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Diffstat (limited to 'llvm/lib/Transforms/Scalar/SCCP.cpp')
| -rw-r--r-- | llvm/lib/Transforms/Scalar/SCCP.cpp | 2232 |
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diff --git a/llvm/lib/Transforms/Scalar/SCCP.cpp b/llvm/lib/Transforms/Scalar/SCCP.cpp new file mode 100644 index 000000000000..10fbdc8aacd2 --- /dev/null +++ b/llvm/lib/Transforms/Scalar/SCCP.cpp @@ -0,0 +1,2232 @@ +//===- SCCP.cpp - Sparse Conditional Constant Propagation -----------------===// +// +// 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 file implements sparse conditional constant propagation and merging: +// +// Specifically, this: +// * Assumes values are constant unless proven otherwise +// * Assumes BasicBlocks are dead unless proven otherwise +// * Proves values to be constant, and replaces them with constants +// * Proves conditional branches to be unconditional +// +//===----------------------------------------------------------------------===// + +#include "llvm/Transforms/Scalar/SCCP.h" +#include "llvm/ADT/ArrayRef.h" +#include "llvm/ADT/DenseMap.h" +#include "llvm/ADT/DenseSet.h" +#include "llvm/ADT/MapVector.h" +#include "llvm/ADT/PointerIntPair.h" +#include "llvm/ADT/STLExtras.h" +#include "llvm/ADT/SmallPtrSet.h" +#include "llvm/ADT/SmallVector.h" +#include "llvm/ADT/Statistic.h" +#include "llvm/Analysis/ConstantFolding.h" +#include "llvm/Analysis/GlobalsModRef.h" +#include "llvm/Analysis/TargetLibraryInfo.h" +#include "llvm/Transforms/Utils/Local.h" +#include "llvm/Analysis/ValueLattice.h" +#include "llvm/Analysis/ValueLatticeUtils.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/DerivedTypes.h" +#include "llvm/IR/Function.h" +#include "llvm/IR/GlobalVariable.h" +#include "llvm/IR/InstVisitor.h" +#include "llvm/IR/InstrTypes.h" +#include "llvm/IR/Instruction.h" +#include "llvm/IR/Instructions.h" +#include "llvm/IR/Module.h" +#include "llvm/IR/PassManager.h" +#include "llvm/IR/Type.h" +#include "llvm/IR/User.h" +#include "llvm/IR/Value.h" +#include "llvm/Pass.h" +#include "llvm/Support/Casting.h" +#include "llvm/Support/Debug.h" +#include "llvm/Support/ErrorHandling.h" +#include "llvm/Support/raw_ostream.h" +#include "llvm/Transforms/Scalar.h" +#include "llvm/Transforms/Utils/PredicateInfo.h" +#include <cassert> +#include <utility> +#include <vector> + +using namespace llvm; + +#define DEBUG_TYPE "sccp" + +STATISTIC(NumInstRemoved, "Number of instructions removed"); +STATISTIC(NumDeadBlocks , "Number of basic blocks unreachable"); + +STATISTIC(IPNumInstRemoved, "Number of instructions removed by IPSCCP"); +STATISTIC(IPNumArgsElimed ,"Number of arguments constant propagated by IPSCCP"); +STATISTIC(IPNumGlobalConst, "Number of globals found to be constant by IPSCCP"); + +namespace { + +/// LatticeVal class - This class represents the different lattice values that +/// an LLVM value may occupy. It is a simple class with value semantics. +/// +class LatticeVal { + enum LatticeValueTy { + /// unknown - This LLVM Value has no known value yet. + unknown, + + /// constant - This LLVM Value has a specific constant value. + constant, + + /// forcedconstant - This LLVM Value was thought to be undef until + /// ResolvedUndefsIn. This is treated just like 'constant', but if merged + /// with another (different) constant, it goes to overdefined, instead of + /// asserting. + forcedconstant, + + /// overdefined - This instruction is not known to be constant, and we know + /// it has a value. + overdefined + }; + + /// Val: This stores the current lattice value along with the Constant* for + /// the constant if this is a 'constant' or 'forcedconstant' value. + PointerIntPair<Constant *, 2, LatticeValueTy> Val; + + LatticeValueTy getLatticeValue() const { + return Val.getInt(); + } + +public: + LatticeVal() : Val(nullptr, unknown) {} + + bool isUnknown() const { return getLatticeValue() == unknown; } + + bool isConstant() const { + return getLatticeValue() == constant || getLatticeValue() == forcedconstant; + } + + bool isOverdefined() const { return getLatticeValue() == overdefined; } + + Constant *getConstant() const { + assert(isConstant() && "Cannot get the constant of a non-constant!"); + return Val.getPointer(); + } + + /// markOverdefined - Return true if this is a change in status. + bool markOverdefined() { + if (isOverdefined()) + return false; + + Val.setInt(overdefined); + return true; + } + + /// markConstant - Return true if this is a change in status. + bool markConstant(Constant *V) { + if (getLatticeValue() == constant) { // Constant but not forcedconstant. + assert(getConstant() == V && "Marking constant with different value"); + return false; + } + + if (isUnknown()) { + Val.setInt(constant); + assert(V && "Marking constant with NULL"); + Val.setPointer(V); + } else { + assert(getLatticeValue() == forcedconstant && + "Cannot move from overdefined to constant!"); + // Stay at forcedconstant if the constant is the same. + if (V == getConstant()) return false; + + // Otherwise, we go to overdefined. Assumptions made based on the + // forced value are possibly wrong. Assuming this is another constant + // could expose a contradiction. + Val.setInt(overdefined); + } + return true; + } + + /// getConstantInt - If this is a constant with a ConstantInt value, return it + /// otherwise return null. + ConstantInt *getConstantInt() const { + if (isConstant()) + return dyn_cast<ConstantInt>(getConstant()); + return nullptr; + } + + /// getBlockAddress - If this is a constant with a BlockAddress value, return + /// it, otherwise return null. + BlockAddress *getBlockAddress() const { + if (isConstant()) + return dyn_cast<BlockAddress>(getConstant()); + return nullptr; + } + + void markForcedConstant(Constant *V) { + assert(isUnknown() && "Can't force a defined value!"); + Val.setInt(forcedconstant); + Val.setPointer(V); + } + + ValueLatticeElement toValueLattice() const { + if (isOverdefined()) + return ValueLatticeElement::getOverdefined(); + if (isConstant()) + return ValueLatticeElement::get(getConstant()); + return ValueLatticeElement(); + } +}; + +//===----------------------------------------------------------------------===// +// +/// SCCPSolver - This class is a general purpose solver for Sparse Conditional +/// Constant Propagation. +/// +class SCCPSolver : public InstVisitor<SCCPSolver> { + const DataLayout &DL; + std::function<const TargetLibraryInfo &(Function &)> GetTLI; + SmallPtrSet<BasicBlock *, 8> BBExecutable; // The BBs that are executable. + DenseMap<Value *, LatticeVal> ValueState; // The state each value is in. + // The state each parameter is in. + DenseMap<Value *, ValueLatticeElement> ParamState; + + /// StructValueState - This maintains ValueState for values that have + /// StructType, for example for formal arguments, calls, insertelement, etc. + DenseMap<std::pair<Value *, unsigned>, LatticeVal> StructValueState; + + /// GlobalValue - If we are tracking any values for the contents of a global + /// variable, we keep a mapping from the constant accessor to the element of + /// the global, to the currently known value. If the value becomes + /// overdefined, it's entry is simply removed from this map. + DenseMap<GlobalVariable *, LatticeVal> TrackedGlobals; + + /// TrackedRetVals - If we are tracking arguments into and the return + /// value out of a function, it will have an entry in this map, indicating + /// what the known return value for the function is. + MapVector<Function *, LatticeVal> TrackedRetVals; + + /// TrackedMultipleRetVals - Same as TrackedRetVals, but used for functions + /// that return multiple values. + MapVector<std::pair<Function *, unsigned>, LatticeVal> TrackedMultipleRetVals; + + /// MRVFunctionsTracked - Each function in TrackedMultipleRetVals is + /// represented here for efficient lookup. + SmallPtrSet<Function *, 16> MRVFunctionsTracked; + + /// MustTailFunctions - Each function here is a callee of non-removable + /// musttail call site. + SmallPtrSet<Function *, 16> MustTailCallees; + + /// TrackingIncomingArguments - This is the set of functions for whose + /// arguments we make optimistic assumptions about and try to prove as + /// constants. + SmallPtrSet<Function *, 16> TrackingIncomingArguments; + + /// The reason for two worklists is that overdefined is the lowest state + /// on the lattice, and moving things to overdefined as fast as possible + /// makes SCCP converge much faster. + /// + /// By having a separate worklist, we accomplish this because everything + /// possibly overdefined will become overdefined at the soonest possible + /// point. + SmallVector<Value *, 64> OverdefinedInstWorkList; + SmallVector<Value *, 64> InstWorkList; + + // The BasicBlock work list + SmallVector<BasicBlock *, 64> BBWorkList; + + /// KnownFeasibleEdges - Entries in this set are edges which have already had + /// PHI nodes retriggered. + using Edge = std::pair<BasicBlock *, BasicBlock *>; + DenseSet<Edge> KnownFeasibleEdges; + + DenseMap<Function *, AnalysisResultsForFn> AnalysisResults; + DenseMap<Value *, SmallPtrSet<User *, 2>> AdditionalUsers; + +public: + void addAnalysis(Function &F, AnalysisResultsForFn A) { + AnalysisResults.insert({&F, std::move(A)}); + } + + const PredicateBase *getPredicateInfoFor(Instruction *I) { + auto A = AnalysisResults.find(I->getParent()->getParent()); + if (A == AnalysisResults.end()) + return nullptr; + return A->second.PredInfo->getPredicateInfoFor(I); + } + + DomTreeUpdater