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Diffstat (limited to 'llvm/lib/Transforms/Scalar/GVN.cpp')
| -rw-r--r-- | llvm/lib/Transforms/Scalar/GVN.cpp | 2714 |
1 files changed, 2714 insertions, 0 deletions
diff --git a/llvm/lib/Transforms/Scalar/GVN.cpp b/llvm/lib/Transforms/Scalar/GVN.cpp new file mode 100644 index 000000000000..743353eaea22 --- /dev/null +++ b/llvm/lib/Transforms/Scalar/GVN.cpp @@ -0,0 +1,2714 @@ +//===- GVN.cpp - Eliminate redundant values and loads ---------------------===// +// +// 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 +// +//===----------------------------------------------------------------------===// +// +// This pass performs global value numbering to eliminate fully redundant +// instructions. It also performs simple dead load elimination. +// +// Note that this pass does the value numbering itself; it does not use the +// ValueNumbering analysis passes. +// +//===----------------------------------------------------------------------===// + +#include "llvm/Transforms/Scalar/GVN.h" +#include "llvm/ADT/DenseMap.h" +#include "llvm/ADT/DepthFirstIterator.h" +#include "llvm/ADT/Hashing.h" +#include "llvm/ADT/MapVector.h" +#include "llvm/ADT/PointerIntPair.h" +#include "llvm/ADT/PostOrderIterator.h" +#include "llvm/ADT/STLExtras.h" +#include "llvm/ADT/SetVector.h" +#include "llvm/ADT/SmallPtrSet.h" +#include "llvm/ADT/SmallVector.h" +#include "llvm/ADT/Statistic.h" +#include "llvm/Analysis/AliasAnalysis.h" +#include "llvm/Analysis/AssumptionCache.h" +#include "llvm/Analysis/CFG.h" +#include "llvm/Analysis/DomTreeUpdater.h" +#include "llvm/Analysis/GlobalsModRef.h" +#include "llvm/Analysis/InstructionSimplify.h" +#include "llvm/Analysis/LoopInfo.h" +#include "llvm/Analysis/MemoryBuiltins.h" +#include "llvm/Analysis/MemoryDependenceAnalysis.h" +#include "llvm/Analysis/OptimizationRemarkEmitter.h" +#include "llvm/Analysis/PHITransAddr.h" +#include "llvm/Analysis/TargetLibraryInfo.h" +#include "llvm/Analysis/ValueTracking.h" +#include "llvm/Config/llvm-config.h" +#include "llvm/IR/Attributes.h" +#include "llvm/IR/BasicBlock.h" +#include "llvm/IR/CallSite.h" +#include "llvm/IR/Constant.h" +#include "llvm/IR/Constants.h" +#include "llvm/IR/DataLayout.h" +#include "llvm/IR/DebugInfoMetadata.h" +#include "llvm/IR/DebugLoc.h" +#include "llvm/IR/Dominators.h" +#include "llvm/IR/Function.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/Metadata.h" +#include "llvm/IR/Module.h" +#include "llvm/IR/Operator.h" +#include "llvm/IR/PassManager.h" +#include "llvm/IR/PatternMatch.h" +#include "llvm/IR/Type.h" +#include "llvm/IR/Use.h" +#include "llvm/IR/Value.h" +#include "llvm/Pass.h" +#include "llvm/Support/Casting.h" +#include "llvm/Support/CommandLine.h" +#include "llvm/Support/Compiler.h" +#include "llvm/Support/Debug.h" +#include "llvm/Support/raw_ostream.h" +#include "llvm/Transforms/Utils.h" +#include "llvm/Transforms/Utils/BasicBlockUtils.h" +#include "llvm/Transforms/Utils/Local.h" +#include "llvm/Transforms/Utils/SSAUpdater.h" +#include "llvm/Transforms/Utils/VNCoercion.h" +#include <algorithm> +#include <cassert> +#include <cstdint> +#include <utility> +#include <vector> + +using namespace llvm; +using namespace llvm::gvn; +using namespace llvm::VNCoercion; +using namespace PatternMatch; + +#define DEBUG_TYPE "gvn" + +STATISTIC(NumGVNInstr, "Number of instructions deleted"); +STATISTIC(NumGVNLoad, "Number of loads deleted"); +STATISTIC(NumGVNPRE, "Number of instructions PRE'd"); +STATISTIC(NumGVNBlocks, "Number of blocks merged"); +STATISTIC(NumGVNSimpl, "Number of instructions simplified"); +STATISTIC(NumGVNEqProp, "Number of equalities propagated"); +STATISTIC(NumPRELoad, "Number of loads PRE'd"); + +static cl::opt<bool> EnablePRE("enable-pre", + cl::init(true), cl::Hidden); +static cl::opt<bool> EnableLoadPRE("enable-load-pre", cl::init(true)); +static cl::opt<bool> EnableMemDep("enable-gvn-memdep", cl::init(true)); + +// Maximum allowed recursion depth. +static cl::opt<uint32_t> +MaxRecurseDepth("gvn-max-recurse-depth", cl::Hidden, cl::init(1000), cl::ZeroOrMore, + cl::desc("Max recurse depth in GVN (default = 1000)")); + +static cl::opt<uint32_t> MaxNumDeps( + "gvn-max-num-deps", cl::Hidden, cl::init(100), cl::ZeroOrMore, + cl::desc("Max number of dependences to attempt Load PRE (default = 100)")); + +struct llvm::GVN::Expression { + uint32_t opcode; + Type *type; + bool commutative = false; + SmallVector<uint32_t, 4> varargs; + + Expression(uint32_t o = ~2U) : opcode(o) {} + + bool operator==(const Expression &other) const { + if (opcode != other.opcode) + return false; + if (opcode == ~0U || opcode == ~1U) + return true; + if (type != other.type) + return false; + if (varargs != other.varargs) + return false; + return true; + } + + friend hash_code hash_value(const Expression &Value) { + return hash_combine( + Value.opcode, Value.type, + hash_combine_range(Value.varargs.begin(), Value.varargs.end())); + } +}; + +namespace llvm { + +template <> struct DenseMapInfo<GVN::Expression> { + static inline GVN::Expression getEmptyKey() { return ~0U; } + static inline GVN::Expression getTombstoneKey() { return ~1U; } + + static unsigned getHashValue(const GVN::Expression &e) { + using llvm::hash_value; + + return static_cast<unsigned>(hash_value(e)); + } + + static bool isEqual(const GVN::Expression &LHS, const GVN::Expression &RHS) { + return LHS == RHS; + } +}; + +} // end namespace llvm + +/// Represents a particular available value that we know how to materialize. +/// Materialization of an AvailableValue never fails. An AvailableValue is +/// implicitly associated with a rematerialization point which is the +/// location of the instruction from which it was formed. +struct llvm::gvn::AvailableValue { + enum ValType { + SimpleVal, // A simple offsetted value that is accessed. + LoadVal, // A value produced by a load. + MemIntrin, // A memory intrinsic which is loaded from. + UndefVal // A UndefValue representing a value from dead block (which + // is not yet physically removed from the CFG). + }; + + /// V - The value that is live out of the block. + PointerIntPair<Value *, 2, ValType> Val; + + /// Offset - The byte offset in Val that is interesting for the load query. + unsigned Offset; + + static AvailableValue get(Value *V, unsigned Offset = 0) { + AvailableValue Res; + Res.Val.setPointer(V); + Res.Val.setInt(SimpleVal); + Res.Offset = Offset; + return Res; + } + + static AvailableValue getMI(MemIntrinsic *MI, unsigned Offset = 0) { + AvailableValue Res; + Res.Val.setPointer(MI); + Res.Val.setInt(MemIntrin); + Res.Offset = Offset; + return Res; + } + + static AvailableValue getLoad(LoadInst *LI, unsigned Offset = 0) { + AvailableValue Res; + Res.Val.setPointer(LI); + Res.Val.setInt(LoadVal); + Res.Offset = Offset; + return Res; + } + + static AvailableValue getUndef() { + AvailableValue Res; + Res.Val.setPointer(nullptr); + Res.Val.setInt(UndefVal); + Res.Offset = 0; + return Res; + } + + bool isSimpleValue() const { return Val.getInt() == SimpleVal; } + bool isCoercedLoadValue() const { return Val.getInt() == LoadVal; } + bool isMemIntrinValue() const { return Val.getInt() == MemIntrin; } + bool isUndefValue() const { return Val.getInt() == UndefVal; } + + Value *getSimpleValue() const { + assert(isSimpleValue() && "Wrong accessor"); + return Val.getPointer(); + } + + LoadInst *getCoercedLoadValue() const { + assert(isCoercedLoadValue() && "Wrong accessor"); + return cast<LoadInst>(Val.getPointer()); + } + + MemIntrinsic *getMemIntrinValue() const { + assert(isMemIntrinValue() && "Wrong accessor"); + return cast<MemIntrinsic>(Val.getPointer()); + } + + /// Emit code at the specified insertion point to adjust the value defined + /// here to the specified type. This handles various coercion cases. + Value *MaterializeAdjustedValue(LoadInst *LI, Instruction *InsertPt, + GVN &gvn) const; +}; + +/// Represents an AvailableValue which can be rematerialized at the end of +/// the associated BasicBlock. +struct llvm::gvn::AvailableValueInBlock { + /// BB - The basic block in question. + BasicBlock *BB; + + /// AV - The actual available value + AvailableValue AV; + + static AvailableValueInBlock get(BasicBlock *BB, AvailableValue &&AV) { + AvailableValueInBlock Res; + Res.BB = BB; + Res.AV = std::move(AV); + return Res; + } + + static AvailableValueInBlock get(BasicBlock *BB, Value *V, + unsigned Offset = 0) { + return get(BB, AvailableValue::get(V, Offset)); + } + + static AvailableValueInBlock getUndef(BasicBlock *BB) { + return get(BB, AvailableValue::getUndef()); + } + + /// Emit code at the end of this block to adjust the value defined here to + /// the specified type. This handles various coercion cases. + Value *MaterializeAdjustedValue(LoadInst *LI, GVN &gvn) const { + return AV.MaterializeAdjustedValue(LI, BB->getTerminator(), gvn); + } +}; + +//===----------------------------------------------------------------------===// +// ValueTable Internal Functions +//===----------------------------------------------------------------------===// + +GVN::Expression GVN::ValueTable::createExpr(Instruction *I) { + Expression e; + e.type = I->getType(); + e.opcode = I->getOpcode(); + for (Instruction::op_iterator OI = I->op_begin(), OE = I->op_end(); + OI != OE; ++OI) + e.varargs.push_back(lookupOrAdd(*OI)); + if (I->isCommutative()) { + // Ensure that commutative instructions that only differ by a permutation + // of their operands get the same value number by sorting the operand value + // numbers. Since all commutative instructions have two operands it is more + // efficient to sort by hand rather than using, say, std::sort. + assert(I->getNumOperands() == 2 && "Unsupported commutative instruction!"); + if (e.varargs[0] > e.varargs[1]) + std::swap(e.varargs[0], e.varargs[1]); + e.commutative = true; + } + + if (CmpInst *C = dyn_cast<CmpInst>(I)) { + // Sort the operand value numbers so x<y and y>x get the same value number. + CmpInst::Predicate Predicate = C->getPredicate(); + if (e.varargs[0] > e.varargs[1]) { + std::swap(e.varargs[0], e.varargs[1]); + Predicate = CmpInst::getSwappedPredicate(Predicate); + } + e.opcode = (C->getOpcode() << 8) | Predicate; + e.commutative = true; + } else if (InsertValueInst *E = dyn_cast<InsertValueInst>(I)) { + for (InsertValueInst::idx_iterator II = E->idx_begin(), IE = E->idx_end(); + II != IE; ++II) + e.varargs.push_back(*II); + } + + return e; +} + +GVN::Expression GVN::ValueTable::createCmpExpr(unsigned Opcode, + CmpInst::Predicate Predicate, + Value *LHS, Value *RHS) { + assert((Opcode == Instruction::ICmp || Opcode == Instruction::FCmp) && + "Not a comparison!"); + Expression e; + e.type = CmpInst::makeCmpResultType(LHS->getType()); + e.varargs.push_back(lookupOrAdd(LHS)); + e.varargs.push_back(lookupOrAdd(RHS)); + + // Sort the operand value numbers so x<y and y>x get the same value number. + if (e.varargs[0] > e.varargs[1]) { + std::swap(e.varargs[0], e.varargs[1]); + Predicate = CmpInst::getSwappedPredicate(Predicate); + } + e.opcode = (Opcode << 8) | Predicate; + e.commutative = true; + return e; +} + +GVN::Expression GVN::ValueTable::createExtractvalueExpr(ExtractValueInst *EI) { + assert(EI && "Not an ExtractValueInst?"); + Expression e; + e.type = EI->getType(); + e.opcode = 0; + + WithOverflowInst *WO = dyn_cast<WithOverflowInst>(EI->getAggregateOperand()); + if (WO != nullptr && EI->getNumIndices() == 1 && *EI->idx_begin() == 0) { + // EI is an extract from one of our with.overflow intrinsics. Synthesize + // a semantically equivalent expression instead of an extract value + // expression. + e.opcode = WO->getBinaryOp(); + e.varargs.push_back(lookupOrAdd(WO->getLHS())); + e.varargs.push_back(lookupOrAdd(WO->getRHS())); + return e; + } + + // Not a recognised intrinsic. Fall back to producing an extract value + // expression. + e.opcode = EI->getOpcode(); + for (Instruction::op_iterator OI = EI->op_begin(), OE = EI->op_end(); + OI != OE; ++OI) + e.varargs.push_back(lookupOrAdd(*OI)); + + for (ExtractValueInst::idx_iterator II = EI->idx_begin(), IE = EI->idx_end(); + II != IE; ++II) + e.varargs.push_back(*II); + + return e; +} + +//===----------------------------------------------------------------------===// +// ValueTable External Functions +//===----------------------------------------------------------------------===// + +GVN::ValueTable::ValueTable() = default; +GVN::ValueTable::ValueTable(const ValueTable &) = default; +GVN::ValueTable::ValueTable(ValueTable &&) = default; +GVN::ValueTable::~ValueTable() = default; + +/// add - Insert a value into the table with a specified value number. +void GVN::ValueTable::add(Value *V, uint32_t num) { + valueNumbering.insert(std::make_pair(V, num)); + if (PHINode *PN = dyn_cast<PHINode>(V)) + NumberingPhi[num] = PN; +} + +uint32_t GVN::ValueTable::lookupOrAddCall(CallInst *C) { + if (AA->doesNotAccessMemory(C)) { + Expression exp = createExpr(C); + uint32_t e = assignExpNewValueNum(exp).first; + valueNumbering[C] = e; + return e; + } else if (MD && AA->onlyReadsMemory(C)) { + Expression exp = createExpr(C); + auto ValNum = assignExpNewValueNum(exp); + if (ValNum.second) { + valueNumbering[C] = ValNum.first; + return ValNum.first; + } + + MemDepResult local_dep = MD->getDependency(C); + + if (!local_dep.isDef() && !local_dep.isNonLocal()) { + valueNumbering[C] = nextValueNumber; + return nextValueNumber++; + } + + if (local_dep.isDef()) { + CallInst* local_cdep = cast<CallInst>(local_dep.getInst()); + + if (local_cdep->getNumArgOperands() != C->getNumArgOperands()) { + valueNumbering[C] = nextValueNumber; + return nextValueNumber++; + } + + for (unsigned i = 0, e = C->getNumArgOperands(); i < e; ++i) { + uint32_t c_vn = lookupOrAdd(C->getArgOperand(i)); + uint32_t cd_vn = lookupOrAdd(local_cdep->getArgOperand(i)); + if (c_vn != cd_vn) { + valueNumbering[C] = nextValueNumber; + return nextValueNumber++; + } + } + + uint32_t v = lookupOrAdd(local_cdep); + valueNumbering[C] = v; + return v; + } + + // Non-local case. + const MemoryDependenceResults::NonLocalDepInfo &deps = + MD->getNonLocalCallDependency(C); + // FIXME: Move the checking logic to MemDep! + CallInst* cdep = nullptr; + + // Check to see if we have a single dominating call instruction that is + // identical to C. + for (unsigned i = 0, e = deps.size(); i != e; ++i) { + const NonLocalDepEntry *I = &deps[i]; + if (I->getResult().isNonLocal()) + continue; + + // We don't handle non-definitions. If we already have a call, reject + // instruction dependencies. + if (!I->getResult().isDef() || cdep != nullptr) { + cdep = nullptr; + break; + } + + CallInst *NonLocalDepCall = dyn_cast<CallInst>(I->getResult().getInst()); + // FIXME: All duplicated with non-local case. + if (NonLocalDepCall && DT->properlyDominates(I->getBB(), C->getParent())){ + cdep = NonLocalDepCall; + continue; + } + + cdep = nullptr; + break; + } + + if (!cdep) { + valueNumbering[C] = nextValueNumber; + return nextValueNumber++; + } + + if (cdep->getNumArgOperands() != C->getNumArgOperands()) { + valueNumbering[C] = nextValueNumber; + return nextValueNumber++; + } + for (unsigned i = 0, e = C->getNumArgOperands(); i < e; ++i) { + uint32_t c_vn = lookupOrAdd(C->getArgOperand(i)); + uint32_t cd_vn = lookupOrAdd(cdep->getArgOperand(i)); + if (c_vn != cd_vn) { + valueNumbering[C] = nextValueNumber; + return nextValueNumber++; + } + } + + uint32_t v = lookupOrAdd(cdep); + valueNumbering[C] = v; + return v; + } else { + valueNumbering[C] = nextValueNumber; + return nextValueNumber++; + } +} + +/// Returns true if a value number exists for the specified value. +bool GVN::ValueTable::exists(Value *V) const { return valueNumbering.count(V) != 0; } + +/// lookup_or_add - Returns the value number for the specified value, assigning +/// it a new number if it did not have one before. +uint32_t GVN::ValueTable::lookupOrAdd(Value *V) { + DenseMap<Value*, uint32_t>::iterator VI = valueNumbering.find(V); + if (VI != valueNumbering.end()) + return VI->second; + + if (!isa<Instruction>(V)) { + valueNumbering[V] = nextValueNumber; + return nextValueNumber++; + } + + Instruction* I = cast<Instruction>(V); + Expression exp; + switch (I->getOpcode()) { + case Instruction::Call: + return lookupOrAddCall(cast<CallInst>(I)); + case Instruction::FNeg: + case Instruction::Add: + case Instruction::FAdd: + case Instruction::Sub: + case Instruction::FSub: + case Instruction::Mul: + case Instruction::FMul: + case Instruction::UDiv: + case Instruction::SDiv: + case Instruction::FDiv: + case Instruction::URem: + case Instruction::SRem: + case Instruction::FRem: + case Instruction::Shl: + case Instruction::LShr: + case Instruction::AShr: + case Instruction::And: + case Instruction::Or: + case Instruction::Xor: + case Instruction::ICmp: + case Instruction::FCmp: + case Instruction::Trunc: + case Instruction::ZExt: + case Instruction::SExt: + case Instruction::FPToUI: + case Instruction::FPToSI: + case Instruction::UIToFP: + case Instruction::SIToFP: + case Instruction::FPTrunc: + case Instruction::FPExt: + case Instruction::PtrToInt: + case Instruction::IntToPtr: + case Instruction::AddrSpaceCast: + case Instruction::BitCast: + case Instruction::Select: + case Instruction::ExtractElement: + case Instruction::InsertElement: + case Instruction::ShuffleVector: + case Instruction::InsertValue: + case Instruction::GetElementPtr: + exp = createExpr(I); + break; + case Instruction::ExtractValue: + exp = createExtractvalueExpr(cast<ExtractValueInst>(I)); + break; + case Instruction::PHI: + valueNumbering[V] = nextValueNumber; + NumberingPhi[nextValueNumber] = cast<PHINode>(V); + return nextValueNumber++; + default: + valueNumbering[V] = nextValueNumber; + return nextValueNumber++; + } + + uint32_t e = assignExpNewValueNum(exp).first; + valueNumbering[V] = e; + return e; +} + +/// Returns the value number of the specified value. Fails if +/// the value has not yet been numbered. +uint32_t GVN::ValueTable::lookup(Value *V, bool Verify) const { + DenseMap<Value*, uint32_t>::const_iterator VI = valueNumbering.find(V); + if (Verify) { + assert(VI != valueNumbering.end() && "Value not numbered?"); + return VI->second; + } + return (VI != valueNumbering.end()) ? VI->second : 0; +} + +/// Returns the value number of the given comparison, +/// assigning it a new number if it did not have one before. Useful when +/// we deduced the result of a comparison, but don't immediately have an +/// instruction realizing that comparison to hand. +uint32_t GVN::ValueTable::lookupOrAddCmp(unsigned Opcode, + CmpInst::Predicate Predicate, + Value *LHS, Value *RHS) { + Expression exp = createCmpExpr(Opcode, Predicate, LHS, RHS); + return assignExpNewValueNum(exp).first; +} + +/// Remove all entries from the ValueTable. +void GVN::ValueTable::clear() { + valueNumbering.clear(); + expressionNumbering.clear(); + NumberingPhi.clear(); + PhiTranslateTable.clear(); + nextValueNumber = 1; + Expressions.clear(); + ExprIdx.clear(); + nextExprNumber = 0; +} + +/// Remove a value from the value numbering. +void GVN::ValueTable::erase(Value *V) { + uint32_t Num = valueNumbering.lookup(V); + valueNumbering.erase(V); + // If V is PHINode, V <--> value number is an one-to-one mapping. + if (isa<PHINode>(V)) + NumberingPhi.erase(Num); +} + +/// verifyRemoved - Verify that the value is removed from all internal data +/// structures. +void GVN::ValueTable::verifyRemoved(const Value *V) const { + for (DenseMap<Value*, uint32_t>::const_iterator + I = valueNumbering.begin(), E = valueNumbering.end(); I != E; ++I) { + assert(I->first != V && "Inst still occurs in value numbering map!"); + } +} + +//===----------------------------------------------------------------------===// +// GVN Pass +//===----------------------------------------------------------------------===// + +PreservedAnalyses GVN::run(Function &F, FunctionAnalysisManager &AM) { + // FIXME: The order of evaluation of these 'getResult' calls is very + // significant! Re-ordering these variables will cause GVN when run alone to + // be less effective! We should fix memdep and basic-aa to not exhibit this + // behavior, but until then don't change the order here. + auto &AC = AM.getResult<AssumptionAnalysis>(F); + auto &DT = AM.getResult<DominatorTreeAnalysis>(F); + auto &TLI = AM.getResult<TargetLibraryAnalysis>(F); + auto &AA = AM.getResult<AAManager>(F); + auto &MemDep = AM.getResult<MemoryDependenceAnalysis>(F); + auto *LI = AM.getCachedResult<LoopAnalysis>(F); + auto &ORE = AM.getResult<OptimizationRemarkEmitterAnalysis>(F); + bool Changed = runImpl(F, AC, DT, TLI, AA, &MemDep, LI, &ORE); + if (!Changed) + return PreservedAnalyses::all(); + PreservedAnalyses PA; + PA.preserve<DominatorTreeAnalysis>(); + PA.preserve<GlobalsAA>(); + PA.preserve<TargetLibraryAnalysis>(); + if (LI) + PA.preserve<LoopAnalysis>(); + return PA; +} + +#if !defined(NDEBUG) || defined(LLVM_ENABLE_DUMP) +LLVM_DUMP_METHOD void GVN::dump(DenseMap<uint32_t, Value*>& d) const { + errs() << "{\n"; + for (DenseMap<uint32_t, Value*>::iterator I = d.begin(), + E = d.end(); I != E; ++I) { + errs() << I->first << "\n"; + I->second->dump(); + } + errs() << "}\n"; +} +#endif + +/// Return true if we can prove that the value +/// we're analyzing is fully available in the specified block. As we go, keep +/// track of which blocks we know are fully alive in FullyAvailableBlocks. This +/// map is actually a tri-state map with the following values: +/// 0) we know the block *is not* fully available. +/// 1) we know the block *is* fully available. +/// 2) we do not know whether the block is fully available or not, but we are +/// currently speculating that it will be. +/// 3) we are speculating for this block and have used that to speculate for +/// other blocks. +static bool IsValueFullyAvailableInBlock(BasicBlock *BB, + DenseMap<BasicBlock*, char> &FullyAvailableBlocks, + uint32_t RecurseDepth) { + if (RecurseDepth > MaxRecurseDepth) + return false; + + // Optimistically assume that the block is fully available and check to see + // if we already know about this block in one lookup. + std::pair<DenseMap<BasicBlock*, char>::iterator, bool> IV = + FullyAvailableBlocks.insert(std::make_pair(BB, 2)); + + // If the entry already existed for this block, return the precomputed value. + if (!IV.second) { + // If this is a speculative "available" value, mark it as being used for + // speculation of other blocks. + if (IV.first->second == 2) + IV.first->second = 3; + return IV.first->second != 0; + } + + // Otherwise, see if it is fully available in all predecessors. + pred_iterator PI = pred_begin(BB), PE = pred_end(BB); + + // If this block has no predecessors, it isn't live-in here. + if (PI == PE) + goto SpeculationFailure; + + for (; PI != PE; ++PI) + // If the value isn't fully available in one of our predecessors, then it + // isn't fully available in this block either. Undo our previous + // optimistic assumption and bail out. + if (!IsValueFullyAvailableInBlock(*PI, FullyAvailableBlocks,RecurseDepth+1)) + goto SpeculationFailure; + + return true; + +// If we get here, we found out that this is not, after +// all, a fully-available block. We have a problem if we speculated on this and +// used the speculation to mark other blocks as available. +SpeculationFailure: + char &BBVal = FullyAvailableBlocks[BB]; + + // If we didn't speculate on this, just return with it set to false. + if (BBVal == 2) { + BBVal = 0; + return false; + } + + // If we did speculate on this value, we could have blocks set to 1 that are + // incorrect. Walk the (transitive) successors of this block and mark them as + // 0 if set to