| //===- 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/SetVector.h" |
| #include "llvm/ADT/SmallPtrSet.h" |
| #include "llvm/ADT/SmallVector.h" |
| #include "llvm/ADT/Statistic.h" |
| #include "llvm/Analysis/ConstantFolding.h" |
| #include "llvm/Analysis/DomTreeUpdater.h" |
| #include "llvm/Analysis/GlobalsModRef.h" |
| #include "llvm/Analysis/InstructionSimplify.h" |
| #include "llvm/Analysis/TargetLibraryInfo.h" |
| #include "llvm/Analysis/ValueLattice.h" |
| #include "llvm/Analysis/ValueLatticeUtils.h" |
| #include "llvm/Analysis/ValueTracking.h" |
| #include "llvm/IR/BasicBlock.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/InitializePasses.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/Local.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(NumInstReplaced, |
| "Number of instructions replaced with (simpler) instruction"); |
| |
| 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"); |
| STATISTIC( |
| IPNumInstReplaced, |
| "Number of instructions replaced with (simpler) instruction by IPSCCP"); |
| |
| // The maximum number of range extensions allowed for operations requiring |
| // widening. |
| static const unsigned MaxNumRangeExtensions = 10; |
| |
| /// Returns MergeOptions with MaxWidenSteps set to MaxNumRangeExtensions. |
| static ValueLatticeElement::MergeOptions getMaxWidenStepsOpts() { |
| return ValueLatticeElement::MergeOptions().setMaxWidenSteps( |
| MaxNumRangeExtensions); |
| } |
| namespace { |
| |
| // Helper to check if \p LV is either a constant or a constant |
| // range with a single element. This should cover exactly the same cases as the |
| // old ValueLatticeElement::isConstant() and is intended to be used in the |
| // transition to ValueLatticeElement. |
| bool isConstant(const ValueLatticeElement &LV) { |
| return LV.isConstant() || |
| (LV.isConstantRange() && LV.getConstantRange().isSingleElement()); |
| } |
| |
| // Helper to check if \p LV is either overdefined or a constant range with more |
| // than a single element. This should cover exactly the same cases as the old |
| // ValueLatticeElement::isOverdefined() and is intended to be used in the |
| // transition to ValueLatticeElement. |
| bool isOverdefined(const ValueLatticeElement &LV) { |
| return !LV.isUnknownOrUndef() && !isConstant(LV); |
| } |
| |
| //===----------------------------------------------------------------------===// |
| // |
| /// 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 *, ValueLatticeElement> |
| ValueState; // The state each value is in. |
| |
| /// StructValueState - This maintains ValueState for values that have |
| /// StructType, for example for formal arguments, calls, insertelement, etc. |
| DenseMap<std::pair<Value *, unsigned>, ValueLatticeElement> 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 *, ValueLatticeElement> 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 *, ValueLatticeElement> TrackedRetVals; |
| |
| /// TrackedMultipleRetVals - Same as TrackedRetVals, but used for functions |
| /// that return multiple values. |
| MapVector<std::pair<Function *, unsigned>, ValueLatticeElement> |
| TrackedMultipleRetVals; |
| |
| /// MRVFunctionsTracked - Each function in TrackedMultipleRetVals is |
| /// represented here for efficient lookup. |
| SmallPtrSet<Function *, 16> MRVFunctionsTracked; |
| |
| /// A list of functions whose return cannot be modified. |
| SmallPtrSet<Function *, 16> MustPreserveReturnsInFunctions; |
| |
| /// 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; |
| |
| LLVMContext &Ctx; |
| |
| 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, |
| LLVMContext &Ctx) |
| : DL(DL), GetTLI(std::move(GetTLI)), Ctx(Ctx) {} |
| |
| /// 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()) { |
| ValueLatticeElement &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), ValueLatticeElement())); |
| } else if (!F->getReturnType()->isVoidTy()) |
| TrackedRetVals.insert(std::make_pair(F, ValueLatticeElement())); |
| } |
| |
| /// Add function to the list of functions whose return cannot be modified. |
| void addToMustPreserveReturnsInFunctions(Function *F) { |
| MustPreserveReturnsInFunctions.insert(F); |
| } |
| |
| /// Returns true if the return of the given function cannot be modified. |
| bool mustPreserveReturn(Function *F) { |
| return MustPreserveReturnsInFunctions.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) const; |
| |
| std::vector<ValueLatticeElement> getStructLatticeValueFor(Value *V) const { |
| std::vector<ValueLatticeElement> 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; |
| } |
| |
| void removeLatticeValueFor(Value *V) { ValueState.erase(V); } |
| |
| const ValueLatticeElement &getLatticeValueFor(Value *V) const { |
| assert(!V->getType()->isStructTy() && |
| "Should use getStructLatticeValueFor"); |
| DenseMap<Value *, ValueLatticeElement>::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 *, ValueLatticeElement> &getTrackedRetVals() { |
| return TrackedRetVals; |
| } |
| |
| /// getTrackedGlobals - Get and return the set of inferred initializers for |
| /// global variables. |
| const DenseMap<GlobalVariable *, ValueLatticeElement> &getTrackedGlobals() { |
| return TrackedGlobals; |
| } |
| |
| /// getMRVFunctionsTracked - Get the set of functions which return multiple |
| /// values tracked by the pass. |
| const SmallPtrSet<Function *, 16> getMRVFunctionsTracked() { |
| return MRVFunctionsTracked; |