getDTU(Function &F) { + auto A = AnalysisResults.find(&F); + assert(A != AnalysisResults.end() && "Need analysis results for function."); + return {A->second.DT, A->second.PDT, DomTreeUpdater::UpdateStrategy::Lazy}; + } + + SCCPSolver(const DataLayout &DL, + std::function<const TargetLibraryInfo &(Function &)> GetTLI) + : DL(DL), GetTLI(std::move(GetTLI)) {} + + /// MarkBlockExecutable - This method can be used by clients to mark all of + /// the blocks that are known to be intrinsically live in the processed unit. + /// + /// This returns true if the block was not considered live before. + bool MarkBlockExecutable(BasicBlock *BB) { + if (!BBExecutable.insert(BB).second) + return false; + LLVM_DEBUG(dbgs() << "Marking Block Executable: " << BB->getName() << '\n'); + BBWorkList.push_back(BB); // Add the block to the work list! + return true; + } + + /// TrackValueOfGlobalVariable - Clients can use this method to + /// inform the SCCPSolver that it should track loads and stores to the + /// specified global variable if it can. This is only legal to call if + /// performing Interprocedural SCCP. + void TrackValueOfGlobalVariable(GlobalVariable *GV) { + // We only track the contents of scalar globals. + if (GV->getValueType()->isSingleValueType()) { + LatticeVal &IV = TrackedGlobals[GV]; + if (!isa<UndefValue>(GV->getInitializer())) + IV.markConstant(GV->getInitializer()); + } + } + + /// AddTrackedFunction - If the SCCP solver is supposed to track calls into + /// and out of the specified function (which cannot have its address taken), + /// this method must be called. + void AddTrackedFunction(Function *F) { + // Add an entry, F -> undef. + if (auto *STy = dyn_cast<StructType>(F->getReturnType())) { + MRVFunctionsTracked.insert(F); + for (unsigned i = 0, e = STy->getNumElements(); i != e; ++i) + TrackedMultipleRetVals.insert(std::make_pair(std::make_pair(F, i), + LatticeVal())); + } else + TrackedRetVals.insert(std::make_pair(F, LatticeVal())); + } + + /// AddMustTailCallee - If the SCCP solver finds that this function is called + /// from non-removable musttail call site. + void AddMustTailCallee(Function *F) { + MustTailCallees.insert(F); + } + + /// Returns true if the given function is called from non-removable musttail + /// call site. + bool isMustTailCallee(Function *F) { + return MustTailCallees.count(F); + } + + void AddArgumentTrackedFunction(Function *F) { + TrackingIncomingArguments.insert(F); + } + + /// Returns true if the given function is in the solver's set of + /// argument-tracked functions. + bool isArgumentTrackedFunction(Function *F) { + return TrackingIncomingArguments.count(F); + } + + /// Solve - Solve for constants and executable blocks. + void Solve(); + + /// ResolvedUndefsIn - While solving the dataflow for a function, we assume + /// that branches on undef values cannot reach any of their successors. + /// However, this is not a safe assumption. After we solve dataflow, this + /// method should be use to handle this. If this returns true, the solver + /// should be rerun. + bool ResolvedUndefsIn(Function &F); + + bool isBlockExecutable(BasicBlock *BB) const { + return BBExecutable.count(BB); + } + + // isEdgeFeasible - Return true if the control flow edge from the 'From' basic + // block to the 'To' basic block is currently feasible. + bool isEdgeFeasible(BasicBlock *From, BasicBlock *To); + + std::vector<LatticeVal> getStructLatticeValueFor(Value *V) const { + std::vector<LatticeVal> StructValues; + auto *STy = dyn_cast<StructType>(V->getType()); + assert(STy && "getStructLatticeValueFor() can be called only on structs"); + for (unsigned i = 0, e = STy->getNumElements(); i != e; ++i) { + auto I = StructValueState.find(std::make_pair(V, i)); + assert(I != StructValueState.end() && "Value not in valuemap!"); + StructValues.push_back(I->second); + } + return StructValues; + } + + const LatticeVal &getLatticeValueFor(Value *V) const { + assert(!V->getType()->isStructTy() && + "Should use getStructLatticeValueFor"); + DenseMap<Value *, LatticeVal>::const_iterator I = ValueState.find(V); + assert(I != ValueState.end() && + "V not found in ValueState nor Paramstate map!"); + return I->second; + } + + /// getTrackedRetVals - Get the inferred return value map. + const MapVector<Function*, LatticeVal> &getTrackedRetVals() { + return TrackedRetVals; + } + + /// getTrackedGlobals - Get and return the set of inferred initializers for + /// global variables. + const DenseMap<GlobalVariable*, LatticeVal> &getTrackedGlobals() { + return TrackedGlobals; + } + + /// getMRVFunctionsTracked - Get the set of functions which return multiple + /// values tracked by the pass. + const SmallPtrSet<Function *, 16> getMRVFunctionsTracked() { + return MRVFunctionsTracked; + } + + /// getMustTailCallees - Get the set of functions which are called + /// from non-removable musttail call sites. + const SmallPtrSet<Function *, 16> getMustTailCallees() { + return MustTailCallees; + } + + /// markOverdefined - Mark the specified value overdefined. This + /// works with both scalars and structs. + void markOverdefined(Value *V) { + if (auto *STy = dyn_cast<StructType>(V->getType())) + for (unsigned i = 0, e = STy->getNumElements(); i != e; ++i) + markOverdefined(getStructValueState(V, i), V); + else + markOverdefined(ValueState[V], V); + } + + // isStructLatticeConstant - Return true if all the lattice values + // corresponding to elements of the structure are not overdefined, + // false otherwise. + bool isStructLatticeConstant(Function *F, StructType *STy) { + for (unsigned i = 0, e = STy->getNumElements(); i != e; ++i) { + const auto &It = TrackedMultipleRetVals.find(std::make_pair(F, i)); + assert(It != TrackedMultipleRetVals.end()); + LatticeVal LV = It->second; + if (LV.isOverdefined()) + return false; + } + return true; + } + +private: + // pushToWorkList - Helper for markConstant/markForcedConstant/markOverdefined + void pushToWorkList(LatticeVal &IV, Value *V) { + if (IV.isOverdefined()) + return OverdefinedInstWorkList.push_back(V); + InstWorkList.push_back(V); + } + + // markConstant - Make a value be marked as "constant". If the value + // is not already a constant, add it to the instruction work list so that + // the users of the instruction are updated later. + bool markConstant(LatticeVal &IV, Value *V, Constant *C) { + if (!IV.markConstant(C)) return false; + LLVM_DEBUG(dbgs() << "markConstant: " << *C << ": " << *V << '\n'); + pushToWorkList(IV, V); + return true; + } + + bool markConstant(Value *V, Constant *C) { + assert(!V->getType()->isStructTy() && "structs should use mergeInValue"); + return markConstant(ValueState[V], V, C); + } + + void markForcedConstant(Value *V, Constant *C) { + assert(!V->getType()->isStructTy() && "structs should use mergeInValue"); + LatticeVal &IV = ValueState[V]; + IV.markForcedConstant(C); + LLVM_DEBUG(dbgs() << "markForcedConstant: " << *C << ": " << *V << '\n'); + pushToWorkList(IV, V); + } + + // markOverdefined - Make a value be marked as "overdefined". If the + // value is not already overdefined, add it to the overdefined instruction + // work list so that the users of the instruction are updated later. + bool markOverdefined(LatticeVal &IV, Value *V) { + if (!IV.markOverdefined()) return false; + + LLVM_DEBUG(dbgs() << "markOverdefined: "; + if (auto *F = dyn_cast<Function>(V)) dbgs() + << "Function '" << F->getName() << "'\n"; + else dbgs() << *V << '\n'); + // Only instructions go on the work list + pushToWorkList(IV, V); + return true; + } + + bool mergeInValue(LatticeVal &IV, Value *V, LatticeVal MergeWithV) { + if (IV.isOverdefined() || MergeWithV.isUnknown()) + return false; // Noop. + if (MergeWithV.isOverdefined()) + return markOverdefined(IV, V); + if (IV.isUnknown()) + return markConstant(IV, V, MergeWithV.getConstant()); + if (IV.getConstant() != MergeWithV.getConstant()) + return markOverdefined(IV, V); + return false; + } + + bool mergeInValue(Value *V, LatticeVal MergeWithV) { + assert(!V->getType()->isStructTy() && + "non-structs should use markConstant"); + return mergeInValue(ValueState[V], V, MergeWithV); + } + + /// getValueState - Return the LatticeVal object that corresponds to the + /// value. This function handles the case when the value hasn't been seen yet + /// by properly seeding constants etc. + LatticeVal &getValueState(Value *V) { + assert(!V->getType()->isStructTy() && "Should use getStructValueState"); + + std::pair<DenseMap<Value*, LatticeVal>::iterator, bool> I = + ValueState.insert(std::make_pair(V, LatticeVal())); + LatticeVal &LV = I.first->second; + + if (!I.second) + return LV; // Common case, already in the map. + + if (auto *C = dyn_cast<Constant>(V)) { + // Undef values remain unknown. + if (!isa<UndefValue>(V)) + LV.markConstant(C); // Constants are constant + } + + // All others are underdefined by default. + return LV; + } + + ValueLatticeElement &getParamState(Value *V) { + assert(!V->getType()->isStructTy() && "Should use getStructValueState"); + + std::pair<DenseMap<Value*, ValueLatticeElement>::iterator, bool> + PI = ParamState.insert(std::make_pair(V, ValueLatticeElement())); + ValueLatticeElement &LV = PI.first->second; + if (PI.second) + LV = getValueState(V).toValueLattice(); + + return LV; + } + + /// getStructValueState - Return the LatticeVal object that corresponds to the + /// value/field pair. This function handles the case when the value hasn't + /// been seen yet by properly seeding constants