| //===- SCCPSolver.cpp - SCCP Utility --------------------------- *- C++ -*-===// |
| // |
| // 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 |
| // |
| //===----------------------------------------------------------------------===// |
| // |
| // \file |
| // This file implements the Sparse Conditional Constant Propagation (SCCP) |
| // utility. |
| // |
| //===----------------------------------------------------------------------===// |
| |
| #include "llvm/Transforms/Utils/SCCPSolver.h" |
| #include "llvm/Analysis/ConstantFolding.h" |
| #include "llvm/Analysis/InstructionSimplify.h" |
| #include "llvm/Analysis/ValueTracking.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/Utils/Local.h" |
| #include <cassert> |
| #include <utility> |
| #include <vector> |
| |
| using namespace llvm; |
| |
| #define DEBUG_TYPE "sccp" |
| |
| // 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); |
| } |
| |
| } // namespace |
| |
| namespace llvm { |
| |
| /// Helper class for SCCPSolver. This implements the instruction visitor and |
| /// holds all the state. |
| class SCCPInstVisitor : public InstVisitor<SCCPInstVisitor> { |
| 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; |
| |
| 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); |
| |
| // 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); |
| |
| // 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); |
| |
| 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); |
| |
| /// 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}); |
| |
| 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); |
| |
| // 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()) { |
| // Copy additional users before notifying them of changes, because new |
| // users may be added, potentially invalidating the iterator. |
| SmallVector<Instruction *, 2> ToNotify; |
| for (User *U : Iter->second) |
| if (auto *UI = dyn_cast<Instruction>(U)) |
| ToNotify.push_back(UI); |
| for (Instruction *UI : ToNotify) |
| operandChangedState(UI); |
| } |
| } |
| void handleCallOverdefined(CallBase &CB); |
| void handleCallResult(CallBase &CB); |
| void handleCallArguments(CallBase &CB); |
| |
| private: |
| friend class InstVisitor<SCCPInstVisitor>; |
| |
| // 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 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); |
| |
| public: |
| void addAnalysis(Function &F, AnalysisResultsForFn A) { |
| AnalysisResults.insert({&F, std::move(A)}); |
| } |
| |
| void visitCallInst(CallInst &I) { visitCallBase(I); } |
| |
| bool markBlockExecutable(BasicBlock *BB); |
| |
| 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}; |
| } |
| |
| SCCPInstVisitor(const DataLayout &DL, |
| std::function<const TargetLibraryInfo &(Function &)> GetTLI, |
| LLVMContext &Ctx) |
| : DL(DL), GetTLI(GetTLI), Ctx(Ctx) {} |
| |
| 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()); |
| } |
| } |
| |
| 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())); |
| } |
| |
| void addToMustPreserveReturnsInFunctions(Function *F) { |
| MustPreserveReturnsInFunctions.insert(F); |
| } |
| |
| bool mustPreserveReturn(Function *F) { |
| return MustPreserveReturnsInFunctions.count(F); |
| } |
| |
| void addArgumentTrackedFunction(Function *F) { |
| TrackingIncomingArguments.insert(F); |
| } |
| |
| bool isArgumentTrackedFunction(Function *F) { |
| return TrackingIncomingArguments.count(F); |
| } |
| |
| void solve(); |
| |
| bool resolvedUndefsIn(Function &F); |
| |
| bool isBlockExecutable(BasicBlock *BB) const { |
| return BBExecutable.count(BB); |
| } |
| |
| 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; |
| } |
| |
| const MapVector<Function *, ValueLatticeElement> &getTrackedRetVals() { |
| return TrackedRetVals; |
| } |
| |
| const DenseMap<GlobalVariable *, ValueLatticeElement> &getTrackedGlobals() { |
| return TrackedGlobals; |
| } |
| |
| const SmallPtrSet<Function *, 16> getMRVFunctionsTracked() { |
| return MRVFunctionsTracked; |
| } |
| |
| 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); |
| } |
| |
| bool isStructLatticeConstant(Function *F, StructType *STy); |
| |
| Constant *getConstant(const ValueLatticeElement &LV) const; |
| |
| SmallPtrSetImpl<Function *> &getArgumentTrackedFunctions() { |
| return TrackingIncomingArguments; |
| } |
| |
| void markArgInFuncSpecialization(Function *F, Argument *A, Constant *C); |
| |
| void markFunctionUnreachable(Function *F) { |