| } |
| |
| /// 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 constants, |
| // 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()); |
| ValueLatticeElement LV = It->second; |
| if (!isConstant(LV)) |
| return false; |
| } |
| return true; |
| } |
| |
| /// Helper to return a Constant if \p LV is either a constant or a constant |
| /// range with a single element. |
| Constant *getConstant(const ValueLatticeElement &LV) const { |
| if (LV.isConstant()) |
| return LV.getConstant(); |
| |
| if (LV.isConstantRange()) { |
| auto &CR = LV.getConstantRange(); |
| if (CR.getSingleElement()) |
| return ConstantInt::get(Ctx, *CR.getSingleElement()); |
| } |
| return nullptr; |
| } |
| |
| private: |
| ConstantInt *getConstantInt(const ValueLatticeElement &IV) const { |
| return dyn_cast_or_null<ConstantInt>(getConstant(IV)); |
| } |
| |
| // pushToWorkList - Helper for markConstant/markOverdefined |
| void pushToWorkList(ValueLatticeElement &IV, Value *V) { |
| if (IV.isOverdefined()) |
| return OverdefinedInstWorkList.push_back(V); |
| InstWorkList.push_back(V); |
| } |
| |
| // Helper to push \p V to the worklist, after updating it to \p IV. Also |
| // prints a debug message with the updated value. |
| void pushToWorkListMsg(ValueLatticeElement &IV, Value *V) { |
| LLVM_DEBUG(dbgs() << "updated " << IV << ": " << *V << '\n'); |
| pushToWorkList(IV, 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(ValueLatticeElement &IV, Value *V, Constant *C, |
| bool MayIncludeUndef = false) { |
| if (!IV.markConstant(C, MayIncludeUndef)) |
| 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); |
| } |
| |
| // 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(ValueLatticeElement &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; |
| } |
| |
| /// Merge \p MergeWithV into \p IV and push \p V to the worklist, if \p IV |
| /// changes. |
| bool mergeInValue(ValueLatticeElement &IV, Value *V, |
| ValueLatticeElement MergeWithV, |
| ValueLatticeElement::MergeOptions Opts = { |
| /*MayIncludeUndef=*/false, /*CheckWiden=*/false}) { |
| if (IV.mergeIn(MergeWithV, Opts)) { |
| pushToWorkList(IV, V); |
| LLVM_DEBUG(dbgs() << "Merged " << MergeWithV << " into " << *V << " : " |
| << IV << "\n"); |
| return true; |
| } |
| return false; |
| } |
| |
| bool mergeInValue(Value *V, ValueLatticeElement MergeWithV, |
| ValueLatticeElement::MergeOptions Opts = { |
| /*MayIncludeUndef=*/false, /*CheckWiden=*/false}) { |
| assert(!V->getType()->isStructTy() && |
| "non-structs should use markConstant"); |
| return mergeInValue(ValueState[V], V, MergeWithV, Opts); |
| } |
| |
| /// getValueState - Return the ValueLatticeElement object that corresponds to |
| /// the value. This function handles the case when the value hasn't been seen |
| /// yet by properly seeding constants etc. |
| ValueLatticeElement &getValueState(Value *V) { |
| assert(!V->getType()->isStructTy() && "Should use getStructValueState"); |
| |
| auto I = ValueState.insert(std::make_pair(V, ValueLatticeElement())); |
| ValueLatticeElement &LV = I.first->second; |
| |
| if (!I.second) |
| return LV; // Common case, already in the map. |
| |
| if (auto *C = dyn_cast<Constant>(V)) |
| LV.markConstant(C); // Constants are constant |
| |
| // All others are unknown by default. |
| return LV; |
| } |
| |
| /// getStructValueState - Return the ValueLatticeElement 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. |
| ValueLatticeElement &getStructValueState(Value *V, unsigned i) { |
| assert(V->getType()->isStructTy() && "Should use getValueState"); |
| assert(i < cast<StructType>(V->getType())->getNumElements() && |
| "Invalid element #"); |
| |
| auto I = StructValueState.insert( |
| std::make_pair(std::make_pair(V, i), ValueLatticeElement())); |
| ValueLatticeElement &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) { |
| // Functions include their arguments in the use-list. Changed function |
| // values mean that the result of the function changed. We only need to |
| // update the call sites with the new function result and do not have to |
| // propagate the call arguments. |
| if (isa<Function>(I)) { |
| for (User *U : I->users()) { |
| if (auto *CB = dyn_cast<CallBase>(U)) |
| handleCallResult(*CB); |
| } |
| } else { |
| 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); |
| } |
| } |
| void handleCallOverdefined(CallBase &CB); |
| void handleCallResult(CallBase &CB); |
| void handleCallArguments(CallBase &CB); |
| |
| 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) { |
| visitCallBase(I); |
| } |
| |
| void visitInvokeInst (InvokeInst &II) { |
| visitCallBase(II); |
| visitTerminator(II); |
| } |
| |
| void visitCallBrInst (CallBrInst &CBI) { |
| visitCallBase(CBI); |
| visitTerminator(CBI); |
| } |
| |
| void visitCallBase (CallBase &CB); |
| 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; |
| } |
| |
| ValueLatticeElement BCValue = getValueState(BI->getCondition()); |
| ConstantInt *CI = getConstantInt(BCValue); |
| if (!CI) { |
| // Overdefined condition variables, and branches on unfoldable constant |
| // conditions, mean the branch could go either way. |
| if (!BCValue.isUnknownOrUndef()) |
| 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; |
| } |
| const ValueLatticeElement &SCValue = getValueState(SI->getCondition()); |
| if (ConstantInt *CI = getConstantInt(SCValue)) { |
| Succs[SI->findCaseValue(CI)->getSuccessorIndex()] = true; |
| return; |