etc. + LatticeVal &getStructValueState(Value *V, unsigned i) { + assert(V->getType()->isStructTy() && "Should use getValueState"); + assert(i < cast<StructType>(V->getType())->getNumElements() && + "Invalid element #"); + + std::pair<DenseMap<std::pair<Value*, unsigned>, LatticeVal>::iterator, + bool> I = StructValueState.insert( + std::make_pair(std::make_pair(V, i), LatticeVal())); + LatticeVal &LV = I.first->second; + + if (!I.second) + return LV; // Common case, already in the map. + + if (auto *C = dyn_cast<Constant>(V)) { + Constant *Elt = C->getAggregateElement(i); + + if (!Elt) + LV.markOverdefined(); // Unknown sort of constant. + else if (isa<UndefValue>(Elt)) + ; // Undef values remain unknown. + else + LV.markConstant(Elt); // Constants are constant. + } + + // All others are underdefined by default. + return LV; + } + + /// markEdgeExecutable - Mark a basic block as executable, adding it to the BB + /// work list if it is not already executable. + bool markEdgeExecutable(BasicBlock *Source, BasicBlock *Dest) { + if (!KnownFeasibleEdges.insert(Edge(Source, Dest)).second) + return false; // This edge is already known to be executable! + + if (!MarkBlockExecutable(Dest)) { + // If the destination is already executable, we just made an *edge* + // feasible that wasn't before. Revisit the PHI nodes in the block + // because they have potentially new operands. + LLVM_DEBUG(dbgs() << "Marking Edge Executable: " << Source->getName() + << " -> " << Dest->getName() << '\n'); + + for (PHINode &PN : Dest->phis()) + visitPHINode(PN); + } + return true; + } + + // getFeasibleSuccessors - Return a vector of booleans to indicate which + // successors are reachable from a given terminator instruction. + void getFeasibleSuccessors(Instruction &TI, SmallVectorImpl<bool> &Succs); + + // OperandChangedState - This method is invoked on all of the users of an + // instruction that was just changed state somehow. Based on this + // information, we need to update the specified user of this instruction. + void OperandChangedState(Instruction *I) { + if (BBExecutable.count(I->getParent())) // Inst is executable? + visit(*I); + } + + // Add U as additional user of V. + void addAdditionalUser(Value *V, User *U) { + auto Iter = AdditionalUsers.insert({V, {}}); + Iter.first->second.insert(U); + } + + // Mark I's users as changed, including AdditionalUsers. + void markUsersAsChanged(Value *I) { + for (User *U : I->users()) + if (auto *UI = dyn_cast<Instruction>(U)) + OperandChangedState(UI); + + auto Iter = AdditionalUsers.find(I); + if (Iter != AdditionalUsers.end()) { + for (User *U : Iter->second) + if (auto *UI = dyn_cast<Instruction>(U)) + OperandChangedState(UI); + } + } + +private: + friend class InstVisitor<SCCPSolver>; + + // visit implementations - Something changed in this instruction. Either an + // operand made a transition, or the instruction is newly executable. Change + // the value type of I to reflect these changes if appropriate. + void visitPHINode(PHINode &I); + + // Terminators + + void visitReturnInst(ReturnInst &I); + void visitTerminator(Instruction &TI); + + void visitCastInst(CastInst &I); + void visitSelectInst(SelectInst &I); + void visitUnaryOperator(Instruction &I); + void visitBinaryOperator(Instruction &I); + void visitCmpInst(CmpInst &I); + void visitExtractValueInst(ExtractValueInst &EVI); + void visitInsertValueInst(InsertValueInst &IVI); + + void visitCatchSwitchInst(CatchSwitchInst &CPI) { + markOverdefined(&CPI); + visitTerminator(CPI); + } + + // Instructions that cannot be folded away. + + void visitStoreInst (StoreInst &I); + void visitLoadInst (LoadInst &I); + void visitGetElementPtrInst(GetElementPtrInst &I); + + void visitCallInst (CallInst &I) { + visitCallSite(&I); + } + + void visitInvokeInst (InvokeInst &II) { + visitCallSite(&II); + visitTerminator(II); + } + + void visitCallBrInst (CallBrInst &CBI) { + visitCallSite(&CBI); + visitTerminator(CBI); + } + + void visitCallSite (CallSite CS); + void visitResumeInst (ResumeInst &I) { /*returns void*/ } + void visitUnreachableInst(UnreachableInst &I) { /*returns void*/ } + void visitFenceInst (FenceInst &I) { /*returns void*/ } + + void visitInstruction(Instruction &I) { + // All the instructions we don't do any special handling for just + // go to overdefined. + LLVM_DEBUG(dbgs() << "SCCP: Don't know how to handle: " << I << '\n'); + markOverdefined(&I); + } +}; + +} // end anonymous namespace + +// getFeasibleSuccessors - Return a vector of booleans to indicate which +// successors are reachable from a given terminator instruction. +void SCCPSolver::getFeasibleSuccessors(Instruction &TI, + SmallVectorImpl<bool> &Succs) { + Succs.resize(TI.getNumSuccessors()); + if (auto *BI = dyn_cast<BranchInst>(&TI)) { + if (BI->isUnconditional()) { + Succs[0] = true; + return; + } + + LatticeVal BCValue = getValueState(BI->getCondition()); + ConstantInt *CI = BCValue.getConstantInt(); + if (!CI) { + // Overdefined condition variables, and branches on unfoldable constant + // conditions, mean the branch could go either way. + if (!BCValue.isUnknown()) + Succs[0] = Succs[1] = true; + return; + } + + // Constant condition variables mean the branch can only go a single way. + Succs[CI->isZero()] = true; + return; + } + + // Unwinding instructions successors are always executable. + if (TI.isExceptionalTerminator()) { + Succs.assign(TI.getNumSuccessors(), true); + return; + } + + if (auto *SI = dyn_cast<SwitchInst>(&TI)) { + if (!SI->getNumCases()) { + Succs[0] = true; + return; + } + LatticeVal SCValue = getValueState(SI->getCondition()); + ConstantInt *CI = SCValue.getConstantInt(); + + if (!CI) { // Overdefined or unknown condition? + // All destinations are executable! + if (!SCValue.isUnknown()) + Succs.assign(TI.getNumSuccessors(), true); + return; + } + + Succs[SI->findCaseValue(CI)->getSuccessorIndex()] = true; + return; + } + + // In case of indirect branch and its address is a blockaddress, we mark + // the target as executable. + if (auto *IBR = dyn_cast<IndirectBrInst>(&TI)) { + // Casts are folded by visitCastInst. + LatticeVal IBRValue = getValueState(IBR->getAddress()); + BlockAddress *Addr = IBRValue.getBlockAddress(); + if (!Addr) { // Overdefined or unknown condition? + // All destinations are executable! + if (!IBRValue.isUnknown()) + Succs.assign(TI.getNumSuccessors(), true); + return; + } + + BasicBlock* T = Addr->getBasicBlock(); + assert(Addr->getFunction() == T->getParent() && + "Block address of a different function ?"); + for (unsigned i = 0; i < IBR->getNumSuccessors(); ++i) { + // This is the target. + if (IBR->getDestination(i) == T) { + Succs[i] = true; + return; + } + } + + // If we didn't find our destination in the IBR successor list, then we + // have undefined behavior. Its ok to assume no successor is executable. + return; + } + + // In case of callbr, we pessimistically assume that all successors are + // feasible. + if (isa<CallBrInst>(&TI)) { + Succs.assign(TI.getNumSuccessors(), true); + return; + } + + LLVM_DEBUG(dbgs() << "Unknown terminator instruction: " << TI << '\n'); + llvm_unreachable("SCCP: Don't know how to handle this terminator!"); +} + +// isEdgeFeasible - Return true if the control flow edge from the 'From' basic +// block to the 'To' basic block is currently feasible. +bool SCCPSolver::isEdgeFeasible(BasicBlock *From, BasicBlock *To) { + // Check if we've called markEdgeExecutable on the edge yet. (We could + // be more aggressive and try to consider edges which haven't been marked + // yet, but there isn't any need.) + return KnownFeasibleEdges.count(Edge(From, To)); +} + +// visit Implementations - Something changed in this instruction, either an +// operand made a transition, or the instruction is newly executable. Change +// the value type of I to reflect these changes if appropriate. This method +// makes sure to do the following actions: +// +// 1. If a phi node merges two constants in, and has conflicting value coming +// from different branches, or if the PHI node merges in an overdefined +// value, then the PHI node becomes overdefined. +// 2. If a phi node merges only constants in, and they all agree on value, the +// PHI node becomes a constant value equal to that. +// 3. If V <- x (op) y && isConstant(x) && isConstant(y) V = Constant +// 4. If V <- x (op) y && (isOverdefined(x) || isOverdefined(y)) V = Overdefined +// 5. If V <- MEM or V <- CALL or V <- (unknown) then V = Overdefined +// 6. If a conditional branch has a value that is constant, make the selected +// destination executable +// 7. If a conditional branch has a value that is overdefined, make all +// successors executable. +void SCCPSolver::visitPHINode(PHINode &PN) { + // If this PN returns a struct, just mark the result overdefined. + // TODO: We could do a lot better than this if code actually uses this. + if (PN.getType()->isStructTy()) + return (void)markOverdefined(&PN); + + if (getValueState(&PN).isOverdefined()) + return; // Quick exit + + // Super-extra-high-degree PHI nodes are unlikely to ever be marked constant, + // and slow us down a lot. Just mark them overdefined. + if (PN.getNumIncomingValues() > 64) + return (void)markOverdefined(&PN); + + // Look at all of the executable operands of the PHI node. If any of them + // are overdefined, the PHI becomes overdefined as well. If they are all + // constant, and they agree with each other, the PHI becomes the identical + // constant. If they are constant and