace PBI's branch probabilities with BI's. + + // Copy any debug value intrinsics into the end of PredBlock. + for (Instruction &I : *BB) + if (isa<DbgInfoIntrinsic>(I)) + I.clone()->insertBefore(PBI); + + return true; + } + return false; +} + +// If there is only one store in BB1 and BB2, return it, otherwise return +// nullptr. +static StoreInst *findUniqueStoreInBlocks(BasicBlock *BB1, BasicBlock *BB2) { + StoreInst *S = nullptr; + for (auto *BB : {BB1, BB2}) { + if (!BB) + continue; + for (auto &I : *BB) + if (auto *SI = dyn_cast<StoreInst>(&I)) { + if (S) + // Multiple stores seen. + return nullptr; + else + S = SI; + } + } + return S; +} + +static Value *ensureValueAvailableInSuccessor(Value *V, BasicBlock *BB, + Value *AlternativeV = nullptr) { + // PHI is going to be a PHI node that allows the value V that is defined in + // BB to be referenced in BB's only successor. + // + // If AlternativeV is nullptr, the only value we care about in PHI is V. It + // doesn't matter to us what the other operand is (it'll never get used). We + // could just create a new PHI with an undef incoming value, but that could + // increase register pressure if EarlyCSE/InstCombine can't fold it with some + // other PHI. So here we directly look for some PHI in BB's successor with V + // as an incoming operand. If we find one, we use it, else we create a new + // one. + // + // If AlternativeV is not nullptr, we care about both incoming values in PHI. + // PHI must be exactly: phi <ty> [ %BB, %V ], [ %OtherBB, %AlternativeV] + // where OtherBB is the single other predecessor of BB's only successor. + PHINode *PHI = nullptr; + BasicBlock *Succ = BB->getSingleSuccessor(); + + for (auto I = Succ->begin(); isa<PHINode>(I); ++I) + if (cast<PHINode>(I)->getIncomingValueForBlock(BB) == V) { + PHI = cast<PHINode>(I); + if (!AlternativeV) + break; + + assert(Succ->hasNPredecessors(2)); + auto PredI = pred_begin(Succ); + BasicBlock *OtherPredBB = *PredI == BB ? *++PredI : *PredI; + if (PHI->getIncomingValueForBlock(OtherPredBB) == AlternativeV) + break; + PHI = nullptr; + } + if (PHI) + return PHI; + + // If V is not an instruction defined in BB, just return it. + if (!AlternativeV && + (!isa<Instruction>(V) || cast<Instruction>(V)->getParent() != BB)) + return V; + + PHI = PHINode::Create(V->getType(), 2, "simplifycfg.merge", &Succ->front()); + PHI->addIncoming(V, BB); + for (BasicBlock *PredBB : predecessors(Succ)) + if (PredBB != BB) + PHI->addIncoming( + AlternativeV ? AlternativeV : UndefValue::get(V->getType()), PredBB); + return PHI; +} + +static bool mergeConditionalStoreToAddress(BasicBlock *PTB, BasicBlock *PFB, + BasicBlock *QTB, BasicBlock *QFB, + BasicBlock *PostBB, Value *Address, + bool InvertPCond, bool InvertQCond, + const DataLayout &DL, + const TargetTransformInfo &TTI) { + // For every pointer, there must be exactly two stores, one coming from + // PTB or PFB, and the other from QTB or QFB. We don't support more than one + // store (to any address) in PTB,PFB or QTB,QFB. + // FIXME: We could relax this restriction with a bit more work and performance + // testing. + StoreInst *PStore = findUniqueStoreInBlocks(PTB, PFB); + StoreInst *QStore = findUniqueStoreInBlocks(QTB, QFB); + if (!PStore || !QStore) + return false; + + // Now check the stores are compatible. + if (!QStore->isUnordered() || !PStore->isUnordered()) + return false; + + // Check that sinking the store won't cause program behavior changes. Sinking + // the store out of the Q blocks won't change any behavior as we're sinking + // from a block to its unconditional successor. But we're moving a store from + // the P blocks down through the middle block (QBI) and past both QFB and QTB. + // So we need to check that there are no aliasing loads or stores in + // QBI, QTB and QFB. We also need to check there are no conflicting memory + // operations between PStore and the end of its parent block. + // + // The ideal way to do this is to query AliasAnalysis, but we don't + // preserve AA currently so that is dangerous. Be super safe and just + // check there are no other memory operations at all. + for (auto &I : *QFB->getSinglePredecessor()) + if (I.mayReadOrWriteMemory()) + return false; + for (auto &I : *QFB) + if (&I != QStore && I.mayReadOrWriteMemory()) + return false; + if (QTB) + for (auto &I : *QTB) + if (&I != QStore && I.mayReadOrWriteMemory()) + return false; + for (auto I = BasicBlock::iterator(PStore), E = PStore->getParent()->end(); + I != E; ++I) + if (&*I != PStore && I->mayReadOrWriteMemory()) + return false; + + // If we're not in aggressive mode, we only optimize if we have some + // confidence that by optimizing we'll allow P and/or Q to be if-converted. + auto IsWorthwhile = [&](BasicBlock *BB, ArrayRef<StoreInst *> FreeStores) { + if (!BB) + return true; + // Heuristic: if the block can be if-converted/phi-folded and the + // instructions inside are all cheap (arithmetic/GEPs), it's worthwhile to + // thread this store. + int BudgetRemaining = + PHINodeFoldingThreshold * TargetTransformInfo::TCC_Basic; + for (auto &I : BB->instructionsWithoutDebug()) { + // Consider terminator instruction to be free. + if (I.isTerminator()) + continue; + // If this is one the stores that we want to speculate out of this BB, + // then don't count it's cost, consider it to be free. + if (auto *S = dyn_cast<StoreInst>(&I)) + if (llvm::find(FreeStores, S)) + continue; + // Else, we have a white-list of instructions that we are ak speculating. + if (!isa<BinaryOperator>(I) && !isa<GetElementPtrInst>(I)) + return false; // Not in white-list - not worthwhile folding. + // And finally, if this is a non-free instruction that we are okay + // speculating, ensure that we consider the speculation budget. + BudgetRemaining -= TTI.getUserCost(&I); + if (BudgetRemaining < 0) + return false; // Eagerly refuse to fold as soon as we're out of budget. + } + assert(BudgetRemaining >= 0 && + "When we run out of budget we will eagerly return from within the " + "per-instruction loop."); + return true; + }; + + const SmallVector<StoreInst *, 2> FreeStores = {PStore, QStore}; + if (!MergeCondStoresAggressively && + (!IsWorthwhile(PTB, FreeStores) || !IsWorthwhile(PFB, FreeStores) || + !IsWorthwhile(QTB, FreeStores) || !IsWorthwhile(QFB, FreeStores))) + return false; + + // If PostBB has more than two predecessors, we need to split it so we can + // sink the store. + if (std::next(pred_begin(PostBB), 2) != pred_end(PostBB)) { + // We know that QFB's only successor is PostBB. And QFB has a single + // predecessor. If QTB exists, then its only successor is also PostBB. + // If QTB does not exist, then QFB's only predecessor has a conditional + // branch to QFB and PostBB. + BasicBlock *TruePred = QTB ? QTB : QFB->getSinglePredecessor(); + BasicBlock *NewBB = SplitBlockPredecessors(PostBB, { QFB, TruePred}, + "condstore.split"); + if (!NewBB) + return false; + PostBB = NewBB; + } + + // OK, we're going to sink the stores to PostBB. The store has to be + // conditional though, so first create the predicate. + Value *PCond = cast<BranchInst>(PFB->getSinglePredecessor()->getTerminator()) + ->getCondition(); + Value *QCond = cast<BranchInst>(QFB->getSinglePredecessor()->getTerminator()) + ->getCondition(); + + Value *PPHI = ensureValueAvailableInSuccessor(PStore->getValueOperand(), + PStore->getParent()); + Value *QPHI = ensureValueAvailableInSuccessor(QStore->getValueOperand(), + QStore->getParent(), PPHI); + + IRBuilder<> QB(&*PostBB->getFirstInsertionPt()); + + Value *PPred = PStore->getParent() == PTB ? PCond : QB.CreateNot(PCond); + Value *QPred = QStore->getParent() == QTB ? QCond : QB.CreateNot(QCond); + + if (InvertPCond) + PPred = QB.CreateNot(PPred); + if (InvertQCond) + QPred = QB.CreateNot(QPred); + Value *CombinedPred = QB.CreateOr(PPred, QPred); + + auto *T = + SplitBlockAndInsertIfThen(CombinedPred, &*QB.GetInsertPoint(), false); + QB.SetInsertPoint(T); + StoreInst *SI = cast<StoreInst>(QB.CreateStore(QPHI, Address)); + AAMDNodes AAMD; + PStore->getAAMetadata(AAMD, /*Merge=*/false); + PStore->getAAMetadata(AAMD, /*Merge=*/true); + SI->setAAMetadata(AAMD); + unsigned PAlignment = PStore->getAlignment(); + unsigned QAlignment = QStore->getAlignment(); + unsigned TypeAlignment = + DL.getABITypeAlignment(SI->getValueOperand()->getType()); + unsigned MinAlignment; + unsigned MaxAlignment; + std::tie(MinAlignment, MaxAlignment) = std::minmax(PAlignment, QAlignment); + // Choose the minimum alignment. If we could prove both stores execute, we + // could use biggest one. In this case, though, we only know that one of the + // stores executes. And we don't know it's safe to take the alignment from a + // store that doesn't execute. + if (MinAlignment != 0) { + // Choose the minimum of all non-zero alignments. + SI->setAlignment(Align(MinAlignment)); + } else if (MaxAlignment != 0) { + // Choose the minimal alignment between the non-zero alignment and the ABI + // default alignment for the type of the stored value. + SI->setAlignment(Align(std::min(MaxAlignment, TypeAlignment))); + } else { + // If both alignments are zero, use ABI default alignment for the type of + // the stored value. + SI->setAlignment(Align(TypeAlignment)); + } + + QStore->eraseFromParent(); + PStore->eraseFromParent(); + + return true; +} + +static bool mergeConditionalStores(BranchInst *PBI, BranchInst *QBI, + const DataLayout &DL, + const TargetTransformInfo &TTI) { + // The intention here is to find diamonds or triangles (see below) where each + // conditional block contains a store to the same address. Both of these + // stores are conditional, so they can't be unconditionally sunk. But it may + // be profitable to speculatively sink the stores into one merged store at the + // end, and predicate the merged store on the union of the two conditions of + // PBI and QBI. + // + // This can reduce the number of stores executed if both of the conditions are + // true, and can allow the blocks to become small enough to be if-converted. + // This optimization will also chain, so that ladders of test-and-set + // sequences can be if-converted away. + // + // We only deal with simple diamonds or triangles: + // + // PBI or PBI or a combination of the two + // / \ | \ + // PTB PFB | PFB + // \ / | / + // QBI QBI + // / \ | \ + // QTB QFB | QFB + // \ / | / + // PostBB PostBB + // + // We model triangles as a type of diamond with a nullptr "true" block. + // Triangles are canonicalized so that the fallthrough edge is represented by + // a true condition, as in the diagram above. + BasicBlock *PTB = PBI->getSuccessor(0); + BasicBlock *PFB = PBI->getSuccessor(1); + BasicBlock *QTB = QBI->getSuccessor(0); + BasicBlock *QFB = QBI->getSuccessor(1); + BasicBlock *PostBB = QFB->getSingleSuccessor(); + + // Make sure we have a good guess for PostBB. If QTB's only successor is + // QFB, then QFB is a better PostBB. + if (QTB->getSingleSuccessor() == QFB) + PostBB = QFB; + + // If we couldn't find a good PostBB, stop. + if (!PostBB) + return false; + + bool InvertPCond = false, InvertQCond = false; + // Canonicalize fallthroughs to the true branches. + if (PFB == QBI->getParent()) { + std::swap(PFB, PTB); + InvertPCond = true; + } + if (QFB == PostBB) { + std::swap(QFB, QTB); + InvertQCond = true; + } + + // From this point on we can assume PTB or QTB may be fallthroughs but PFB + // and QFB may not. Model fallthroughs as a nullptr block. + if (PTB == QBI->getParent()) + PTB = nullptr; + if (QTB == PostBB) + QTB = nullptr; + + // Legality bailouts. We must have at least the non-fallthrough blocks and + // the post-dominating block, and the non-fallthroughs must only have one + // predecessor. + auto HasOnePredAndOneSucc = [](BasicBlock *BB, BasicBlock *P, BasicBlock *S) { + return BB->getSinglePredecessor() == P && BB->getSingleSuccessor() == S; + }; + if (!HasOnePredAndOneSucc(PFB, PBI->getParent(), QBI->getParent()) || + !HasOnePredAndOneSucc(QFB, QBI->getParent(), PostBB)) + return false; + if ((PTB && !HasOnePredAndOneSucc(PTB, PBI->getParent(), QBI->getParent())) || + (QTB && !HasOnePredAndOneSucc(QTB, QBI->getParent(), PostBB))) + return false; + if (!QBI->getParent()->hasNUses(2)) + return false; + + // OK, this is a sequence of two diamonds or triangles. + // Check if there are stores in PTB or PFB that are repeated in QTB or QFB. + SmallPtrSet<Value *, 4> PStoreAddresses, QStoreAddresses; + for (auto *BB : {PTB, PFB}) { + if (!BB) + continue; + for (auto &I : *BB) + if (StoreInst *SI = dyn_cast<StoreInst>(&I)) + PStoreAddresses.insert(SI->getPointerOperand()); + } + for (auto *BB : {QTB, QFB}) { + if (!BB) + continue; + for (auto &I : *BB) + if (StoreInst *SI = dyn_cast<StoreInst>(&I)) + QStoreAddresses.insert(SI->getPointerOperand()); + } + + set_intersect(PStoreAddresses, QStoreAddresses); + // set_intersect mutates PStoreAddresses in place. Rename it here to make it + // clear what it contains. + auto &CommonAddresses = PStoreAddresses; + + bool Changed = false; + for (auto *Address : CommonAddresses) + Changed |= mergeConditionalStoreToAddress( + PTB, PFB, QTB, QFB, PostBB, Address, InvertPCond, InvertQCond, DL, TTI); + return Changed; +} + +/// If we have a conditional branch as a predecessor of another block, +/// this function tries to simplify it. We know +/// that PBI and BI are both conditional branches, and BI is in one of the +/// successor blocks of PBI - PBI branches to BI. +static bool SimplifyCondBranchToCondBranch(BranchInst *PBI, BranchInst *BI, + const DataLayout &DL, + const TargetTransformInfo &TTI) { + assert(PBI->isConditional() && BI->isConditional()); + BasicBlock *BB = BI->getParent(); + + // If this block ends with a branch instruction, and if there is a + // predecessor that ends on a branch of the same condition, make + // this conditional branch redundant. + if (PBI->getCondition() == BI->getCondition() && + PBI->getSuccessor(0) != PBI->getSuccessor(1)) { + // Okay, the outcome of this conditional branch is statically + // knowable. If this block had a single pred, handle specially. + if (BB->getSinglePredecessor()) { + // Turn this into a branch on constant. + bool CondIsTrue = PBI->getSuccessor(0) == BB; + BI->setCondition( + ConstantInt::get(Type::getInt1Ty(BB->getContext()), CondIsTrue)); + return true; // Nuke the branch on constant. + } + + // Otherwise, if there are multiple predecessors, insert a PHI that merges + // in the constant and simplify the block result. Subsequent passes of + // simplifycfg will thread the block. + if (BlockIsSimpleEnoughToThreadThrough(BB)) { + pred_iterator PB = pred_begin(BB), PE = pred_end(BB); + PHINode *NewPN = PHINode::Create( + Type::getInt1Ty(BB->getContext()), std::distance(PB, PE), + BI->getCondition()->getName() + ".pr", &BB->front()); + // Okay, we're going to insert the PHI node. Since PBI is not the only + // predecessor, compute the PHI'd conditional value for all of the preds. + // Any predecessor where the condition is not computable we keep symbolic. + for (pred_iterator PI = PB; PI != PE; ++PI) { + BasicBlock *P = *PI; + if ((PBI = dyn_cast<BranchInst>(P->getTerminator())) && PBI != BI && + PBI->isConditional() && PBI->getCondition() == BI->getCondition() && + PBI->getSuccessor(0) != PBI->getSuccessor(1)) { + bool CondIsTrue = PBI->getSuccessor(0) == BB; + NewPN->addIncoming( + ConstantInt::get(Type::getInt1Ty(BB->getContext()), CondIsTrue), + P); + } else { + NewPN->addIncoming(BI->getCondition(), P); + } + } + + BI->setCondition(NewPN); + return true; + } + } + + if (auto *CE = dyn_cast<ConstantExpr>(BI->getCondition())) + if (CE->canTrap()) + return false; + + // If both branches are conditional and both contain stores to the same + // address, remove the stores from the conditionals and create a conditional + // merged store at the end. + if (MergeCondStores && mergeConditionalStores(PBI, BI, DL, TTI)) + return true; + + // If this is a conditional branch in an empty block, and if any + // predecessors are a conditional branch to one of our destinations, + // fold the conditions into logical ops and one cond br. + + // Ignore dbg intrinsics. + if (&*BB->instructionsWithoutDebug().begin() != BI) + return false; + + int PBIOp, BIOp; + if (PBI->getSuccessor(0) == BI->getSuccessor(0)) { + PBIOp = 0; + BIOp = 0; + } else if (PBI->getSuccessor(0) == BI->getSuccessor(1)) { + PBIOp = 0; + BIOp = 1; + } else if (PBI->getSuccessor(1) == BI->getSuccessor(0)) { + PBIOp = 1; + BIOp = 0; + } else if (PBI->getSuccessor(1) == BI->getSuccessor(1)) { + PBIOp = 1; + BIOp = 1; + } else { + return false; + } + + // Check to make sure that the other destination of this branch + // isn't BB itself. If so, this is an infinite loop that will + // keep getting unwound. + if (PBI->getSuccessor(PBIOp) == BB) + return false; + + // Do not perform this transformation if it would require + // insertion of a large number of select instructions. For targets + // without predication/cmovs, this is a big pessimization. + + // Also do not perform this transformation if any phi node in the common + // destination block can trap when reached by BB or PBB (PR17073). In that + // case, it would be unsafe to hoist the operation into a select instruction. + + BasicBlock *CommonDest = PBI->getSuccessor(PBIOp); + unsigned NumPhis = 0; + for (BasicBlock::iterator II = CommonDest->begin(); isa<PHINode>(II); + ++II, ++NumPhis) { + if (NumPhis > 2) // Disable this xform. + return false; + + PHINode *PN = cast<PHINode>(II); + Value *BIV = PN->getIncomingValueForBlock(BB); + if (ConstantExpr *CE = dyn_cast<ConstantExpr>(BIV)) + if (CE->canTrap()) + return false; + + unsigned PBBIdx = PN->getBasicBlockIndex(PBI->getParent()); + Value *PBIV = PN->getIncomingValue(PBBIdx); + if (ConstantExpr *CE = dyn_cast<ConstantExpr>(PBIV)) + if (CE->canTrap()) + return false; + } + + // Finally, if everything is ok, fold the branches to logical ops. + BasicBlock *OtherDest = BI->getSuccessor(BIOp ^ 1); + + LLVM_DEBUG(dbgs() << "FOLDING BRs:" << *PBI->getParent() + << "AND: " << *BI->getParent()); + + // If OtherDest *is* BB, then BB is a basic block with a single conditional + // branch in it, where one edge (OtherDest) goes back to itself but the other + // exits. We don't *know* that the program avoids the infinite loop + // (even though that seems likely). If we do this xform naively, we'll end up + // recursively unpeeling the loop. Since we know that (after the xform is + // done) that the block *is* infinite if reached, we just make it an obviously + // infinite loop with no cond branch. + if (OtherDest == BB) { + // Insert it at the end of the function, because it's either code, + // or it won't matter if it's hot. :) + BasicBlock *InfLoopBlock = + BasicBlock::Create(BB->getContext(), "infloop", BB->getParent()); + BranchInst::Create(InfLoopBlock, InfLoopBlock); + OtherDest = InfLoopBlock; + } + + LLVM_DEBUG(dbgs() << *PBI->getParent()->getParent()); + + // BI may have other predecessors. Because of this, we leave + // it alone, but modify PBI. + + // Make sure we get to CommonDest on True&True directions. + Value *PBICond = PBI->getCondition(); + IRBuilder<NoFolder> Builder(PBI); + if (PBIOp) + PBICond = Builder.CreateNot(PBICond, PBICond->getName() + ".not"); + + Value *BICond = BI->getCondition(); + if (BIOp) + BICond = Builder.CreateNot(BICond, BICond->getName() + ".not"); + + // Merge the conditions. + Value *Cond = Builder.CreateOr(PBICond, BICond, "brmerge"); + + // Modify PBI to branch on the new condition to the new dests. + PBI->setCondition(Cond); + PBI->setSuccessor(0, CommonDest); + PBI->setSuccessor(1, OtherDest); + + // Update branch weight for PBI. + uint64_t PredTrueWeight, PredFalseWeight, SuccTrueWeight, SuccFalseWeight; + uint64_t PredCommon, PredOther, SuccCommon, SuccOther; + bool HasWeights = + extractPredSuccWeights(PBI, BI, PredTrueWeight, PredFalseWeight, + SuccTrueWeight, SuccFalseWeight); + if (HasWeights) { + PredCommon = PBIOp ? PredFalseWeight : PredTrueWeight; + PredOther = PBIOp ? PredTrueWeight : PredFalseWeight; + SuccCommon = BIOp ? SuccFalseWeight : SuccTrueWeight; + SuccOther = BIOp ? SuccTrueWeight : SuccFalseWeight; + // The weight to CommonDest should be PredCommon * SuccTotal + + // PredOther * SuccCommon. + // The weight to OtherDest should be PredOther * SuccOther. + uint64_t NewWeights[2] = {PredCommon * (SuccCommon + SuccOther) + + PredOther * SuccCommon, + PredOther * SuccOther}; + // Halve the weights if any of them cannot fit in an uint32_t + FitWeights(NewWeights); + + setBranchWeights(PBI, NewWeights[0], NewWeights[1]); + } + + // OtherDest may have phi nodes. If so, add an entry from PBI's + // block that are identical to the entries for BI's block. + AddPredecessorToBlock(OtherDest, PBI->getParent(), BB); + + // We know that the CommonDest already had an edge from PBI to + // it. If it has PHIs though, the PHIs may have different + // entries for BB and PBI's BB. If so, insert a select to make + // them agree. + for (PHINode &PN : CommonDest->phis()) { + Value *BIV = PN.getIncomingValueForBlock(BB); + unsigned PBBIdx = PN.getBasicBlockIndex(PBI->getParent()); + Value *PBIV = PN.getIncomingValue(PBBIdx); + if (BIV != PBIV) { + // Insert a select in PBI to pick the right value. + SelectInst *NV = cast<SelectInst>( + Builder.CreateSelect(PBICond, PBIV, BIV, PBIV->getName() + ".mux")); + PN.setIncomingValue(PBBIdx, NV); + // Although the select has the same condition as PBI, the original branch + // weights for PBI do not apply to the new select because the select's + // 'logical' edges are incoming edges of the phi that is eliminated, not + // the outgoing edges of PBI. + if (HasWeights) { + uint64_t PredCommon = PBIOp ? PredFalseWeight : PredTrueWeight; + uint64_t PredOther = PBIOp ? PredTrueWeight : PredFalseWeight; + uint64_t SuccCommon = BIOp ? SuccFalseWeight : SuccTrueWeight; + uint64_t SuccOther = BIOp ? SuccTrueWeight : SuccFalseWeight; + // The weight to PredCommonDest should be PredCommon * SuccTotal. + // The weight to PredOtherDest should be PredOther * SuccCommon. + uint64_t NewWeights[2] = {PredCommon * (SuccCommon + SuccOther), + PredOther * SuccCommon}; + + FitWeights(NewWeights); + + setBranchWeights(NV, NewWeights[0], NewWeights[1]); + } + } + } + + LLVM_DEBUG(dbgs() << "INTO: " << *PBI->getParent()); + LLVM_DEBUG(dbgs() << *PBI->getParent()->getParent()); + + // This basic block is probably dead. We know it has at least + // one fewer predecessor. + return true; +} + +// Simplifies a terminator by replacing it with a branch to TrueBB if Cond is +// true or to FalseBB if Cond is false. +// Takes care of updating the successors and removing the old terminator. +// Also makes sure not to introduce new successors by assuming that edges to +// non-successor TrueBBs and FalseBBs aren't reachable. +static bool SimplifyTerminatorOnSelect(Instruction *OldTerm, Value *Cond, + BasicBlock *TrueBB, BasicBlock *FalseBB, + uint32_t TrueWeight, + uint32_t FalseWeight) { + // Remove any superfluous successor edges from the CFG. + // First, figure out which successors to preserve. + // If TrueBB and FalseBB are equal, only try to preserve one copy of that + // successor. + BasicBlock *KeepEdge1 = TrueBB; + BasicBlock *KeepEdge2 = TrueBB != FalseBB ? FalseBB : nullptr; + + // Then remove the rest. + for (BasicBlock *Succ : successors(OldTerm)) { + // Make sure only to keep exactly one copy of each edge. + if (Succ == KeepEdge1) + KeepEdge1 = nullptr; + else if (Succ == KeepEdge2) + KeepEdge2 = nullptr; + else + Succ->removePredecessor(OldTerm->getParent(), + /*KeepOneInputPHIs=*/true); + } + + IRBuilder<> Builder(OldTerm); + Builder.SetCurrentDebugLocation(OldTerm->getDebugLoc()); + + // Insert an appropriate new terminator. + if (!KeepEdge1 && !KeepEdge2) { + if (TrueBB == FalseBB) + // We were only looking for one successor, and it was present. + // Create an unconditional branch to it. + Builder.CreateBr(TrueBB); + else { + // We found both of the successors we were looking for. + // Create a conditional branch sharing the condition of the select. + BranchInst *NewBI = Builder.CreateCondBr(Cond, TrueBB, FalseBB); + if (TrueWeight != FalseWeight) + setBranchWeights(NewBI, TrueWeight, FalseWeight); + } + } else if (KeepEdge1 && (KeepEdge2 || TrueBB == FalseBB)) { + // Neither of the selected blocks were successors, so this + // terminator must be unreachable. + new UnreachableInst(OldTerm->getContext(), OldTerm); + } else { + // One of the selected values was a successor, but the other wasn't. + // Insert an unconditional branch to the one that was found; + // the edge to the one that wasn't must be unreachable. + if (!KeepEdge1) + // Only TrueBB was found. + Builder.CreateBr(TrueBB); + else + // Only FalseBB was found. + Builder.CreateBr(FalseBB); + } + + EraseTerminatorAndDCECond(OldTerm); + return true; +} + +// Replaces +// (switch (select cond, X, Y)) on constant X, Y +// with a branch - conditional if X and Y lead to distinct BBs, +// unconditional otherwise. +static bool SimplifySwitchOnSelect(SwitchInst *SI, SelectInst *Select) { + // Check for constant integer values in the select. + ConstantInt *TrueVal = dyn_cast<ConstantInt>(Select->getTrueValue()); + ConstantInt *FalseVal = dyn_cast<ConstantInt>(Select->getFalseValue()); + if (!TrueVal || !FalseVal) + return false; + + // Find the relevant condition and destinations. + Value *Condition = Select->getCondition(); + BasicBlock *TrueBB = SI->findCaseValue(TrueVal)->getCaseSuccessor(); + BasicBlock *FalseBB = SI->findCaseValue(FalseVal)->getCaseSuccessor(); + + // Get weight for TrueBB and FalseBB. + uint32_t TrueWeight = 0, FalseWeight = 0; + SmallVector<uint64_t, 8> Weights; + bool HasWeights = HasBranchWeights(SI); + if (HasWeights) { + GetBranchWeights(SI, Weights); + if (Weights.size() == 1 + SI->getNumCases()) { + TrueWeight = + (uint32_t)Weights[SI->findCaseValue(TrueVal)->getSuccessorIndex()]; + FalseWeight = + (uint32_t)Weights[SI->findCaseValue(FalseVal)->getSuccessorIndex()]; + } + } + + // Perform the actual simplification. + return SimplifyTerminatorOnSelect(SI, Condition, TrueBB, FalseBB, TrueWeight, + FalseWeight); +} + +// Replaces +// (indirectbr (select cond, blockaddress(@fn, BlockA), +// blockaddress(@fn, BlockB))) +// with +// (br cond, BlockA, BlockB). +static bool SimplifyIndirectBrOnSelect(IndirectBrInst *IBI, SelectInst *SI) { + // Check that both operands of the select are block addresses. + BlockAddress *TBA = dyn_cast<BlockAddress>(SI->getTrueValue()); + BlockAddress *FBA = dyn_cast<BlockAddress>(SI->getFalseValue()); + if (!TBA || !FBA) + return false; + + // Extract the actual blocks. + BasicBlock *TrueBB = TBA->getBasicBlock(); + BasicBlock *FalseBB = FBA->getBasicBlock(); + + // Perform the actual simplification. + return SimplifyTerminatorOnSelect(IBI, SI->getCondition(), TrueBB, FalseBB, 0, + 0); +} + +/// This is called when we find an icmp instruction +/// (a seteq/setne with a constant) as the only instruction in a +/// block that ends with an uncond branch. We are looking for a very specific +/// pattern that occurs when "A == 1 || A == 2 || A == 3" gets simplified. In +/// this case, we merge the first two "or's of icmp" into a switch, but then the +/// default value goes to an uncond block with a seteq in it, we get something +/// like: +/// +/// switch i8 %A, label %DEFAULT [ i8 1, label %end i8 2, label %end ] +/// DEFAULT: +/// %tmp = icmp eq i8 %A, 92 +/// br label %end +/// end: +/// ... = phi i1 [ true, %entry ], [ %tmp, %DEFAULT ], [ true, %entry ] +/// +/// We prefer to split the edge to 'end' so that there is a true/false entry to +/// the PHI, merging the third icmp into the switch. +bool SimplifyCFGOpt::tryToSimplifyUncondBranchWithICmpInIt( + ICmpInst *ICI, IRBuilder<> &Builder) { + BasicBlock *BB = ICI->getParent(); + + // If the block has any PHIs in it or the icmp has multiple uses, it is too + // complex. + if (isa<PHINode>(BB->begin()) || !ICI->hasOneUse()) + return false; + + Value *V = ICI->getOperand(0); + ConstantInt *Cst = cast<ConstantInt>(ICI->getOperand(1)); + + // The pattern we're looking for is where our only predecessor is a switch on + // 'V' and this block is the default case for the switch. In this case we can + // fold the compared value into the switch to simplify things. + BasicBlock *Pred = BB->getSinglePredecessor(); + if (!Pred || !isa<SwitchInst>(Pred->getTerminator())) + return false; + + SwitchInst *SI = cast<SwitchInst>(Pred->getTerminator()); + if (SI->getCondition() != V) + return false; + + // If BB is reachable on a non-default case, then we simply know the value of + // V in this block. Substitute it and constant fold the icmp instruction + // away. + if (SI->getDefaultDest() != BB) { + ConstantInt *VVal = SI->findCaseDest(BB); + assert(VVal && "Should have a unique destination value"); + ICI->setOperand(0, VVal); + + if (Value *V = SimplifyInstruction(ICI, {DL, ICI})) { + ICI->replaceAllUsesWith(V); + ICI->eraseFromParent(); + } + // BB is now empty, so it is likely to simplify away. + return requestResimplify(); + } + + // Ok, the block is reachable from the default dest. If the constant we're + // comparing exists in one of the other edges, then we can constant fold ICI + // and zap it. + if (SI->findCaseValue(Cst) != SI->case_default()) { + Value *V; + if (ICI->getPredicate() == ICmpInst::ICMP_EQ) + V = ConstantInt::getFalse(BB->getContext()); + else + V = ConstantInt::getTrue(BB->getContext()); + + ICI->replaceAllUsesWith(V); + ICI->eraseFromParent(); + // BB is now empty, so it is likely to simplify away. + return requestResimplify(); + } + + // The use of the icmp has to be in the 'end' block, by the only PHI node in + // the