| } |
| |
| // TODO: Switch on undef is UB. Stop passing false once the rest of LLVM |
| // is ready. |
| if (SCValue.isConstantRange(/*UndefAllowed=*/false)) { |
| const ConstantRange &Range = SCValue.getConstantRange(); |
| for (const auto &Case : SI->cases()) { |
| const APInt &CaseValue = Case.getCaseValue()->getValue(); |
| if (Range.contains(CaseValue)) |
| Succs[Case.getSuccessorIndex()] = true; |
| } |
| |
| // TODO: Determine whether default case is reachable. |
| Succs[SI->case_default()->getSuccessorIndex()] = true; |
| return; |
| } |
| |
| // Overdefined or unknown condition? All destinations are executable! |
| if (!SCValue.isUnknownOrUndef()) |
| Succs.assign(TI.getNumSuccessors(), 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. |
| ValueLatticeElement IBRValue = getValueState(IBR->getAddress()); |
| BlockAddress *Addr = dyn_cast_or_null<BlockAddress>(getConstant(IBRValue)); |
| if (!Addr) { // Overdefined or unknown condition? |
| // All destinations are executable! |
| if (!IBRValue.isUnknownOrUndef()) |
| 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) const { |
| // 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); |
| |
| unsigned NumActiveIncoming = 0; |
| |
| // 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 a constant |
| // range. If there are no executable operands, the PHI remains unknown. |
| ValueLatticeElement PhiState = getValueState(&PN); |
| for (unsigned i = 0, e = PN.getNumIncomingValues(); i != e; ++i) { |
| if (!isEdgeFeasible(PN.getIncomingBlock(i), PN.getParent())) |
| continue; |
| |
| ValueLatticeElement IV = getValueState(PN.getIncomingValue(i)); |
| PhiState.mergeIn(IV); |
| NumActiveIncoming++; |
| if (PhiState.isOverdefined()) |
| break; |
| } |
| |
| // We allow up to 1 range extension per active incoming value and one |
| // additional extension. Note that we manually adjust the number of range |
| // extensions to match the number of active incoming values. This helps to |
| // limit multiple extensions caused by the same incoming value, if other |
| // incoming values are equal. |
| mergeInValue(&PN, PhiState, |
| ValueLatticeElement::MergeOptions().setMaxWidenSteps( |
| NumActiveIncoming + 1)); |
| ValueLatticeElement &PhiStateRef = getValueState(&PN); |
| PhiStateRef.setNumRangeExtensions( |
| std::max(NumActiveIncoming, PhiStateRef.getNumRangeExtensions())); |
| } |
| |
| 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()) { |
| auto 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) { |
| // ResolvedUndefsIn might mark I as overdefined. Bail out, even if we would |
| // discover a concrete value later. |
| if (ValueState[&I].isOverdefined()) |
| return; |
| |
| ValueLatticeElement OpSt = getValueState(I.getOperand(0)); |
| if (Constant *OpC = getConstant(OpSt)) { |
| // Fold the constant as we build. |
| Constant *C = ConstantFoldCastOperand(I.getOpcode(), OpC, I.getType(), DL); |
| if (isa<UndefValue>(C)) |
| return; |
| // Propagate constant value |
| markConstant(&I, C); |
| } else if (OpSt.isConstantRange() && I.getDestTy()->isIntegerTy()) { |
| auto &LV = getValueState(&I); |
| ConstantRange OpRange = OpSt.getConstantRange(); |
| Type *DestTy = I.getDestTy(); |
| // Vectors where all elements have the same known constant range are treated |
| // as a single constant range in the lattice. When bitcasting such vectors, |
| // there is a mis-match between the width of the lattice value (single |
| // constant range) and the original operands (vector). Go to overdefined in |
| // that case. |
| if (I.getOpcode() == Instruction::BitCast && |
| I.getOperand(0)->getType()->isVectorTy() && |
| OpRange.getBitWidth() < DL.getTypeSizeInBits(DestTy)) |
| return (void)markOverdefined(&I); |
| |
| ConstantRange Res = |
| OpRange.castOp(I.getOpcode(), DL.getTypeSizeInBits(DestTy)); |
| mergeInValue(LV, &I, ValueLatticeElement::getRange(Res)); |
| } else if (!OpSt.isUnknownOrUndef()) |
| markOverdefined(&I); |
| } |
| |
| 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); |
| |
| // ResolvedUndefsIn might mark I as overdefined. Bail out, even if we would |
| // discover a concrete value later. |
| if (ValueState[&EVI].isOverdefined()) |
| 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(); |
| ValueLatticeElement 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); |
| |
| // ResolvedUndefsIn might mark I as overdefined. Bail out, even if we would |
| // discover a concrete value later. |
| if (isOverdefined(ValueState[&IVI])) |
| 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) { |
| ValueLatticeElement 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 { |
| ValueLatticeElement 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); |
| |
| // ResolvedUndefsIn might mark I as overdefined. Bail out, even if we would |
| // discover a concrete value later. |
| if (ValueState[&I].isOverdefined()) |
| return (void)markOverdefined(&I); |
| |
| ValueLatticeElement CondValue = getValueState(I.getCondition()); |
| if (CondValue.isUnknownOrUndef()) |
| return; |
| |
| if (ConstantInt *CondCB = getConstantInt(CondValue)) { |
| 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. |
| ValueLatticeElement TVal = getValueState(I.getTrueValue()); |
| ValueLatticeElement FVal = getValueState(I.getFalseValue()); |
| |
| bool Changed = ValueState[&I].mergeIn(TVal); |
| Changed |= ValueState[&I].mergeIn(FVal); |
| if (Changed) |
| pushToWorkListMsg(ValueState[&I], &I); |