| for (auto &BB : *F) |
| BBExecutable.erase(&BB); |
| } |
| }; |
| |
| } // namespace llvm |
| |
| bool SCCPInstVisitor::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; |
| } |
| |
| void SCCPInstVisitor::pushToWorkList(ValueLatticeElement &IV, Value *V) { |
| if (IV.isOverdefined()) |
| return OverdefinedInstWorkList.push_back(V); |
| InstWorkList.push_back(V); |
| } |
| |
| void SCCPInstVisitor::pushToWorkListMsg(ValueLatticeElement &IV, Value *V) { |
| LLVM_DEBUG(dbgs() << "updated " << IV << ": " << *V << '\n'); |
| pushToWorkList(IV, V); |
| } |
| |
| bool SCCPInstVisitor::markConstant(ValueLatticeElement &IV, Value *V, |
| Constant *C, bool MayIncludeUndef) { |
| if (!IV.markConstant(C, MayIncludeUndef)) |
| return false; |
| LLVM_DEBUG(dbgs() << "markConstant: " << *C << ": " << *V << '\n'); |
| pushToWorkList(IV, V); |
| return true; |
| } |
| |
| bool SCCPInstVisitor::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; |
| } |
| |
| bool SCCPInstVisitor::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; |
| } |
| |
| Constant *SCCPInstVisitor::getConstant(const ValueLatticeElement &LV) const { |
| if (LV.isConstant()) |
| return LV.getConstant(); |
| |
| if (LV.isConstantRange()) { |
| const auto &CR = LV.getConstantRange(); |
| if (CR.getSingleElement()) |
| return ConstantInt::get(Ctx, *CR.getSingleElement()); |
| } |
| return nullptr; |
| } |
| |
| void SCCPInstVisitor::markArgInFuncSpecialization(Function *F, Argument *A, |
| Constant *C) { |
| assert(F->arg_size() == A->getParent()->arg_size() && |
| "Functions should have the same number of arguments"); |
| |
| // Mark the argument constant in the new function. |
| markConstant(A, C); |
| |
| // For the remaining arguments in the new function, copy the lattice state |
| // over from the old function. |
| for (auto I = F->arg_begin(), J = A->getParent()->arg_begin(), |
| E = F->arg_end(); |
| I != E; ++I, ++J) |
| if (J != A && ValueState.count(I)) { |
| // Note: This previously looked like this: |
| // ValueState[J] = ValueState[I]; |
| // This is incorrect because the DenseMap class may resize the underlying |
| // memory when inserting `J`, which will invalidate the reference to `I`. |
| // Instead, we make sure `J` exists, then set it to `I` afterwards. |
| auto &NewValue = ValueState[J]; |
| NewValue = ValueState[I]; |
| pushToWorkList(NewValue, J); |
| } |
| } |
| |
| void SCCPInstVisitor::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); |
| } |
| |
| bool SCCPInstVisitor::mergeInValue(ValueLatticeElement &IV, Value *V, |
| ValueLatticeElement MergeWithV, |
| ValueLatticeElement::MergeOptions Opts) { |
| if (IV.mergeIn(MergeWithV, Opts)) { |
| pushToWorkList(IV, V); |
| LLVM_DEBUG(dbgs() << "Merged " << MergeWithV << " into " << *V << " : " |
| << IV << "\n"); |
| return true; |
| } |
| return false; |
| } |
| |
| bool SCCPInstVisitor::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 SCCPInstVisitor::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 SCCPInstVisitor::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 SCCPInstVisitor::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 SCCPInstVisitor::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 SCCPInstVisitor::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 SCCPInstVisitor::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 (OpSt.isUnknownOrUndef()) |
| return; |
| |
| 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 (I.getDestTy()->isIntegerTy()) { |
| auto &LV = getValueState(&I); |
| ConstantRange OpRange = |
| OpSt.isConstantRange() |
| ? OpSt.getConstantRange() |
| : ConstantRange::getFull( |
| I.getOperand(0)->getType()->getScalarSizeInBits()); |
| |
| 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 |
| markOverdefined(&I); |
| } |
| |
| void SCCPInstVisitor::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 SCCPInstVisitor::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 SCCPInstVisitor::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 SCCPInstVisitor::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 SCCPInstVisitor::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 SCCPInstVisitor::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 SCCPInstVisitor::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 SCCPInstVisitor::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 SCCPInstVisitor::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 SCCPInstVisitor::visitCallBase(CallBase &CB) { |