one. + SmallVector<BasicBlock*, 32> BBWorklist; + BBWorklist.push_back(BB); + + do { + BasicBlock *Entry = BBWorklist.pop_back_val(); + // Note that this sets blocks to 0 (unavailable) if they happen to not + // already be in FullyAvailableBlocks. This is safe. + char &EntryVal = FullyAvailableBlocks[Entry]; + if (EntryVal == 0) continue; // Already unavailable. + + // Mark as unavailable. + EntryVal = 0; + + BBWorklist.append(succ_begin(Entry), succ_end(Entry)); + } while (!BBWorklist.empty()); + + return false; +} + +/// Given a set of loads specified by ValuesPerBlock, +/// construct SSA form, allowing us to eliminate LI. This returns the value +/// that should be used at LI's definition site. +static Value *ConstructSSAForLoadSet(LoadInst *LI, + SmallVectorImpl<AvailableValueInBlock> &ValuesPerBlock, + GVN &gvn) { + // Check for the fully redundant, dominating load case. In this case, we can + // just use the dominating value directly. + if (ValuesPerBlock.size() == 1 && + gvn.getDominatorTree().properlyDominates(ValuesPerBlock[0].BB, + LI->getParent())) { + assert(!ValuesPerBlock[0].AV.isUndefValue() && + "Dead BB dominate this block"); + return ValuesPerBlock[0].MaterializeAdjustedValue(LI, gvn); + } + + // Otherwise, we have to construct SSA form. + SmallVector<PHINode*, 8> NewPHIs; + SSAUpdater SSAUpdate(&NewPHIs); + SSAUpdate.Initialize(LI->getType(), LI->getName()); + + for (const AvailableValueInBlock &AV : ValuesPerBlock) { + BasicBlock *BB = AV.BB; + + if (SSAUpdate.HasValueForBlock(BB)) + continue; + + // If the value is the load that we will be eliminating, and the block it's + // available in is the block that the load is in, then don't add it as + // SSAUpdater will resolve the value to the relevant phi which may let it + // avoid phi construction entirely if there's actually only one value. + if (BB == LI->getParent() && + ((AV.AV.isSimpleValue() && AV.AV.getSimpleValue() == LI) || + (AV.AV.isCoercedLoadValue() && AV.AV.getCoercedLoadValue() == LI))) + continue; + + SSAUpdate.AddAvailableValue(BB, AV.MaterializeAdjustedValue(LI, gvn)); + } + + // Perform PHI construction. + return SSAUpdate.GetValueInMiddleOfBlock(LI->getParent()); +} + +Value *AvailableValue::MaterializeAdjustedValue(LoadInst *LI, + Instruction *InsertPt, + GVN &gvn) const { + Value *Res; + Type *LoadTy = LI->getType(); + const DataLayout &DL = LI->getModule()->getDataLayout(); + if (isSimpleValue()) { + Res = getSimpleValue(); + if (Res->getType() != LoadTy) { + Res = getStoreValueForLoad(Res, Offset, LoadTy, InsertPt, DL); + + LLVM_DEBUG(dbgs() << "GVN COERCED NONLOCAL VAL:\nOffset: " << Offset + << " " << *getSimpleValue() << '\n' + << *Res << '\n' + << "\n\n\n"); + } + } else if (isCoercedLoadValue()) { + LoadInst *Load = getCoercedLoadValue(); + if (Load->getType() == LoadTy && Offset == 0) { + Res = Load; + } else { + Res = getLoadValueForLoad(Load, Offset, LoadTy, InsertPt, DL); + // We would like to use gvn.markInstructionForDeletion here, but we can't + // because the load is already memoized into the leader map table that GVN + // tracks. It is potentially possible to remove the load from the table, + // but then there all of the operations based on it would need to be + // rehashed. Just leave the dead load around. + gvn.getMemDep().removeInstruction(Load); + LLVM_DEBUG(dbgs() << "GVN COERCED NONLOCAL LOAD:\nOffset: " << Offset + << " " << *getCoercedLoadValue() << '\n' + << *Res << '\n' + << "\n\n\n"); + } + } else if (isMemIntrinValue()) { + Res = getMemInstValueForLoad(getMemIntrinValue(), Offset, LoadTy, + InsertPt, DL); + LLVM_DEBUG(dbgs() << "GVN COERCED NONLOCAL MEM INTRIN:\nOffset: " << Offset + << " " << *getMemIntrinValue() << '\n' + << *Res << '\n' + << "\n\n\n"); + } else { + assert(isUndefValue() && "Should be UndefVal"); + LLVM_DEBUG(dbgs() << "GVN COERCED NONLOCAL Undef:\n";); + return UndefValue::get(LoadTy); + } + assert(Res && "failed to materialize?"); + return Res; +} + +static bool isLifetimeStart(const Instruction *Inst) { + if (const IntrinsicInst* II = dyn_cast<IntrinsicInst>(Inst)) + return II->getIntrinsicID() == Intrinsic::lifetime_start; + return false; +} + +/// Try to locate the three instruction involved in a missed +/// load-elimination case that is due to an intervening store. +static void reportMayClobberedLoad(LoadInst *LI, MemDepResult DepInfo, + DominatorTree *DT, + OptimizationRemarkEmitter *ORE) { + using namespace ore; + + User *OtherAccess = nullptr; + + OptimizationRemarkMissed R(DEBUG_TYPE, "LoadClobbered", LI); + R << "load of type " << NV("Type", LI->getType()) << " not eliminated" + << setExtraArgs(); + + for (auto *U : LI->getPointerOperand()->users()) + if (U != LI && (isa<LoadInst>(U) || isa<StoreInst>(U)) && + DT->dominates(cast<Instruction>(U), LI)) { + // FIXME: for now give up if there are multiple memory accesses that + // dominate the load. We need further analysis to decide which one is + // that we're forwarding from. + if (OtherAccess) + OtherAccess = nullptr; + else + OtherAccess = U; + } + + if (OtherAccess) + R << " in favor of " << NV("OtherAccess", OtherAccess); + + R << " because it is clobbered by " << NV("ClobberedBy", DepInfo.getInst()); + + ORE->emit(R); +} + +bool GVN::AnalyzeLoadAvailability(LoadInst *LI, MemDepResult DepInfo, + Value *Address, AvailableValue &Res) { + assert((DepInfo.isDef() || DepInfo.isClobber()) && + "expected a local dependence"); + assert(LI->isUnordered() && "rules below are incorrect for ordered access"); + + const DataLayout &DL = LI->getModule()->getDataLayout(); + + Instruction *DepInst = DepInfo.getInst(); + if (DepInfo.isClobber()) { + // If the dependence is to a store that writes to a superset of the bits + // read by the load, we can extract the bits we need for the load from the + // stored value. + if (StoreInst *DepSI = dyn_cast<StoreInst>(DepInst)) { + // Can't forward from non-atomic to atomic without violating memory model. + if (Address && LI->isAtomic() <= DepSI->isAtomic()) { + int Offset = + analyzeLoadFromClobberingStore(LI->getType(), Address, DepSI, DL); + if (Offset != -1) { + Res = AvailableValue::get(DepSI->getValueOperand(), Offset); + return true; + } + } + } + + // Check to see if we have something like this: + // load i32* P + // load i8* (P+1) + // if we have this, replace the later with an extraction from the former. + if (LoadInst *DepLI = dyn_cast<LoadInst>(DepInst)) { + // If this is a clobber and L is the first instruction in its block, then + // we have the first instruction in the entry block. + // Can't forward from non-atomic to atomic without violating memory model. + if (DepLI != LI && Address && LI->isAtomic() <= DepLI->isAtomic()) { + int Offset = + analyzeLoadFromClobberingLoad(LI->getType(), Address, DepLI, DL); + + if (Offset != -1) { + Res = AvailableValue::getLoad(DepLI, Offset); + return true; + } + } + } + + // If the clobbering value is a memset/memcpy/memmove, see if we can + // forward a value on from it. + if (MemIntrinsic *DepMI = dyn_cast<MemIntrinsic>(DepInst)) { + if (Address && !LI->isAtomic()) { + int Offset = analyzeLoadFromClobberingMemInst(LI->getType(), Address, + DepMI, DL); + if (Offset != -1) { + Res = AvailableValue::getMI(DepMI, Offset); + return true; + } + } + } + // Nothing known about this clobber, have to be conservative + LLVM_DEBUG( + // fast print dep, using operator<< on instruction is too slow. + dbgs() << "GVN: load "; LI->printAsOperand(dbgs()); + dbgs() << " is clobbered by " << *DepInst << '\n';); + if (ORE->allowExtraAnalysis(DEBUG_TYPE)) + reportMayClobberedLoad(LI, DepInfo, DT, ORE); + + return false; + } + assert(DepInfo.isDef() && "follows from above"); + + // Loading the allocation -> undef. + if (isa<AllocaInst>(DepInst) || isMallocLikeFn(DepInst, TLI) || + // Loading immediately after lifetime begin -> undef. + isLifetimeStart(DepInst)) { + Res = AvailableValue::get(UndefValue::get(LI->getType())); + return true; + } + + // Loading from calloc (which zero initializes memory) -> zero + if (isCallocLikeFn(DepInst, TLI)) { + Res = AvailableValue::get(Constant::getNullValue(LI->getType())); + return true; + } + + if (StoreInst *S = dyn_cast<StoreInst>(DepInst)) { + // Reject loads and stores that are to the same address but are of + // different types if we have to. If the stored value is larger or equal to + // the loaded value, we can reuse it. + if (!canCoerceMustAliasedValueToLoad(S->getValueOperand(), LI->getType(), + DL)) + return false; + + // Can't forward from non-atomic to atomic without violating memory model. + if (S->isAtomic() < LI->isAtomic()) + return false; + + Res = AvailableValue::get(S->getValueOperand()); + return true; + } + + if (LoadInst *LD = dyn_cast<LoadInst>(DepInst)) { + // If the types mismatch and we can't handle it, reject reuse of the load. + // If the stored value is larger or equal to the loaded value, we can reuse + // it. + if (!canCoerceMustAliasedValueToLoad(LD, LI->getType(), DL)) + return false; + + // Can't forward from non-atomic to atomic without violating memory model. + if (LD->isAtomic() < LI->isAtomic()) + return false; + + Res = AvailableValue::getLoad(LD); + return true; + } + + // Unknown def - must be conservative + LLVM_DEBUG( + // fast print dep, using operator<< on instruction is too slow. + dbgs() << "GVN: load "; LI->printAsOperand(dbgs()); + dbgs() << " has unknown def " << *DepInst << '\n';); + return false; +} + +void GVN::AnalyzeLoadAvailability(LoadInst *LI, LoadDepVect &Deps, + AvailValInBlkVect &ValuesPerBlock, + UnavailBlkVect &UnavailableBlocks) { + // Filter out useless results (non-locals, etc). Keep track of the blocks + // where we have a value available in repl, also keep track of whether we see + // dependencies that produce an unknown value for the load (such as a call + // that could potentially clobber the load). + unsigned NumDeps = Deps.size(); + for (unsigned i = 0, e = NumDeps; i != e; ++i) { + BasicBlock *DepBB = Deps[i].getBB(); + MemDepResult DepInfo = Deps[i].getResult(); + + if (DeadBlocks.count(DepBB)) { + // Dead dependent mem-op disguise as a load evaluating the same value + // as the load in question. + ValuesPerBlock.push_back(AvailableValueInBlock::getUndef(DepBB)); + continue; + } + + if (!DepInfo.isDef() && !DepInfo.isClobber()) { + UnavailableBlocks.push_back(DepBB); + continue; + } + + // The address being loaded in this non-local block may not be the same as + // the pointer operand of the load if PHI translation occurs. Make sure + // to consider the right address. + Value *Address = Deps[i].getAddress(); + + AvailableValue AV; + if (AnalyzeLoadAvailability(LI, DepInfo, Address, AV)) { + // subtlety: because we know this was a non-local dependency, we know + // it's safe to materialize anywhere between the instruction within + // DepInfo and the end of it's block. + ValuesPerBlock.push_back(AvailableValueInBlock::get(DepBB, + std::move(AV))); + } else { + UnavailableBlocks.push_back(DepBB); + } + } + + assert(NumDeps == ValuesPerBlock.size() + UnavailableBlocks.size() && + "post condition violation"); +} + +bool GVN::PerformLoadPRE(LoadInst *LI, AvailValInBlkVect &ValuesPerBlock, + UnavailBlkVect &UnavailableBlocks) { + // Okay, we have *some* definitions of the value. This means that the value + // is available in some of our (transitive) predecessors. Lets think about + // doing PRE of this load. This will involve inserting a new load into the + // predecessor when it's not available. We could do this in general, but + // prefer to not increase code size. As such, we only do this when we know + // that we only have to insert *one* load (which means we're basically moving + // the load, not inserting a new one). + + SmallPtrSet<BasicBlock *, 4> Blockers(UnavailableBlocks.begin(), + UnavailableBlocks.end()); + + // Let's find the first basic