| } |
| |
| // Handle Unary Operators. |
| void SCCPSolver::visitUnaryOperator(Instruction &I) { |
| ValueLatticeElement V0State = getValueState(I.getOperand(0)); |
| |
| ValueLatticeElement &IV = ValueState[&I]; |
| // ResolvedUndefsIn might mark I as overdefined. Bail out, even if we would |
| // discover a concrete value later. |
| if (isOverdefined(IV)) |
| return (void)markOverdefined(&I); |
| |
| if (isConstant(V0State)) { |
| Constant *C = ConstantExpr::get(I.getOpcode(), getConstant(V0State)); |
| |
| // op Y -> undef. |
| if (isa<UndefValue>(C)) |
| return; |
| return (void)markConstant(IV, &I, C); |
| } |
| |
| // If something is undef, wait for it to resolve. |
| if (!isOverdefined(V0State)) |
| return; |
| |
| markOverdefined(&I); |
| } |
| |
| // Handle Binary Operators. |
| void SCCPSolver::visitBinaryOperator(Instruction &I) { |
| ValueLatticeElement V1State = getValueState(I.getOperand(0)); |
| ValueLatticeElement V2State = getValueState(I.getOperand(1)); |
| |
| ValueLatticeElement &IV = ValueState[&I]; |
| if (IV.isOverdefined()) |
| return; |
| |
| // If something is undef, wait for it to resolve. |
| if (V1State.isUnknownOrUndef() || V2State.isUnknownOrUndef()) |
| return; |
| |
| if (V1State.isOverdefined() && V2State.isOverdefined()) |
| return (void)markOverdefined(&I); |
| |
| // If either of the operands is a constant, try to fold it to a constant. |
| // TODO: Use information from notconstant better. |
| if ((V1State.isConstant() || V2State.isConstant())) { |
| Value *V1 = isConstant(V1State) ? getConstant(V1State) : I.getOperand(0); |
| Value *V2 = isConstant(V2State) ? getConstant(V2State) : I.getOperand(1); |
| Value *R = SimplifyBinOp(I.getOpcode(), V1, V2, SimplifyQuery(DL)); |
| auto *C = dyn_cast_or_null<Constant>(R); |
| if (C) { |
| // X op Y -> undef. |
| if (isa<UndefValue>(C)) |
| return; |
| // Conservatively assume that the result may be based on operands that may |
| // be undef. Note that we use mergeInValue to combine the constant with |
| // the existing lattice value for I, as different constants might be found |
| // after one of the operands go to overdefined, e.g. due to one operand |
| // being a special floating value. |
| ValueLatticeElement NewV; |
| NewV.markConstant(C, /*MayIncludeUndef=*/true); |
| return (void)mergeInValue(&I, NewV); |
| } |
| } |
| |
| // Only use ranges for binary operators on integers. |
| if (!I.getType()->isIntegerTy()) |
| return markOverdefined(&I); |
| |
| // Try to simplify to a constant range. |
| ConstantRange A = ConstantRange::getFull(I.getType()->getScalarSizeInBits()); |
| ConstantRange B = ConstantRange::getFull(I.getType()->getScalarSizeInBits()); |
| if (V1State.isConstantRange()) |
| A = V1State.getConstantRange(); |
| if (V2State.isConstantRange()) |
| B = V2State.getConstantRange(); |
| |
| ConstantRange R = A.binaryOp(cast<BinaryOperator>(&I)->getOpcode(), B); |
| mergeInValue(&I, ValueLatticeElement::getRange(R)); |
| |
| // TODO: Currently we do not exploit special values that produce something |
| // better than overdefined with an overdefined operand for vector or floating |
| // point types, like and <4 x i32> overdefined, zeroinitializer. |
| } |
| |
| // Handle ICmpInst instruction. |
| void SCCPSolver::visitCmpInst(CmpInst &I) { |
| // Do not cache this lookup, getValueState calls later in the function might |
| // invalidate the reference. |
| if (isOverdefined(ValueState[&I])) |
| return (void)markOverdefined(&I); |
| |
| Value *Op1 = I.getOperand(0); |
| Value *Op2 = I.getOperand(1); |
| |
| // For parameters, use ParamState which includes constant range info if |
| // available. |
| auto V1State = getValueState(Op1); |
| auto V2State = getValueState(Op2); |
| |
| Constant *C = V1State.getCompare(I.getPredicate(), I.getType(), V2State); |
| if (C) { |
| if (isa<UndefValue>(C)) |
| return; |
| ValueLatticeElement CV; |
| CV.markConstant(C); |
| mergeInValue(&I, CV); |
| return; |
| } |
| |
| // If operands are still unknown, wait for it to resolve. |
| if ((V1State.isUnknownOrUndef() || V2State.isUnknownOrUndef()) && |
| !isConstant(ValueState[&I])) |
| 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 (isOverdefined(ValueState[&I])) |
| return (void)markOverdefined(&I); |
| |
| SmallVector<Constant*, 8> Operands; |
| Operands.reserve(I.getNumOperands()); |
| |
| for (unsigned i = 0, e = I.getNumOperands(); i != e; ++i) { |
| ValueLatticeElement State = getValueState(I.getOperand(i)); |
| if (State.isUnknownOrUndef()) |
| return; // Operands are not resolved yet. |
| |
| if (isOverdefined(State)) |
| return (void)markOverdefined(&I); |
| |
| if (Constant *C = getConstant(State)) { |
| Operands.push_back(C); |
| continue; |
| } |
| |
| return (void)markOverdefined(&I); |
| } |
| |
| 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)); |
| auto I = TrackedGlobals.find(GV); |
| if (I == TrackedGlobals.end()) |
| return; |
| |
| // Get the value we are storing into the global, then merge it. |
| mergeInValue(I->second, GV, getValueState(SI.getOperand(0)), |
| ValueLatticeElement::MergeOptions().setCheckWiden(false)); |
| if (I->second.isOverdefined()) |
| TrackedGlobals.erase(I); // No need to keep tracking this! |
| } |
| |
| static ValueLatticeElement getValueFromMetadata(const Instruction *I) { |
| if (MDNode *Ranges = I->getMetadata(LLVMContext::MD_range)) |
| if (I->getType()->isIntegerTy()) |