don't agree, the PHI is overdefined. + // If there are no executable operands, the PHI remains unknown. + Constant *OperandVal = nullptr; + for (unsigned i = 0, e = PN.getNumIncomingValues(); i != e; ++i) { + LatticeVal IV = getValueState(PN.getIncomingValue(i)); + if (IV.isUnknown()) continue; // Doesn't influence PHI node. + + if (!isEdgeFeasible(PN.getIncomingBlock(i), PN.getParent())) + continue; + + if (IV.isOverdefined()) // PHI node becomes overdefined! + return (void)markOverdefined(&PN); + + if (!OperandVal) { // Grab the first value. + OperandVal = IV.getConstant(); + continue; + } + + // There is already a reachable operand. If we conflict with it, + // then the PHI node becomes overdefined. If we agree with it, we + // can continue on. + + // Check to see if there are two different constants merging, if so, the PHI + // node is overdefined. + if (IV.getConstant() != OperandVal) + return (void)markOverdefined(&PN); + } + + // If we exited the loop, this means that the PHI node only has constant + // arguments that agree with each other(and OperandVal is the constant) or + // OperandVal is null because there are no defined incoming arguments. If + // this is the case, the PHI remains unknown. + if (OperandVal) + markConstant(&PN, OperandVal); // Acquire operand value +} + +void SCCPSolver::visitReturnInst(ReturnInst &I) { + if (I.getNumOperands() == 0) return; // ret void + + Function *F = I.getParent()->getParent(); + Value *ResultOp = I.getOperand(0); + + // If we are tracking the return value of this function, merge it in. + if (!TrackedRetVals.empty() && !ResultOp->getType()->isStructTy()) { + MapVector<Function*, LatticeVal>::iterator TFRVI = + TrackedRetVals.find(F); + if (TFRVI != TrackedRetVals.end()) { + mergeInValue(TFRVI->second, F, getValueState(ResultOp)); + return; + } + } + + // Handle functions that return multiple values. + if (!TrackedMultipleRetVals.empty()) { + if (auto *STy = dyn_cast<StructType>(ResultOp->getType())) + if (MRVFunctionsTracked.count(F)) + for (unsigned i = 0, e = STy->getNumElements(); i != e; ++i) + mergeInValue(TrackedMultipleRetVals[std::make_pair(F, i)], F, + getStructValueState(ResultOp, i)); + } +} + +void SCCPSolver::visitTerminator(Instruction &TI) { + SmallVector<bool, 16> SuccFeasible; + getFeasibleSuccessors(TI, SuccFeasible); + + BasicBlock *BB = TI.getParent(); + + // Mark all feasible successors executable. + for (unsigned i = 0, e = SuccFeasible.size(); i != e; ++i) + if (SuccFeasible[i]) + markEdgeExecutable(BB, TI.getSuccessor(i)); +} + +void SCCPSolver::visitCastInst(CastInst &I) { + LatticeVal OpSt = getValueState(I.getOperand(0)); + if (OpSt.isOverdefined()) // Inherit overdefinedness of operand + markOverdefined(&I); + else if (OpSt.isConstant()) { + // Fold the constant as we build. + Constant *C = ConstantFoldCastOperand(I.getOpcode(), OpSt.getConstant(), + I.getType(), DL); + if (isa<UndefValue>(C)) + return; + // Propagate constant value + markConstant(&I, C); + } +} + +void SCCPSolver::visitExtractValueInst(ExtractValueInst &EVI) { + // If this returns a struct, mark all elements over defined, we don't track + // structs in structs. + if (EVI.getType()->isStructTy()) + return (void)markOverdefined(&EVI); + + // If this is extracting from more than one level of struct, we don't know. + if (EVI.getNumIndices() != 1) + return (void)markOverdefined(&EVI); + + Value *AggVal = EVI.getAggregateOperand(); + if (AggVal->getType()->isStructTy()) { + unsigned i = *EVI.idx_begin(); + LatticeVal EltVal = getStructValueState(AggVal, i); + mergeInValue(getValueState(&EVI), &EVI, EltVal); + } else { + // Otherwise, must be extracting from an array. + return (void)markOverdefined(&EVI); + } +} + +void SCCPSolver::visitInsertValueInst(InsertValueInst &IVI) { + auto *STy = dyn_cast<StructType>(IVI.getType()); + if (!STy) + return (void)markOverdefined(&IVI); + + // If this has more than one index, we can't handle it, drive all results to + // undef. + if (IVI.getNumIndices() != 1) + return (void)markOverdefined(&IVI); + + Value *Aggr = IVI.getAggregateOperand(); + unsigned Idx = *IVI.idx_begin(); + + // Compute the result based on what we're inserting. + for (unsigned i = 0, e = STy->getNumElements(); i != e; ++i) { + // This passes through all values that aren't the inserted element. + if (i != Idx) { + LatticeVal EltVal = getStructValueState(Aggr, i); + mergeInValue(getStructValueState(&IVI, i), &IVI, EltVal); + continue; + } + + Value *Val = IVI.getInsertedValueOperand(); + if (Val->getType()->isStructTy()) + // We don't track structs in structs. + markOverdefined(getStructValueState(&IVI, i), &IVI); + else { + LatticeVal InVal = getValueState(Val); + mergeInValue(getStructValueState(&IVI, i), &IVI, InVal); + } + } +} + +void SCCPSolver::visitSelectInst(SelectInst &I) { + // If this select returns a struct, just mark the result overdefined. + // TODO: We could do a lot better than this if code actually uses this. + if (I.getType()->isStructTy()) + return (void)markOverdefined(&I); + + LatticeVal CondValue = getValueState(I.getCondition()); + if (CondValue.isUnknown()) + return; + + if (ConstantInt *CondCB = CondValue.getConstantInt()) { + Value *OpVal = CondCB->isZero() ? I.getFalseValue() : I.getTrueValue(); + mergeInValue(&I, getValueState(OpVal)); + return; + } + + // Otherwise, the condition is overdefined or a constant we can't evaluate. + // See if we can produce something better than overdefined based on the T/F + // value. + LatticeVal TVal = getValueState(I.getTrueValue()); + LatticeVal FVal = getValueState(I.getFalseValue()); + + // select ?, C, C -> C. + if (TVal.isConstant() && FVal.isConstant() && + TVal.getConstant() == FVal.getConstant()) + return (void)markConstant(&I, FVal.getConstant()); + + if (TVal.isUnknown()) // select ?, undef, X -> X. + return (void)mergeInValue(&I, FVal); + if (FVal.isUnknown()) // select ?, X, undef -> X. + return (void)mergeInValue(&I, TVal); + markOverdefined(&I); +} + +// Handle Unary Operators. +void SCCPSolver::visitUnaryOperator(Instruction &I) { + LatticeVal V0State = getValueState(I.getOperand(0)); + + LatticeVal &IV = ValueState[&I]; + if (IV.isOverdefined()) return; + + if (V0State.isConstant()) { + Constant *C = ConstantExpr::get(I.getOpcode(), V0State.getConstant()); + + // op Y -> undef. + if (isa<UndefValue>(C)) + return; + return (void)markConstant(IV, &I, C); + } + + // If something is undef, wait for it to resolve. + if (!V0State.isOverdefined()) + return; + + markOverdefined(&I); +} + +// Handle Binary Operators. +void SCCPSolver::visitBinaryOperator(Instruction &I) { + LatticeVal V1State = getValueState(I.getOperand(0)); + LatticeVal V2State = getValueState(I.getOperand(1)); + + LatticeVal &IV = ValueState[&I]; + if (IV.isOverdefined()) return; + + if (V1State.isConstant() && V2State.isConstant()) { + Constant *C = ConstantExpr::get(I.getOpcode(), V1State.getConstant(), + V2State.getConstant()); + // X op Y -> undef. + if (isa<UndefValue>(C)) + return; + return (void)markConstant(IV, &I, C); + } + + // If something is undef, wait for it to resolve. + if (!V1State.isOverdefined() && !V2State.isOverdefined()) + return; + + // Otherwise, one of our operands is overdefined. Try to produce something + // better than overdefined with some tricks. + // If this is 0 / Y, it doesn't matter that the second operand is + // overdefined, and we can replace it with zero. + if (I.getOpcode() == Instruction::UDiv || I.getOpcode() == Instruction::SDiv) + if (V1State.isConstant() && V1State.getConstant()->isNullValue()) + return (void)markConstant(IV, &I, V1State.getConstant()); + + // If this is: + // -> AND/MUL with 0 + // -> OR with -1 + // it doesn't matter that the other operand is overdefined. + if (I.getOpcode() == Instruction::And || I.getOpcode() == Instruction::Mul || + I.getOpcode() == Instruction::Or) { + LatticeVal *NonOverdefVal = nullptr; + if (!V1State.isOverdefined()) + NonOverdefVal = &V1State; + else if (!V2State.isOverdefined()) + NonOverdefVal = &V2State; + + if (NonOverdefVal) { + if (NonOverdefVal->isUnknown()) + return; + + if (I.getOpcode() == Instruction::And || + I.getOpcode() == Instruction::Mul) { + // X and 0 = 0 + // X * 0 = 0 + if (NonOverdefVal->getConstant()->isNullValue()) + return (void)markConstant(IV, &I, NonOverdefVal->getConstant()); + } else { + // X or -1 = -1 + if (ConstantInt *CI = NonOverdefVal->getConstantInt()) + if (CI->isMinusOne()) + return (void)markConstant(IV, &I, NonOverdefVal->getConstant()); + } + } + } + + markOverdefined(&I); +} + +// Handle ICmpInst instruction. +void SCCPSolver::visitCmpInst(CmpInst &I) { + // Do not cache this lookup, getValueState calls later in the function might + // invalidate the reference. + if (ValueState[&I].isOverdefined()) return; + + Value *Op1 = I.getOperand(0); + Value *Op2 = I.getOperand(1); + + // For parameters, use ParamState which includes constant range info if + // available. + auto V1Param = ParamState.find(Op1); + ValueLatticeElement V1State = (V1Param != ParamState.end()) + ? V1Param->second + : getValueState(Op1).toValueLattice(); + + auto V2Param = ParamState.find(Op2); + ValueLatticeElement V2State = V2Param != ParamState.end() + ? V2Param->second + : getValueState(Op2).toValueLattice(); + + Constant *C = V1State.getCompare(I.getPredicate(), I.getType(), V2State); + if (C) { + if (isa<UndefValue>(C)) + return; + LatticeVal CV; + CV.markConstant(C); + mergeInValue(&I, CV); + return; + } + + // If operands