block with more than one predecessor. Walk + // backwards through predecessors if needed. + BasicBlock *LoadBB = LI->getParent(); + BasicBlock *TmpBB = LoadBB; + bool IsSafeToSpeculativelyExecute = isSafeToSpeculativelyExecute(LI); + + // Check that there is no implicit control flow instructions above our load in + // its block. If there is an instruction that doesn't always pass the + // execution to the following instruction, then moving through it may become + // invalid. For example: + // + // int arr[LEN]; + // int index = ???; + // ... + // guard(0 <= index && index < LEN); + // use(arr[index]); + // + // It is illegal to move the array access to any point above the guard, + // because if the index is out of bounds we should deoptimize rather than + // access the array. + // Check that there is no guard in this block above our instruction. + if (!IsSafeToSpeculativelyExecute && ICF->isDominatedByICFIFromSameBlock(LI)) + return false; + while (TmpBB->getSinglePredecessor()) { + TmpBB = TmpBB->getSinglePredecessor(); + if (TmpBB == LoadBB) // Infinite (unreachable) loop. + return false; + if (Blockers.count(TmpBB)) + return false; + + // If any of these blocks has more than one successor (i.e. if the edge we + // just traversed was critical), then there are other paths through this + // block along which the load may not be anticipated. Hoisting the load + // above this block would be adding the load to execution paths along + // which it was not previously executed. + if (TmpBB->getTerminator()->getNumSuccessors() != 1) + return false; + + // Check that there is no implicit control flow in a block above. + if (!IsSafeToSpeculativelyExecute && ICF->hasICF(TmpBB)) + return false; + } + + assert(TmpBB); + LoadBB = TmpBB; + + // Check to see how many predecessors have the loaded value fully + // available. + MapVector<BasicBlock *, Value *> PredLoads; + DenseMap<BasicBlock*, char> FullyAvailableBlocks; + for (const AvailableValueInBlock &AV : ValuesPerBlock) + FullyAvailableBlocks[AV.BB] = true; + for (BasicBlock *UnavailableBB : UnavailableBlocks) + FullyAvailableBlocks[UnavailableBB] = false; + + SmallVector<BasicBlock *, 4> CriticalEdgePred; + for (BasicBlock *Pred : predecessors(LoadBB)) { + // If any predecessor block is an EH pad that does not allow non-PHI + // instructions before the terminator, we can't PRE the load. + if (Pred->getTerminator()->isEHPad()) { + LLVM_DEBUG( + dbgs() << "COULD NOT PRE LOAD BECAUSE OF AN EH PAD PREDECESSOR '" + << Pred->getName() << "': " << *LI << '\n'); + return false; + } + + if (IsValueFullyAvailableInBlock(Pred, FullyAvailableBlocks, 0)) { + continue; + } + + if (Pred->getTerminator()->getNumSuccessors() != 1) { + if (isa<IndirectBrInst>(Pred->getTerminator())) { + LLVM_DEBUG( + dbgs() << "COULD NOT PRE LOAD BECAUSE OF INDBR CRITICAL EDGE '" + << Pred->getName() << "': " << *LI << '\n'); + return false; + } + + // FIXME: Can we support the fallthrough edge? + if (isa<CallBrInst>(Pred->getTerminator())) { + LLVM_DEBUG( + dbgs() << "COULD NOT PRE LOAD BECAUSE OF CALLBR CRITICAL EDGE '" + << Pred->getName() << "': " << *LI << '\n'); + return false; + } + + if (LoadBB->isEHPad()) { + LLVM_DEBUG( + dbgs() << "COULD NOT PRE LOAD BECAUSE OF AN EH PAD CRITICAL EDGE '" + << Pred->getName() << "': " << *LI << '\n'); + return false; + } + + CriticalEdgePred.push_back(Pred); + } else { + // Only add the predecessors that will not be split for now. + PredLoads[Pred] = nullptr; + } + } + + // Decide whether PRE is profitable for this load. + unsigned NumUnavailablePreds = PredLoads.size() + CriticalEdgePred.size(); + assert(NumUnavailablePreds != 0 && + "Fully available value should already be eliminated!"); + + // If this load is unavailable in multiple predecessors, reject it. + // FIXME: If we could restructure the CFG, we could make a common pred with + // all the preds that don't have an available LI and insert a new load into + // that one block. + if (NumUnavailablePreds != 1) + return false; + + // Split critical edges, and update the unavailable predecessors accordingly. + for (BasicBlock *OrigPred : CriticalEdgePred) { + BasicBlock *NewPred = splitCriticalEdges(OrigPred, LoadBB); + assert(!PredLoads.count(OrigPred) && "Split edges shouldn't be in map!"); + PredLoads[NewPred] = nullptr; + LLVM_DEBUG(dbgs() << "Split critical edge " << OrigPred->getName() << "->" + << LoadBB->getName() << '\n'); + } + + // Check if the load can safely be moved to all the unavailable predecessors. + bool CanDoPRE = true; + const DataLayout &DL = LI->getModule()->getDataLayout(); + SmallVector<Instruction*, 8> NewInsts; + for (auto &PredLoad : PredLoads) { + BasicBlock *UnavailablePred = PredLoad.first; + + // Do PHI translation to get its value in the predecessor if necessary. The + // returned pointer (if non-null) is guaranteed to dominate UnavailablePred. + // We do the translation for each edge we skipped by going from LI's block + // to LoadBB, otherwise we might miss pieces needing translation. + + // If all preds have a single successor, then we know it is safe to insert + // the load on the pred (?!?), so we can insert code to materialize the + // pointer if it is not available. + Value *LoadPtr = LI->getPointerOperand(); + BasicBlock *Cur = LI->getParent(); + while (Cur != LoadBB) { + PHITransAddr Address(LoadPtr, DL, AC); + LoadPtr = Address.PHITranslateWithInsertion( + Cur, Cur->getSinglePredecessor(), *DT, NewInsts); + if (!LoadPtr) { + CanDoPRE = false; + break; + } + Cur = Cur->getSinglePredecessor(); + } + + if (LoadPtr) { + PHITransAddr Address(LoadPtr, DL, AC); + LoadPtr = Address.PHITranslateWithInsertion(LoadBB, UnavailablePred, *DT, + NewInsts); + } + // If we couldn't find or insert a computation of this phi translated value, + // we fail PRE. + if (!LoadPtr) { + LLVM_DEBUG(dbgs() << "COULDN'T INSERT PHI TRANSLATED VALUE OF: " + << *LI->getPointerOperand() << "\n"); + CanDoPRE = false; + break; + } + + PredLoad.second = LoadPtr; + } + + if (!CanDoPRE) { + while (!NewInsts.empty()) { + // Erase instructions generated by the failed PHI translation before + // trying to number them. PHI translation might insert instructions + // in basic blocks other than the current one, and we delete them + // directly, as markInstructionForDeletion only allows removing from the + // current basic block. + NewInsts.pop_back_val()->eraseFromParent(); + } + // HINT: Don't revert the edge-splitting as following transformation may + // also need to split these critical edges. + return !CriticalEdgePred.empty(); + } + + // Okay, we can eliminate this load by inserting a reload in the predecessor + // and using PHI construction to get the value in the other predecessors, do + // it. + LLVM_DEBUG(dbgs() << "GVN REMOVING PRE LOAD: " << *LI << '\n'); + LLVM_DEBUG(if (!NewInsts.empty()) dbgs() + << "INSERTED " << NewInsts.size() << " INSTS: " << *NewInsts.back() + << '\n'); + + // Assign value numbers to the new instructions. + for (Instruction *I : NewInsts) { + // Instructions that have been inserted in predecessor(s) to materialize + // the load address do not retain their original debug locations. Doing + // so could lead to confusing (but correct) source attributions. + if (const DebugLoc &DL = I->getDebugLoc()) + I->setDebugLoc(DebugLoc::get(0, 0, DL.getScope(), DL.getInlinedAt())); + + // FIXME: We really _ought_ to insert these value numbers into their + // parent's availability map. However, in doing so, we risk getting into + // ordering issues. If a block hasn't been processed yet, we would be + // marking a value as AVAIL-IN, which isn't what we intend. + VN.lookupOrAdd(I); + } + + for (const auto &PredLoad : PredLoads) { + BasicBlock *UnavailablePred = PredLoad.first; + Value *LoadPtr = PredLoad.second; + + auto *NewLoad = new LoadInst( + LI->getType(), LoadPtr, LI->getName() + ".pre", LI->isVolatile(), + MaybeAlign(LI->getAlignment()), LI->getOrdering(), LI->getSyncScopeID(), + UnavailablePred->getTerminator()); + NewLoad->setDebugLoc(LI->getDebugLoc()); + + // Transfer the old load's AA tags to the new load. + AAMDNodes Tags; + LI->getAAMetadata(Tags); + if (Tags) + NewLoad->setAAMetadata(Tags); + + if (auto *MD = LI->getMetadata(LLVMContext::MD_invariant_load)) + NewLoad->setMetadata(LLVMContext::MD_invariant_load, MD); + if (auto *InvGroupMD = LI->getMetadata(LLVMContext::MD_invariant_group)) + NewLoad->setMetadata(LLVMContext::MD_invariant_group, InvGroupMD); + if (auto *RangeMD = LI->getMetadata(LLVMContext::MD_range)) + NewLoad->setMetadata(LLVMContext::MD_range, RangeMD); + + // We do not propagate the old load's debug location, because the new + // load now lives in a different BB, and we want to avoid a jumpy line + // table. + // FIXME: How do we retain source locations without causing poor debugging + // behavior? + + // Add the newly created load. + ValuesPerBlock.push_back(AvailableValueInBlock::get(UnavailablePred, + NewLoad)); + MD->invalidateCachedPointerInfo(LoadPtr); + LLVM_DEBUG(dbgs() << "GVN INSERTED " << *NewLoad << '\n'); + } + + // Perform PHI construction. + Value *V = ConstructSSAForLoadSet(LI, ValuesPerBlock, *this); + LI->replaceAllUsesWith(V); + if (isa<PHINode>(V)) + V->takeName(LI); + if (Instruction *I = dyn_cast<Instruction>(V)) + I->setDebugLoc(LI->getDebugLoc()); + if (V->getType()->isPtrOrPtrVectorTy()) + MD->invalidateCachedPointerInfo(V); + markInstructionForDeletion(LI); + ORE->emit([&]() { + return OptimizationRemark(DEBUG_TYPE, "LoadPRE", LI) + << "load eliminated by PRE"; + }); + ++NumPRELoad; + return true; +} + +static void reportLoadElim(LoadInst *LI, Value *AvailableValue, + OptimizationRemarkEmitter *ORE) { + using namespace ore; + + ORE->emit([&]() { + return OptimizationRemark(DEBUG_TYPE, "LoadElim", LI) + << "load of type " << NV("Type", LI->getType()) << " eliminated" + << setExtraArgs() << " in favor of " + << NV("InfavorOfValue", AvailableValue); + }); +} + +/// Attempt to eliminate a load whose dependencies are +/// non-local by performing PHI construction. +bool GVN::processNonLocalLoad(LoadInst *LI) { + // non-local speculations are not allowed under asan. + if (LI->getParent()->getParent()->hasFnAttribute( + Attribute::SanitizeAddress) || + LI->getParent()->getParent()->hasFnAttribute( + Attribute::SanitizeHWAddress)) + return false; + + // Step 1: Find the non-local dependencies of the load. + LoadDepVect Deps; + MD->getNonLocalPointerDependency(LI, Deps); + + // If we had to process more than one hundred blocks to find the + // dependencies, this load isn't worth worrying about. Optimizing + // it will be too expensive. + unsigned NumDeps = Deps.size(); + if (NumDeps > MaxNumDeps) + return false; + + // If we had a phi translation failure, we'll have a single entry which is a + // clobber in the current block. Reject this early. + if (NumDeps == 1 && + !Deps[0].getResult().isDef() && !Deps[0].getResult().isClobber()) { + LLVM_DEBUG(dbgs() << "GVN: non-local load "; LI->printAsOperand(dbgs()); + dbgs() << " has unknown dependencies\n";); + return false; + } + + // If this load follows a GEP, see if we can PRE the indices before analyzing. + if (GetElementPtrInst *GEP = dyn_cast<GetElementPtrInst>(LI->getOperand(0))) { + for (GetElementPtrInst::op_iterator OI = GEP->idx_begin(), + OE = GEP->idx_end(); + OI != OE; ++OI) + if (Instruction *I = dyn_cast<Instruction>(OI->get())) + performScalarPRE(I); + } + + // Step 2: Analyze the availability of the load + AvailValInBlkVect ValuesPerBlock; + UnavailBlkVect UnavailableBlocks; + AnalyzeLoadAvailability(LI, Deps, ValuesPerBlock, UnavailableBlocks); + + // If we have no predecessors that produce a known value for this load, exit + // early. + if (ValuesPerBlock.empty()) + return false; + + // Step 3: Eliminate fully redundancy. + // + // If all of the instructions we depend