| return ValueLatticeElement::getRange( |
| getConstantRangeFromMetadata(*Ranges)); |
| if (I->hasMetadata(LLVMContext::MD_nonnull)) |
| return ValueLatticeElement::getNot( |
| ConstantPointerNull::get(cast<PointerType>(I->getType()))); |
| return ValueLatticeElement::getOverdefined(); |
| } |
| |
| // 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 or the load is volatile, just mark the result |
| // as overdefined. |
| if (I.getType()->isStructTy() || I.isVolatile()) |
| return (void)markOverdefined(&I); |
| |
| // ResolvedUndefsIn might mark I as overdefined. Bail out, even if we would |
| // discover a concrete value later. |
| if (ValueState[&I].isOverdefined()) |
| return (void)markOverdefined(&I); |
| |
| ValueLatticeElement PtrVal = getValueState(I.getOperand(0)); |
| if (PtrVal.isUnknownOrUndef()) |
| return; // The pointer is not resolved yet! |
| |
| ValueLatticeElement &IV = ValueState[&I]; |
| |
| if (isConstant(PtrVal)) { |
| Constant *Ptr = getConstant(PtrVal); |
| |
| // 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. |
| auto It = TrackedGlobals.find(GV); |
| if (It != TrackedGlobals.end()) { |
| mergeInValue(IV, &I, It->second, getMaxWidenStepsOpts()); |
| 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); |
| } |
| } |
| |
| // Fall back to metadata. |
| mergeInValue(&I, getValueFromMetadata(&I)); |
| } |
| |
| void SCCPSolver::visitCallBase(CallBase &CB) { |
| handleCallResult(CB); |
| handleCallArguments(CB); |
| } |
| |
| void SCCPSolver::handleCallOverdefined(CallBase &CB) { |
| Function *F = CB.getCalledFunction(); |
| |
| // Void return and not tracking callee, just bail. |
| if (CB.getType()->isVoidTy()) |
| return; |
| |
| // Always mark struct return as overdefined. |
| if (CB.getType()->isStructTy()) |
| return (void)markOverdefined(&CB); |
| |
| // 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() && canConstantFoldCallTo(&CB, F)) { |
| SmallVector<Constant *, 8> Operands; |
| for (auto AI = CB.arg_begin(), E = CB.arg_end(); AI != E; ++AI) { |
| if (AI->get()->getType()->isStructTy()) |
| return markOverdefined(&CB); // Can't handle struct args. |
| ValueLatticeElement State = getValueState(*AI); |
| |
| if (State.isUnknownOrUndef()) |
| return; // Operands are not resolved yet. |
| if (isOverdefined(State)) |
| return (void)markOverdefined(&CB); |
| assert(isConstant(State) && "Unknown state!"); |
| Operands.push_back(getConstant(State)); |
| } |
| |
| if (isOverdefined(getValueState(&CB))) |
| return (void)markOverdefined(&CB); |
| |
| // If we can constant fold this, mark the result of the call as a |
| // constant. |
| if (Constant *C = ConstantFoldCall(&CB, F, Operands, &GetTLI(*F))) { |
| // call -> undef. |
| if (isa<UndefValue>(C)) |
| return; |
| return (void)markConstant(&CB, C); |
| } |
| } |
| |
| // Fall back to metadata. |
| mergeInValue(&CB, getValueFromMetadata(&CB)); |
| } |
| |
| void SCCPSolver::handleCallArguments(CallBase &CB) { |
| Function *F = CB.getCalledFunction(); |
| // 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. |
| auto CAI = CB.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) { |
| ValueLatticeElement CallArg = getStructValueState(*CAI, i); |
| mergeInValue(getStructValueState(&*AI, i), &*AI, CallArg, |
| getMaxWidenStepsOpts()); |
| } |
| } else |
| mergeInValue(&*AI, getValueState(*CAI), getMaxWidenStepsOpts()); |
| } |
| } |
| } |
| |
| void SCCPSolver::handleCallResult(CallBase &CB) { |
| Function *F = CB.getCalledFunction(); |
| |
| if (auto *II = dyn_cast<IntrinsicInst>(&CB)) { |
| if (II->getIntrinsicID() == Intrinsic::ssa_copy) { |
| if (ValueState[&CB].isOverdefined()) |
| return; |
| |
| Value *CopyOf = CB.getOperand(0); |
| ValueLatticeElement CopyOfVal = getValueState(CopyOf); |
| auto *PI = getPredicateInfoFor(&CB); |
| assert(PI && "Missing predicate info for ssa.copy"); |
| |
| const Optional<PredicateConstraint> &Constraint = PI->getConstraint(); |
| if (!Constraint) { |
| mergeInValue(ValueState[&CB], &CB, CopyOfVal); |
| return; |
| } |
| |
| CmpInst::Predicate Pred = Constraint->Predicate; |
| Value *OtherOp = Constraint->OtherOp; |
| |
| // Wait until OtherOp is resolved. |
| if (getValueState(OtherOp).isUnknown()) { |
| addAdditionalUser(OtherOp, &CB); |
| return; |
| } |
| |
| // TODO: Actually filp MayIncludeUndef for the created range to false, |
| // once most places in the optimizer respect the branches on |
| // undef/poison are UB rule. The reason why the new range cannot be |
| // undef is as follows below: |
| // The new range is based on a branch condition. That guarantees that |
| // neither of the compare operands can be undef in the branch targets, |
| // unless we have conditions that are always true/false (e.g. icmp ule |
| // i32, %a, i32_max). For the latter overdefined/empty range will be |
| // inferred, but the branch will get folded accordingly anyways. |
| bool MayIncludeUndef = !isa<PredicateAssume>(PI); |
| |
| ValueLatticeElement CondVal = getValueState(OtherOp); |
| ValueLatticeElement &IV = ValueState[&CB]; |
| if (CondVal.isConstantRange() || CopyOfVal.isConstantRange()) { |
| auto ImposedCR = |
| ConstantRange::getFull(DL.getTypeSizeInBits(CopyOf->getType())); |
| |
| // Get the range imposed by the condition. |
| if (CondVal.isConstantRange()) |
| ImposedCR = ConstantRange::makeAllowedICmpRegion( |
| Pred, CondVal.getConstantRange()); |
| |
| // Combine range info for the original value with the new range from the |