block. + BasicBlock *SuccBlock = BB->getTerminator()->getSuccessor(0); + PHINode *PHIUse = dyn_cast<PHINode>(ICI->user_back()); + if (PHIUse == nullptr || PHIUse != &SuccBlock->front() || + isa<PHINode>(++BasicBlock::iterator(PHIUse))) + return false; + + // If the icmp is a SETEQ, then the default dest gets false, the new edge gets + // true in the PHI. + Constant *DefaultCst = ConstantInt::getTrue(BB->getContext()); + Constant *NewCst = ConstantInt::getFalse(BB->getContext()); + + if (ICI->getPredicate() == ICmpInst::ICMP_EQ) + std::swap(DefaultCst, NewCst); + + // Replace ICI (which is used by the PHI for the default value) with true or + // false depending on if it is EQ or NE. + ICI->replaceAllUsesWith(DefaultCst); + ICI->eraseFromParent(); + + // Okay, the switch goes to this block on a default value. Add an edge from + // the switch to the merge point on the compared value. + BasicBlock *NewBB = + BasicBlock::Create(BB->getContext(), "switch.edge", BB->getParent(), BB); + { + SwitchInstProfUpdateWrapper SIW(*SI); + auto W0 = SIW.getSuccessorWeight(0); + SwitchInstProfUpdateWrapper::CaseWeightOpt NewW; + if (W0) { + NewW = ((uint64_t(*W0) + 1) >> 1); + SIW.setSuccessorWeight(0, *NewW); + } + SIW.addCase(Cst, NewBB, NewW); + } + + // NewBB branches to the phi block, add the uncond branch and the phi entry. + Builder.SetInsertPoint(NewBB); + Builder.SetCurrentDebugLocation(SI->getDebugLoc()); + Builder.CreateBr(SuccBlock); + PHIUse->addIncoming(NewCst, NewBB); + return true; +} + +/// The specified branch is a conditional branch. +/// Check to see if it is branching on an or/and chain of icmp instructions, and +/// fold it into a switch instruction if so. +static bool SimplifyBranchOnICmpChain(BranchInst *BI, IRBuilder<> &Builder, + const DataLayout &DL) { + Instruction *Cond = dyn_cast<Instruction>(BI->getCondition()); + if (!Cond) + return false; + + // Change br (X == 0 | X == 1), T, F into a switch instruction. + // If this is a bunch of seteq's or'd together, or if it's a bunch of + // 'setne's and'ed together, collect them. + + // Try to gather values from a chain of and/or to be turned into a switch + ConstantComparesGatherer ConstantCompare(Cond, DL); + // Unpack the result + SmallVectorImpl<ConstantInt *> &Values = ConstantCompare.Vals; + Value *CompVal = ConstantCompare.CompValue; + unsigned UsedICmps = ConstantCompare.UsedICmps; + Value *ExtraCase = ConstantCompare.Extra; + + // If we didn't have a multiply compared value, fail. + if (!CompVal) + return false; + + // Avoid turning single icmps into a switch. + if (UsedICmps <= 1) + return false; + + bool TrueWhenEqual = (Cond->getOpcode() == Instruction::Or); + + // There might be duplicate constants in the list, which the switch + // instruction can't handle, remove them now. + array_pod_sort(Values.begin(), Values.end(), ConstantIntSortPredicate); + Values.erase(std::unique(Values.begin(), Values.end()), Values.end()); + + // If Extra was used, we require at least two switch values to do the + // transformation. A switch with one value is just a conditional branch. + if (ExtraCase && Values.size() < 2) + return false; + + // TODO: Preserve branch weight metadata, similarly to how + // FoldValueComparisonIntoPredecessors preserves it. + + // Figure out which block is which destination. + BasicBlock *DefaultBB = BI->getSuccessor(1); + BasicBlock *EdgeBB = BI->getSuccessor(0); + if (!TrueWhenEqual) + std::swap(DefaultBB, EdgeBB); + + BasicBlock *BB = BI->getParent(); + + // MSAN does not like undefs as branch condition which can be introduced + // with "explicit branch". + if (ExtraCase && BB->getParent()->hasFnAttribute(Attribute::SanitizeMemory)) + return false; + + LLVM_DEBUG(dbgs() << "Converting 'icmp' chain with " << Values.size() + << " cases into SWITCH. BB is:\n" + << *BB); + + // If there are any extra values that couldn't be folded into the switch + // then we evaluate them with an explicit branch first. Split the block + // right before the condbr to handle it. + if (ExtraCase) { + BasicBlock *NewBB = + BB->splitBasicBlock(BI->getIterator(), "switch.early.test"); + // Remove the uncond branch added to the old block. + Instruction *OldTI = BB->getTerminator(); + Builder.SetInsertPoint(OldTI); + + if (TrueWhenEqual) + Builder.CreateCondBr(ExtraCase, EdgeBB, NewBB); + else + Builder.CreateCondBr(ExtraCase, NewBB, EdgeBB); + + OldTI->eraseFromParent(); + + // If there are PHI nodes in EdgeBB, then we need to add a new entry to them + // for the edge we just added. + AddPredecessorToBlock(EdgeBB, BB, NewBB); + + LLVM_DEBUG(dbgs() << " ** 'icmp' chain unhandled condition: " << *ExtraCase + << "\nEXTRABB = " << *BB); + BB = NewBB; + } + + Builder.SetInsertPoint(BI); + // Convert pointer to int before we switch. + if (CompVal->getType()->isPointerTy()) { + CompVal = Builder.CreatePtrToInt( + CompVal, DL.getIntPtrType(CompVal->getType()), "magicptr"); + } + + // Create the new switch instruction now. + SwitchInst *New = Builder.CreateSwitch(CompVal, DefaultBB, Values.size()); + + // Add all of the 'cases' to the switch instruction. + for (unsigned i = 0, e = Values.size(); i != e; ++i) + New->addCase(Values[i], EdgeBB); + + // We added edges from PI to the EdgeBB. As such, if there were any + // PHI nodes in EdgeBB, they need entries to be added corresponding to + // the number of edges added. + for (BasicBlock::iterator BBI = EdgeBB->begin(); isa<PHINode>(BBI); ++BBI) { + PHINode *PN = cast<PHINode>(BBI); + Value *InVal = PN->getIncomingValueForBlock(BB); + for (unsigned i = 0, e = Values.size() - 1; i != e; ++i) + PN->addIncoming(InVal, BB); + } + + // Erase the old branch instruction. + EraseTerminatorAndDCECond(BI); + + LLVM_DEBUG(dbgs() << " ** 'icmp' chain result is:\n" << *BB << '\n'); + return true; +} + +bool SimplifyCFGOpt::SimplifyResume(ResumeInst *RI, IRBuilder<> &Builder) { + if (isa<PHINode>(RI->getValue())) + return SimplifyCommonResume(RI); + else if (isa<LandingPadInst>(RI->getParent()->getFirstNonPHI()) && + RI->getValue() == RI->getParent()->getFirstNonPHI()) + // The resume must unwind the exception that caused control to branch here. + return SimplifySingleResume(RI); + + return false; +} + +// Simplify resume that is shared by several landing pads (phi of landing pad). +bool SimplifyCFGOpt::SimplifyCommonResume(ResumeInst *RI) { + BasicBlock *BB = RI->getParent(); + + // Check that there are no other instructions except for debug intrinsics + // between the phi of landing pads (RI->getValue()) and resume instruction. + BasicBlock::iterator I = cast<Instruction>(RI->getValue())->getIterator(), + E = RI->getIterator(); + while (++I != E) + if (!isa<DbgInfoIntrinsic>(I)) + return false; + + SmallSetVector<BasicBlock *, 4> TrivialUnwindBlocks; + auto *PhiLPInst = cast<PHINode>(RI->getValue()); + + // Check incoming blocks to see if any of them are trivial. + for (unsigned Idx = 0, End = PhiLPInst->getNumIncomingValues(); Idx != End; + Idx++) { + auto *IncomingBB = PhiLPInst->getIncomingBlock(Idx); + auto *IncomingValue = PhiLPInst->getIncomingValue(Idx); + + // If the block has other successors, we can not delete it because + // it has other dependents. + if (IncomingBB->getUniqueSuccessor() != BB) + continue; + + auto *LandingPad = dyn_cast<LandingPadInst>(IncomingBB->getFirstNonPHI()); + // Not the landing pad that caused the control to branch here. + if (IncomingValue != LandingPad) + continue; + + bool isTrivial = true; + + I = IncomingBB->getFirstNonPHI()->getIterator(); + E = IncomingBB->getTerminator()->getIterator(); + while (++I != E) + if (!isa<DbgInfoIntrinsic>(I)) { + isTrivial = false; + break; + } + + if (isTrivial) + TrivialUnwindBlocks.insert(IncomingBB); + } + + // If no trivial unwind blocks, don't do any simplifications. + if (TrivialUnwindBlocks.empty()) + return false; + + // Turn all invokes that unwind here into calls. + for (auto *TrivialBB : TrivialUnwindBlocks) { + // Blocks that will be simplified should be removed from the phi node. + // Note there could be multiple edges to the resume block, and we need + // to remove them all. + while (PhiLPInst->getBasicBlockIndex(TrivialBB) != -1) + BB->removePredecessor(TrivialBB, true); + + for (pred_iterator PI = pred_begin(TrivialBB), PE = pred_end(TrivialBB); + PI != PE;) { + BasicBlock *Pred = *PI++; + removeUnwindEdge(Pred); + } + + // In each SimplifyCFG run, only the current processed block can be erased. + // Otherwise, it will break the iteration of SimplifyCFG pass. So instead + // of erasing TrivialBB, we only remove the branch to the common resume + // block so that we can later erase the resume block since it has no + // predecessors. + TrivialBB->getTerminator()->eraseFromParent(); + new UnreachableInst(RI->getContext(), TrivialBB); + } + + // Delete the resume block if all its predecessors have been removed. + if (pred_empty(BB)) + BB->eraseFromParent(); + + return !TrivialUnwindBlocks.empty(); +} + +// Simplify resume that is only used by a single (non-phi) landing pad. +bool SimplifyCFGOpt::SimplifySingleResume(ResumeInst *RI) { + BasicBlock *BB = RI->getParent(); + auto *LPInst = cast<LandingPadInst>(BB->getFirstNonPHI()); + assert(RI->getValue() == LPInst && + "Resume must unwind the exception that caused control to here"); + + // Check that there are no other instructions except for debug intrinsics. + BasicBlock::iterator I = LPInst->getIterator(), E = RI->getIterator(); + while (++I != E) + if (!isa<DbgInfoIntrinsic>(I)) + return false; + + // Turn all invokes that unwind here into calls and delete the basic block. + for (pred_iterator PI = pred_begin(BB), PE = pred_end(BB); PI != PE;) { + BasicBlock *Pred = *PI++; + removeUnwindEdge(Pred); + } + + // The landingpad is now unreachable. Zap it. + if (LoopHeaders) + LoopHeaders->erase(BB); + BB->eraseFromParent(); + return true; +} + +static bool removeEmptyCleanup(CleanupReturnInst *RI) { + // If this is a trivial cleanup pad that executes no instructions, it can be + // eliminated. If the cleanup pad continues to the caller, any predecessor + // that is an EH pad will be updated to continue to the caller and any + // predecessor that terminates with an invoke instruction will have its invoke + // instruction converted to a call instruction. If the cleanup pad being + // simplified does not continue to the caller, each predecessor will be + // updated to continue to the unwind destination of the cleanup pad being + // simplified. + BasicBlock *BB = RI->getParent(); + CleanupPadInst *CPInst = RI->getCleanupPad(); + if (CPInst->getParent() != BB) + // This isn't an empty cleanup. + return false; + + // We cannot kill the pad if it has multiple uses. This typically arises + // from unreachable basic blocks. + if (!CPInst->hasOneUse()) + return false; + + // Check that there are no other instructions except for benign intrinsics. + BasicBlock::iterator I = CPInst->getIterator(), E = RI->getIterator(); + while (++I != E) { + auto *II = dyn_cast<IntrinsicInst>(I); + if (!II) + return false; + + Intrinsic::ID IntrinsicID = II->getIntrinsicID(); + switch (IntrinsicID) { + case Intrinsic::dbg_declare: + case Intrinsic::dbg_value: + case Intrinsic::dbg_label: + case Intrinsic::lifetime_end: + break; + default: + return false; + } + } + + // If the cleanup return we are simplifying unwinds to the caller, this will + // set UnwindDest to nullptr. + BasicBlock *UnwindDest = RI->getUnwindDest(); + Instruction *DestEHPad = UnwindDest ? UnwindDest->getFirstNonPHI() : nullptr; + + // We're about to remove BB from the control flow. Before we do, sink any + // PHINodes into the unwind destination. Doing this before changing the + // control flow avoids some potentially slow checks, since we can currently + // be certain that UnwindDest and BB have no common predecessors (since they + // are both EH pads). + if (UnwindDest) { + // First, go through the PHI nodes in UnwindDest and update any nodes that + // reference the block we are removing + for (BasicBlock::iterator I = UnwindDest->begin(), + IE = DestEHPad->getIterator(); + I != IE; ++I) { + PHINode *DestPN = cast<PHINode>(I); + + int Idx = DestPN->getBasicBlockIndex(BB); + // Since BB unwinds to UnwindDest, it has to be in the PHI node. + assert(Idx != -1); + // This PHI node has an incoming value that corresponds to a control + // path through the cleanup pad we are removing. If the incoming + // value is in the cleanup pad, it must be a PHINode (because we + // verified above that the block is otherwise empty). Otherwise, the + // value is either a constant or a value that dominates the cleanup + // pad being removed. + // + // Because BB and UnwindDest are both EH pads, all of their + // predecessors must unwind to these blocks, and since no instruction + // can have multiple unwind destinations, there will be no overlap in + // incoming blocks between SrcPN and DestPN. + Value *SrcVal = DestPN->getIncomingValue(Idx); + PHINode *SrcPN = dyn_cast<PHINode>(SrcVal); + + // Remove the entry for the block we are deleting. + DestPN->removeIncomingValue(Idx, false); + + if (SrcPN && SrcPN->getParent() == BB) { + // If the incoming value was a PHI node in the cleanup pad we are + // removing, we need to merge that PHI node's incoming values into + // DestPN. + for (unsigned SrcIdx = 0, SrcE = SrcPN->getNumIncomingValues(); + SrcIdx != SrcE; ++SrcIdx) { + DestPN->addIncoming(SrcPN->getIncomingValue(SrcIdx), + SrcPN->getIncomingBlock(SrcIdx)); + } + } else { + // Otherwise, the incoming value came from above BB and + // so we can just reuse it. We must associate all of BB's + // predecessors with this value. + for (auto *pred : predecessors(BB)) { + DestPN->addIncoming(SrcVal, pred); + } + } + } + + // Sink any remaining PHI nodes directly into UnwindDest. + Instruction *InsertPt = DestEHPad; + for (BasicBlock::iterator I = BB->begin(), + IE = BB->getFirstNonPHI()->getIterator(); + I != IE;) { + // The iterator must be incremented here because the instructions are + // being moved to another block. + PHINode *PN = cast<PHINode>(I++); + if (PN->use_empty()) + // If the PHI node has no uses, just leave it. It will be erased + // when we erase BB below. + continue; + + // Otherwise, sink this PHI node into UnwindDest. + // Any predecessors to UnwindDest which are not already represented + // must be back edges which inherit the value from the path through + // BB. In this case, the PHI value must reference itself. + for (auto *pred : predecessors(UnwindDest)) + if (pred != BB) + PN->addIncoming(PN, pred); + PN->moveBefore(InsertPt); + } + } + + for (pred_iterator PI = pred_begin(BB), PE = pred_end(BB); PI != PE;) { + // The iterator must be updated here because we are removing this pred. + BasicBlock *PredBB = *PI++; + if (UnwindDest == nullptr) { + removeUnwindEdge(PredBB); + } else { + Instruction *TI = PredBB->getTerminator(); + TI->replaceUsesOfWith(BB, UnwindDest); + } + } + + // The cleanup pad is now unreachable. Zap it. + BB->eraseFromParent(); + return true; +} + +// Try to merge two cleanuppads together. +static bool mergeCleanupPad(CleanupReturnInst *RI) { + // Skip any cleanuprets which unwind to caller, there is nothing to merge + // with. + BasicBlock *UnwindDest = RI->getUnwindDest(); + if (!UnwindDest) + return false; + + // This cleanupret isn't the only predecessor of this cleanuppad, it wouldn't + // be safe to merge without code duplication. + if (UnwindDest->getSinglePredecessor() != RI->getParent()) + return false; + + // Verify that our cleanuppad's unwind destination is another cleanuppad. + auto *SuccessorCleanupPad = dyn_cast<CleanupPadInst>(&UnwindDest->front()); + if (!SuccessorCleanupPad) + return false; + + CleanupPadInst *PredecessorCleanupPad = RI->getCleanupPad(); + // Replace any uses of the successor cleanupad with the predecessor pad + // The only cleanuppad uses should be this cleanupret, it's cleanupret and + // funclet bundle operands. + SuccessorCleanupPad->replaceAllUsesWith(PredecessorCleanupPad); + // Remove the old cleanuppad. + SuccessorCleanupPad->eraseFromParent(); + // Now, we simply replace the cleanupret with a branch to the unwind + // destination. + BranchInst::Create(UnwindDest, RI->getParent()); + RI->eraseFromParent(); + + return true; +} + +bool SimplifyCFGOpt::SimplifyCleanupReturn(CleanupReturnInst *RI) { + // It is possible to transiantly have an undef cleanuppad operand because we + // have deleted some, but not all, dead blocks. + // Eventually, this block will be deleted. + if (isa<UndefValue>(RI->getOperand(0))) + return false; + + if (mergeCleanupPad(RI)) + return true; + + if (removeEmptyCleanup(RI)) + return true; + + return false; +} + +bool SimplifyCFGOpt::SimplifyReturn(ReturnInst *RI, IRBuilder<> &Builder) { + BasicBlock *BB = RI->getParent(); + if (!BB->getFirstNonPHIOrDbg()->isTerminator()) + return false; + + // Find predecessors that end with branches. + SmallVector<BasicBlock *, 8> UncondBranchPreds; + SmallVector<BranchInst *, 8> CondBranchPreds; + for (pred_iterator PI = pred_begin(BB), E = pred_end(BB); PI != E; ++PI) { + BasicBlock *P = *PI; + Instruction *PTI = P->getTerminator(); + if (BranchInst *BI = dyn_cast<BranchInst>(PTI)) { + if (BI->isUnconditional()) + UncondBranchPreds.push_back(P); + else + CondBranchPreds.push_back(BI); + } + } + + // If we found some, do the transformation! + if (!UncondBranchPreds.empty() && DupRet) { + while (!UncondBranchPreds.empty()) { + BasicBlock *Pred = UncondBranchPreds.pop_back_val(); + LLVM_DEBUG(dbgs() << "FOLDING: " << *BB + << "INTO UNCOND BRANCH PRED: " << *Pred); + (void)FoldReturnIntoUncondBranch(RI, BB, Pred); + } + + // If we eliminated all predecessors of the block, delete the block now. + if (pred_empty(BB)) { + // We know there are no successors, so just nuke the block. + if (LoopHeaders) + LoopHeaders->erase(BB); + BB->eraseFromParent(); + } + + return true; + } + + // Check out all of the conditional branches going to this return + // instruction. If any of them just select between returns, change the + // branch itself into a select/return pair. + while (!CondBranchPreds.empty()) { + BranchInst *BI = CondBranchPreds.pop_back_val(); + + // Check to see if the non-BB successor is also a return block. + if (isa<ReturnInst>(BI->getSuccessor(0)->getTerminator()) && + isa<ReturnInst>(BI->getSuccessor(1)->getTerminator()) && + SimplifyCondBranchToTwoReturns(BI, Builder)) + return true; + } + return false; +} + +bool SimplifyCFGOpt::SimplifyUnreachable(UnreachableInst *UI) { + BasicBlock *BB = UI->getParent(); + + bool Changed = false; + + // If there are any instructions immediately before the unreachable that can + // be removed, do so. + while (UI->getIterator() != BB->begin()) { + BasicBlock::iterator BBI = UI->getIterator(); + --BBI; + // Do not delete instructions that can have side effects which might cause + // the unreachable to not be reachable; specifically, calls and volatile + // operations may have this effect. + if (isa<CallInst>(BBI) && !isa<DbgInfoIntrinsic>(BBI)) + break; + + if (BBI->mayHaveSideEffects()) { + if (auto *SI = dyn_cast<StoreInst>(BBI)) { + if (SI->isVolatile()) + break; + } else if (auto *LI = dyn_cast<LoadInst>(BBI)) { + if (LI->isVolatile()) + break; + } else if (auto *RMWI = dyn_cast<AtomicRMWInst>(BBI)) { + if (RMWI->isVolatile()) + break; + } else if (auto *CXI = dyn_cast<AtomicCmpXchgInst>(BBI)) { + if (CXI->isVolatile()) + break; + } else if (isa<CatchPadInst>(BBI)) { + // A catchpad may invoke exception object constructors and such, which + // in some languages can be arbitrary code, so be conservative by + // default. + // For CoreCLR, it just involves a type test, so can be removed. + if (classifyEHPersonality(BB->getParent()->getPersonalityFn()) != + EHPersonality::CoreCLR) + break; + } else if (!isa<FenceInst>(BBI) && !isa<VAArgInst>(BBI) && + !isa<LandingPadInst>(BBI)) { + break; + } + // Note that deleting LandingPad's here is in fact okay, although it + // involves a bit of subtle reasoning. If this inst is a LandingPad, + // all the predecessors of this block will be the unwind edges of Invokes, + // and we can therefore guarantee this block will be erased. + } + + // Delete this instruction (any uses are guaranteed to be dead) + if (!BBI->use_empty()) + BBI->replaceAllUsesWith(UndefValue::get(BBI->getType())); + BBI->eraseFromParent(); + Changed = true; + } + + // If the unreachable instruction is the first in the block, take a gander + // at all of the predecessors of this instruction, and simplify them. + if (&BB->front() != UI) + return Changed; + + SmallVector<BasicBlock *, 8> Preds(pred_begin(BB), pred_end(BB)); + for (unsigned i = 0, e = Preds.size(); i != e; ++i) { + Instruction *TI = Preds[i]->getTerminator(); + IRBuilder<> Builder(TI); + if (auto *BI = dyn_cast<BranchInst>(TI)) { + if (BI->isUnconditional()) { + assert(BI->getSuccessor(0) == BB && "Incorrect CFG"); + new UnreachableInst(TI->getContext(), TI); + TI->eraseFromParent(); + Changed = true; + } else { + Value* Cond = BI->getCondition(); + if (BI->getSuccessor(0) == BB) { + Builder.CreateAssumption(Builder.CreateNot(Cond)); + Builder.CreateBr(BI->getSuccessor(1)); + } else { + assert(BI->getSuccessor(1) == BB && "Incorrect CFG"); + Builder.CreateAssumption(Cond); + Builder.CreateBr(BI->getSuccessor(0)); + } + EraseTerminatorAndDCECond(BI); + Changed = true; + } + } else if (auto *SI = dyn_cast<SwitchInst>(TI)) { + SwitchInstProfUpdateWrapper SU(*SI); + for (auto i = SU->case_begin(), e = SU->case_end(); i != e;) { + if (i->getCaseSuccessor() != BB) { + ++i; + continue; + } + BB->removePredecessor(SU->getParent()); + i = SU.removeCase(i); + e = SU->case_end(); + Changed = true; + } + } else if (auto *II = dyn_cast<InvokeInst>(TI)) { + if (II->getUnwindDest() == BB) { + removeUnwindEdge(TI->getParent()); + Changed = true; + } + } else if (auto *CSI = dyn_cast<CatchSwitchInst>(TI)) { + if (CSI->getUnwindDest() == BB) { + removeUnwindEdge(TI->getParent()); + Changed = true; + continue; + } + + for (CatchSwitchInst::handler_iterator I = CSI->handler_begin(), + E = CSI->handler_end(); + I != E; ++I) { + if (*I == BB) { + CSI->removeHandler(I); + --I; + --E; + Changed = true; + } + } + if (CSI->getNumHandlers() == 0) { + BasicBlock *CatchSwitchBB = CSI->getParent(); + if (CSI->hasUnwindDest()) { + // Redirect preds to the unwind dest + CatchSwitchBB->replaceAllUsesWith(CSI->getUnwindDest()); + } else { + // Rewrite all preds to unwind to caller (or from invoke to call). + SmallVector<BasicBlock *, 8> EHPreds(predecessors(CatchSwitchBB)); + for (BasicBlock *EHPred : EHPreds) + removeUnwindEdge(EHPred); + } + // The catchswitch is no longer reachable. + new UnreachableInst(CSI->getContext(), CSI); + CSI->eraseFromParent(); + Changed = true; + } + } else if (isa<CleanupReturnInst>(TI)) { + new UnreachableInst(TI->getContext(), TI); + TI->eraseFromParent(); + Changed = true; + } + } + + // If this block is now dead, remove it. + if (pred_empty(BB) && BB != &BB->getParent()->getEntryBlock()) { + // We know there are no successors, so just nuke the block. + if (LoopHeaders) + LoopHeaders->erase(BB); + BB->eraseFromParent(); + return true; + } + + return Changed; +} + +static bool CasesAreContiguous(SmallVectorImpl<ConstantInt *> &Cases) { + assert(Cases.size() >= 1); + + array_pod_sort(Cases.begin(), Cases.end(), ConstantIntSortPredicate); + for (size_t I = 1, E = Cases.size(); I != E; ++I) { + if (Cases[I - 1]->getValue() != Cases[I]->getValue() + 1) + return false; + } + return true; +} + +static void createUnreachableSwitchDefault(SwitchInst *Switch) { + LLVM_DEBUG(dbgs() << "SimplifyCFG: switch default is dead.\n"); + BasicBlock *NewDefaultBlock = + SplitBlockPredecessors(Switch->getDefaultDest(), Switch->getParent(), ""); + Switch->setDefaultDest(&*NewDefaultBlock); + SplitBlock(&*NewDefaultBlock, &NewDefaultBlock->front()); + auto *NewTerminator = NewDefaultBlock->getTerminator(); + new UnreachableInst(Switch->getContext(), NewTerminator); + EraseTerminatorAndDCECond(NewTerminator); +} + +/// Turn a switch with two reachable destinations into an integer range +/// comparison and branch. +static bool TurnSwitchRangeIntoICmp(SwitchInst *SI, IRBuilder<> &Builder) { + assert(SI->getNumCases() > 1 && "Degenerate switch?"); + + bool HasDefault = + !isa<UnreachableInst>(SI->getDefaultDest()->getFirstNonPHIOrDbg()); + + // Partition the cases into two sets with different destinations. + BasicBlock *DestA = HasDefault ? SI->getDefaultDest() : nullptr; + BasicBlock *DestB = nullptr; + SmallVector<ConstantInt *, 16> CasesA; + SmallVector<ConstantInt *, 16> CasesB; + + for (auto Case : SI->cases()) { + BasicBlock *Dest = Case.getCaseSuccessor(); + if (!DestA) + DestA = Dest; + if (Dest == DestA) { + CasesA.push_back(Case.getCaseValue()); + continue; + } + if (!DestB) + DestB = Dest; + if (Dest == DestB) { + CasesB.push_back(Case.getCaseValue()); + continue; + } + return false; // More than two destinations. + } + + assert(DestA && DestB && + "Single-destination switch should have been folded."); + assert(DestA != DestB); + assert(DestB != SI->getDefaultDest()); + assert(!CasesB.empty() && "There must be non-default cases."); + assert(!CasesA.empty() || HasDefault); + + // Figure out if one of the sets of cases form a contiguous range. + SmallVectorImpl<ConstantInt *> *ContiguousCases = nullptr; + BasicBlock *ContiguousDest = nullptr; + BasicBlock *OtherDest = nullptr; + if (!CasesA.empty() && CasesAreContiguous(CasesA)) { + ContiguousCases = &CasesA; + ContiguousDest = DestA; + OtherDest = DestB; + } else if (CasesAreContiguous(CasesB)) { + ContiguousCases = &CasesB; + ContiguousDest = DestB; + OtherDest = DestA; + } else + return false; + + // Start building the compare and branch. + + Constant *Offset = ConstantExpr::getNeg(ContiguousCases->back()); + Constant *NumCases = + ConstantInt::get(Offset->getType(), ContiguousCases->size()); + + Value *Sub = SI->getCondition(); + if (!Offset->isNullValue()) + Sub = Builder.CreateAdd(Sub, Offset, Sub->getName() + ".off"); + + Value *Cmp; + // If NumCases overflowed, then all possible values jump to the successor. + if (NumCases->isNullValue() && !ContiguousCases->empty()) + Cmp = ConstantInt::getTrue(SI->getContext()); + else + Cmp = Builder.CreateICmpULT(Sub, NumCases, "switch"); + BranchInst *NewBI = Builder.CreateCondBr(Cmp, ContiguousDest, OtherDest); + + // Update weight for the newly-created conditional branch. + if (HasBranchWeights(SI)) { + SmallVector<uint64_t, 8> Weights; + GetBranchWeights(SI, Weights); + if (Weights.size() == 1 + SI->getNumCases()) { + uint64_t TrueWeight = 0; + uint64_t FalseWeight = 0; + for (size_t I = 0, E = Weights.size(); I != E; ++I) { + if (SI->getSuccessor(I) == ContiguousDest) + TrueWeight += Weights[I]; + else + FalseWeight += Weights[I]; + } + while (TrueWeight > UINT32_MAX || FalseWeight > UINT32_MAX) { + TrueWeight /= 2; + FalseWeight /= 2; + } + setBranchWeights(NewBI, TrueWeight, FalseWeight); + } + } + + // Prune obsolete incoming values off the successors' PHI nodes. + for (auto BBI = ContiguousDest->begin(); isa<PHINode>(BBI); ++BBI) { + unsigned PreviousEdges = ContiguousCases->size(); + if (ContiguousDest == SI->getDefaultDest()) + ++PreviousEdges; + for (unsigned I = 0, E = PreviousEdges - 1; I != E; ++I) + cast<PHINode>(BBI)->removeIncomingValue(SI->getParent()); + } + for (auto BBI = OtherDest->begin(); isa<PHINode>(BBI); ++BBI) { + unsigned PreviousEdges = SI->getNumCases() - ContiguousCases->size(); + if (OtherDest == SI->getDefaultDest()) + ++PreviousEdges; + for (unsigned I = 0, E = PreviousEdges - 1; I != E; ++I) + cast<PHINode>(BBI)->removeIncomingValue(SI->getParent()); + } + + // Clean up the default block - it may have phis or other instructions before + // the unreachable terminator. + if (!HasDefault) + createUnreachableSwitchDefault(SI); + + // Drop the switch. + SI->eraseFromParent(); + + return true; +} + +/// Compute masked bits for the condition of a switch +/// and use it to remove dead cases. +static bool eliminateDeadSwitchCases(SwitchInst *SI, AssumptionCache *AC, + const DataLayout &DL) { + Value *Cond = SI->getCondition(); + unsigned Bits = Cond->getType()->getIntegerBitWidth(); + KnownBits Known = computeKnownBits(Cond, DL, 0, AC, SI); + + // We can also eliminate cases by determining that their values are outside of + // the limited range of the condition based on how many significant (non-sign) + // bits are in the condition value. + unsigned ExtraSignBits = ComputeNumSignBits(Cond, DL, 0, AC, SI) - 1; + unsigned MaxSignificantBitsInCond = Bits - ExtraSignBits; + + // Gather dead cases. + SmallVector<ConstantInt *, 8> DeadCases; + for (auto &Case : SI->cases()) { + const APInt &CaseVal = Case.getCaseValue()->getValue(); + if (Known.Zero.intersects(CaseVal) || !Known.One.isSubsetOf(CaseVal) || + (CaseVal.getMinSignedBits() > MaxSignificantBitsInCond)) { + DeadCases.push_back(Case.getCaseValue()); + LLVM_DEBUG(dbgs() << "SimplifyCFG: switch case " << CaseVal + << " is dead.