on produce a known value for this + // load, then it is fully redundant and we can use PHI insertion to compute + // its value. Insert PHIs and remove the fully redundant value now. + if (UnavailableBlocks.empty()) { + LLVM_DEBUG(dbgs() << "GVN REMOVING NONLOCAL LOAD: " << *LI << '\n'); + + // Perform PHI construction. + Value *V = ConstructSSAForLoadSet(LI, ValuesPerBlock, *this); + LI->replaceAllUsesWith(V); + + if (isa<PHINode>(V)) + V->takeName(LI); + if (Instruction *I = dyn_cast<Instruction>(V)) + // If instruction I has debug info, then we should not update it. + // Also, if I has a null DebugLoc, then it is still potentially incorrect + // to propagate LI's DebugLoc because LI may not post-dominate I. + if (LI->getDebugLoc() && LI->getParent() == I->getParent()) + I->setDebugLoc(LI->getDebugLoc()); + if (V->getType()->isPtrOrPtrVectorTy()) + MD->invalidateCachedPointerInfo(V); + markInstructionForDeletion(LI); + ++NumGVNLoad; + reportLoadElim(LI, V, ORE); + return true; + } + + // Step 4: Eliminate partial redundancy. + if (!EnablePRE || !EnableLoadPRE) + return false; + + return PerformLoadPRE(LI, ValuesPerBlock, UnavailableBlocks); +} + +static bool hasUsersIn(Value *V, BasicBlock *BB) { + for (User *U : V->users()) + if (isa<Instruction>(U) && + cast<Instruction>(U)->getParent() == BB) + return true; + return false; +} + +bool GVN::processAssumeIntrinsic(IntrinsicInst *IntrinsicI) { + assert(IntrinsicI->getIntrinsicID() == Intrinsic::assume && + "This function can only be called with llvm.assume intrinsic"); + Value *V = IntrinsicI->getArgOperand(0); + + if (ConstantInt *Cond = dyn_cast<ConstantInt>(V)) { + if (Cond->isZero()) { + Type *Int8Ty = Type::getInt8Ty(V->getContext()); + // Insert a new store to null instruction before the load to indicate that + // this code is not reachable. FIXME: We could insert unreachable + // instruction directly because we can modify the CFG. + new StoreInst(UndefValue::get(Int8Ty), + Constant::getNullValue(Int8Ty->getPointerTo()), + IntrinsicI); + } + markInstructionForDeletion(IntrinsicI); + return false; + } else if (isa<Constant>(V)) { + // If it's not false, and constant, it must evaluate to true. This means our + // assume is assume(true), and thus, pointless, and we don't want to do + // anything more here. + return false; + } + + Constant *True = ConstantInt::getTrue(V->getContext()); + bool Changed = false; + + for (BasicBlock *Successor : successors(IntrinsicI->getParent())) { + BasicBlockEdge Edge(IntrinsicI->getParent(), Successor); + + // This property is only true in dominated successors, propagateEquality + // will check dominance for us. + Changed |= propagateEquality(V, True, Edge, false); + } + + // We can replace assume value with true, which covers cases like this: + // call void @llvm.assume(i1 %cmp) + // br i1 %cmp, label %bb1, label %bb2 ; will change %cmp to true + ReplaceOperandsWithMap[V] = True; + + // If we find an equality fact, canonicalize all dominated uses in this block + // to one of the two values. We heuristically choice the "oldest" of the + // two where age is determined by value number. (Note that propagateEquality + // above handles the cross block case.) + // + // Key case to cover are: + // 1) + // %cmp = fcmp oeq float 3.000000e+00, %0 ; const on lhs could happen + // call void @llvm.assume(i1 %cmp) + // ret float %0 ; will change it to ret float 3.000000e+00 + // 2) + // %load = load float, float* %addr + // %cmp = fcmp oeq float %load, %0 + // call void @llvm.assume(i1 %cmp) + // ret float %load ; will change it to ret float %0 + if (auto *CmpI = dyn_cast<CmpInst>(V)) { + if (CmpI->getPredicate() == CmpInst::Predicate::ICMP_EQ || + CmpI->getPredicate() == CmpInst::Predicate::FCMP_OEQ || + (CmpI->getPredicate() == CmpInst::Predicate::FCMP_UEQ && + CmpI->getFastMathFlags().noNaNs())) { + Value *CmpLHS = CmpI->getOperand(0); + Value *CmpRHS = CmpI->getOperand(1); + // Heuristically pick the better replacement -- the choice of heuristic + // isn't terribly important here, but the fact we canonicalize on some + // replacement is for exposing other simplifications. + // TODO: pull this out as a helper function and reuse w/existing + // (slightly different) logic. + if (isa<Constant>(CmpLHS) && !isa<Constant>(CmpRHS)) + std::swap(CmpLHS, CmpRHS); + if (!isa<Instruction>(CmpLHS) && isa<Instruction>(CmpRHS)) + std::swap(CmpLHS, CmpRHS); + if ((isa<Argument>(CmpLHS) && isa<Argument>(CmpRHS)) || + (isa<Instruction>(CmpLHS) && isa<Instruction>(CmpRHS))) { + // Move the 'oldest' value to the right-hand side, using the value + // number as a proxy for age. + uint32_t LVN = VN.lookupOrAdd(CmpLHS); + uint32_t RVN = VN.lookupOrAdd(CmpRHS); + if (LVN < RVN) + std::swap(CmpLHS, CmpRHS); + } + + // Handle degenerate case where we either haven't pruned a dead path or a + // removed a trivial assume yet. + if (isa<Constant>(CmpLHS) && isa<Constant>(CmpRHS)) + return Changed; + + // +0.0 and -0.0 compare equal, but do not imply equivalence. Unless we + // can prove equivalence, bail. + if (CmpRHS->getType()->isFloatTy() && + (!isa<ConstantFP>(CmpRHS) || cast<ConstantFP>(CmpRHS)->isZero())) + return Changed; + + LLVM_DEBUG(dbgs() << "Replacing dominated uses of " + << *CmpLHS << " with " + << *CmpRHS << " in block " + << IntrinsicI->getParent()->getName() << "\n"); + + + // Setup the replacement map - this handles uses within the same block + if (hasUsersIn(CmpLHS, IntrinsicI->getParent())) + ReplaceOperandsWithMap[CmpLHS] = CmpRHS; + + // NOTE: The non-block local cases are handled by the call to + // propagateEquality above; this block is just about handling the block + // local cases. TODO: There's a bunch of logic in propagateEqualiy which + // isn't duplicated for the block local case, can we share it somehow? + } + } + return Changed; +} + +static void patchAndReplaceAllUsesWith(Instruction *I, Value *Repl) { + patchReplacementInstruction(I, Repl); + I->replaceAllUsesWith(Repl); +} + +/// Attempt to eliminate a load, first by eliminating it +/// locally, and then attempting non-local elimination if that fails. +bool GVN::processLoad(LoadInst *L) { + if (!MD) + return false; + + // This code hasn't been audited for ordered or volatile memory access + if (!L->isUnordered()) + return false; + + if (L->use_empty()) { + markInstructionForDeletion(L); + return true; + } + + // ... to a pointer that has been loaded from before... + MemDepResult Dep = MD->getDependency(L); + + // If it is defined in another block, try harder. + if (Dep.isNonLocal()) + return processNonLocalLoad(L); + + // Only handle the local case below + if (!Dep.isDef() && !Dep.isClobber()) { + // This might be a NonFuncLocal or an Unknown + LLVM_DEBUG( + // fast print dep, using operator<< on instruction is too slow. + dbgs() << "GVN: load "; L->printAsOperand(dbgs()); + dbgs() << " has unknown dependence\n";); + return false; + } + + AvailableValue AV; + if (AnalyzeLoadAvailability(L, Dep, L->getPointerOperand(), AV)) { + Value *AvailableValue = AV.MaterializeAdjustedValue(L, L, *this); + + // Replace the load! + patchAndReplaceAllUsesWith(L, AvailableValue); + markInstructionForDeletion(L); + ++NumGVNLoad; + reportLoadElim(L, AvailableValue, ORE); + // Tell MDA to rexamine the reused pointer since we might have more + // information after forwarding it. + if (MD && AvailableValue->getType()->isPtrOrPtrVectorTy()) + MD->invalidateCachedPointerInfo(AvailableValue); + return true; + } + + return false; +} + +/// Return a pair the first field showing the value number of \p Exp and the +/// second field showing whether it is a value number newly created. +std::pair<uint32_t, bool> +GVN::ValueTable::assignExpNewValueNum(Expression &Exp) { + uint32_t &e = expressionNumbering[Exp]; + bool CreateNewValNum = !e; + if (CreateNewValNum) { + Expressions.push_back(Exp); + if (ExprIdx.size() < nextValueNumber + 1) + ExprIdx.resize(nextValueNumber * 2); + e = nextValueNumber; + ExprIdx[nextValueNumber++] = nextExprNumber++; + } + return {e, CreateNewValNum}; +} + +/// Return whether all the values related with the same \p num are +/// defined in \p BB. +bool GVN::ValueTable::areAllValsInBB(uint32_t Num, const BasicBlock *BB, + GVN &Gvn) { + LeaderTableEntry *Vals = &Gvn.LeaderTable[Num]; + while (Vals && Vals->BB == BB) + Vals = Vals->Next; + return !Vals; +} + +/// Wrap phiTranslateImpl to provide caching functionality. +uint32_t GVN::ValueTable::phiTranslate(const BasicBlock *Pred, + const BasicBlock *PhiBlock, uint32_t Num, + GVN &Gvn) { + auto FindRes = PhiTranslateTable.find({Num, Pred}); + if (FindRes != PhiTranslateTable.end()) + return FindRes->second; + uint32_t NewNum = phiTranslateImpl(Pred, PhiBlock, Num, Gvn); + PhiTranslateTable.insert({{Num, Pred}, NewNum}); + return NewNum; +} + +// Return true if the value number \p Num and NewNum have equal value. +// Return false if the result is unknown. +bool GVN::ValueTable::areCallValsEqual(uint32_t Num, uint32_t NewNum, + const BasicBlock *Pred, + const BasicBlock *PhiBlock, GVN &Gvn) { + CallInst *Call = nullptr; + LeaderTableEntry *Vals = &Gvn.LeaderTable[Num]; + while (Vals) { + Call = dyn_cast<CallInst>(Vals->Val); + if (Call && Call->getParent() == PhiBlock) + break; + Vals = Vals->Next; + } + + if (AA->doesNotAccessMemory(Call)) + return true; + + if (!MD || !AA->onlyReadsMemory(Call)) + return false; + + MemDepResult local_dep = MD->getDependency(Call); + if (!local_dep.isNonLocal()) + return false; + + const MemoryDependenceResults::NonLocalDepInfo &deps = + MD->getNonLocalCallDependency(Call); + + // Check to see if the Call has no function local clobber. + for (unsigned i = 0; i < deps.size(); i++) { + if (deps[i].getResult().isNonFuncLocal()) + return true; + } + return false; +} + +/// Translate value number \p Num using phis, so that it has the values of +/// the phis in BB. +uint32_t GVN::ValueTable::phiTranslateImpl(const BasicBlock *Pred, + const BasicBlock *PhiBlock, + uint32_t Num, GVN &Gvn) { + if (PHINode *PN = NumberingPhi[Num]) { + for (unsigned i = 0; i != PN->getNumIncomingValues(); ++i) { + if (PN->getParent() == PhiBlock && PN->getIncomingBlock(i) == Pred) + if (uint32_t TransVal = lookup(PN->getIncomingValue(i), false)) + return TransVal; + } + return Num; + } + + // If there is any value related with Num is defined in a BB other than + // PhiBlock, it cannot depend on a phi in PhiBlock without going through + // a backedge. We can do an early exit in that case to save compile time. + if (!areAllValsInBB(Num, PhiBlock, Gvn)) + return Num; + + if (Num >= ExprIdx.size() || ExprIdx[Num] == 0) + return Num; + Expression Exp = Expressions[ExprIdx[Num]]; + + for (unsigned i = 0; i < Exp.varargs.size(); i++) { + // For InsertValue and ExtractValue, some varargs are index numbers + // instead of value numbers. Those index numbers should not be + // translated. + if ((i > 1 && Exp.opcode == Instruction::InsertValue) || + (i > 0 && Exp.opcode == Instruction::ExtractValue)) + continue; + Exp.varargs[i] = phiTranslate(Pred, PhiBlock, Exp.varargs[i], Gvn); + } + + if (Exp.commutative) { + assert(Exp.varargs.size() == 2 && "Unsupported commutative expression!"); + if (Exp.varargs[0] > Exp.varargs[1]) { + std::swap(Exp.varargs[0], Exp.varargs[1]); + uint32_t Opcode = Exp.opcode >> 8; + if (Opcode == Instruction::ICmp || Opcode == Instruction::FCmp) + Exp.opcode = (Opcode << 8) | + CmpInst::getSwappedPredicate( + static_cast<CmpInst::Predicate>(Exp.opcode & 255)); + } + } + + if (uint32_t NewNum = expressionNumbering[Exp]) { + if (Exp.opcode == Instruction::Call && NewNum != Num) + return areCallValsEqual(Num, NewNum, Pred, PhiBlock, Gvn) ? NewNum : Num; + return NewNum; + } + return Num; +} + +/// Erase stale entry from phiTranslate cache so phiTranslate can be computed +/// again. +void