| // condition. |
| auto CopyOfCR = CopyOfVal.isConstantRange() |
| ? CopyOfVal.getConstantRange() |
| : ConstantRange::getFull( |
| DL.getTypeSizeInBits(CopyOf->getType())); |
| auto NewCR = ImposedCR.intersectWith(CopyOfCR); |
| // If the existing information is != x, do not use the information from |
| // a chained predicate, as the != x information is more likely to be |
| // helpful in practice. |
| if (!CopyOfCR.contains(NewCR) && CopyOfCR.getSingleMissingElement()) |
| NewCR = CopyOfCR; |
| |
| addAdditionalUser(OtherOp, &CB); |
| mergeInValue( |
| IV, &CB, |
| ValueLatticeElement::getRange(NewCR, MayIncludeUndef)); |
| return; |
| } else if (Pred == CmpInst::ICMP_EQ && CondVal.isConstant()) { |
| // For non-integer values or integer constant expressions, only |
| // propagate equal constants. |
| addAdditionalUser(OtherOp, &CB); |
| mergeInValue(IV, &CB, CondVal); |
| return; |
| } else if (Pred == CmpInst::ICMP_NE && CondVal.isConstant() && |
| !MayIncludeUndef) { |
| // Propagate inequalities. |
| addAdditionalUser(OtherOp, &CB); |
| mergeInValue(IV, &CB, |
| ValueLatticeElement::getNot(CondVal.getConstant())); |
| return; |
| } |
| |
| return (void)mergeInValue(IV, &CB, CopyOfVal); |
| } |
| |
| if (ConstantRange::isIntrinsicSupported(II->getIntrinsicID())) { |
| // Compute result range for intrinsics supported by ConstantRange. |
| // Do this even if we don't know a range for all operands, as we may |
| // still know something about the result range, e.g. of abs(x). |
| SmallVector<ConstantRange, 2> OpRanges; |
| for (Value *Op : II->args()) { |
| const ValueLatticeElement &State = getValueState(Op); |
| if (State.isConstantRange()) |
| OpRanges.push_back(State.getConstantRange()); |
| else |
| OpRanges.push_back( |
| ConstantRange::getFull(Op->getType()->getScalarSizeInBits())); |
| } |
| |
| ConstantRange Result = |
| ConstantRange::intrinsic(II->getIntrinsicID(), OpRanges); |
| return (void)mergeInValue(II, ValueLatticeElement::getRange(Result)); |
| } |
| } |
| |
| // 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()) |
| return handleCallOverdefined(CB); |
| |
| // 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)) |
| return handleCallOverdefined(CB); // 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(&CB, i), &CB, |
| TrackedMultipleRetVals[std::make_pair(F, i)], |
| getMaxWidenStepsOpts()); |
| } else { |
| auto TFRVI = TrackedRetVals.find(F); |
| if (TFRVI == TrackedRetVals.end()) |
| return handleCallOverdefined(CB); // Not tracking this callee. |
| |
| // If so, propagate the return value of the callee into this call result. |
| mergeInValue(&CB, TFRVI->second, getMaxWidenStepsOpts()); |
| } |
| } |
| |
| 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.pop_back_val(); |
| |
| 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. It conservatively marks |
| /// them as overdefined. |
| bool SCCPSolver::ResolvedUndefsIn(Function &F) { |
| bool MadeChange = false; |
| 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 (auto *CB = dyn_cast<CallBase>(&I)) |
| if (Function *F = CB->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) { |
| ValueLatticeElement &LV = getStructValueState(&I, i); |
| if (LV.isUnknownOrUndef()) { |
| markOverdefined(LV, &I); |
| MadeChange = true; |
| } |
| } |
| continue; |
| } |
| |
| ValueLatticeElement &LV = getValueState(&I); |
| if (!LV.isUnknownOrUndef()) |
| 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 (auto *CB = dyn_cast<CallBase>(&I)) |
| if (Function *F = CB->getCalledFunction()) |
| if (TrackedRetVals.count(F)) |
| continue; |
| |
| if (isa<LoadInst>(I)) { |
| // 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. |
| continue; |
| } |
| |
| markOverdefined(&I); |
| MadeChange = 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()).isUnknownOrUndef()) |
| 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)); |
| MadeChange = true; |
| continue; |
| } |
| |
| // 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)) |
| MadeChange = 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()).isUnknownOrUndef()) |
| 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)); |
| MadeChange = true; |
| continue; |
| } |
| |
| // 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)) |
| MadeChange = true; |
| |
| continue; |
| } |
| |
| if (auto *SI = dyn_cast<SwitchInst>(TI)) { |
| if (!SI->getNumCases() || |
| !getValueState(SI->getCondition()).isUnknownOrUndef()) |
| 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()); |
| MadeChange = true; |
| continue; |
| } |
| |
| // 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)) |
| MadeChange = true; |
| |
| continue; |
| } |
| } |
| |
| return MadeChange; |
| } |
| |
| static bool tryToReplaceWithConstant(SCCPSolver &Solver, Value *V) { |
| Constant *Const = nullptr; |
| if (V->getType()->isStructTy()) { |
| std::vector<ValueLatticeElement> IVs = Solver.getStructLatticeValueFor(V); |
| if (any_of(IVs, |
| [](const ValueLatticeElement &LV) { return isOverdefined(LV); })) |
| return false; |
| std::vector<Constant *> ConstVals; |
| auto *ST = cast<StructType>(V->getType()); |
| for (unsigned i = 0, e = ST->getNumElements(); i != e; ++i) { |
| ValueLatticeElement V = IVs[i]; |
| ConstVals.push_back(isConstant(V) |
| ? Solver.getConstant(V) |
| : UndefValue::get(ST->getElementType(i))); |
| } |
| Const = ConstantStruct::get(ST, ConstVals); |
| } else { |