\n"); + } + } + + // If we can prove that the cases must cover all possible values, the + // default destination becomes dead and we can remove it. If we know some + // of the bits in the value, we can use that to more precisely compute the + // number of possible unique case values. + bool HasDefault = + !isa<UnreachableInst>(SI->getDefaultDest()->getFirstNonPHIOrDbg()); + const unsigned NumUnknownBits = + Bits - (Known.Zero | Known.One).countPopulation(); + assert(NumUnknownBits <= Bits); + if (HasDefault && DeadCases.empty() && + NumUnknownBits < 64 /* avoid overflow */ && + SI->getNumCases() == (1ULL << NumUnknownBits)) { + createUnreachableSwitchDefault(SI); + return true; + } + + if (DeadCases.empty()) + return false; + + SwitchInstProfUpdateWrapper SIW(*SI); + for (ConstantInt *DeadCase : DeadCases) { + SwitchInst::CaseIt CaseI = SI->findCaseValue(DeadCase); + assert(CaseI != SI->case_default() && + "Case was not found. Probably mistake in DeadCases forming."); + // Prune unused values from PHI nodes. + CaseI->getCaseSuccessor()->removePredecessor(SI->getParent()); + SIW.removeCase(CaseI); + } + + return true; +} + +/// If BB would be eligible for simplification by +/// TryToSimplifyUncondBranchFromEmptyBlock (i.e. it is empty and terminated +/// by an unconditional branch), look at the phi node for BB in the successor +/// block and see if the incoming value is equal to CaseValue. If so, return +/// the phi node, and set PhiIndex to BB's index in the phi node. +static PHINode *FindPHIForConditionForwarding(ConstantInt *CaseValue, + BasicBlock *BB, int *PhiIndex) { + if (BB->getFirstNonPHIOrDbg() != BB->getTerminator()) + return nullptr; // BB must be empty to be a candidate for simplification. + if (!BB->getSinglePredecessor()) + return nullptr; // BB must be dominated by the switch. + + BranchInst *Branch = dyn_cast<BranchInst>(BB->getTerminator()); + if (!Branch || !Branch->isUnconditional()) + return nullptr; // Terminator must be unconditional branch. + + BasicBlock *Succ = Branch->getSuccessor(0); + + for (PHINode &PHI : Succ->phis()) { + int Idx = PHI.getBasicBlockIndex(BB); + assert(Idx >= 0 && "PHI has no entry for predecessor?"); + + Value *InValue = PHI.getIncomingValue(Idx); + if (InValue != CaseValue) + continue; + + *PhiIndex = Idx; + return &PHI; + } + + return nullptr; +} + +/// Try to forward the condition of a switch instruction to a phi node +/// dominated by the switch, if that would mean that some of the destination +/// blocks of the switch can be folded away. Return true if a change is made. +static bool ForwardSwitchConditionToPHI(SwitchInst *SI) { + using ForwardingNodesMap = DenseMap<PHINode *, SmallVector<int, 4>>; + + ForwardingNodesMap ForwardingNodes; + BasicBlock *SwitchBlock = SI->getParent(); + bool Changed = false; + for (auto &Case : SI->cases()) { + ConstantInt *CaseValue = Case.getCaseValue(); + BasicBlock *CaseDest = Case.getCaseSuccessor(); + + // Replace phi operands in successor blocks that are using the constant case + // value rather than the switch condition variable: + // switchbb: + // switch i32 %x, label %default [ + // i32 17, label %succ + // ... + // succ: + // %r = phi i32 ... [ 17, %switchbb ] ... + // --> + // %r = phi i32 ... [ %x, %switchbb ] ... + + for (PHINode &Phi : CaseDest->phis()) { + // This only works if there is exactly 1 incoming edge from the switch to + // a phi. If there is >1, that means multiple cases of the switch map to 1 + // value in the phi, and that phi value is not the switch condition. Thus, + // this transform would not make sense (the phi would be invalid because + // a phi can't have different incoming values from the same block). + int SwitchBBIdx = Phi.getBasicBlockIndex(SwitchBlock); + if (Phi.getIncomingValue(SwitchBBIdx) == CaseValue && + count(Phi.blocks(), SwitchBlock) == 1) { + Phi.setIncomingValue(SwitchBBIdx, SI->getCondition()); + Changed = true; + } + } + + // Collect phi nodes that are indirectly using this switch's case constants. + int PhiIdx; + if (auto *Phi = FindPHIForConditionForwarding(CaseValue, CaseDest, &PhiIdx)) + ForwardingNodes[Phi].push_back(PhiIdx); + } + + for (auto &ForwardingNode : ForwardingNodes) { + PHINode *Phi = ForwardingNode.first; + SmallVectorImpl<int> &Indexes = ForwardingNode.second; + if (Indexes.size() < 2) + continue; + + for (int Index : Indexes) + Phi->setIncomingValue(Index, SI->getCondition()); + Changed = true; + } + + return Changed; +} + +/// Return true if the backend will be able to handle +/// initializing an array of constants like C. +static bool ValidLookupTableConstant(Constant *C, const TargetTransformInfo &TTI) { + if (C->isThreadDependent()) + return false; + if (C->isDLLImportDependent()) + return false; + + if (!isa<ConstantFP>(C) && !isa<ConstantInt>(C) && + !isa<ConstantPointerNull>(C) && !isa<GlobalValue>(C) && + !isa<UndefValue>(C) && !isa<ConstantExpr>(C)) + return false; + + if (ConstantExpr *CE = dyn_cast<ConstantExpr>(C)) { + if (!CE->isGEPWithNoNotionalOverIndexing()) + return false; + if (!ValidLookupTableConstant(CE->getOperand(0), TTI)) + return false; + } + + if (!TTI.shouldBuildLookupTablesForConstant(C)) + return false; + + return true; +} + +/// If V is a Constant, return it. Otherwise, try to look up +/// its constant value in ConstantPool, returning 0 if it's not there. +static Constant * +LookupConstant(Value *V, + const SmallDenseMap<Value *, Constant *> &ConstantPool) { + if (Constant *C = dyn_cast<Constant>(V)) + return C; + return ConstantPool.lookup(V); +} + +/// Try to fold instruction I into a constant. This works for +/// simple instructions such as binary operations where both operands are +/// constant or can be replaced by constants from the ConstantPool. Returns the +/// resulting constant on success, 0 otherwise. +static Constant * +ConstantFold(Instruction *I, const DataLayout &DL, + const SmallDenseMap<Value *, Constant *> &ConstantPool) { + if (SelectInst *Select = dyn_cast<SelectInst>(I)) { + Constant *A = LookupConstant(Select->getCondition(), ConstantPool); + if (!A) + return nullptr; + if (A->isAllOnesValue()) + return LookupConstant(Select->getTrueValue(), ConstantPool); + if (A->isNullValue()) + return LookupConstant(Select->getFalseValue(), ConstantPool); + return nullptr; + } + + SmallVector<Constant *, 4> COps; + for (unsigned N = 0, E = I->getNumOperands(); N != E; ++N) { + if (Constant *A = LookupConstant(I->getOperand(N), ConstantPool)) + COps.push_back(A); + else + return nullptr; + } + + if (CmpInst *Cmp = dyn_cast<CmpInst>(I)) { + return ConstantFoldCompareInstOperands(Cmp->getPredicate(), COps[0], + COps[1], DL); + } + + return ConstantFoldInstOperands(I, COps, DL); +} + +/// Try to determine the resulting constant values in phi nodes +/// at the common destination basic block, *CommonDest, for one of the case +/// destionations CaseDest corresponding to value CaseVal (0 for the default +/// case), of a switch instruction SI. +static bool +GetCaseResults(SwitchInst *SI, ConstantInt *CaseVal, BasicBlock *CaseDest, + BasicBlock **CommonDest, + SmallVectorImpl<std::pair<PHINode *, Constant *>> &Res, + const DataLayout &DL, const TargetTransformInfo &TTI) { + // The block from which we enter the common destination. + BasicBlock *Pred = SI->getParent(); + + // If CaseDest is empty except for some side-effect free instructions through + // which we can constant-propagate the CaseVal, continue to its successor. + SmallDenseMap<Value *, Constant *> ConstantPool; + ConstantPool.insert(std::make_pair(SI->getCondition(), CaseVal)); + for (Instruction &I :CaseDest->instructionsWithoutDebug()) { + if (I.isTerminator()) { + // If the terminator is a simple branch, continue to the next block. + if (I.getNumSuccessors() != 1 || I.isExceptionalTerminator()) + return false; + Pred = CaseDest; + CaseDest = I.getSuccessor(0); + } else if (Constant *C = ConstantFold(&I, DL, ConstantPool)) { + // Instruction is side-effect free and constant. + + // If the instruction has uses outside this block or a phi node slot for + // the block, it is not safe to bypass the instruction since it would then + // no longer dominate all its uses. + for (auto &Use : I.uses()) { + User *User = Use.getUser(); + if (Instruction *I = dyn_cast<Instruction>(User)) + if (I->getParent() == CaseDest) + continue; + if (PHINode *Phi = dyn_cast<PHINode>(User)) + if (Phi->getIncomingBlock(Use) == CaseDest) + continue; + return false; + } + + ConstantPool.insert(std::make_pair(&I, C)); + } else { + break; + } + } + + // If we did not have a CommonDest before, use the current one. + if (!*CommonDest) + *CommonDest = CaseDest; + // If the destination isn't the common one, abort. + if (CaseDest != *CommonDest) + return false; + + // Get the values for this case from phi nodes in the destination block. + for (PHINode &PHI : (*CommonDest)->phis()) { + int Idx = PHI.getBasicBlockIndex(Pred); + if (Idx == -1) + continue; + + Constant *ConstVal = + LookupConstant(PHI.getIncomingValue(Idx), ConstantPool); + if (!ConstVal) + return false; + + // Be conservative about which kinds of constants we support. + if (!ValidLookupTableConstant(ConstVal, TTI)) + return false; + + Res.push_back(std::make_pair(&PHI, ConstVal)); + } + + return Res.size() > 0; +} + +// Helper function used to add CaseVal to the list of cases that generate +// Result. Returns the updated number of cases that generate this result. +static uintptr_t MapCaseToResult(ConstantInt *CaseVal, + SwitchCaseResultVectorTy &UniqueResults, + Constant *Result) { + for (auto &I : UniqueResults) { + if (I.first == Result) { + I.second.push_back(CaseVal); + return I.second.size(); + } + } + UniqueResults.push_back( + std::make_pair(Result, SmallVector<ConstantInt *, 4>(1, CaseVal))); + return 1; +} + +// Helper function that initializes a map containing +// results for the PHI node of the common destination block for a switch +// instruction. Returns false if multiple PHI nodes have been found or if +// there is not a common destination block for the switch. +static bool +InitializeUniqueCases(SwitchInst *SI, PHINode *&PHI, BasicBlock *&CommonDest, + SwitchCaseResultVectorTy &UniqueResults, + Constant *&DefaultResult, const DataLayout &DL, + const TargetTransformInfo &TTI, + uintptr_t MaxUniqueResults, uintptr_t MaxCasesPerResult) { + for (auto &I : SI->cases()) { + ConstantInt *CaseVal = I.getCaseValue(); + + // Resulting value at phi nodes for this case value. + SwitchCaseResultsTy Results; + if (!GetCaseResults(SI, CaseVal, I.getCaseSuccessor(), &CommonDest, Results, + DL, TTI)) + return false; + + // Only one value per case is permitted. + if (Results.size() > 1) + return false; + + // Add the case->result mapping to UniqueResults. + const uintptr_t NumCasesForResult = + MapCaseToResult(CaseVal, UniqueResults, Results.begin()->second); + + // Early out if there are too many cases for this result. + if (NumCasesForResult > MaxCasesPerResult) + return false; + + // Early out if there are too many unique results. + if (UniqueResults.size() > MaxUniqueResults) + return false; + + // Check the PHI consistency. + if (!PHI) + PHI = Results[0].first; + else if (PHI != Results[0].first) + return false; + } + // Find the default result value. + SmallVector<std::pair<PHINode *, Constant *>, 1> DefaultResults; + BasicBlock *DefaultDest = SI->getDefaultDest(); + GetCaseResults(SI, nullptr, SI->getDefaultDest(), &CommonDest, DefaultResults, + DL, TTI); + // If the default value is not found abort unless the default destination + // is unreachable. + DefaultResult = + DefaultResults.size() == 1 ? DefaultResults.begin()->second : nullptr; + if ((!DefaultResult && + !isa<UnreachableInst>(DefaultDest->getFirstNonPHIOrDbg()))) + return false; + + return true; +} + +// Helper function that checks if it is possible to transform a switch with only +// two cases (or two cases + default) that produces a result into a select. +// Example: +// switch (a) { +// case 10: %0 = icmp eq i32 %a, 10 +// return 10; %1 = select i1 %0, i32 10, i32 4 +// case 20: ----> %2 = icmp eq i32 %a, 20 +// return 2; %3 = select i1 %2, i32 2, i32 %1 +// default: +// return 4; +// } +static Value *ConvertTwoCaseSwitch(const SwitchCaseResultVectorTy &ResultVector, + Constant *DefaultResult, Value *Condition, + IRBuilder<> &Builder) { + assert(ResultVector.size() == 2 && + "We should have exactly two unique results at this point"); + // If we are selecting between only two cases transform into a simple + // select or a two-way select if default is possible. + if (ResultVector[0].second.size() == 1 && + ResultVector[1].second.size() == 1) { + ConstantInt *const FirstCase = ResultVector[0].second[0]; + ConstantInt *const SecondCase = ResultVector[1].second[0]; + + bool DefaultCanTrigger = DefaultResult; + Value *SelectValue = ResultVector[1].first; + if (DefaultCanTrigger) { + Value *const ValueCompare = + Builder.CreateICmpEQ(Condition, SecondCase, "switch.selectcmp"); + SelectValue = Builder.CreateSelect(ValueCompare, ResultVector[1].first, + DefaultResult, "switch.select"); + } + Value *const ValueCompare = + Builder.CreateICmpEQ(Condition, FirstCase, "switch.selectcmp"); + return Builder.CreateSelect(ValueCompare, ResultVector[0].first, + SelectValue, "switch.select"); + } + + return nullptr; +} + +// Helper function to cleanup a switch instruction that has been converted into +// a select, fixing up PHI nodes and basic blocks. +static void RemoveSwitchAfterSelectConversion(SwitchInst *SI, PHINode *PHI, + Value *SelectValue, + IRBuilder<> &Builder) { + BasicBlock *SelectBB = SI->getParent(); + while (PHI->getBasicBlockIndex(SelectBB) >= 0) + PHI->removeIncomingValue(SelectBB); + PHI->addIncoming(SelectValue, SelectBB); + + Builder.CreateBr(PHI->getParent()); + + // Remove the switch. + for (unsigned i = 0, e = SI->getNumSuccessors(); i < e; ++i) { + BasicBlock *Succ = SI->getSuccessor(i); + + if (Succ == PHI->getParent()) + continue; + Succ->removePredecessor(SelectBB); + } + SI->eraseFromParent(); +} + +/// If the switch is only used to initialize one or more +/// phi nodes in a common successor block with only two different +/// constant values, replace the switch with select. +static bool switchToSelect(SwitchInst *SI, IRBuilder<> &Builder, + const DataLayout &DL, + const TargetTransformInfo &TTI) { + Value *const Cond = SI->getCondition(); + PHINode *PHI = nullptr; + BasicBlock *CommonDest = nullptr; + Constant *DefaultResult; + SwitchCaseResultVectorTy UniqueResults; + // Collect all the cases that will deliver the same value from the switch. + if (!InitializeUniqueCases(SI, PHI, CommonDest, UniqueResults, DefaultResult, + DL, TTI, 2, 1)) + return false; + // Selects choose between maximum two values. + if (UniqueResults.size() != 2) + return false; + assert(PHI != nullptr && "PHI for value select not found"); + + Builder.SetInsertPoint(SI); + Value *SelectValue = + ConvertTwoCaseSwitch(UniqueResults, DefaultResult, Cond, Builder); + if (SelectValue) { + RemoveSwitchAfterSelectConversion(SI, PHI, SelectValue, Builder); + return true; + } + // The switch couldn't be converted into a select. + return false; +} + +namespace { + +/// This class represents a lookup table that can be used to replace a switch. +class SwitchLookupTable { +public: + /// Create a lookup table to use as a switch replacement with the contents + /// of Values, using DefaultValue to fill any holes in the table. + SwitchLookupTable( + Module &M, uint64_t TableSize, ConstantInt *Offset, + const SmallVectorImpl<std::pair<ConstantInt *, Constant *>> &Values, + Constant *DefaultValue, const DataLayout &DL, const StringRef &FuncName); + + /// Build instructions with Builder to retrieve the value at + /// the position given by Index in the lookup table. + Value *BuildLookup(Value *Index, IRBuilder<> &Builder); + + /// Return true if a table with TableSize elements of + /// type ElementType would fit in a target-legal register. + static bool WouldFitInRegister(const DataLayout &DL, uint64_t TableSize, + Type *ElementType); + +private: + // Depending on the contents of the table, it can be represented in + // different ways. + enum { + // For tables where each element contains the same value, we just have to + // store that single value and return it for each lookup. + SingleValueKind, + + // For tables where there is a linear relationship between table index + // and values. We calculate the result with a simple multiplication + // and addition instead of a table lookup. + LinearMapKind, + + // For small tables with integer elements, we can pack them into a bitmap + // that fits into a target-legal register. Values are retrieved by + // shift and mask operations. + BitMapKind, + + // The table is stored as an array of values. Values are retrieved by load + // instructions from the table. + ArrayKind + } Kind; + + // For SingleValueKind, this is the single value. + Constant *SingleValue = nullptr; + + // For BitMapKind, this is the bitmap. + ConstantInt *BitMap = nullptr; + IntegerType *BitMapElementTy = nullptr; + + // For LinearMapKind, these are the constants used to derive the value. + ConstantInt *LinearOffset = nullptr; + ConstantInt *LinearMultiplier = nullptr; + + // For ArrayKind, this is the array. + GlobalVariable *Array = nullptr; +}; + +} // end anonymous namespace + +SwitchLookupTable::SwitchLookupTable( + Module &M, uint64_t TableSize, ConstantInt *Offset, + const SmallVectorImpl<std::pair<ConstantInt *, Constant *>> &Values, + Constant *DefaultValue, const DataLayout &DL, const StringRef &FuncName) { + assert(Values.size() && "Can't build lookup table without values!"); + assert(TableSize >= Values.size() && "Can't fit values in table!"); + + // If all values in the table are equal, this is that value. + SingleValue = Values.begin()->second; + + Type *ValueType = Values.begin()->second->getType(); + + // Build up the table contents. + SmallVector<Constant *, 64> TableContents(TableSize); + for (size_t I = 0, E = Values.size(); I != E; ++I) { + ConstantInt *CaseVal = Values[I].first; + Constant *CaseRes = Values[I].second; + assert(CaseRes->getType() == ValueType); + + uint64_t Idx = (CaseVal->getValue() - Offset->getValue()).getLimitedValue(); + TableContents[Idx] = CaseRes; + + if (CaseRes != SingleValue) + SingleValue = nullptr; + } + + // Fill in any holes in the table with the default result. + if (Values.size() < TableSize) { + assert(DefaultValue && + "Need a default value to fill the lookup table holes."); + assert(DefaultValue->getType() == ValueType); + for (uint64_t I = 0; I < TableSize; ++I) { + if (!TableContents[I]) + TableContents[I] = DefaultValue; + } + + if (DefaultValue != SingleValue) + SingleValue = nullptr; + } + + // If each element in the table contains the same value, we only need to store + // that single value. + if (SingleValue) { + Kind = SingleValueKind; + return; + } + + // Check if we can derive the value with a linear transformation from the + // table index. + if (isa<IntegerType>(ValueType)) { + bool LinearMappingPossible = true; + APInt PrevVal; + APInt DistToPrev; + assert(TableSize >= 2 && "Should be a SingleValue table."); + // Check if there is the same distance between two consecutive values. + for (uint64_t I = 0; I < TableSize; ++I) { + ConstantInt *ConstVal = dyn_cast<ConstantInt>(TableContents[I]); + if (!ConstVal) { + // This is an undef. We could deal with it, but undefs in lookup tables + // are very seldom. It's probably not worth the additional complexity. + LinearMappingPossible = false; + break; + } + const APInt &Val = ConstVal->getValue(); + if (I != 0) { + APInt Dist = Val - PrevVal; + if (I == 1) { + DistToPrev = Dist; + } else if (Dist != DistToPrev) { + LinearMappingPossible = false; + break; + } + } + PrevVal = Val; + } + if (LinearMappingPossible) { + LinearOffset = cast<ConstantInt>(TableContents[0]); + LinearMultiplier = ConstantInt::get(M.getContext(), DistToPrev); + Kind = LinearMapKind; + ++NumLinearMaps; + return; + } + } + + // If the type is integer and the table fits in a register, build a bitmap. + if (WouldFitInRegister(DL, TableSize, ValueType)) { + IntegerType *IT = cast<IntegerType>(ValueType); + APInt TableInt(TableSize * IT->getBitWidth(), 0); + for (uint64_t I = TableSize; I > 0; --I) { + TableInt <<= IT->getBitWidth(); + // Insert values into the bitmap. Undef values are set to zero. + if (!isa<UndefValue>(TableContents[I - 1])) { + ConstantInt *Val = cast<ConstantInt>(TableContents[I - 1]); + TableInt |= Val->getValue().zext(TableInt.getBitWidth()); + } + } + BitMap = ConstantInt::get(M.getContext(), TableInt); + BitMapElementTy = IT; + Kind = BitMapKind; + ++NumBitMaps; + return; + } + + // Store the table in an array. + ArrayType *ArrayTy = ArrayType::get(ValueType, TableSize); + Constant *Initializer = ConstantArray::get(ArrayTy, TableContents); + + Array = new GlobalVariable(M, ArrayTy, /*isConstant=*/true, + GlobalVariable::PrivateLinkage, Initializer, + "switch.table." + FuncName); + Array->setUnnamedAddr(GlobalValue::UnnamedAddr::Global); + // Set the alignment to that of an array items. We will be only loading one + // value out of it. + Array->setAlignment(Align(DL.getPrefTypeAlignment(ValueType))); + Kind = ArrayKind; +} + +Value *SwitchLookupTable::BuildLookup(Value *Index, IRBuilder<> &Builder) { + switch (Kind) { + case SingleValueKind: + return SingleValue; + case LinearMapKind: { + // Derive the result value from the input value. + Value *Result = Builder.CreateIntCast(Index, LinearMultiplier->getType(), + false, "switch.idx.cast"); + if (!LinearMultiplier->isOne()) + Result = Builder.CreateMul(Result, LinearMultiplier, "switch.idx.mult"); + if (!LinearOffset->isZero()) + Result = Builder.CreateAdd(Result, LinearOffset, "switch.offset"); + return Result; + } + case BitMapKind: { + // Type of the bitmap (e.g. i59). + IntegerType *MapTy = BitMap->getType(); + + // Cast Index to the same type as the bitmap. + // Note: The Index is <= the number of elements in the table, so + // truncating it to the width of the bitmask is safe. + Value *ShiftAmt = Builder.CreateZExtOrTrunc(Index, MapTy, "switch.cast"); + + // Multiply the shift amount by the element width. + ShiftAmt = Builder.CreateMul( + ShiftAmt, ConstantInt::get(MapTy, BitMapElementTy->getBitWidth()), + "switch.shiftamt"); + + // Shift down. + Value *DownShifted = + Builder.CreateLShr(BitMap, ShiftAmt, "switch.downshift"); + // Mask off. + return Builder.CreateTrunc(DownShifted, BitMapElementTy, "switch.masked"); + } + case ArrayKind: { + // Make sure the table index will not overflow when treated as signed. + IntegerType *IT = cast<IntegerType>(Index->getType()); + uint64_t TableSize = + Array->getInitializer()->getType()->getArrayNumElements(); + if (TableSize > (1ULL << (IT->getBitWidth() - 1))) + Index = Builder.CreateZExt( + Index, IntegerType::get(IT->getContext(), IT->getBitWidth() + 1), + "switch.tableidx.zext"); + + Value *GEPIndices[] = {Builder.getInt32(0), Index}; + Value *GEP = Builder.CreateInBoundsGEP(Array->getValueType(), Array, + GEPIndices, "switch.gep"); + return Builder.CreateLoad( + cast<ArrayType>(Array->getValueType())->getElementType(), GEP, + "switch.load"); + } + } + llvm_unreachable("Unknown lookup table kind!"); +} + +bool SwitchLookupTable::WouldFitInRegister(const DataLayout &DL, + uint64_t TableSize, + Type *ElementType) { + auto *IT = dyn_cast<IntegerType>(ElementType); + if (!IT) + return false; + // FIXME: If the type is wider than it needs to be, e.g. i8 but all values + // are <= 15, we could try to narrow the type. + + // Avoid overflow, fitsInLegalInteger uses unsigned int for the width. + if (TableSize >= UINT_MAX / IT->getBitWidth()) + return false; + return DL.fitsInLegalInteger(TableSize * IT->getBitWidth()); +} + +/// Determine whether a lookup table should be built for this switch, based on +/// the number of cases, size of the table, and the types of the results. +static bool +ShouldBuildLookupTable(SwitchInst *SI, uint64_t TableSize, + const TargetTransformInfo &TTI, const DataLayout &DL, + const SmallDenseMap<PHINode *, Type *> &ResultTypes) { + if (SI->getNumCases() > TableSize || TableSize >= UINT64_MAX / 10) + return false; // TableSize overflowed, or mul below might overflow. + + bool AllTablesFitInRegister = true; + bool HasIllegalType = false; + for (const auto &I : ResultTypes) { + Type *Ty = I.second; + + // Saturate this flag to true. + HasIllegalType = HasIllegalType || !TTI.isTypeLegal(Ty); + + // Saturate this flag to false. + AllTablesFitInRegister = + AllTablesFitInRegister && + SwitchLookupTable::WouldFitInRegister(DL, TableSize, Ty); + + // If both flags saturate, we're done. NOTE: This *only* works with + // saturating flags, and all flags have to saturate first due to the + // non-deterministic behavior of iterating over a dense map. + if (HasIllegalType && !AllTablesFitInRegister) + break; + } + + // If each table would fit in a register, we should build it anyway. + if (AllTablesFitInRegister) + return true; + + // Don't build a table that doesn't fit in-register if it has illegal types. + if (HasIllegalType) + return false; + + // The table density should be at least 40%. This is the same criterion as for + // jump tables, see SelectionDAGBuilder::handleJTSwitchCase. + // FIXME: Find the best cut-off. + return SI->getNumCases() * 10 >= TableSize * 4; +} + +/// Try to reuse the switch table index compare. Following pattern: +/// \code +/// if (idx < tablesize) +/// r = table[idx]; // table does not contain default_value +/// else +/// r = default_value; +/// if (r != default_value) +/// ... +/// \endcode +/// Is optimized to: +/// \code +/// cond = idx < tablesize; +/// if (cond) +/// r = table[idx]; +/// else +/// r = default_value; +/// if (cond) +/// ... +/// \endcode +/// Jump threading will then eliminate the second if(cond). +static void reuseTableCompare( + User *PhiUser, BasicBlock *PhiBlock, BranchInst *RangeCheckBranch, + Constant *DefaultValue, + const SmallVectorImpl<std::pair<ConstantInt *, Constant *>> &Values) { + ICmpInst *CmpInst = dyn_cast<ICmpInst>(PhiUser); + if (!CmpInst) + return; + + // We require that the compare is in the same block as the phi so that jump + // threading can do its work afterwards. + if (CmpInst->getParent() != PhiBlock) + return; + + Constant *CmpOp1 = dyn_cast<Constant>(CmpInst->getOperand(1)); + if (!CmpOp1) + return; + + Value *RangeCmp = RangeCheckBranch->getCondition(); + Constant *TrueConst = ConstantInt::getTrue(RangeCmp->getType()); + Constant *FalseConst = ConstantInt::getFalse(RangeCmp->getType()); + + // Check if the compare with the default value is constant true or false. + Constant *DefaultConst = ConstantExpr::getICmp(CmpInst->getPredicate(), + DefaultValue, CmpOp1, true); + if (DefaultConst != TrueConst && DefaultConst != FalseConst) + return; + + // Check if the compare with the case values is distinct from the default + // compare result. + for (auto ValuePair : Values) { + Constant *CaseConst = ConstantExpr::getICmp(CmpInst->getPredicate(), + ValuePair.second, CmpOp1, true); + if (!CaseConst || CaseConst == DefaultConst || isa<UndefValue>(CaseConst)) + return; + assert((CaseConst == TrueConst || CaseConst == FalseConst) && + "Expect true or false as compare result."); + } + + // Check if the branch instruction dominates the phi node. It's a simple + // dominance check, but sufficient for our needs. + // Although this check is invariant in the calling loops, it's better to do it + // at this late stage. Practically we do it at most once for a switch. + BasicBlock *BranchBlock = RangeCheckBranch->getParent(); + for (auto PI = pred_begin(PhiBlock), E = pred_end(PhiBlock); PI != E; ++PI) { + BasicBlock *Pred = *PI; + if (Pred != BranchBlock && Pred->getUniquePredecessor() != BranchBlock) + return; + } + + if (DefaultConst == FalseConst) { + // The compare yields the same result. We can replace it. + CmpInst->replaceAllUsesWith(RangeCmp); + ++NumTableCmpReuses; + } else { + // The compare yields the same result, just inverted. We can replace it. + Value *InvertedTableCmp = BinaryOperator::CreateXor( + RangeCmp, ConstantInt::get(RangeCmp->getType(), 1), "inverted.cmp", + RangeCheckBranch); + CmpInst->replaceAllUsesWith(InvertedTableCmp); + ++NumTableCmpReuses; + } +} + +/// If the switch is only used to initialize one or more phi nodes in a common +/// successor block with different constant values, replace the switch with +/// lookup tables. +static bool SwitchToLookupTable(SwitchInst *SI, IRBuilder<> &Builder, + const DataLayout &DL, + const TargetTransformInfo &TTI) { + assert(SI->getNumCases() > 1 && "Degenerate switch?"); + + Function *Fn = SI->getParent()->getParent(); + // Only build lookup table when we have a target that supports it or the + // attribute is not set. + if (!TTI.shouldBuildLookupTables() || + (Fn->getFnAttribute("no-jump-tables").getValueAsString() == "true")) + return false; + + // FIXME: If the switch is too sparse for a lookup table, perhaps we could + // split off a dense part and build a lookup table for that. + + // FIXME: This creates arrays of GEPs to constant strings, which means each + // GEP needs a runtime relocation in PIC code. We should just build one big + // string and lookup indices into that. + + // Ignore switches with less than three cases. Lookup tables will not make + // them faster, so we don't analyze them. + if (SI->getNumCases() < 3) + return false; + + // Figure out the corresponding result for each case value and phi node in the + // common destination, as well as the min and max case values. + assert(!SI->cases().empty()); + SwitchInst::CaseIt CI = SI->case_begin(); + ConstantInt *MinCaseVal = CI->getCaseValue(); + ConstantInt *MaxCaseVal = CI->getCaseValue(); + + BasicBlock *CommonDest = nullptr; + + using ResultListTy = SmallVector<std::pair<ConstantInt *, Constant *>, 4>; + SmallDenseMap<PHINode *, ResultListTy> ResultLists; + + SmallDenseMap<PHINode *, Constant *> DefaultResults; + SmallDenseMap<PHINode *, Type *> ResultTypes; + SmallVector<PHINode *, 4> PHIs; + + for (SwitchInst::CaseIt E = SI->case_end(); CI != E; ++CI) { + ConstantInt *CaseVal = CI->getCaseValue(); + if (CaseVal->getValue().slt(MinCaseVal->getValue())) + MinCaseVal = CaseVal; + if (CaseVal->getValue().sgt(MaxCaseVal->getValue())) + MaxCaseVal = CaseVal; + + // Resulting value at phi nodes for this case value. + using ResultsTy = SmallVector<std::pair<PHINode *, Constant *>, 4>; + ResultsTy Results; + if (!GetCaseResults(SI, CaseVal, CI->getCaseSuccessor(), &CommonDest, + Results, DL, TTI)) + return false; + + // Append the result from this case to the list for each phi. + for (const auto &I : Results) { + PHINode *PHI = I.first; + Constant *Value = I.second; + if (!ResultLists.count(PHI)) + PHIs.push_back(PHI); + ResultLists[PHI].push_back(std::make_pair(CaseVal, Value)); + } + } + + // Keep track of the result types. + for (PHINode *PHI : PHIs) { + ResultTypes[PHI] = ResultLists[PHI][0].second->getType(); + } + + uint64_t NumResults = ResultLists[PHIs[0]].size(); + APInt RangeSpread = MaxCaseVal->getValue() - MinCaseVal->getValue(); + uint64_t TableSize = RangeSpread.getLimitedValue() + 1; + bool TableHasHoles = (NumResults < TableSize); + + // If the table has holes, we need a constant result for the default case + // or a bitmask that fits in a register. + SmallVector<std::pair<PHINode *, Constant *>, 4> DefaultResultsList; + bool HasDefaultResults = + GetCaseResults(SI, nullptr, SI->getDefaultDest(), &CommonDest, + DefaultResultsList, DL, TTI); + + bool NeedMask = (TableHasHoles && !HasDefaultResults); + if (NeedMask) { + // As an extra penalty for the validity test we require more cases. + if (SI->getNumCases() < 4) // FIXME: Find best threshold value (benchmark). + return false; + if (!DL.fitsInLegalInteger(TableSize)) + return false; + } + + for (const auto &I : DefaultResultsList) { + PHINode *PHI = I.first; + Constant *Result = I.second; + DefaultResults[PHI] = Result; + } + + if (!ShouldBuildLookupTable(SI, TableSize, TTI, DL, ResultTypes)) + return false; + + // Create the BB that does the lookups. + Module &Mod = *CommonDest->getParent()->getParent(); + BasicBlock *LookupBB = BasicBlock::Create( + Mod.getContext(), "switch.lookup", CommonDest->getParent(), CommonDest); + + // Compute the table index value. + Builder.SetInsertPoint(SI); + Value *TableIndex; + if (MinCaseVal->isNullValue()) + TableIndex = SI->getCondition(); + else + TableIndex = Builder.CreateSub(SI->getCondition(), MinCaseVal, + "switch.tableidx"); + + // Compute the maximum table size representable by the integer type we are + // switching upon. + unsigned CaseSize = MinCaseVal->getType()->getPrimitiveSizeInBits(); + uint64_t MaxTableSize = CaseSize > 63 ? UINT64_MAX : 1ULL << CaseSize; + assert(MaxTableSize >= TableSize && + "It is impossible for a switch to have more entries than the max " + "representable value of its input integer type's size."); + + // If the default destination is unreachable, or if the lookup table covers + // all values of the conditional variable, branch directly to the lookup table + // BB. Otherwise, check that the condition is within the case range. + const bool DefaultIsReachable = + !isa<UnreachableInst>(SI->getDefaultDest()->getFirstNonPHIOrDbg()); + const bool GeneratingCoveredLookupTable = (MaxTableSize == TableSize); + BranchInst *RangeCheckBranch = nullptr; + + if (!DefaultIsReachable || GeneratingCoveredLookupTable) { + Builder.CreateBr(LookupBB); + // Note: We call removeProdecessor later since we need to be able to get the + // PHI value for the default case in case we're using a bit mask. + } else { + Value *Cmp = Builder.CreateICmpULT( + TableIndex, ConstantInt::get(MinCaseVal->getType(), TableSize)); + RangeCheckBranch = + Builder.CreateCondBr(Cmp, LookupBB, SI->getDefaultDest()); + } + + // Populate the BB that does the lookups. + Builder.SetInsertPoint(LookupBB); + + if (NeedMask) { + // Before doing the lookup, we do the hole check. The LookupBB is therefore + // re-purposed to do the hole check, and we create a new LookupBB. + BasicBlock *MaskBB = LookupBB; + MaskBB->setName("switch.hole_check"); + LookupBB = BasicBlock::Create(Mod.getContext(), "switch.lookup", + CommonDest->getParent(), CommonDest); + + // Make the mask's bitwidth at least 8-bit and a power-of-2 to avoid + // unnecessary illegal types. + uint64_t TableSizePowOf2 = NextPowerOf2(std::max(7ULL, TableSize - 1ULL)); + APInt MaskInt(TableSizePowOf2, 0); + APInt One(TableSizePowOf2, 1); + // Build bitmask; fill in a 1 bit for every case. + const ResultListTy &ResultList = ResultLists[PHIs[0]]; + for (size_t I = 0, E = ResultList.size(); I != E; ++I) { + uint64_t Idx = (ResultList[I].first->getValue() - MinCaseVal->getValue()) + .getLimitedValue(); + MaskInt |= One << Idx; + } + ConstantInt *TableMask = ConstantInt::get(Mod.getContext(), MaskInt); + + // Get the TableIndex'th bit of the bitmask. + // If this bit is 0 (meaning hole) jump to the default destination, + // else continue with table lookup. + IntegerType *MapTy = TableMask->getType(); + Value *MaskIndex = + Builder.CreateZExtOrTrunc(TableIndex, MapTy, "switch.maskindex"); + Value *Shifted = Builder.CreateLShr(TableMask, MaskIndex, "switch.shifted"); + Value *LoBit = Builder.CreateTrunc( + Shifted, Type::getInt1Ty(Mod.getContext()), "switch.lobit"); + Builder.CreateCondBr(LoBit, LookupBB, SI->getDefaultDest()); + + Builder.SetInsertPoint(LookupBB); + AddPredecessorToBlock(SI->getDefaultDest(), MaskBB, SI->getParent()); + } + + if (!DefaultIsReachable || GeneratingCoveredLookupTable) { + // We cached PHINodes in PHIs. To avoid accessing deleted PHINodes later, + // do not delete PHINodes here. + SI->getDefaultDest()->removePredecessor(SI->getParent(), + /*KeepOneInputPHIs=*/true); + } + + bool ReturnedEarly = false; + for (PHINode *PHI : PHIs) { + const ResultListTy &ResultList = ResultLists[PHI]; + + // If using a bitmask, use any value to fill the lookup table holes. + Constant *DV = NeedMask ? ResultLists[PHI][0].second : DefaultResults[PHI]; + StringRef FuncName = Fn->getName(); + SwitchLookupTable Table(Mod, TableSize, MinCaseVal, ResultList, DV, DL, + FuncName); + + Value *Result = Table.BuildLookup(TableIndex, Builder); + + // If the result is used to return immediately from the function, we want to + // do that right here. + if (PHI->hasOneUse() && isa<ReturnInst>(*PHI->user_begin()) && + PHI->user_back() == CommonDest->getFirstNonPHIOrDbg()) { + Builder.CreateRet(Result); + ReturnedEarly = true; + break; + } + + // Do a small peephole optimization: re-use the switch table compare if + // possible. + if (!TableHasHoles && HasDefaultResults && RangeCheckBranch) { + BasicBlock *PhiBlock = PHI->getParent(); + // Search for compare instructions which use the phi. + for (auto *User : PHI->users()) { + reuseTableCompare(User, PhiBlock, RangeCheckBranch, DV, ResultList); + } + } + + PHI->addIncoming(Result, LookupBB); + } + + if (!ReturnedEarly) + Builder.CreateBr(CommonDest); + + // Remove the switch. + for (unsigned i = 0, e = SI->getNumSuccessors(); i < e; ++i) { + BasicBlock *Succ = SI->getSuccessor(i); + + if (Succ == SI->getDefaultDest()) + continue; + Succ->removePredecessor(SI->getParent()); + } + SI->eraseFromParent(); + + ++NumLookupTables; + if (NeedMask) + ++NumLookupTablesHoles; + return true; +} + +static bool isSwitchDense(ArrayRef<int64_t> Values) { + // See also SelectionDAGBuilder::isDense(), which this function was based on. + uint64_t Diff = (uint64_t)Values.back() - (uint64_t)Values.front(); + uint64_t Range = Diff + 1; + uint64_t NumCases = Values.size(); + // 40% is the default density for building a jump table in optsize/minsize mode. + uint64_t MinDensity = 40; + + return NumCases * 100 >= Range * MinDensity; +} + +/// Try to transform a switch that has "holes" in it to a contiguous sequence +/// of cases. +/// +/// A switch such as: switch(i) {case 5: case 9: case 13: case 17:} can be +/// range-reduced to: switch ((i-5) / 4) {case 0: case 1: case 2: case 3:}. +/// +/// This converts a sparse switch into a dense switch which allows better +/// lowering and could also allow transforming into a lookup table. +static bool ReduceSwitchRange(SwitchInst *SI, IRBuilder<> &Builder, + const DataLayout &DL, + const TargetTransformInfo &TTI) { + auto *CondTy = cast<IntegerType>(SI->getCondition()->getType()); + if (CondTy->getIntegerBitWidth() > 64 || + !DL.fitsInLegalInteger(CondTy->getIntegerBitWidth())) + return false; + // Only bother with this optimization if there are more than 3 switch cases; + // SDAG will only bother creating jump tables for 4 or more cases. + if (SI->getNumCases() < 4) + return false; + + // This transform is agnostic to the signedness of the input or case values. We + // can treat the case values as signed or unsigned. We can optimize more common + // cases such as a sequence crossing zero {-4,0,4,8} if we interpret case values + // as signed. + SmallVector<int64_t,4> Values; + for (auto &C : SI->cases()) + Values.push_back(C.getCaseValue()->getValue().getSExtValue()); + llvm::sort(Values); + + // If the switch is already dense, there's nothing useful to do here. + if (isSwitchDense(Values)) + return false; + + // First, transform the values such that they start at zero and ascend. + int64_t Base = Values[0]; + for (auto &V : Values) + V -= (uint64_t)(Base); + + // Now we have signed numbers that have been shifted so that, given enough + // precision, there are no negative values. Since the rest of the transform + // is bitwise only, we switch now to an unsigned representation. + + // This transform can be done speculatively because it is so cheap - it + // results in a single rotate operation being inserted. + // FIXME: It's possible that optimizing a switch on powers of two might also + // be beneficial - flag values are often powers of two and we could use a CLZ + // as the key function. + + // countTrailingZeros(0) returns 64. As Values is guaranteed to have more than + // one element and LLVM disallows duplicate cases, Shift is guaranteed to be + // less than 64. + unsigned Shift = 64; + for (auto &V : Values) + Shift = std::min(Shift, countTrailingZeros((uint64_t)V)); + assert(Shift < 64); + if (Shift > 0) + for (auto &V : Values) + V = (int64_t)((uint64_t)V >> Shift); + + if (!isSwitchDense(Values)) + // Transform didn't create a dense switch. + return false; + + // The obvious transform is to shift the switch condition right and emit a + // check that the condition actually cleanly divided by GCD, i.e. + // C & (1 << Shift - 1) == 0 + // inserting a new CFG edge to handle the case where it didn't divide cleanly. + // + // A cheaper way of doing this is a simple ROTR(C, Shift). This performs the + // shift and puts the shifted-off bits in the uppermost bits. If any of these + // are nonzero then the switch condition will be very large and will hit the + // default case. + + auto *Ty = cast<IntegerType>(SI->getCondition()->getType()); + Builder.SetInsertPoint(SI); + auto *ShiftC = ConstantInt::get(Ty, Shift); + auto *Sub = Builder.CreateSub(SI->getCondition(), ConstantInt::get(Ty, Base)); + auto *LShr = Builder.CreateLShr(Sub, ShiftC); + auto *Shl = Builder.CreateShl(Sub, Ty->getBitWidth() - Shift); + auto *Rot = Builder.CreateOr(LShr, Shl); + SI->replaceUsesOfWith(SI->getCondition(), Rot); + + for (auto Case : SI->cases()) { + auto *Orig = Case.getCaseValue(); + auto Sub = Orig->getValue() - APInt(Ty->getBitWidth(), Base); + Case.setValue( + cast<ConstantInt>(ConstantInt::get(Ty, Sub.lshr(ShiftC->getValue())))); + } + return true; +} + +bool SimplifyCFGOpt::SimplifySwitch(SwitchInst *SI, IRBuilder<> &Builder) { + BasicBlock *BB = SI->getParent(); + + if (isValueEqualityComparison(SI)) { + // If we only have one predecessor, and if it is a branch on this value, + // see if that predecessor totally determines the outcome of this switch. + if (BasicBlock *OnlyPred = BB->getSinglePredecessor()) + if (SimplifyEqualityComparisonWithOnlyPredecessor(SI, OnlyPred, Builder)) + return requestResimplify(); + + Value *Cond = SI->getCondition(); + if (SelectInst *Select = dyn_cast<SelectInst>(Cond)) + if (SimplifySwitchOnSelect(SI, Select)) + return requestResimplify(); + + // If the block only contains the switch, see if we can fold the block + // away into any preds. + if (SI == &*BB->instructionsWithoutDebug().begin()) + if (FoldValueComparisonIntoPredecessors(SI, Builder)) + return requestResimplify(); + } + + // Try to transform the switch into an icmp and a branch. + if (TurnSwitchRangeIntoICmp(SI, Builder)) + return requestResimplify(); + + // Remove unreachable cases. + if (eliminateDeadSwitchCases(SI, Options.AC, DL)) + return requestResimplify(); + + if (switchToSelect(SI, Builder, DL, TTI)) + return requestResimplify(); + + if (Options.ForwardSwitchCondToPhi && ForwardSwitchConditionToPHI(SI)) + return requestResimplify(); + + // The conversion from switch to lookup tables results in difficult-to-analyze + // code and makes pruning branches much harder. This is a problem if the + // switch expression itself can still be restricted as a result of inlining or + // CVP. Therefore, only apply this transformation during late stages of the + // optimisation pipeline. + if (Options.ConvertSwitchToLookupTable && + SwitchToLookupTable(SI, Builder, DL, TTI)) + return requestResimplify(); + + if (ReduceSwitchRange(SI, Builder, DL, TTI)) + return requestResimplify(); + + return false; +} + +bool SimplifyCFGOpt::SimplifyIndirectBr(IndirectBrInst *IBI) { + BasicBlock *BB = IBI->getParent(); + bool Changed = false; + + // Eliminate redundant destinations. + SmallPtrSet<Value *, 8> Succs; + for (unsigned i = 0, e = IBI->getNumDestinations(); i != e; ++i) { + BasicBlock *Dest = IBI->getDestination(i); + if (!Dest->hasAddressTaken() || !Succs.insert(Dest).second) { + Dest->removePredecessor(BB); + IBI->removeDestination(i); + --i; + --e; + Changed = true; + } + } + + if (IBI->getNumDestinations() == 0) { + // If the indirectbr has no successors, change it to unreachable. + new UnreachableInst(IBI->getContext(), IBI); + EraseTerminatorAndDCECond(IBI); + return true; + } + + if (IBI->getNumDestinations() == 1) { + // If the indirectbr has one successor, change it to a direct branch. + BranchInst::Create(IBI->getDestination(0), IBI); + EraseTerminatorAndDCECond(IBI); + return true; + } + + if (SelectInst *SI = dyn_cast<SelectInst>(IBI->getAddress())) { + if (SimplifyIndirectBrOnSelect(IBI, SI)) + return requestResimplify(); + } + return Changed; +} + +/// Given an block with only a single landing pad and a unconditional branch +/// try to find another basic block which this one can be merged with. This +/// handles cases where we have multiple invokes with unique landing pads, but +/// a shared handler. +/// +/// We specifically choose to not worry about merging non-empty blocks +/// here. That is a PRE/scheduling problem and is best solved elsewhere. In +/// practice, the optimizer produces empty landing pad blocks quite frequently +/// when dealing with exception dense code. (see: instcombine, gvn, if-else +/// sinking in this file) +/// +/// This is primarily a code size optimization. We need to avoid performing +/// any transform which might