GVN::ValueTable::eraseTranslateCacheEntry(uint32_t Num, + const BasicBlock &CurrBlock) { + for (const BasicBlock *Pred : predecessors(&CurrBlock)) { + auto FindRes = PhiTranslateTable.find({Num, Pred}); + if (FindRes != PhiTranslateTable.end()) + PhiTranslateTable.erase(FindRes); + } +} + +// In order to find a leader for a given value number at a +// specific basic block, we first obtain the list of all Values for that number, +// and then scan the list to find one whose block dominates the block in +// question. This is fast because dominator tree queries consist of only +// a few comparisons of DFS numbers. +Value *GVN::findLeader(const BasicBlock *BB, uint32_t num) { + LeaderTableEntry Vals = LeaderTable[num]; + if (!Vals.Val) return nullptr; + + Value *Val = nullptr; + if (DT->dominates(Vals.BB, BB)) { + Val = Vals.Val; + if (isa<Constant>(Val)) return Val; + } + + LeaderTableEntry* Next = Vals.Next; + while (Next) { + if (DT->dominates(Next->BB, BB)) { + if (isa<Constant>(Next->Val)) return Next->Val; + if (!Val) Val = Next->Val; + } + + Next = Next->Next; + } + + return Val; +} + +/// There is an edge from 'Src' to 'Dst'. Return +/// true if every path from the entry block to 'Dst' passes via this edge. In +/// particular 'Dst' must not be reachable via another edge from 'Src'. +static bool isOnlyReachableViaThisEdge(const BasicBlockEdge &E, + DominatorTree *DT) { + // While in theory it is interesting to consider the case in which Dst has + // more than one predecessor, because Dst might be part of a loop which is + // only reachable from Src, in practice it is pointless since at the time + // GVN runs all such loops have preheaders, which means that Dst will have + // been changed to have only one predecessor, namely Src. + const BasicBlock *Pred = E.getEnd()->getSinglePredecessor(); + assert((!Pred || Pred == E.getStart()) && + "No edge between these basic blocks!"); + return Pred != nullptr; +} + +void GVN::assignBlockRPONumber(Function &F) { + BlockRPONumber.clear(); + uint32_t NextBlockNumber = 1; + ReversePostOrderTraversal<Function *> RPOT(&F); + for (BasicBlock *BB : RPOT) + BlockRPONumber[BB] = NextBlockNumber++; + InvalidBlockRPONumbers = false; +} + +bool GVN::replaceOperandsForInBlockEquality(Instruction *Instr) const { + bool Changed = false; + for (unsigned OpNum = 0; OpNum < Instr->getNumOperands(); ++OpNum) { + Value *Operand = Instr->getOperand(OpNum); + auto it = ReplaceOperandsWithMap.find(Operand); + if (it != ReplaceOperandsWithMap.end()) { + LLVM_DEBUG(dbgs() << "GVN replacing: " << *Operand << " with " + << *it->second << " in instruction " << *Instr << '\n'); + Instr->setOperand(OpNum, it->second); + Changed = true; + } + } + return Changed; +} + +/// The given values are known to be equal in every block +/// dominated by 'Root'. Exploit this, for example by replacing 'LHS' with +/// 'RHS' everywhere in the scope. Returns whether a change was made. +/// If DominatesByEdge is false, then it means that we will propagate the RHS +/// value starting from the end of Root.Start. +bool GVN::propagateEquality(Value *LHS, Value *RHS, const BasicBlockEdge &Root, + bool DominatesByEdge) { + SmallVector<std::pair<Value*, Value*>, 4> Worklist; + Worklist.push_back(std::make_pair(LHS, RHS)); + bool Changed = false; + // For speed, compute a conservative fast approximation to + // DT->dominates(Root, Root.getEnd()); + const bool RootDominatesEnd = isOnlyReachableViaThisEdge(Root, DT); + + while (!Worklist.empty()) { + std::pair<Value*, Value*> Item = Worklist.pop_back_val(); + LHS = Item.first; RHS = Item.second; + + if (LHS == RHS) + continue; + assert(LHS->getType() == RHS->getType() && "Equality but unequal types!"); + + // Don't try to propagate equalities between constants. + if (isa<Constant>(LHS) && isa<Constant>(RHS)) + continue; + + // Prefer a constant on the right-hand side, or an Argument if no constants. + if (isa<Constant>(LHS) || (isa<Argument>(LHS) && !isa<Constant>(RHS))) + std::swap(LHS, RHS); + assert((isa<Argument>(LHS) || isa<Instruction>(LHS)) && "Unexpected value!"); + + // If there is no obvious reason to prefer the left-hand side over the + // right-hand side, ensure the longest lived term is on the right-hand side, + // so the shortest lived term will be replaced by the longest lived. + // This tends to expose more simplifications. + uint32_t LVN = VN.lookupOrAdd(LHS); + if ((isa<Argument>(LHS) && isa<Argument>(RHS)) || + (isa<Instruction>(LHS) && isa<Instruction>(RHS))) { + // Move the 'oldest' value to the right-hand side, using the value number + // as a proxy for age. + uint32_t RVN = VN.lookupOrAdd(RHS); + if (LVN < RVN) { + std::swap(LHS, RHS); + LVN = RVN; + } + } + + // If value numbering later sees that an instruction in the scope is equal + // to 'LHS' then ensure it will be turned into 'RHS'. In order to preserve + // the invariant that instructions only occur in the leader table for their + // own value number (this is used by removeFromLeaderTable), do not do this + // if RHS is an instruction (if an instruction in the scope is morphed into + // LHS then it will be turned into RHS by the next GVN iteration anyway, so + // using the leader table is about compiling faster, not optimizing better). + // The leader table only tracks basic blocks, not edges. Only add to if we + // have the simple case where the edge dominates the end. + if (RootDominatesEnd && !isa<Instruction>(RHS)) + addToLeaderTable(LVN, RHS, Root.getEnd()); + + // Replace all occurrences of 'LHS' with 'RHS' everywhere in the scope. As + // LHS always has at least one use that is not dominated by Root, this will + // never do anything if LHS has only one use. + if (!LHS->hasOneUse()) { + unsigned NumReplacements = + DominatesByEdge + ? replaceDominatedUsesWith(LHS, RHS, *DT, Root) + : replaceDominatedUsesWith(LHS, RHS, *DT, Root.getStart()); + + Changed |= NumReplacements > 0; + NumGVNEqProp += NumReplacements; + // Cached information for anything that uses LHS will be invalid. + if (MD) + MD->invalidateCachedPointerInfo(LHS); + } + + // Now try to deduce additional equalities from this one. For example, if + // the known equality was "(A != B)" == "false" then it follows that A and B + // are equal in the scope. Only boolean equalities with an explicit true or + // false RHS are currently supported. + if (!RHS->getType()->isIntegerTy(1)) + // Not a boolean equality - bail out. + continue; + ConstantInt *CI = dyn_cast<ConstantInt>(RHS); + if (!CI) + // RHS neither 'true' nor 'false' - bail out. + continue; + // Whether RHS equals 'true'. Otherwise it equals 'false'. + bool isKnownTrue = CI->isMinusOne(); + bool isKnownFalse = !isKnownTrue; + + // If "A && B" is known true then both A and B are known true. If "A || B" + // is known false then both A and B are known false. + Value *A, *B; + if ((isKnownTrue && match(LHS, m_And(m_Value(A), m_Value(B)))) || + (isKnownFalse && match(LHS, m_Or(m_Value(A), m_Value(B))))) { + Worklist.push_back(std::make_pair(A, RHS)); + Worklist.push_back(std::make_pair(B, RHS)); + continue; + } + + // If we are propagating an equality like "(A == B)" == "true" then also + // propagate the equality A == B. When propagating a comparison such as + // "(A >= B)" == "true", replace all instances of "A < B" with "false". + if (CmpInst *Cmp = dyn_cast<CmpInst>(LHS)) { + Value *Op0 = Cmp->getOperand(0), *Op1 = Cmp->getOperand(1); + + // If "A == B" is known true, or "A != B" is known false, then replace + // A with B everywhere in the scope. + if ((isKnownTrue && Cmp->getPredicate() == CmpInst::ICMP_EQ) || + (isKnownFalse && Cmp->getPredicate() == CmpInst::ICMP_NE)) + Worklist.push_back(std::make_pair(Op0, Op1)); + + // Handle the floating point versions of equality comparisons too. + if ((isKnownTrue && Cmp->getPredicate() == CmpInst::FCMP_OEQ) || + (isKnownFalse && Cmp->getPredicate() == CmpInst::FCMP_UNE)) { + + // Floating point -0.0 and 0.0 compare equal, so we can only + // propagate values if we know that we have a constant and that + // its value is non-zero. + + // FIXME: We should do this optimization if 'no signed zeros' is + // applicable via an instruction-level fast-math-flag or some other + // indicator that relaxed FP semantics are being used. + + if (isa<ConstantFP>(Op1) && !cast<ConstantFP>(Op1)->isZero()) + Worklist.push_back(std::make_pair(Op0, Op1)); + } + + // If "A >= B" is known true, replace "A < B" with false everywhere. + CmpInst::Predicate NotPred = Cmp->getInversePredicate(); + Constant *NotVal = ConstantInt::get(Cmp->getType(), isKnownFalse); + // Since we don't have the instruction "A < B" immediately to hand, work + // out the value number that it would have and use that to find an + // appropriate instruction (if any). + uint32_t NextNum = VN.getNextUnusedValueNumber(); + uint32_t Num = VN.lookupOrAddCmp(Cmp->getOpcode(), NotPred, Op0, Op1); + // If the number we were assigned was brand new then there is no point in + // looking for an instruction realizing it: there cannot be one! + if (Num < NextNum) { + Value *NotCmp = findLeader(Root.getEnd(), Num); + if (NotCmp && isa<Instruction>(NotCmp)) { + unsigned NumReplacements = + DominatesByEdge + ? replaceDominatedUsesWith(NotCmp, NotVal, *DT, Root) + : replaceDominatedUsesWith(NotCmp, NotVal, *DT, + Root.getStart()); + Changed |= NumReplacements > 0; + NumGVNEqProp += NumReplacements; + // Cached information for anything that uses NotCmp will be invalid. + if (MD) + MD->invalidateCachedPointerInfo(NotCmp); + } + } + // Ensure that any instruction in scope that gets the "A < B" value number + // is replaced with false. + // The leader table only tracks basic blocks, not edges. Only add to if we + // have the simple case where the edge dominates the end. + if (RootDominatesEnd) + addToLeaderTable(Num, NotVal, Root.getEnd()); + + continue; + } + } + + return Changed; +} + +/// When calculating availability, handle an instruction +/// by inserting it into the appropriate sets +bool GVN::processInstruction(Instruction *I) { + // Ignore dbg info intrinsics. + if (isa<DbgInfoIntrinsic>(I)) + return false; + + // If the instruction can be easily simplified then do so now in preference + // to value numbering it. Value numbering often exposes redundancies, for + // example if it determines that %y is equal to %x then the instruction + // "%z = and i32 %x, %y" becomes "%z = and i32 %x, %x" which we now simplify. + const DataLayout &DL = I->getModule()->getDataLayout(); + if (Value *V = SimplifyInstruction(I, {DL, TLI, DT, AC})) { + bool Changed = false; + if (!I->use_empty()) { + I->replaceAllUsesWith(V); + Changed = true; + } + if (isInstructionTriviallyDead(I, TLI)) { + markInstructionForDeletion(I); + Changed = true; + } + if (Changed) { + if (MD && V->getType()->isPtrOrPtrVectorTy()) + MD->invalidateCachedPointerInfo(V); + ++NumGVNSimpl; + return true; + } + } + + if (IntrinsicInst *IntrinsicI = dyn_cast<IntrinsicInst>(I)) + if (IntrinsicI->getIntrinsicID() == Intrinsic::assume) + return processAssumeIntrinsic(IntrinsicI); + + if (LoadInst *LI = dyn_cast<LoadInst>(I)) { + if (processLoad(LI)) + return true; + + unsigned Num = VN.lookupOrAdd(LI); + addToLeaderTable(Num, LI, LI->getParent()); + return false; + } + + // For conditional branches, we can perform simple conditional propagation on + // the condition value itself. + if (BranchInst *BI = dyn_cast<BranchInst>(I)) { + if (!BI->isConditional()) + return false; + + if (isa<Constant>(BI->getCondition())) + return processFoldableCondBr(BI); + + Value *BranchCond = BI->getCondition(); + BasicBlock *TrueSucc = BI->getSuccessor(0); + BasicBlock *FalseSucc = BI->getSuccessor(1); + // Avoid multiple edges early. + if (TrueSucc == FalseSucc) + return false; + + BasicBlock *Parent = BI->getParent(); + bool Changed = false; + + Value *TrueVal = ConstantInt::getTrue(TrueSucc->getContext()); + BasicBlockEdge TrueE(Parent, TrueSucc); + Changed |= propagateEquality(BranchCond, TrueVal, TrueE, true); + + Value *FalseVal = ConstantInt::getFalse(FalseSucc->getContext()); + BasicBlockEdge FalseE(Parent, FalseSucc); + Changed |= propagateEquality(BranchCond, FalseVal, FalseE, true); + + return Changed; + } + + // For switches, propagate the case values into the case destinations. + if (SwitchInst *SI = dyn_cast<SwitchInst>(I)) { + Value *SwitchCond = SI->getCondition(); + BasicBlock *Parent = SI->getParent(); + bool Changed = false; + + // Remember how many outgoing edges there are to every successor. + SmallDenseMap<BasicBlock *, unsigned, 16> SwitchEdges; + for (unsigned i = 0, n = SI->getNumSuccessors(); i != n; ++i) + ++SwitchEdges[SI->getSuccessor(i)]; + + for (SwitchInst::CaseIt i = SI->case_begin(), e = SI->case_end(); + i != e; ++i) { + BasicBlock *Dst = i->getCaseSuccessor(); + // If there is only a single edge, propagate the case value into it. + if (SwitchEdges.lookup(Dst) == 1) { + BasicBlockEdge E(Parent, Dst); + Changed |= propagateEquality(SwitchCond, i->getCaseValue(), E, true); + } + } + return Changed; + } + + // Instructions with void type don't return a value, so there's + // no point in trying to find redundancies in them. + if (I->getType()->isVoidTy()) + return false; + + uint32_t NextNum = VN.getNextUnusedValueNumber(); + unsigned Num = VN.lookupOrAdd(I); + + // Allocations are always uniquely numbered, so we can save time and memory + // by fast failing them. + if (isa<AllocaInst>(I) || I->isTerminator() || isa<PHINode>(I)) { + addToLeaderTable(Num, I, I->getParent()); + return false; + } + + // If the number we were assigned was a brand new VN, then we don't + // need to do a lookup to see if the number already exists + // somewhere in the domtree: it can't! + if (Num >= NextNum) { + addToLeaderTable(Num, I, I->getParent()); + return false; + } + + // Perform fast-path value-number based elimination of values inherited from + // dominators. + Value *Repl = findLeader(I->getParent(), Num); + if (!Repl) { + // Failure, just remember this instance for future use. + addToLeaderTable(Num, I, I->getParent()); + return false; + } else if (Repl == I) { + // If I was the result of a shortcut PRE, it might already be in the table + // and the best replacement for itself. Nothing to do. + return false; + } + + // Remove it! + patchAndReplaceAllUsesWith(I, Repl); + if (MD && Repl->getType()->isPtrOrPtrVectorTy()) + MD->invalidateCachedPointerInfo(Repl); + markInstructionForDeletion(I); + return true; +} + +/// runOnFunction - This is the main transformation entry point for a function. +bool GVN::runImpl(Function &F, AssumptionCache &RunAC, DominatorTree &RunDT, + const TargetLibraryInfo &RunTLI, AAResults &RunAA, + MemoryDependenceResults *RunMD, LoopInfo *LI, + OptimizationRemarkEmitter *RunORE) { + AC = &RunAC; + DT = &RunDT; + VN.setDomTree(DT); + TLI = &RunTLI; + VN.setAliasAnalysis(&RunAA); + MD = RunMD; + ImplicitControlFlowTracking ImplicitCFT(DT); + ICF = &ImplicitCFT; + this->LI = LI; + VN.setMemDep(MD); + ORE = RunORE; + InvalidBlockRPONumbers = true; + + bool Changed = false; + bool ShouldContinue = true; + + DomTreeUpdater DTU(DT, DomTreeUpdater::UpdateStrategy::Eager); + // Merge unconditional branches, allowing PRE to catch more + // optimization opportunities. + for (Function::iterator FI = F.begin(), FE = F.end(); FI != FE; ) { + BasicBlock *BB = &*FI++; + + bool removedBlock = MergeBlockIntoPredecessor(BB, &DTU, LI, nullptr, MD); + if (removedBlock) + ++NumGVNBlocks; + + Changed |= removedBlock; + } + + unsigned Iteration = 0; + while (ShouldContinue) { + LLVM_DEBUG(dbgs() << "GVN iteration: " << Iteration << "\n"); + ShouldContinue = iterateOnFunction(F); + Changed |= ShouldContinue; + ++Iteration; + } + + if (EnablePRE) { + // Fabricate val-num for dead-code in order to suppress assertion in + // performPRE(). + assignValNumForDeadCode(); + bool PREChanged = true; + while (PREChanged) { + PREChanged = performPRE(F); + Changed |= PREChanged; + } + } + + // FIXME: Should perform GVN again after PRE does something. PRE can move + // computations into blocks where they become fully redundant. Note that + // we can't do this until PRE's critical edge splitting updates memdep. + // Actually, when this happens, we should just fully integrate PRE into GVN. + + cleanupGlobalSets(); + // Do not cleanup DeadBlocks in cleanupGlobalSets() as it's called for each + // iteration. + DeadBlocks.clear(); + + return Changed; +} + +bool GVN::processBlock(BasicBlock *BB) { + // FIXME: Kill off InstrsToErase by doing erasing eagerly in a helper function + // (and incrementing BI before processing an instruction). + assert(InstrsToErase.empty() && + "We expect InstrsToErase to be empty across iterations"); + if (DeadBlocks.count(BB)) + return false; + + // Clearing map before every BB because it can be used only for single BB. + ReplaceOperandsWithMap.clear(); + bool ChangedFunction = false; + + for (BasicBlock::iterator BI = BB->begin(), BE = BB->end(); + BI != BE;) { + if (!ReplaceOperandsWithMap.empty()) + ChangedFunction |= replaceOperandsForInBlockEquality(&*BI); + ChangedFunction |= processInstruction(&*BI); + + if (InstrsToErase.empty()) { + ++BI; + continue; + } + + // If we need some instructions deleted, do it now. + NumGVNInstr += InstrsToErase.size(); + + // Avoid iterator invalidation. + bool AtStart = BI == BB->begin(); + if (!AtStart) + --BI; + + for (auto *I : InstrsToErase) { + assert(I->getParent() == BB && "Removing instruction from wrong block?"); + LLVM_DEBUG(dbgs() << "GVN removed: " << *I << '\n'); + salvageDebugInfo(*I); + if (MD) MD->removeInstruction(I); + LLVM_DEBUG(verifyRemoved(I)); + ICF->removeInstruction(I); + I->eraseFromParent(); + } + InstrsToErase.clear(); + + if (AtStart) + BI = BB->begin(); + else + ++BI; + } + + return ChangedFunction; +} + +// Instantiate an expression in a predecessor that lacked it. +bool GVN::performScalarPREInsertion(Instruction *Instr, BasicBlock *Pred, + BasicBlock *Curr, unsigned int ValNo) { + // Because we are going top-down through the block, all value numbers + // will be available in the predecessor by the time we need them. Any + // that weren't originally present will have been instantiated earlier + // in this loop. + bool success = true; + for (unsigned i = 0, e = Instr->getNumOperands(); i != e; ++i) { + Value *Op = Instr->getOperand(i); + if (isa<Argument>(Op) || isa<Constant>(Op) || isa<GlobalValue>(Op)) + continue; + // This could be a newly inserted instruction, in which case, we won't + // find a value number, and should give up before we hurt ourselves. + // FIXME: Rewrite the infrastructure to let it easier to value number + // and process newly inserted instructions. + if (!VN.exists(Op)) { + success = false; + break; + } + uint32_t TValNo = + VN.phiTranslate(Pred, Curr, VN.lookup(Op), *this); + if (Value *V = findLeader(Pred, TValNo)) { + Instr->setOperand(i, V); + } else { + success = false; + break; + } + } + + // Fail out if we encounter an operand that is not available in + // the PRE predecessor. This is typically because of loads which + // are not value numbered precisely. + if (!success) + return false; + + Instr->insertBefore(Pred->getTerminator()); + Instr->setName(Instr->getName() + ".pre"); + Instr->setDebugLoc(Instr->getDebugLoc()); + + unsigned Num = VN.lookupOrAdd(Instr); + VN.add(Instr, Num); + + // Update the availability map to include the new instruction. + addToLeaderTable(Num, Instr, Pred); + return true; +} + +bool GVN::performScalarPRE(Instruction *CurInst) { + if (isa<AllocaInst>(CurInst) || CurInst->isTerminator() || + isa<PHINode>(CurInst) || CurInst->getType()->isVoidTy() || + CurInst->mayReadFromMemory() || CurInst->mayHaveSideEffects() || + isa<DbgInfoIntrinsic>(CurInst)) + return false; + + // Don't do PRE on compares. The PHI would prevent CodeGenPrepare from + // sinking the compare again, and it would force the code generator to + // move the i1 from processor flags or predicate registers into a general + // purpose register. + if (isa<CmpInst>(CurInst)) + return false; + + // Don't do PRE on GEPs. The inserted PHI would prevent CodeGenPrepare from + // sinking the addressing mode computation back to its uses. Extending the + // GEP's live range increases the register pressure, and therefore it can + // introduce unnecessary spills. + // + // This doesn't prevent Load PRE. PHI translation will make the GEP available + // to the load by moving it to the predecessor block if necessary. + if (isa<GetElementPtrInst>(CurInst)) + return false; + + // We don't currently value number ANY inline asm calls. + if (auto *CallB = dyn_cast<CallBase>(CurInst)) + if (CallB->isInlineAsm()) + return false; + + uint32_t ValNo = VN.lookup(CurInst); + + // Look for the predecessors for PRE opportunities. We're + // only trying to solve the basic diamond case, where + // a value is computed in the successor and one predecessor, + // but not the other. We also explicitly disallow cases + // where the successor is its own predecessor, because they're + // more complicated to get right. + unsigned NumWith = 0; + unsigned NumWithout = 0; + BasicBlock *PREPred = nullptr; + BasicBlock *CurrentBlock = CurInst->getParent(); + + // Update the RPO numbers for this function. + if (InvalidBlockRPONumbers) + assignBlockRPONumber(*CurrentBlock->getParent()); + + SmallVector<std::pair<Value *, BasicBlock *>, 8> predMap; + for (BasicBlock *P : predecessors(CurrentBlock)) { + // We're not interested in PRE where blocks with predecessors that are + // not reachable. + if (!DT->isReachableFromEntry(P)) { + NumWithout = 2; + break; + } + // It is not safe to do PRE when P->CurrentBlock is a loop backedge, and + // when CurInst has operand defined in CurrentBlock (so it may be defined + // by phi in the loop header). + assert(BlockRPONumber.count(P) && BlockRPONumber.count(CurrentBlock) && + "Invalid BlockRPONumber map."); + if (BlockRPONumber[P] >= BlockRPONumber[CurrentBlock] && + llvm::any_of(CurInst->operands(), [&](const Use &U) { + if (auto *Inst = dyn_cast<Instruction>(U.get())) + return Inst->getParent() == CurrentBlock; + return false; + })) { + NumWithout = 2; + break; + } + + uint32_t TValNo = VN.phiTranslate(P, CurrentBlock, ValNo, *this); + Value *predV = findLeader(P, TValNo); + if (!predV) { + predMap.push_back(std::make_pair(static_cast<Value *>(nullptr), P)); + PREPred = P; + ++NumWithout; + } else if (predV == CurInst) { + /* CurInst dominates this predecessor. */ + NumWithout = 2; + break; + } else { + predMap.push_back(std::make_pair(predV, P)); + ++NumWith; + } + } + + // Don't do PRE when it might increase code size, i.e. when + // we would need to insert instructions in more than one pred. + if (NumWithout > 1 || NumWith == 0) + return false; + + // We may have a case where all predecessors have the instruction, + // and we just need to insert a phi node. Otherwise, perform + // insertion. + Instruction *PREInstr = nullptr; + + if (NumWithout != 0) { + if (!isSafeToSpeculativelyExecute(CurInst)) { + // It is only valid to insert a new instruction if the current instruction + // is always executed. An instruction with implicit control flow could + // prevent us from doing it. If we cannot speculate the execution, then + // PRE should be prohibited. + if (ICF->isDominatedByICFIFromSameBlock(CurInst)) + return false; + } + + // Don't do PRE across indirect branch. + if (isa<IndirectBrInst>(PREPred->getTerminator())) + return false; + + // Don't do PRE across callbr. + // FIXME: Can we do this across the fallthrough edge? + if (isa<CallBrInst>(PREPred->getTerminator())) + return false; + + // We can't do PRE safely on a critical edge, so instead we schedule + // the