| const ValueLatticeElement &IV = Solver.getLatticeValueFor(V); |
| if (isOverdefined(IV)) |
| return false; |
| |
| Const = |
| isConstant(IV) ? Solver.getConstant(IV) : 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. |
| // Calls with "clang.arc.attachedcall" implicitly use the return value and |
| // those uses cannot be updated with a constant. |
| CallBase *CB = dyn_cast<CallBase>(V); |
| if (CB && ((CB->isMustTailCall() && !CB->isSafeToRemove()) || |
| CB->getOperandBundle(LLVMContext::OB_clang_arc_attachedcall))) { |
| Function *F = CB->getCalledFunction(); |
| |
| // Don't zap returns of the callee |
| if (F) |
| Solver.addToMustPreserveReturnsInFunctions(F); |
| |
| LLVM_DEBUG(dbgs() << " Can\'t treat the result of call " << *CB |
| << " 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; |
| } |
| |
| static bool simplifyInstsInBlock(SCCPSolver &Solver, BasicBlock &BB, |
| SmallPtrSetImpl<Value *> &InsertedValues, |
| Statistic &InstRemovedStat, |
| Statistic &InstReplacedStat) { |
| bool MadeChanges = false; |
| for (Instruction &Inst : make_early_inc_range(BB)) { |
| if (Inst.getType()->isVoidTy()) |
| continue; |
| if (tryToReplaceWithConstant(Solver, &Inst)) { |
| if (Inst.isSafeToRemove()) |
| Inst.eraseFromParent(); |
| // Hey, we just changed something! |
| MadeChanges = true; |
| ++InstRemovedStat; |
| } else if (isa<SExtInst>(&Inst)) { |
| Value *ExtOp = Inst.getOperand(0); |
| if (isa<Constant>(ExtOp) || InsertedValues.count(ExtOp)) |
| continue; |
| const ValueLatticeElement &IV = Solver.getLatticeValueFor(ExtOp); |
| if (!IV.isConstantRange(/*UndefAllowed=*/false)) |
| continue; |
| if (IV.getConstantRange().isAllNonNegative()) { |
| auto *ZExt = new ZExtInst(ExtOp, Inst.getType(), "", &Inst); |
| InsertedValues.insert(ZExt); |
| Inst.replaceAllUsesWith(ZExt); |
| Solver.removeLatticeValueFor(&Inst); |
| Inst.eraseFromParent(); |
| InstReplacedStat++; |
| MadeChanges = true; |
| } |
| } |
| } |
| return MadeChanges; |
| } |
| |
| // 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; }, |
| F.getContext()); |
| |
| // 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. |
| |
| SmallPtrSet<Value *, 32> InsertedValues; |
| for (BasicBlock &BB : F) { |
| if (!Solver.isBlockExecutable(&BB)) { |
| LLVM_DEBUG(dbgs() << " BasicBlock Dead:" << BB); |
| |
| ++NumDeadBlocks; |
| NumInstRemoved += removeAllNonTerminatorAndEHPadInstructions(&BB).first; |
| |
| MadeChanges = true; |
| continue; |
| } |
| |
| MadeChanges |= simplifyInstsInBlock(Solver, BB, InsertedValues, |
| NumInstRemoved, NumInstReplaced); |
| } |
| |
| 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; |
| |
| if (Solver.mustPreserveReturn(&F)) { |
| LLVM_DEBUG( |
| dbgs() |
| << "Can't zap returns of the function : " << F.getName() |
| << " due to present musttail or \"clang.arc.attachedcall\" 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 (!isa<CallBase>(U)) |
| return true; |
| if (U->getType()->isStructTy()) { |
| return all_of(Solver.getStructLatticeValueFor(U), |
| [](const ValueLatticeElement &LV) { |
| return !isOverdefined(LV); |
| }); |
| } |
| return !isOverdefined(Solver.getLatticeValueFor(U)); |
| }) && |
| "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); |
| } |
| } |
| |
| static bool removeNonFeasibleEdges(const SCCPSolver &Solver, BasicBlock *BB, |
| DomTreeUpdater &DTU) { |
| SmallPtrSet<BasicBlock *, 8> FeasibleSuccessors; |
| bool HasNonFeasibleEdges = false; |
| for (BasicBlock *Succ : successors(BB)) { |
| if (Solver.isEdgeFeasible(BB, Succ)) |
| FeasibleSuccessors.insert(Succ); |
| else |
| HasNonFeasibleEdges = true; |
| } |
| |
| // All edges feasible, nothing to do. |
| if (!HasNonFeasibleEdges) |
| return false; |
| |
| // SCCP can only determine non-feasible edges for br, switch and indirectbr. |
| Instruction *TI = BB->getTerminator(); |
| assert((isa<BranchInst>(TI) || isa<SwitchInst>(TI) || |
| isa<IndirectBrInst>(TI)) && |
| "Terminator must be a br, switch or indirectbr"); |
| |
| if (FeasibleSuccessors.size() == 1) { |
| // Replace with an unconditional branch to the only feasible successor. |
| BasicBlock *OnlyFeasibleSuccessor = *FeasibleSuccessors.begin(); |
| SmallVector<DominatorTree::UpdateType, 8> Updates; |
| bool HaveSeenOnlyFeasibleSuccessor = false; |
| for (BasicBlock *Succ : successors(BB)) { |
| if (Succ == OnlyFeasibleSuccessor && !HaveSeenOnlyFeasibleSuccessor) { |
| // Don't remove the edge to the only feasible successor the first time |
| // we see it. We still do need to remove any multi-edges to it though. |
| HaveSeenOnlyFeasibleSuccessor = true; |
| continue; |
| } |
| |
| Succ->removePredecessor(BB); |
| Updates.push_back({DominatorTree::Delete, BB, Succ}); |
| } |
| |
| BranchInst::Create(OnlyFeasibleSuccessor, BB); |
| TI->eraseFromParent(); |
| DTU.applyUpdatesPermissive(Updates); |
| } else if (FeasibleSuccessors.size() > 1) { |
| SwitchInstProfUpdateWrapper SI(*cast<SwitchInst>(TI)); |
| SmallVector<DominatorTree::UpdateType, 8> Updates; |
| for (auto CI = SI->case_begin(); CI != SI->case_end();) { |
| if (FeasibleSuccessors.contains(CI->getCaseSuccessor())) { |
| ++CI; |
| continue; |
| } |
| |
| BasicBlock *Succ = CI->getCaseSuccessor(); |
| Succ->removePredecessor(BB); |
| Updates.push_back({DominatorTree::Delete, BB, Succ}); |
| SI.removeCase(CI); |
| // Don't increment CI, as we removed a case. |
| } |
| |
| DTU.applyUpdatesPermissive(Updates); |
| } else { |