are still unknown, wait for it to resolve. + if (!V1State.isOverdefined() && !V2State.isOverdefined() && + !ValueState[&I].isConstant()) + return; + + markOverdefined(&I); +} + +// Handle getelementptr instructions. If all operands are constants then we +// can turn this into a getelementptr ConstantExpr. +void SCCPSolver::visitGetElementPtrInst(GetElementPtrInst &I) { + if (ValueState[&I].isOverdefined()) return; + + SmallVector<Constant*, 8> Operands; + Operands.reserve(I.getNumOperands()); + + for (unsigned i = 0, e = I.getNumOperands(); i != e; ++i) { + LatticeVal State = getValueState(I.getOperand(i)); + if (State.isUnknown()) + return; // Operands are not resolved yet. + + if (State.isOverdefined()) + return (void)markOverdefined(&I); + + assert(State.isConstant() && "Unknown state!"); + Operands.push_back(State.getConstant()); + } + + Constant *Ptr = Operands[0]; + auto Indices = makeArrayRef(Operands.begin() + 1, Operands.end()); + Constant *C = + ConstantExpr::getGetElementPtr(I.getSourceElementType(), Ptr, Indices); + if (isa<UndefValue>(C)) + return; + markConstant(&I, C); +} + +void SCCPSolver::visitStoreInst(StoreInst &SI) { + // If this store is of a struct, ignore it. + if (SI.getOperand(0)->getType()->isStructTy()) + return; + + if (TrackedGlobals.empty() || !isa<GlobalVariable>(SI.getOperand(1))) + return; + + GlobalVariable *GV = cast<GlobalVariable>(SI.getOperand(1)); + DenseMap<GlobalVariable*, LatticeVal>::iterator I = TrackedGlobals.find(GV); + if (I == TrackedGlobals.end() || I->second.isOverdefined()) return; + + // Get the value we are storing into the global, then merge it. + mergeInValue(I->second, GV, getValueState(SI.getOperand(0))); + if (I->second.isOverdefined()) + TrackedGlobals.erase(I); // No need to keep tracking this! +} + +// Handle load instructions. If the operand is a constant pointer to a constant +// global, we can replace the load with the loaded constant value! +void SCCPSolver::visitLoadInst(LoadInst &I) { + // If this load is of a struct, just mark the result overdefined. + if (I.getType()->isStructTy()) + return (void)markOverdefined(&I); + + LatticeVal PtrVal = getValueState(I.getOperand(0)); + if (PtrVal.isUnknown()) return; // The pointer is not resolved yet! + + LatticeVal &IV = ValueState[&I]; + if (IV.isOverdefined()) return; + + if (!PtrVal.isConstant() || I.isVolatile()) + return (void)markOverdefined(IV, &I); + + Constant *Ptr = PtrVal.getConstant(); + + // load null is undefined. + if (isa<ConstantPointerNull>(Ptr)) { + if (NullPointerIsDefined(I.getFunction(), I.getPointerAddressSpace())) + return (void)markOverdefined(IV, &I); + else + return; + } + + // Transform load (constant global) into the value loaded. + if (auto *GV = dyn_cast<GlobalVariable>(Ptr)) { + if (!TrackedGlobals.empty()) { + // If we are tracking this global, merge in the known value for it. + DenseMap<GlobalVariable*, LatticeVal>::iterator It = + TrackedGlobals.find(GV); + if (It != TrackedGlobals.end()) { + mergeInValue(IV, &I, It->second); + return; + } + } + } + + // Transform load from a constant into a constant if possible. + if (Constant *C = ConstantFoldLoadFromConstPtr(Ptr, I.getType(), DL)) { + if (isa<UndefValue>(C)) + return; + return (void)markConstant(IV, &I, C); + } + + // Otherwise we cannot say for certain what value this load will produce. + // Bail out. + markOverdefined(IV, &I); +} + +void SCCPSolver::visitCallSite(CallSite CS) { + Function *F = CS.getCalledFunction(); + Instruction *I = CS.getInstruction(); + + if (auto *II = dyn_cast<IntrinsicInst>(I)) { + if (II->getIntrinsicID() == Intrinsic::ssa_copy) { + if (ValueState[I].isOverdefined()) + return; + + auto *PI = getPredicateInfoFor(I); + if (!PI) + return; + + Value *CopyOf = I->getOperand(0); + auto *PBranch = dyn_cast<PredicateBranch>(PI); + if (!PBranch) { + mergeInValue(ValueState[I], I, getValueState(CopyOf)); + return; + } + + Value *Cond = PBranch->Condition; + + // Everything below relies on the condition being a comparison. + auto *Cmp = dyn_cast<CmpInst>(Cond); + if (!Cmp) { + mergeInValue(ValueState[I], I, getValueState(CopyOf)); + return; + } + + Value *CmpOp0 = Cmp->getOperand(0); + Value *CmpOp1 = Cmp->getOperand(1); + if (CopyOf != CmpOp0 && CopyOf != CmpOp1) { + mergeInValue(ValueState[I], I, getValueState(CopyOf)); + return; + } + + if (CmpOp0 != CopyOf) + std::swap(CmpOp0, CmpOp1); + + LatticeVal OriginalVal = getValueState(CopyOf); + LatticeVal EqVal = getValueState(CmpOp1); + LatticeVal &IV = ValueState[I]; + if (PBranch->TrueEdge && Cmp->getPredicate() == CmpInst::ICMP_EQ) { + addAdditionalUser(CmpOp1, I); + if (OriginalVal.isConstant()) + mergeInValue(IV, I, OriginalVal); + else + mergeInValue(IV, I, EqVal); + return; + } + if (!PBranch->TrueEdge && Cmp->getPredicate() == CmpInst::ICMP_NE) { + addAdditionalUser(CmpOp1, I); + if (OriginalVal.isConstant()) + mergeInValue(IV, I, OriginalVal); + else + mergeInValue(IV, I, EqVal); + return; + } + + return (void)mergeInValue(IV, I, getValueState(CopyOf)); + } + } + + // The common case is that we aren't tracking the callee, either because we + // are not doing interprocedural analysis or the callee is indirect, or is + // external. Handle these cases first. + if (!F || F->isDeclaration()) { +CallOverdefined: + // Void return and not tracking callee, just bail. + if (I->getType()->isVoidTy()) return; + + // Otherwise, if we have a single return value case, and if the function is + // a declaration, maybe we can constant fold it. + if (F && F->isDeclaration() && !I->getType()->isStructTy() && + canConstantFoldCallTo(cast<CallBase>(CS.getInstruction()), F)) { + SmallVector<Constant*, 8> Operands; + for (CallSite::arg_iterator AI = CS.arg_begin(), E = CS.arg_end(); + AI != E; ++AI) { + if (AI->get()->getType()->isStructTy()) + return markOverdefined(I); // Can't handle struct args. + LatticeVal State = getValueState(*AI); + + if (State.isUnknown()) + return; // Operands are not resolved yet. + if (State.isOverdefined()) + return (void)markOverdefined(I); + assert(State.isConstant() && "Unknown state!"); + Operands.push_back(State.getConstant()); + } + + if (getValueState(I).isOverdefined()) + return; + + // If we can constant fold this, mark the result of the call as a + // constant. + if (Constant *C = ConstantFoldCall(cast<CallBase>(CS.getInstruction()), F, + Operands, &GetTLI(*F))) { + // call -> undef. + if (isa<UndefValue>(C)) + return; + return (void)markConstant(I, C); + } + } + + // Otherwise, we don't know anything about this call, mark it overdefined. + return (void)markOverdefined(I); + } + + // If this is a local function that doesn't have its address taken, mark its + // entry block executable and merge in the actual arguments to the call into + // the formal arguments of the function. + if (!TrackingIncomingArguments.empty() && TrackingIncomingArguments.count(F)){ + MarkBlockExecutable(&F->front()); + + // Propagate information from this call site into the callee. + CallSite::arg_iterator CAI = CS.arg_begin(); + for (Function::arg_iterator AI = F->arg_begin(), E = F->arg_end(); + AI != E; ++AI, ++CAI) { + // If this argument is byval, and if the function is not readonly, there + // will be an implicit copy formed of the input aggregate. + if (AI->hasByValAttr() && !F->onlyReadsMemory()) { + markOverdefined(&*AI); + continue; + } + + if (auto *STy = dyn_cast<StructType>(AI->getType())) { + for (unsigned i = 0, e = STy->getNumElements(); i != e; ++i) { + LatticeVal CallArg = getStructValueState(*CAI, i); + mergeInValue(getStructValueState(&*AI, i), &*AI, CallArg); + } + } else { + // Most other parts of the Solver still only use the simpler value + // lattice, so we propagate changes for parameters to both lattices. + LatticeVal ConcreteArgument = getValueState(*CAI); + bool ParamChanged = + getParamState(&*AI).mergeIn(ConcreteArgument.toValueLattice(), DL); + bool ValueChanged = mergeInValue(&*AI, ConcreteArgument); + // Add argument to work list, if the state of a parameter changes but + // ValueState does not change (because it is already overdefined there), + // We have to take changes in ParamState into account, as it is used + // when evaluating Cmp instructions. + if (!ValueChanged && ParamChanged) + pushToWorkList(ValueState[&*AI], &*AI); + } + } + } + + // If this is a single/zero retval case, see if we're tracking the function. + if (auto *STy = dyn_cast<StructType>(F->getReturnType())) { + if (!MRVFunctionsTracked.count(F)) + goto CallOverdefined; // Not tracking this callee. + + // If we are tracking this callee, propagate the result of the function + // into this call site. + for (unsigned i = 0, e = STy->getNumElements(); i != e; ++i) + mergeInValue(getStructValueState(I, i), I, + TrackedMultipleRetVals[std::make_pair(F, i)]); + } else { + MapVector<Function*, LatticeVal>::iterator TFRVI = TrackedRetVals.find(F); + if (TFRVI == TrackedRetVals.end()) + goto CallOverdefined; // Not tracking this callee. + + // If so, propagate the return value of the callee into this call result. + mergeInValue(I, TFRVI->second); + } +} + +void SCCPSolver::Solve() { + // Process the work lists until they are empty! + while (!BBWorkList.empty() || !InstWorkList.empty() || + !OverdefinedInstWorkList.empty()) { + // Process the overdefined instruction's work list first, which drives other + // things to overdefined more quickly. + while (!OverdefinedInstWorkList.empty()) { + Value *I = OverdefinedInstWorkList.pop_back_val(); + + LLVM_DEBUG(dbgs() << "\nPopped