| handleCallResult(CB); |
| handleCallArguments(CB); |
| } |
| |
| void SCCPInstVisitor::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 (const Use &A : CB.args()) { |
| if (A.get()->getType()->isStructTy()) |
| return markOverdefined(&CB); // Can't handle struct args. |
| ValueLatticeElement State = getValueState(A); |
| |
| 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 SCCPInstVisitor::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 SCCPInstVisitor::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); |
| const 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 SCCPInstVisitor::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 SCCPInstVisitor::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; |
| } |
| |
| //===----------------------------------------------------------------------===// |
| // |
| // SCCPSolver implementations |
| // |
| SCCPSolver::SCCPSolver( |
| const DataLayout &DL, |
| std::function<const TargetLibraryInfo &(Function &)> GetTLI, |
| LLVMContext &Ctx) |
| : Visitor(new SCCPInstVisitor(DL, std::move(GetTLI), Ctx)) {} |
| |
| SCCPSolver::~SCCPSolver() {} |
| |
| void SCCPSolver::addAnalysis(Function &F, AnalysisResultsForFn A) { |
| return Visitor->addAnalysis(F, std::move(A)); |
| } |
| |
| bool SCCPSolver::markBlockExecutable(BasicBlock *BB) { |
| return Visitor->markBlockExecutable(BB); |
| } |
| |
| const PredicateBase *SCCPSolver::getPredicateInfoFor(Instruction *I) { |
| return Visitor->getPredicateInfoFor(I); |
| } |
| |
| DomTreeUpdater SCCPSolver::getDTU(Function &F) { return Visitor->getDTU(F); } |
| |
| void SCCPSolver::trackValueOfGlobalVariable(GlobalVariable *GV) { |
| Visitor->trackValueOfGlobalVariable(GV); |
| } |
| |
| void SCCPSolver::addTrackedFunction(Function *F) { |
| Visitor->addTrackedFunction(F); |
| } |
| |
| void SCCPSolver::addToMustPreserveReturnsInFunctions(Function *F) { |
| Visitor->addToMustPreserveReturnsInFunctions(F); |
| } |
| |
| bool SCCPSolver::mustPreserveReturn(Function *F) { |
| return Visitor->mustPreserveReturn(F); |
| } |
| |
| void SCCPSolver::addArgumentTrackedFunction(Function *F) { |
| Visitor->addArgumentTrackedFunction(F); |
| } |
| |
| bool SCCPSolver::isArgumentTrackedFunction(Function *F) { |
| return Visitor->isArgumentTrackedFunction(F); |
| } |
| |
| void SCCPSolver::solve() { Visitor->solve(); } |
| |
| bool SCCPSolver::resolvedUndefsIn(Function &F) { |
| return Visitor->resolvedUndefsIn(F); |
| } |
| |
| bool SCCPSolver::isBlockExecutable(BasicBlock *BB) const { |
| return Visitor->isBlockExecutable(BB); |
| } |
| |
| bool SCCPSolver::isEdgeFeasible(BasicBlock *From, BasicBlock *To) const { |
| return Visitor->isEdgeFeasible(From, To); |
| } |
| |
| std::vector<ValueLatticeElement> |
| SCCPSolver::getStructLatticeValueFor(Value *V) const { |
| return Visitor->getStructLatticeValueFor(V); |
| } |
| |
| void SCCPSolver::removeLatticeValueFor(Value *V) { |
| return Visitor->removeLatticeValueFor(V); |
| } |
| |
| const ValueLatticeElement &SCCPSolver::getLatticeValueFor(Value *V) const { |
| return Visitor->getLatticeValueFor(V); |
| } |
| |
| const MapVector<Function *, ValueLatticeElement> & |
| SCCPSolver::getTrackedRetVals() { |
| return Visitor->getTrackedRetVals(); |
| } |
| |
| const DenseMap<GlobalVariable *, ValueLatticeElement> & |
| SCCPSolver::getTrackedGlobals() { |
| return Visitor->getTrackedGlobals(); |
| } |
| |
| const SmallPtrSet<Function *, 16> SCCPSolver::getMRVFunctionsTracked() { |
| return Visitor->getMRVFunctionsTracked(); |
| } |
| |
| void SCCPSolver::markOverdefined(Value *V) { Visitor->markOverdefined(V); } |
| |
| bool SCCPSolver::isStructLatticeConstant(Function *F, StructType *STy) { |
| return Visitor->isStructLatticeConstant(F, STy); |
| } |
| |
| Constant *SCCPSolver::getConstant(const ValueLatticeElement &LV) const { |
| return Visitor->getConstant(LV); |
| } |
| |
| SmallPtrSetImpl<Function *> &SCCPSolver::getArgumentTrackedFunctions() { |
| return Visitor->getArgumentTrackedFunctions(); |
| } |
| |
| void SCCPSolver::markArgInFuncSpecialization(Function *F, Argument *A, |
| Constant *C) { |
| Visitor->markArgInFuncSpecialization(F, A, C); |
| } |
| |
| void SCCPSolver::markFunctionUnreachable(Function *F) { |
| Visitor->markFunctionUnreachable(F); |
| } |
| |
| void SCCPSolver::visit(Instruction *I) { Visitor->visit(I); } |
| |
| void SCCPSolver::visitCall(CallInst &I) { Visitor->visitCall(I); } |