| llvm_unreachable("Must have at least one feasible successor"); |
| } |
| return true; |
| } |
| |
| bool llvm::runIPSCCP( |
| Module &M, const DataLayout &DL, |
| std::function<const TargetLibraryInfo &(Function &)> GetTLI, |
| function_ref<AnalysisResultsForFn(Function &)> getAnalysis) { |
| SCCPSolver Solver(DL, GetTLI, M.getContext()); |
| |
| // 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)) |
| ResolvedUndefs = true; |
| } |
| if (ResolvedUndefs) |
| Solver.Solve(); |
| } |
| |
| 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())) { |
| bool ReplacedPointerArg = false; |
| for (Argument &Arg : F.args()) { |
| if (!Arg.use_empty() && tryToReplaceWithConstant(Solver, &Arg)) { |
| ReplacedPointerArg |= Arg.getType()->isPointerTy(); |
| ++IPNumArgsElimed; |
| } |
| } |
| |
| // If we replaced an argument, the argmemonly and |
| // inaccessiblemem_or_argmemonly attributes do not hold any longer. Remove |
| // them from both the function and callsites. |
| if (ReplacedPointerArg) { |
| AttrBuilder AttributesToRemove; |
| AttributesToRemove.addAttribute(Attribute::ArgMemOnly); |
| AttributesToRemove.addAttribute(Attribute::InaccessibleMemOrArgMemOnly); |
| F.removeAttributes(AttributeList::FunctionIndex, AttributesToRemove); |
| |
| for (User *U : F.users()) { |
| auto *CB = dyn_cast<CallBase>(U); |
| if (!CB || CB->getCalledFunction() != &F) |
| continue; |
| |
| CB->removeAttributes(AttributeList::FunctionIndex, |
| AttributesToRemove); |
| } |
| } |
| } |
| |
| SmallPtrSet<Value *, 32> InsertedValues; |
| for (BasicBlock &BB : F) { |
| if (!Solver.isBlockExecutable(&BB)) { |
| LLVM_DEBUG(dbgs() << " BasicBlock Dead:" << BB); |
| ++NumDeadBlocks; |
| |
| MadeChanges = true; |
| |
| if (&BB != &F.front()) |
| BlocksToErase.push_back(&BB); |
| continue; |
| } |
| |
| MadeChanges |= simplifyInstsInBlock(Solver, BB, InsertedValues, |
| IPNumInstRemoved, IPNumInstReplaced); |
| } |
| |
| 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); |
| |
| for (BasicBlock &BB : F) |
| MadeChanges |= removeNonFeasibleEdges(Solver, &BB, DTU); |
| |
| for (BasicBlock *DeadBB : BlocksToErase) |
| 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; |
| |
| for (const auto &I : Solver.getTrackedRetVals()) { |
| Function *F = I.first; |
| const ValueLatticeElement &ReturnValue = I.second; |
| |
| // If there is a known constant range for the return value, add !range |
| // metadata to the function's call sites. |
| if (ReturnValue.isConstantRange() && |
| !ReturnValue.getConstantRange().isSingleElement()) { |
| // Do not add range metadata if the return value may include undef. |
| if (ReturnValue.isConstantRangeIncludingUndef()) |
| continue; |
| |
| auto &CR = ReturnValue.getConstantRange(); |
| for (User *User : F->users()) { |
| auto *CB = dyn_cast<CallBase>(User); |
| if (!CB || CB->getCalledFunction() != F) |
| continue; |
| |
| // Limit to cases where the return value is guaranteed to be neither |
| // poison nor undef. Poison will be outside any range and currently |
| // values outside of the specified range cause immediate undefined |
| // behavior. |
| if (!isGuaranteedNotToBeUndefOrPoison(CB, nullptr, CB)) |
| continue; |
| |
| // Do not touch existing metadata for now. |
| // TODO: We should be able to take the intersection of the existing |
| // metadata and the inferred range. |
| if (CB->getMetadata(LLVMContext::MD_range)) |
| continue; |
| |
| LLVMContext &Context = CB->getParent()->getContext(); |
| Metadata *RangeMD[] = { |
| ConstantAsMetadata::get(ConstantInt::get(Context, CR.getLower())), |
| ConstantAsMetadata::get(ConstantInt::get(Context, CR.getUpper()))}; |
| CB->setMetadata(LLVMContext::MD_range, MDNode::get(Context, RangeMD)); |
| } |
| continue; |
| } |
| if (F->getReturnType()->isVoidTy()) |
| continue; |
| if (isConstant(ReturnValue) || ReturnValue.isUnknownOrUndef()) |
| findReturnsToZap(*F, ReturnsToZap, Solver); |
| } |
| |
| for (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. |
| SmallSetVector<Function *, 8> FuncZappedReturn; |
| for (unsigned i = 0, e = ReturnsToZap.size(); i != e; ++i) { |
| Function *F = ReturnsToZap[i]->getParent()->getParent(); |
| ReturnsToZap[i]->setOperand(0, UndefValue::get(F->getReturnType())); |
| // Record all functions that are zapped. |
| FuncZappedReturn.insert(F); |
| } |
| |
| // Remove the returned attribute for zapped functions and the |
| // corresponding call sites. |
| for (Function *F : FuncZappedReturn) { |
| for (Argument &A : F->args()) |
| F->removeParamAttr(A.getArgNo(), Attribute::Returned); |
| for (Use &U : F->uses()) { |
| // Skip over blockaddr users. |
| if (isa<BlockAddress>(U.getUser())) |
| continue; |
| CallBase *CB = cast<CallBase>(U.getUser()); |
| for (Use &Arg : CB->args()) |
| CB->removeParamAttr(CB->getArgOperandNo(&Arg), Attribute::Returned); |
| } |
| } |
| |
| // If we inferred constant or undef values for globals variables, we can |
| // delete the global and any stores that remain to it. |
| for (auto &I : make_early_inc_range(Solver.getTrackedGlobals())) { |
| GlobalVariable *GV = I.first; |
| if (isOverdefined(I.second)) |
| continue; |
| LLVM_DEBUG(dbgs() << "Found that GV '" << GV->getName() |
| << "' is constant!\n"); |
| while (!GV->use_empty()) { |
| StoreInst *SI = cast<StoreInst>(GV->user_back()); |
| SI->eraseFromParent(); |
| MadeChanges = true; |
| } |
| M.getGlobalList().erase(GV); |
| ++IPNumGlobalConst; |
| } |
| |
| return MadeChanges; |
| } |