off OI-WL: " << *I << '\n'); + + // "I" got into the work list because it either made the transition from + // bottom to constant, or to overdefined. + // + // Anything on this worklist that is overdefined need not be visited + // since all of its users will have already been marked as overdefined + // Update all of the users of this instruction's value. + // + markUsersAsChanged(I); + } + + // Process the instruction work list. + while (!InstWorkList.empty()) { + Value *I = InstWorkList.pop_back_val(); + + LLVM_DEBUG(dbgs() << "\nPopped off I-WL: " << *I << '\n'); + + // "I" got into the work list because it made the transition from undef to + // constant. + // + // Anything on this worklist that is overdefined need not be visited + // since all of its users will have already been marked as overdefined. + // Update all of the users of this instruction's value. + // + if (I->getType()->isStructTy() || !getValueState(I).isOverdefined()) + markUsersAsChanged(I); + } + + // Process the basic block work list. + while (!BBWorkList.empty()) { + BasicBlock *BB = BBWorkList.back(); + BBWorkList.pop_back(); + + LLVM_DEBUG(dbgs() << "\nPopped off BBWL: " << *BB << '\n'); + + // Notify all instructions in this basic block that they are newly + // executable. + visit(BB); + } + } +} + +/// ResolvedUndefsIn - While solving the dataflow for a function, we assume +/// that branches on undef values cannot reach any of their successors. +/// However, this is not a safe assumption. After we solve dataflow, this +/// method should be use to handle this. If this returns true, the solver +/// should be rerun. +/// +/// This method handles this by finding an unresolved branch and marking it one +/// of the edges from the block as being feasible, even though the condition +/// doesn't say it would otherwise be. This allows SCCP to find the rest of the +/// CFG and only slightly pessimizes the analysis results (by marking one, +/// potentially infeasible, edge feasible). This cannot usefully modify the +/// constraints on the condition of the branch, as that would impact other users +/// of the value. +/// +/// This scan also checks for values that use undefs, whose results are actually +/// defined. For example, 'zext i8 undef to i32' should produce all zeros +/// conservatively, as "(zext i8 X -> i32) & 0xFF00" must always return zero, +/// even if X isn't defined. +bool SCCPSolver::ResolvedUndefsIn(Function &F) { + for (BasicBlock &BB : F) { + if (!BBExecutable.count(&BB)) + continue; + + for (Instruction &I : BB) { + // Look for instructions which produce undef values. + if (I.getType()->isVoidTy()) continue; + + if (auto *STy = dyn_cast<StructType>(I.getType())) { + // Only a few things that can be structs matter for undef. + + // Tracked calls must never be marked overdefined in ResolvedUndefsIn. + if (CallSite CS = CallSite(&I)) + if (Function *F = CS.getCalledFunction()) + if (MRVFunctionsTracked.count(F)) + continue; + + // extractvalue and insertvalue don't need to be marked; they are + // tracked as precisely as their operands. + if (isa<ExtractValueInst>(I) || isa<InsertValueInst>(I)) + continue; + + // Send the results of everything else to overdefined. We could be + // more precise than this but it isn't worth bothering. + for (unsigned i = 0, e = STy->getNumElements(); i != e; ++i) { + LatticeVal &LV = getStructValueState(&I, i); + if (LV.isUnknown()) + markOverdefined(LV, &I); + } + continue; + } + + LatticeVal &LV = getValueState(&I); + if (!LV.isUnknown()) + continue; + + // There are two reasons a call can have an undef result + // 1. It could be tracked. + // 2. It could be constant-foldable. + // Because of the way we solve return values, tracked calls must + // never be marked overdefined in ResolvedUndefsIn. + if (CallSite CS = CallSite(&I)) { + if (Function *F = CS.getCalledFunction()) + if (TrackedRetVals.count(F)) + continue; + + // If the call is constant-foldable, we mark it overdefined because + // we do not know what return values are valid. + markOverdefined(&I); + return true; + } + + // extractvalue is safe; check here because the argument is a struct. + if (isa<ExtractValueInst>(I)) + continue; + + // Compute the operand LatticeVals, for convenience below. + // Anything taking a struct is conservatively assumed to require + // overdefined markings. + if (I.getOperand(0)->getType()->isStructTy()) { + markOverdefined(&I); + return true; + } + LatticeVal Op0LV = getValueState(I.getOperand(0)); + LatticeVal Op1LV; + if (I.getNumOperands() == 2) { + if (I.getOperand(1)->getType()->isStructTy()) { + markOverdefined(&I); + return true; + } + + Op1LV = getValueState(I.getOperand(1)); + } + // If this is an instructions whose result is defined even if the input is + // not fully defined, propagate the information. + Type *ITy = I.getType(); + switch (I.getOpcode()) { + case Instruction::Add: + case Instruction::Sub: + case Instruction::Trunc: + case Instruction::FPTrunc: + case Instruction::BitCast: + break; // Any undef -> undef + case Instruction::FSub: + case Instruction::FAdd: + case Instruction::FMul: + case Instruction::FDiv: + case Instruction::FRem: + // Floating-point binary operation: be conservative. + if (Op0LV.isUnknown() && Op1LV.isUnknown()) + markForcedConstant(&I, Constant::getNullValue(ITy)); + else + markOverdefined(&I); + return true; + case Instruction::FNeg: + break; // fneg undef -> undef + case Instruction::ZExt: + case Instruction::SExt: + case Instruction::FPToUI: + case Instruction::FPToSI: + case Instruction::FPExt: + case Instruction::PtrToInt: + case Instruction::IntToPtr: + case Instruction::SIToFP: + case Instruction::UIToFP: + // undef -> 0; some outputs are impossible + markForcedConstant(&I, Constant::getNullValue(ITy)); + return true; + case Instruction::Mul: + case Instruction::And: + // Both operands undef -> undef + if (Op0LV.isUnknown() && Op1LV.isUnknown()) + break; + // undef * X -> 0. X could be zero. + // undef & X -> 0. X could be zero. + markForcedConstant(&I, Constant::getNullValue(ITy)); + return true; + case Instruction::Or: + // Both operands undef -> undef + if (Op0LV.isUnknown() && Op1LV.isUnknown()) + break; + // undef | X -> -1. X could be -1. + markForcedConstant(&I, Constant::getAllOnesValue(ITy)); + return true; + case Instruction::Xor: + // undef ^ undef -> 0; strictly speaking, this is not strictly + // necessary, but we try to be nice to people who expect this + // behavior in simple cases + if (Op0LV.isUnknown() && Op1LV.isUnknown()) { + markForcedConstant(&I, Constant::getNullValue(ITy)); + return true; + } + // undef ^ X -> undef + break; + case Instruction::SDiv: + case Instruction::UDiv: + case Instruction::SRem: + case Instruction::URem: + // X / undef -> undef. No change. + // X % undef -> undef. No change. + if (Op1LV.isUnknown()) break; + + // X / 0 -> undef. No change. + // X % 0 -> undef. No change. + if (Op1LV.isConstant() && Op1LV.getConstant()->isZeroValue()) + break; + + // undef / X -> 0. X could be maxint. + // undef % X -> 0. X could be 1. + markForcedConstant(&I, Constant::getNullValue(ITy)); + return true; + case Instruction::AShr: + // X >>a undef -> undef. + if (Op1LV.isUnknown()) break; + + // Shifting by the bitwidth or more is undefined. + if (Op1LV.isConstant()) { + if (auto *ShiftAmt = Op1LV.getConstantInt()) + if (ShiftAmt->getLimitedValue() >= + ShiftAmt->getType()->getScalarSizeInBits()) + break; + } + + // undef >>a X -> 0 + markForcedConstant(&I, Constant::getNullValue(ITy)); + return true; + case Instruction::LShr: + case Instruction::Shl: + // X << undef -> undef. + // X >> undef -> undef. + if (Op1LV.isUnknown()) break; + + // Shifting by the bitwidth or more is undefined. + if (Op1LV.isConstant()) { + if (auto *ShiftAmt = Op1LV.getConstantInt()) + if (ShiftAmt->getLimitedValue() >= + ShiftAmt->getType()->getScalarSizeInBits()) + break; + } + + // undef << X -> 0 + // undef >> X -> 0 + markForcedConstant(&I, Constant::getNullValue(ITy)); + return true; + case Instruction::Select: + Op1LV = getValueState(I.getOperand(1)); + // undef ? X : Y -> X or Y. There could be commonality between X/Y. + if (Op0LV.isUnknown()) { + if (!Op1LV.isConstant()) // Pick the constant one if there is any. + Op1LV = getValueState(I.getOperand(2)); + } else if (Op1LV.isUnknown()) { + // c ? undef : undef -> undef. No change. + Op1LV = getValueState(I.getOperand(2)); + if (Op1LV.isUnknown()) + break; + // Otherwise, c ? undef : x -> x. + } else { + // Leave Op1LV as Operand(1)'s LatticeValue. + } + + if (Op1LV.isConstant()) + markForcedConstant(&I, Op1LV.getConstant()); + else + markOverdefined(&I); + return true; + case Instruction::Load: + // A load here means one of two things: a load of undef from a global, + // a load from an unknown pointer. Either way, having it return undef + // is okay. + break; + case Instruction::ICmp: + // X == undef -> undef. Other comparisons get more complicated. + Op0LV = getValueState(I.getOperand(0)); + Op1LV = getValueState(I.getOperand(1)); + + if ((Op0LV.isUnknown() || Op1LV.isUnknown()) && + cast<ICmpInst>(&I)->isEquality()) + break; + markOverdefined(&I); + return true; + case Instruction::Call: + case Instruction::Invoke: + case Instruction::CallBr: + llvm_unreachable("Call-like instructions should have be handled early"); + default: + // If we don't know what should happen here, conservatively mark it + // overdefined. + markOverdefined(&I); + return true; + } + } + + // Check