edge to be split and perform the PRE the next time we iterate + // on the function. + unsigned SuccNum = GetSuccessorNumber(PREPred, CurrentBlock); + if (isCriticalEdge(PREPred->getTerminator(), SuccNum)) { + toSplit.push_back(std::make_pair(PREPred->getTerminator(), SuccNum)); + return false; + } + // We need to insert somewhere, so let's give it a shot + PREInstr = CurInst->clone(); + if (!performScalarPREInsertion(PREInstr, PREPred, CurrentBlock, ValNo)) { + // If we failed insertion, make sure we remove the instruction. + LLVM_DEBUG(verifyRemoved(PREInstr)); + PREInstr->deleteValue(); + return false; + } + } + + // Either we should have filled in the PRE instruction, or we should + // not have needed insertions. + assert(PREInstr != nullptr || NumWithout == 0); + + ++NumGVNPRE; + + // Create a PHI to make the value available in this block. + PHINode *Phi = + PHINode::Create(CurInst->getType(), predMap.size(), + CurInst->getName() + ".pre-phi", &CurrentBlock->front()); + for (unsigned i = 0, e = predMap.size(); i != e; ++i) { + if (Value *V = predMap[i].first) { + // If we use an existing value in this phi, we have to patch the original + // value because the phi will be used to replace a later value. + patchReplacementInstruction(CurInst, V); + Phi->addIncoming(V, predMap[i].second); + } else + Phi->addIncoming(PREInstr, PREPred); + } + + VN.add(Phi, ValNo); + // After creating a new PHI for ValNo, the phi translate result for ValNo will + // be changed, so erase the related stale entries in phi translate cache. + VN.eraseTranslateCacheEntry(ValNo, *CurrentBlock); + addToLeaderTable(ValNo, Phi, CurrentBlock); + Phi->setDebugLoc(CurInst->getDebugLoc()); + CurInst->replaceAllUsesWith(Phi); + if (MD && Phi->getType()->isPtrOrPtrVectorTy()) + MD->invalidateCachedPointerInfo(Phi); + VN.erase(CurInst); + removeFromLeaderTable(ValNo, CurInst, CurrentBlock); + + LLVM_DEBUG(dbgs() << "GVN PRE removed: " << *CurInst << '\n'); + if (MD) + MD->removeInstruction(CurInst); + LLVM_DEBUG(verifyRemoved(CurInst)); + // FIXME: Intended to be markInstructionForDeletion(CurInst), but it causes + // some assertion failures. + ICF->removeInstruction(CurInst); + CurInst->eraseFromParent(); + ++NumGVNInstr; + + return true; +} + +/// Perform a purely local form of PRE that looks for diamond +/// control flow patterns and attempts to perform simple PRE at the join point. +bool GVN::performPRE(Function &F) { + bool Changed = false; + for (BasicBlock *CurrentBlock : depth_first(&F.getEntryBlock())) { + // Nothing to PRE in the entry block. + if (CurrentBlock == &F.getEntryBlock()) + continue; + + // Don't perform PRE on an EH pad. + if (CurrentBlock->isEHPad()) + continue; + + for (BasicBlock::iterator BI = CurrentBlock->begin(), + BE = CurrentBlock->end(); + BI != BE;) { + Instruction *CurInst = &*BI++; + Changed |= performScalarPRE(CurInst); + } + } + + if (splitCriticalEdges()) + Changed = true; + + return Changed; +} + +/// Split the critical edge connecting the given two blocks, and return +/// the block inserted to the critical edge. +BasicBlock *GVN::splitCriticalEdges(BasicBlock *Pred, BasicBlock *Succ) { + BasicBlock *BB = + SplitCriticalEdge(Pred, Succ, CriticalEdgeSplittingOptions(DT, LI)); + if (MD) + MD->invalidateCachedPredecessors(); + InvalidBlockRPONumbers = true; + return BB; +} + +/// Split critical edges found during the previous +/// iteration that may enable further optimization. +bool GVN::splitCriticalEdges() { + if (toSplit.empty()) + return false; + do { + std::pair<Instruction *, unsigned> Edge = toSplit.pop_back_val(); + SplitCriticalEdge(Edge.first, Edge.second, + CriticalEdgeSplittingOptions(DT, LI)); + } while (!toSplit.empty()); + if (MD) MD->invalidateCachedPredecessors(); + InvalidBlockRPONumbers = true; + return true; +} + +/// Executes one iteration of GVN +bool GVN::iterateOnFunction(Function &F) { + cleanupGlobalSets(); + + // Top-down walk of the dominator tree + bool Changed = false; + // Needed for value numbering with phi construction to work. + // RPOT walks the graph in its constructor and will not be invalidated during + // processBlock. + ReversePostOrderTraversal<Function *> RPOT(&F); + + for (BasicBlock *BB : RPOT) + Changed |= processBlock(BB); + + return Changed; +} + +void GVN::cleanupGlobalSets() { + VN.clear(); + LeaderTable.clear(); + BlockRPONumber.clear(); + TableAllocator.Reset(); + ICF->clear(); + InvalidBlockRPONumbers = true; +} + +/// Verify that the specified instruction does not occur in our +/// internal data structures. +void GVN::verifyRemoved(const Instruction *Inst) const { + VN.verifyRemoved(Inst); + + // Walk through the value number scope to make sure the instruction isn't + // ferreted away in it. + for (DenseMap<uint32_t, LeaderTableEntry>::const_iterator + I = LeaderTable.begin(), E = LeaderTable.end(); I != E; ++I) { + const LeaderTableEntry *Node = &I->second; + assert(Node->Val != Inst && "Inst still in value numbering scope!"); + + while (Node->Next) { + Node = Node->Next; + assert(Node->Val != Inst && "Inst still in value numbering scope!"); + } + } +} + +/// BB is declared dead, which implied other blocks become dead as well. This +/// function is to add all these blocks to "DeadBlocks". For the dead blocks' +/// live successors, update their phi nodes by replacing the operands +/// corresponding to dead blocks with UndefVal. +void GVN::addDeadBlock(BasicBlock *BB) { + SmallVector<BasicBlock *, 4> NewDead; + SmallSetVector<BasicBlock *, 4> DF; + + NewDead.push_back(BB); + while (!NewDead.empty()) { + BasicBlock *D = NewDead.pop_back_val(); + if (DeadBlocks.count(D)) + continue; + + // All blocks dominated by D are dead. + SmallVector<BasicBlock *, 8> Dom; + DT->getDescendants(D, Dom); + DeadBlocks.insert(Dom.begin(), Dom.end()); + + // Figure out the dominance-frontier(D). + for (BasicBlock *B : Dom) { + for (BasicBlock *S : successors(B)) { + if (DeadBlocks.count(S)) + continue; + + bool AllPredDead = true; + for (BasicBlock *P : predecessors(S)) + if (!DeadBlocks.count(P)) { + AllPredDead = false; + break; + } + + if (!AllPredDead) { + // S could be proved dead later on. That is why we don't update phi + // operands at this moment. + DF.insert(S); + } else { + // While S is not dominated by D, it is dead by now. This could take + // place if S already have a dead predecessor before D is declared + // dead. + NewDead.push_back(S); + } + } + } + } + + // For the dead blocks' live successors, update their phi nodes by replacing + // the operands corresponding to dead blocks with UndefVal. + for(SmallSetVector<BasicBlock *, 4>::iterator I = DF.begin(), E = DF.end(); + I != E; I++) { + BasicBlock *B = *I; + if (DeadBlocks.count(B)) + continue; + + // First, split the critical edges. This might also create additional blocks + // to preserve LoopSimplify form and adjust edges accordingly. + SmallVector<BasicBlock *, 4> Preds(pred_begin(B), pred_end(B)); + for (BasicBlock *P : Preds) { + if (!DeadBlocks.count(P)) + continue; + + if (llvm::any_of(successors(P), + [B](BasicBlock *Succ) { return Succ == B; }) && + isCriticalEdge(P->getTerminator(), B)) { + if (BasicBlock *S = splitCriticalEdges(P, B)) + DeadBlocks.insert(P = S); + } + } + + // Now undef the incoming values from the dead predecessors. + for (BasicBlock *P : predecessors(B)) { + if (!DeadBlocks.count(P)) + continue; + for (PHINode &Phi : B->phis()) { + Phi.setIncomingValueForBlock(P, UndefValue::get(Phi.getType())); + if (MD) + MD->invalidateCachedPointerInfo(&Phi); + } + } + } +} + +// If the given branch is recognized as a foldable branch (i.e. conditional +// branch with constant condition), it will perform following analyses and +// transformation. +// 1) If the dead out-coming edge is a critical-edge, split it. Let +// R be the target of the dead out-coming edge. +// 1) Identify the set of dead blocks implied by the branch's dead outcoming +// edge. The result of this step will be {X| X is dominated by R} +// 2) Identify those blocks which haves at least one dead predecessor. The +// result of this step will be dominance-frontier(R). +// 3) Update the PHIs in DF(R) by replacing the operands corresponding to +// dead blocks with "UndefVal" in an hope these PHIs will optimized away. +// +// Return true iff *NEW* dead code are found. +bool GVN::processFoldableCondBr(BranchInst *BI) { + if (!BI || BI->isUnconditional()) + return false; + + // If a branch has two identical successors, we cannot declare either dead. + if (BI->getSuccessor(0) == BI->getSuccessor(1)) + return false; + + ConstantInt *Cond = dyn_cast<ConstantInt>(BI->getCondition()); + if (!Cond) + return false; + + BasicBlock *DeadRoot = + Cond->getZExtValue() ? BI->getSuccessor(1) : BI->getSuccessor(0); + if (DeadBlocks.count(DeadRoot)) + return false; + + if (!DeadRoot->getSinglePredecessor()) + DeadRoot = splitCriticalEdges(BI->getParent(), DeadRoot); + + addDeadBlock(DeadRoot); + return true; +} + +// performPRE() will trigger assert if it comes across an instruction without +// associated val-num. As it normally has far more live instructions than dead +// instructions, it makes more sense just to "fabricate" a val-number for the +// dead code than checking if instruction involved is dead or not. +void GVN::assignValNumForDeadCode() { + for (BasicBlock *BB : DeadBlocks) { + for (Instruction &Inst : *BB) { + unsigned ValNum = VN.lookupOrAdd(&Inst); + addToLeaderTable(ValNum, &Inst, BB); + } + } +} + +class llvm::gvn::GVNLegacyPass : public FunctionPass { +public: + static char ID; // Pass identification, replacement for typeid + + explicit GVNLegacyPass(bool NoMemDepAnalysis = !EnableMemDep) + : FunctionPass(ID), NoMemDepAnalysis(NoMemDepAnalysis) { + initializeGVNLegacyPassPass(*PassRegistry::getPassRegistry()); + } + + bool runOnFunction(Function &F) override { + if (skipFunction(F)) + return false; + + auto *LIWP = getAnalysisIfAvailable<LoopInfoWrapperPass>(); + + return Impl.runImpl( + F, getAnalysis<AssumptionCacheTracker>().getAssumptionCache(F), + getAnalysis<DominatorTreeWrapperPass>().getDomTree(), + getAnalysis<TargetLibraryInfoWrapperPass>().getTLI(F), + getAnalysis<AAResultsWrapperPass>().getAAResults(), + NoMemDepAnalysis + ? nullptr + : &getAnalysis<MemoryDependenceWrapperPass>().getMemDep(), + LIWP ? &LIWP->getLoopInfo() : nullptr, + &getAnalysis<OptimizationRemarkEmitterWrapperPass>().getORE()); + } + + void getAnalysisUsage(AnalysisUsage &AU) const override { + AU.addRequired<AssumptionCacheTracker>(); + AU.addRequired<DominatorTreeWrapperPass>(); + AU.addRequired<TargetLibraryInfoWrapperPass>(); + AU.addRequired<LoopInfoWrapperPass>(); + if (!NoMemDepAnalysis) + AU.addRequired<MemoryDependenceWrapperPass>(); + AU.addRequired<AAResultsWrapperPass>(); + + AU.addPreserved<DominatorTreeWrapperPass>(); + AU.addPreserved<GlobalsAAWrapperPass>(); + AU.addPreserved<TargetLibraryInfoWrapperPass>(); + AU.addPreserved<LoopInfoWrapperPass>(); + AU.addPreservedID(LoopSimplifyID); + AU.addRequired<OptimizationRemarkEmitterWrapperPass>(); + } + +private: + bool NoMemDepAnalysis; + GVN Impl; +}; + +char GVNLegacyPass::ID = 0; + +INITIALIZE_PASS_BEGIN(GVNLegacyPass, "gvn", "Global Value Numbering", false, false) +INITIALIZE_PASS_DEPENDENCY(AssumptionCacheTracker) +INITIALIZE_PASS_DEPENDENCY(MemoryDependenceWrapperPass) +INITIALIZE_PASS_DEPENDENCY(DominatorTreeWrapperPass) +INITIALIZE_PASS_DEPENDENCY(TargetLibraryInfoWrapperPass) +INITIALIZE_PASS_DEPENDENCY(AAResultsWrapperPass) +INITIALIZE_PASS_DEPENDENCY(GlobalsAAWrapperPass) +INITIALIZE_PASS_DEPENDENCY(OptimizationRemarkEmitterWrapperPass) +INITIALIZE_PASS_END(GVNLegacyPass, "gvn", "Global Value Numbering", false, false) + +// The public interface to this file... +FunctionPass *llvm::createGVNPass(bool NoMemDepAnalysis) { + return new GVNLegacyPass(NoMemDepAnalysis); +} |