inhibit optimization (such as our ability to +/// specialize a particular handler via tail commoning). We do this by not +/// merging any blocks which require us to introduce a phi. Since the same +/// values are flowing through both blocks, we don't lose any ability to +/// specialize. If anything, we make such specialization more likely. +/// +/// TODO - This transformation could remove entries from a phi in the target +/// block when the inputs in the phi are the same for the two blocks being +/// merged. In some cases, this could result in removal of the PHI entirely. +static bool TryToMergeLandingPad(LandingPadInst *LPad, BranchInst *BI, + BasicBlock *BB) { + auto Succ = BB->getUniqueSuccessor(); + assert(Succ); + // If there's a phi in the successor block, we'd likely have to introduce + // a phi into the merged landing pad block. + if (isa<PHINode>(*Succ->begin())) + return false; + + for (BasicBlock *OtherPred : predecessors(Succ)) { + if (BB == OtherPred) + continue; + BasicBlock::iterator I = OtherPred->begin(); + LandingPadInst *LPad2 = dyn_cast<LandingPadInst>(I); + if (!LPad2 || !LPad2->isIdenticalTo(LPad)) + continue; + for (++I; isa<DbgInfoIntrinsic>(I); ++I) + ; + BranchInst *BI2 = dyn_cast<BranchInst>(I); + if (!BI2 || !BI2->isIdenticalTo(BI)) + continue; + + // We've found an identical block. Update our predecessors to take that + // path instead and make ourselves dead. + SmallPtrSet<BasicBlock *, 16> Preds; + Preds.insert(pred_begin(BB), pred_end(BB)); + for (BasicBlock *Pred : Preds) { + InvokeInst *II = cast<InvokeInst>(Pred->getTerminator()); + assert(II->getNormalDest() != BB && II->getUnwindDest() == BB && + "unexpected successor"); + II->setUnwindDest(OtherPred); + } + + // The debug info in OtherPred doesn't cover the merged control flow that + // used to go through BB. We need to delete it or update it. + for (auto I = OtherPred->begin(), E = OtherPred->end(); I != E;) { + Instruction &Inst = *I; + I++; + if (isa<DbgInfoIntrinsic>(Inst)) + Inst.eraseFromParent(); + } + + SmallPtrSet<BasicBlock *, 16> Succs; + Succs.insert(succ_begin(BB), succ_end(BB)); + for (BasicBlock *Succ : Succs) { + Succ->removePredecessor(BB); + } + + IRBuilder<> Builder(BI); + Builder.CreateUnreachable(); + BI->eraseFromParent(); + return true; + } + return false; +} + +bool SimplifyCFGOpt::SimplifyUncondBranch(BranchInst *BI, + IRBuilder<> &Builder) { + BasicBlock *BB = BI->getParent(); + BasicBlock *Succ = BI->getSuccessor(0); + + // If the Terminator is the only non-phi instruction, simplify the block. + // If LoopHeader is provided, check if the block or its successor is a loop + // header. (This is for early invocations before loop simplify and + // vectorization to keep canonical loop forms for nested loops. These blocks + // can be eliminated when the pass is invoked later in the back-end.) + // Note that if BB has only one predecessor then we do not introduce new + // backedge, so we can eliminate BB. + bool NeedCanonicalLoop = + Options.NeedCanonicalLoop && + (LoopHeaders && BB->hasNPredecessorsOrMore(2) && + (LoopHeaders->count(BB) || LoopHeaders->count(Succ))); + BasicBlock::iterator I = BB->getFirstNonPHIOrDbg()->getIterator(); + if (I->isTerminator() && BB != &BB->getParent()->getEntryBlock() && + !NeedCanonicalLoop && TryToSimplifyUncondBranchFromEmptyBlock(BB)) + return true; + + // If the only instruction in the block is a seteq/setne comparison against a + // constant, try to simplify the block. + if (ICmpInst *ICI = dyn_cast<ICmpInst>(I)) + if (ICI->isEquality() && isa<ConstantInt>(ICI->getOperand(1))) { + for (++I; isa<DbgInfoIntrinsic>(I); ++I) + ; + if (I->isTerminator() && + tryToSimplifyUncondBranchWithICmpInIt(ICI, Builder)) + return true; + } + + // See if we can merge an empty landing pad block with another which is + // equivalent. + if (LandingPadInst *LPad = dyn_cast<LandingPadInst>(I)) { + for (++I; isa<DbgInfoIntrinsic>(I); ++I) + ; + if (I->isTerminator() && TryToMergeLandingPad(LPad, BI, BB)) + return true; + } + + // If this basic block is ONLY a compare and a branch, and if a predecessor + // branches to us and our successor, fold the comparison into the + // predecessor and use logical operations to update the incoming value + // for PHI nodes in common successor. + if (FoldBranchToCommonDest(BI, nullptr, Options.BonusInstThreshold)) + return requestResimplify(); + return false; +} + +static BasicBlock *allPredecessorsComeFromSameSource(BasicBlock *BB) { + BasicBlock *PredPred = nullptr; + for (auto *P : predecessors(BB)) { + BasicBlock *PPred = P->getSinglePredecessor(); + if (!PPred || (PredPred && PredPred != PPred)) + return nullptr; + PredPred = PPred; + } + return PredPred; +} + +bool SimplifyCFGOpt::SimplifyCondBranch(BranchInst *BI, IRBuilder<> &Builder) { + BasicBlock *BB = BI->getParent(); + const Function *Fn = BB->getParent(); + if (Fn && Fn->hasFnAttribute(Attribute::OptForFuzzing)) + return false; + + // Conditional branch + if (isValueEqualityComparison(BI)) { + // If we only have one predecessor, and if it is a branch on this value, + // see if that predecessor totally determines the outcome of this + // switch. + if (BasicBlock *OnlyPred = BB->getSinglePredecessor()) + if (SimplifyEqualityComparisonWithOnlyPredecessor(BI, OnlyPred, Builder)) + return requestResimplify(); + + // This block must be empty, except for the setcond inst, if it exists. + // Ignore dbg intrinsics. + auto I = BB->instructionsWithoutDebug().begin(); + if (&*I == BI) { + if (FoldValueComparisonIntoPredecessors(BI, Builder)) + return requestResimplify(); + } else if (&*I == cast<Instruction>(BI->getCondition())) { + ++I; + if (&*I == BI && FoldValueComparisonIntoPredecessors(BI, Builder)) + return requestResimplify(); + } + } + + // Try to turn "br (X == 0 | X == 1), T, F" into a switch instruction. + if (SimplifyBranchOnICmpChain(BI, Builder, DL)) + return true; + + // If this basic block has dominating predecessor blocks and the dominating + // blocks' conditions imply BI's condition, we know the direction of BI. + Optional<bool> Imp = isImpliedByDomCondition(BI->getCondition(), BI, DL); + if (Imp) { + // Turn this into a branch on constant. + auto *OldCond = BI->getCondition(); + ConstantInt *TorF = *Imp ? ConstantInt::getTrue(BB->getContext()) + : ConstantInt::getFalse(BB->getContext()); + BI->setCondition(TorF); + RecursivelyDeleteTriviallyDeadInstructions(OldCond); + return requestResimplify(); + } + + // If this basic block is ONLY a compare and a branch, and if a predecessor + // branches to us and one of our successors, fold the comparison into the + // predecessor and use logical operations to pick the right destination. + if (FoldBranchToCommonDest(BI, nullptr, Options.BonusInstThreshold)) + return requestResimplify(); + + // We have a conditional branch to two blocks that are only reachable + // from BI. We know that the condbr dominates the two blocks, so see if + // there is any identical code in the "then" and "else" blocks. If so, we + // can hoist it up to the branching block. + if (BI->getSuccessor(0)->getSinglePredecessor()) { + if (BI->getSuccessor(1)->getSinglePredecessor()) { + if (HoistThenElseCodeToIf(BI, TTI)) + return requestResimplify(); + } else { + // If Successor #1 has multiple preds, we may be able to conditionally + // execute Successor #0 if it branches to Successor #1. + Instruction *Succ0TI = BI->getSuccessor(0)->getTerminator(); + if (Succ0TI->getNumSuccessors() == 1 && + Succ0TI->getSuccessor(0) == BI->getSuccessor(1)) + if (SpeculativelyExecuteBB(BI, BI->getSuccessor(0), TTI)) + return requestResimplify(); + } + } else if (BI->getSuccessor(1)->getSinglePredecessor()) { + // If Successor #0 has multiple preds, we may be able to conditionally + // execute Successor #1 if it branches to Successor #0. + Instruction *Succ1TI = BI->getSuccessor(1)->getTerminator(); + if (Succ1TI->getNumSuccessors() == 1 && + Succ1TI->getSuccessor(0) == BI->getSuccessor(0)) + if (SpeculativelyExecuteBB(BI, BI->getSuccessor(1), TTI)) + return requestResimplify(); + } + + // If this is a branch on a phi node in the current block, thread control + // through this block if any PHI node entries are constants. + if (PHINode *PN = dyn_cast<PHINode>(BI->getCondition())) + if (PN->getParent() == BI->getParent()) + if (FoldCondBranchOnPHI(BI, DL, Options.AC)) + return requestResimplify(); + + // Scan predecessor blocks for conditional branches. + for (pred_iterator PI = pred_begin(BB), E = pred_end(BB); PI != E; ++PI) + if (BranchInst *PBI = dyn_cast<BranchInst>((*PI)->getTerminator())) + if (PBI != BI && PBI->isConditional()) + if (SimplifyCondBranchToCondBranch(PBI, BI, DL, TTI)) + return requestResimplify(); + + // Look for diamond patterns. + if (MergeCondStores) + if (BasicBlock *PrevBB = allPredecessorsComeFromSameSource(BB)) + if (BranchInst *PBI = dyn_cast<BranchInst>(PrevBB->getTerminator())) + if (PBI != BI && PBI->isConditional()) + if (mergeConditionalStores(PBI, BI, DL, TTI)) + return requestResimplify(); + + return false; +} + +/// Check if passing a value to an instruction will cause undefined behavior. +static bool passingValueIsAlwaysUndefined(Value *V, Instruction *I) { + Constant *C = dyn_cast<Constant>(V); + if (!C) + return false; + + if (I->use_empty()) + return false; + + if (C->isNullValue() || isa<UndefValue>(C)) { + // Only look at the first use, avoid hurting compile time with long uselists + User *Use = *I->user_begin(); + + // Now make sure that there are no instructions in between that can alter + // control flow (eg. calls) + for (BasicBlock::iterator + i = ++BasicBlock::iterator(I), + UI = BasicBlock::iterator(dyn_cast<Instruction>(Use)); + i != UI; ++i) + if (i == I->getParent()->end() || i->mayHaveSideEffects()) + return false; + + // Look through GEPs. A load from a GEP derived from NULL is still undefined + if (GetElementPtrInst *GEP = dyn_cast<GetElementPtrInst>(Use)) + if (GEP->getPointerOperand() == I) + return passingValueIsAlwaysUndefined(V, GEP); + + // Look through bitcasts. + if (BitCastInst *BC = dyn_cast<BitCastInst>(Use)) + return passingValueIsAlwaysUndefined(V, BC); + + // Load from null is undefined. + if (LoadInst *LI = dyn_cast<LoadInst>(Use)) + if (!LI->isVolatile()) + return !NullPointerIsDefined(LI->getFunction(), + LI->getPointerAddressSpace()); + + // Store to null is undefined. + if (StoreInst *SI = dyn_cast<StoreInst>(Use)) + if (!SI->isVolatile()) + return (!NullPointerIsDefined(SI->getFunction(), + SI->getPointerAddressSpace())) && + SI->getPointerOperand() == I; + + // A call to null is undefined. + if (auto CS = CallSite(Use)) + return !NullPointerIsDefined(CS->getFunction()) && + CS.getCalledValue() == I; + } + return false; +} + +/// If BB has an incoming value that will always trigger undefined behavior +/// (eg. null pointer dereference), remove the branch leading here. +static bool removeUndefIntroducingPredecessor(BasicBlock *BB) { + for (PHINode &PHI : BB->phis()) + for (unsigned i = 0, e = PHI.getNumIncomingValues(); i != e; ++i) + if (passingValueIsAlwaysUndefined(PHI.getIncomingValue(i), &PHI)) { + Instruction *T = PHI.getIncomingBlock(i)->getTerminator(); + IRBuilder<> Builder(T); + if (BranchInst *BI = dyn_cast<BranchInst>(T)) { + BB->removePredecessor(PHI.getIncomingBlock(i)); + // Turn uncoditional branches into unreachables and remove the dead + // destination from conditional branches. + if (BI->isUnconditional()) + Builder.CreateUnreachable(); + else + Builder.CreateBr(BI->getSuccessor(0) == BB ? BI->getSuccessor(1) + : BI->getSuccessor(0)); + BI->eraseFromParent(); + return true; + } + // TODO: SwitchInst. + } + + return false; +} + +bool SimplifyCFGOpt::simplifyOnce(BasicBlock *BB) { + bool Changed = false; + + assert(BB && BB->getParent() && "Block not embedded in function!"); + assert(BB->getTerminator() && "Degenerate basic block encountered!"); + + // Remove basic blocks that have no predecessors (except the entry block)... + // or that just have themself as a predecessor. These are unreachable. + if ((pred_empty(BB) && BB != &BB->getParent()->getEntryBlock()) || + BB->getSinglePredecessor() == BB) { + LLVM_DEBUG(dbgs() << "Removing BB: \n" << *BB); + DeleteDeadBlock(BB); + return true; + } + + // Check to see if we can constant propagate this terminator instruction + // away... + Changed |= ConstantFoldTerminator(BB, true); + + // Check for and eliminate duplicate PHI nodes in this block. + Changed |= EliminateDuplicatePHINodes(BB); + + // Check for and remove branches that will always cause undefined behavior. + Changed |= removeUndefIntroducingPredecessor(BB); + + // Merge basic blocks into their predecessor if there is only one distinct + // pred, and if there is only one distinct successor of the predecessor, and + // if there are no PHI nodes. + if (MergeBlockIntoPredecessor(BB)) + return true; + + if (SinkCommon && Options.SinkCommonInsts) + Changed |= SinkCommonCodeFromPredecessors(BB); + + IRBuilder<> Builder(BB); + + // If there is a trivial two-entry PHI node in this basic block, and we can + // eliminate it, do so now. + if (auto *PN = dyn_cast<PHINode>(BB->begin())) + if (PN->getNumIncomingValues() == 2) + Changed |= FoldTwoEntryPHINode(PN, TTI, DL); + + Builder.SetInsertPoint(BB->getTerminator()); + if (auto *BI = dyn_cast<BranchInst>(BB->getTerminator())) { + if (BI->isUnconditional()) { + if (SimplifyUncondBranch(BI, Builder)) + return true; + } else { + if (SimplifyCondBranch(BI, Builder)) + return true; + } + } else if (auto *RI = dyn_cast<ReturnInst>(BB->getTerminator())) { + if (SimplifyReturn(RI, Builder)) + return true; + } else if (auto *RI = dyn_cast<ResumeInst>(BB->getTerminator())) { + if (SimplifyResume(RI, Builder)) + return true; + } else if (auto *RI = dyn_cast<CleanupReturnInst>(BB->getTerminator())) { + if (SimplifyCleanupReturn(RI)) + return true; + } else if (auto *SI = dyn_cast<SwitchInst>(BB->getTerminator())) { + if (SimplifySwitch(SI, Builder)) + return true; + } else if (auto *UI = dyn_cast<UnreachableInst>(BB->getTerminator())) { + if (SimplifyUnreachable(UI)) + return true; + } else if (auto *IBI = dyn_cast<IndirectBrInst>(BB->getTerminator())) { + if (SimplifyIndirectBr(IBI)) + return true; + } + + return Changed; +} + +bool SimplifyCFGOpt::run(BasicBlock *BB) { + bool Changed = false; + + // Repeated simplify BB as long as resimplification is requested. + do { + Resimplify = false; + + // Perform one round of simplifcation. Resimplify flag will be set if + // another iteration is requested. + Changed |= simplifyOnce(BB); + } while (Resimplify); + + return Changed; +} + +bool llvm::simplifyCFG(BasicBlock *BB, const TargetTransformInfo &TTI, + const SimplifyCFGOptions &Options, + SmallPtrSetImpl<BasicBlock *> *LoopHeaders) { + return SimplifyCFGOpt(TTI, BB->getModule()->getDataLayout(), LoopHeaders, + Options) + .run(BB); +} |