to see if we have a branch or switch on an undefined value. If so + // we force the branch to go one way or the other to make the successor + // values live. It doesn't really matter which way we force it. + Instruction *TI = BB.getTerminator(); + if (auto *BI = dyn_cast<BranchInst>(TI)) { + if (!BI->isConditional()) continue; + if (!getValueState(BI->getCondition()).isUnknown()) + continue; + + // If the input to SCCP is actually branch on undef, fix the undef to + // false. + if (isa<UndefValue>(BI->getCondition())) { + BI->setCondition(ConstantInt::getFalse(BI->getContext())); + markEdgeExecutable(&BB, TI->getSuccessor(1)); + return true; + } + + // Otherwise, it is a branch on a symbolic value which is currently + // considered to be undef. Make sure some edge is executable, so a + // branch on "undef" always flows somewhere. + // FIXME: Distinguish between dead code and an LLVM "undef" value. + BasicBlock *DefaultSuccessor = TI->getSuccessor(1); + if (markEdgeExecutable(&BB, DefaultSuccessor)) + return true; + + continue; + } + + if (auto *IBR = dyn_cast<IndirectBrInst>(TI)) { + // Indirect branch with no successor ?. Its ok to assume it branches + // to no target. + if (IBR->getNumSuccessors() < 1) + continue; + + if (!getValueState(IBR->getAddress()).isUnknown()) + continue; + + // If the input to SCCP is actually branch on undef, fix the undef to + // the first successor of the indirect branch. + if (isa<UndefValue>(IBR->getAddress())) { + IBR->setAddress(BlockAddress::get(IBR->getSuccessor(0))); + markEdgeExecutable(&BB, IBR->getSuccessor(0)); + return true; + } + + // Otherwise, it is a branch on a symbolic value which is currently + // considered to be undef. Make sure some edge is executable, so a + // branch on "undef" always flows somewhere. + // FIXME: IndirectBr on "undef" doesn't actually need to go anywhere: + // we can assume the branch has undefined behavior instead. + BasicBlock *DefaultSuccessor = IBR->getSuccessor(0); + if (markEdgeExecutable(&BB, DefaultSuccessor)) + return true; + + continue; + } + + if (auto *SI = dyn_cast<SwitchInst>(TI)) { + if (!SI->getNumCases() || !getValueState(SI->getCondition()).isUnknown()) + continue; + + // If the input to SCCP is actually switch on undef, fix the undef to + // the first constant. + if (isa<UndefValue>(SI->getCondition())) { + SI->setCondition(SI->case_begin()->getCaseValue()); + markEdgeExecutable(&BB, SI->case_begin()->getCaseSuccessor()); + return true; + } + + // Otherwise, it is a branch on a symbolic value which is currently + // considered to be undef. Make sure some edge is executable, so a + // branch on "undef" always flows somewhere. + // FIXME: Distinguish between dead code and an LLVM "undef" value. + BasicBlock *DefaultSuccessor = SI->case_begin()->getCaseSuccessor(); + if (markEdgeExecutable(&BB, DefaultSuccessor)) + return true; + + continue; + } + } + + return false; +} + +static bool tryToReplaceWithConstant(SCCPSolver &Solver, Value *V) { + Constant *Const = nullptr; + if (V->getType()->isStructTy()) { + std::vector<LatticeVal> IVs = Solver.getStructLatticeValueFor(V); + if (llvm::any_of(IVs, + [](const LatticeVal &LV) { return LV.isOverdefined(); })) + return false; + std::vector<Constant *> ConstVals; + auto *ST = cast<StructType>(V->getType()); + for (unsigned i = 0, e = ST->getNumElements(); i != e; ++i) { + LatticeVal V = IVs[i]; + ConstVals.push_back(V.isConstant() + ? V.getConstant() + : UndefValue::get(ST->getElementType(i))); + } + Const = ConstantStruct::get(ST, ConstVals); + } else { + const LatticeVal &IV = Solver.getLatticeValueFor(V); + if (IV.isOverdefined()) + return false; + + Const = IV.isConstant() ? IV.getConstant() : UndefValue::get(V->getType()); + } + assert(Const && "Constant is nullptr here!"); + + // Replacing `musttail` instructions with constant breaks `musttail` invariant + // unless the call itself can be removed + CallInst *CI = dyn_cast<CallInst>(V); + if (CI && CI->isMustTailCall() && !CI->isSafeToRemove()) { + CallSite CS(CI); + Function *F = CS.getCalledFunction(); + + // Don't zap returns of the callee + if (F) + Solver.AddMustTailCallee(F); + + LLVM_DEBUG(dbgs() << " Can\'t treat the result of musttail call : " << *CI + << " as a constant\n"); + return false; + } + + LLVM_DEBUG(dbgs() << " Constant: " << *Const << " = " << *V << '\n'); + + // Replaces all of the uses of a variable with uses of the constant. + V->replaceAllUsesWith(Const); + return true; +} + +// runSCCP() - Run the Sparse Conditional Constant Propagation algorithm, +// and return true if the function was modified. +static bool runSCCP(Function &F, const DataLayout &DL, + const TargetLibraryInfo *TLI) { + LLVM_DEBUG(dbgs() << "SCCP on function '" << F.getName() << "'\n"); + SCCPSolver Solver( + DL, [TLI](Function &F) -> const TargetLibraryInfo & { return *TLI; }); + + // Mark the first block of the function as being executable. + Solver.MarkBlockExecutable(&F.front()); + + // Mark all arguments to the function as being overdefined. + for (Argument &AI : F.args()) + Solver.markOverdefined(&AI); + + // Solve for constants. + bool ResolvedUndefs = true; + while (ResolvedUndefs) { + Solver.Solve(); + LLVM_DEBUG(dbgs() << "RESOLVING UNDEFs\n"); + ResolvedUndefs = Solver.ResolvedUndefsIn(F); + } + + bool MadeChanges = false; + + // If we decided that there are basic blocks that are dead in this function, + // delete their contents now. Note that we cannot actually delete the blocks, + // as we cannot modify the CFG of the function. + + for (BasicBlock &BB : F) { + if (!Solver.isBlockExecutable(&BB)) { + LLVM_DEBUG(dbgs() << " BasicBlock Dead:" << BB); + + ++NumDeadBlocks; + NumInstRemoved += removeAllNonTerminatorAndEHPadInstructions(&BB); + + MadeChanges = true; + continue; + } + + // Iterate over all of the instructions in a function, replacing them with + // constants if we have found them to be of constant values. + for (BasicBlock::iterator BI = BB.begin(), E = BB.end(); BI != E;) { + Instruction *Inst = &*BI++; + if (Inst->getType()->isVoidTy() || Inst->isTerminator()) + continue; + + if (tryToReplaceWithConstant(Solver, Inst)) { + if (isInstructionTriviallyDead(Inst)) + Inst->eraseFromParent(); + // Hey, we just changed something! + MadeChanges = true; + ++NumInstRemoved; + } + } + } + + return MadeChanges; +} + +PreservedAnalyses SCCPPass::run(Function &F, FunctionAnalysisManager &AM) { + const DataLayout &DL = F.getParent()->getDataLayout(); + auto &TLI = AM.getResult<TargetLibraryAnalysis>(F); + if (!runSCCP(F, DL, &TLI)) + return PreservedAnalyses::all(); + + auto PA = PreservedAnalyses(); + PA.preserve<GlobalsAA>(); + PA.preserveSet<CFGAnalyses>(); + return PA; +} + +namespace { + +//===--------------------------------------------------------------------===// +// +/// SCCP Class - This class uses the SCCPSolver to implement a per-function +/// Sparse Conditional Constant Propagator. +/// +class SCCPLegacyPass : public FunctionPass { +public: + // Pass identification, replacement for typeid + static char ID; + + SCCPLegacyPass() : FunctionPass(ID) { + initializeSCCPLegacyPassPass(*PassRegistry::getPassRegistry()); + } + + void getAnalysisUsage(AnalysisUsage &AU) const override { + AU.addRequired<TargetLibraryInfoWrapperPass>(); + AU.addPreserved<GlobalsAAWrapperPass>(); + AU.setPreservesCFG(); + } + + // runOnFunction - Run the Sparse Conditional Constant Propagation + // algorithm, and return true if the function was modified. + bool runOnFunction(Function &F) override { + if (skipFunction(F)) + return false; + const DataLayout &DL = F.getParent()->getDataLayout(); + const TargetLibraryInfo *TLI = + &getAnalysis<TargetLibraryInfoWrapperPass>().getTLI(F); + return runSCCP(F, DL, TLI); + } +}; + +} // end anonymous namespace + +char SCCPLegacyPass::ID = 0; + +INITIALIZE_PASS_BEGIN(SCCPLegacyPass, "sccp", + "Sparse Conditional Constant Propagation", false, false) +INITIALIZE_PASS_DEPENDENCY(TargetLibraryInfoWrapperPass) +INITIALIZE_PASS_END(SCCPLegacyPass, "sccp", + "Sparse Conditional Constant Propagation", false, false) + +// createSCCPPass - This is the public interface to this file. +FunctionPass *llvm::createSCCPPass() { return new SCCPLegacyPass(); } + +static void findReturnsToZap(Function &F, + SmallVector<ReturnInst *, 8> &ReturnsToZap, + SCCPSolver &Solver) { + // We can only do this if we know that nothing else can call the function. + if (!Solver.isArgumentTrackedFunction(&F)) + return; + + // There is a non-removable musttail call site of this function. Zapping + // returns is not allowed. + if (Solver.isMustTailCallee(&F)) { + LLVM_DEBUG(dbgs() << "Can't zap returns of the function : " << F.getName() + << " due to present musttail call of it\n"); + return; + } + + assert( + all_of(F.users(), + [&Solver](User *U) { + if (isa<Instruction>(U) && + !Solver.isBlockExecutable(cast<Instruction>(U)->getParent())) + return true; + // Non-callsite uses are not impacted by zapping. Also, constant + // uses (like blockaddresses) could stuck around, without being + // used in the underlying IR, meaning we do not have lattice + // values for them. + if (!CallSite(U)) + return true; + if (U->getType()->isStructTy()) { + return all_of( + Solver.getStructLatticeValueFor(U), + [](const LatticeVal &LV) { return !LV.isOverdefined(); }); + } + return !Solver.getLatticeValueFor(U).isOverdefined(); + }) && + "We can only zap functions where all live users have a concrete value"); + + for (BasicBlock &BB : F) { + if (CallInst *CI = BB.getTerminatingMustTailCall()) { + LLVM_DEBUG(dbgs() << "Can't zap return of the block due to present " + << "musttail call : " << *CI << "\n"); + (void)CI; + return; + } + + if (auto *RI = dyn_cast<ReturnInst>(BB.getTerminator())) + if (!isa<UndefValue>(RI->getOperand(0))) + ReturnsToZap.push_back(RI); + } +} + +// Update the condition for terminators that are branching on indeterminate +// values, forcing them to use a specific edge. +static void forceIndeterminateEdge(Instruction* I, SCCPSolver &Solver) { + BasicBlock *Dest = nullptr; + Constant *C = nullptr; + if (SwitchInst *SI = dyn_cast<SwitchInst>(I)) { + if (!isa<ConstantInt>(SI->getCondition())) { + // Indeterminate switch; use first case value. + Dest = SI->case_begin()->getCaseSuccessor(); + C = SI->case_begin()->getCaseValue(); + } + } else if (BranchInst *BI = dyn_cast<BranchInst>(I)) { + if (!isa<ConstantInt>(BI->getCondition())) { + // Indeterminate branch; use false. + Dest = BI->getSuccessor(1); + C = ConstantInt::getFalse(BI->getContext()); + } + } else if (IndirectBrInst *IBR = dyn_cast<IndirectBrInst>(I)) { + if (!isa<BlockAddress>(IBR->getAddress()->stripPointerCasts())) { + // Indeterminate indirectbr; use successor 0. + Dest = IBR->getSuccessor(0); + C = BlockAddress::get(IBR->getSuccessor(0)); + } + } else { + llvm_unreachable("Unexpected terminator instruction"); + } + if (C) { + assert(Solver.isEdgeFeasible(I->getParent(), Dest) && + "Didn't find feasible edge?"); + (void)Dest; + + I->setOperand(0, C); + } +} + +bool llvm::runIPSCCP( + Module &M, const DataLayout &DL, + std::function<const TargetLibraryInfo &(Function &)> GetTLI, + function_ref<AnalysisResultsForFn(Function &)> getAnalysis) { + SCCPSolver Solver(DL, GetTLI); + + // Loop over all functions, marking arguments to those with their addresses + // taken or that are external as overdefined. + for (Function &F : M) { + if (F.isDeclaration()) + continue; + + Solver.addAnalysis(F, getAnalysis(F)); + + // Determine if we can track the function's return values. If so, add the + // function to the solver's set of return-tracked functions. + if (canTrackReturnsInterprocedurally(&F)) + Solver.AddTrackedFunction(&F); + + // Determine if we can track the function's arguments. If so, add the + // function to the solver's set of argument-tracked functions. + if (canTrackArgumentsInterprocedurally(&F)) { + Solver.AddArgumentTrackedFunction(&F); + continue; + } + + // Assume the function is called. + Solver.MarkBlockExecutable(&F.front()); + + // Assume nothing about the incoming arguments. + for (Argument &AI : F.args()) + Solver.markOverdefined(&AI); + } + + // Determine if we can track any of the module's global variables. If so, add + // the global variables we can track to the solver's set of tracked global + // variables. + for (GlobalVariable &G : M.globals()) { + G.removeDeadConstantUsers(); + if (canTrackGlobalVariableInterprocedurally(&G)) + Solver.TrackValueOfGlobalVariable(&G); + } + + // Solve for constants. + bool ResolvedUndefs = true; + Solver.Solve(); + while (ResolvedUndefs) { + LLVM_DEBUG(dbgs() << "RESOLVING UNDEFS\n"); + ResolvedUndefs = false; + for (Function &F : M) + if (Solver.ResolvedUndefsIn(F)) { + // We run Solve() after we resolved an undef in a function, because + // we might deduce a fact that eliminates an undef in another function. + Solver.Solve(); + ResolvedUndefs = true; + } + } + + bool MadeChanges = false; + + // Iterate over all of the instructions in the module, replacing them with + // constants if we have found them to be of constant values. + + for (Function &F : M) { + if (F.isDeclaration()) + continue; + + SmallVector<BasicBlock *, 512> BlocksToErase; + + if (Solver.isBlockExecutable(&F.front())) + for (Function::arg_iterator AI = F.arg_begin(), E = F.arg_end(); AI != E; + ++AI) { + if (!AI->use_empty() && tryToReplaceWithConstant(Solver, &*AI)) { + ++IPNumArgsElimed; + continue; + } + } + + for (Function::iterator BB = F.begin(), E = F.end(); BB != E; ++BB) { + if (!Solver.isBlockExecutable(&*BB)) { + LLVM_DEBUG(dbgs() << " BasicBlock Dead:" << *BB); + ++NumDeadBlocks; + + MadeChanges = true; + + if (&*BB != &F.front()) + BlocksToErase.push_back(&*BB); + continue; + } + + for (BasicBlock::iterator BI = BB->begin(), E = BB->end(); BI != E; ) { + Instruction *Inst = &*BI++; + if (Inst->getType()->isVoidTy()) + continue; + if (tryToReplaceWithConstant(Solver, Inst)) { + if (Inst->isSafeToRemove()) + Inst->eraseFromParent(); + // Hey, we just changed something! + MadeChanges = true; + ++IPNumInstRemoved; + } + } + } + + DomTreeUpdater DTU = Solver.getDTU(F); + // Change dead blocks to unreachable. We do it after replacing constants + // in all executable blocks, because changeToUnreachable may remove PHI + // nodes in executable blocks we found values for. The function's entry + // block is not part of BlocksToErase, so we have to handle it separately. + for (BasicBlock *BB : BlocksToErase) { + NumInstRemoved += + changeToUnreachable(BB->getFirstNonPHI(), /*UseLLVMTrap=*/false, + /*PreserveLCSSA=*/false, &DTU); + } + if (!Solver.isBlockExecutable(&F.front())) + NumInstRemoved += changeToUnreachable(F.front().getFirstNonPHI(), + /*UseLLVMTrap=*/false, + /*PreserveLCSSA=*/false, &DTU); + + // Now that all instructions in the function are constant folded, + // use ConstantFoldTerminator to get rid of in-edges, record DT updates and + // delete dead BBs. + for (BasicBlock *DeadBB : BlocksToErase) { + // If there are any PHI nodes in this successor, drop entries for BB now. + for (Value::user_iterator UI = DeadBB->user_begin(), + UE = DeadBB->user_end(); + UI != UE;) { + // Grab the user and then increment the iterator early, as the user + // will be deleted. Step past all adjacent uses from the same user. + auto *I = dyn_cast<Instruction>(*UI); + do { ++UI; } while (UI != UE && *UI == I); + + // Ignore blockaddress users; BasicBlock's dtor will handle them. + if (!I) continue; + + // If we have forced an edge for an indeterminate value, then force the + // terminator to fold to that edge. + forceIndeterminateEdge(I, Solver); + BasicBlock *InstBB = I->getParent(); + bool Folded = ConstantFoldTerminator(InstBB, + /*DeleteDeadConditions=*/false, + /*TLI=*/nullptr, &DTU); + assert(Folded && + "Expect TermInst on constantint or blockaddress to be folded"); + (void) Folded; + // If we folded the terminator to an unconditional branch to another + // dead block, replace it with Unreachable, to avoid trying to fold that + // branch again. + BranchInst *BI = cast<BranchInst>(InstBB->getTerminator()); + if (BI && BI->isUnconditional() && + !Solver.isBlockExecutable(BI->getSuccessor(0))) { + InstBB->getTerminator()->eraseFromParent(); + new UnreachableInst(InstBB->getContext(), InstBB); + } + } + // Mark dead BB for deletion. + DTU.deleteBB(DeadBB); + } + + for (BasicBlock &BB : F) { + for (BasicBlock::iterator BI = BB.begin(), E = BB.end(); BI != E;) { + Instruction *Inst = &*BI++; + if (Solver.getPredicateInfoFor(Inst)) { + if (auto *II = dyn_cast<IntrinsicInst>(Inst)) { + if (II->getIntrinsicID() == Intrinsic::ssa_copy) { + Value *Op = II->getOperand(0); + Inst->replaceAllUsesWith(Op); + Inst->eraseFromParent(); + } + } + } + } + } + } + + // If we inferred constant or undef return values for a function, we replaced + // all call uses with the inferred value. This means we don't need to bother + // actually returning anything from the function. Replace all return + // instructions with return undef. + // + // Do this in two stages: first identify the functions we should process, then + // actually zap their returns. This is important because we can only do this + // if the address of the function isn't taken. In cases where a return is the + // last use of a function, the order of processing functions would affect + // whether other functions are optimizable. + SmallVector<ReturnInst*, 8> ReturnsToZap; + + const MapVector<Function*, LatticeVal> &RV = Solver.getTrackedRetVals(); + for (const auto &I : RV) { + Function *F = I.first; + if (I.second.isOverdefined() || F->getReturnType()->isVoidTy()) + continue; + findReturnsToZap(*F, ReturnsToZap, Solver); + } + + for (const auto &F : Solver.getMRVFunctionsTracked()) { + assert(F->getReturnType()->isStructTy() && + "The return type should be a struct"); + StructType *STy = cast<StructType>(F->getReturnType()); + if (Solver.isStructLatticeConstant(F, STy)) + findReturnsToZap(*F, ReturnsToZap, Solver); + } + + // Zap all returns which we've identified as zap to change. + for (unsigned i = 0, e = ReturnsToZap.size(); i != e; ++i) { + Function *F = ReturnsToZap[i]->getParent()->getParent(); + ReturnsToZap[i]->setOperand(0, UndefValue::get(F->getReturnType())); + } + + // If we inferred constant or undef values for globals variables, we can + // delete the global and any stores that remain to it. + const DenseMap<GlobalVariable*, LatticeVal> &TG = Solver.getTrackedGlobals(); + for (DenseMap<GlobalVariable*, LatticeVal>::const_iterator I = TG.begin(), + E = TG.end(); I != E; ++I) { + GlobalVariable *GV = I->first; + assert(!I->second.isOverdefined() && + "Overdefined values should have been taken out of the map!"); + LLVM_DEBUG(dbgs() << "Found that GV '" << GV->getName() + << "' is constant!\n"); + while (!GV->use_empty()) { + StoreInst *SI = cast<StoreInst>(GV->user_back()); + SI->eraseFromParent(); + } + M.getGlobalList().erase(GV); + ++IPNumGlobalConst; + } + + return MadeChanges; +} |