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Diffstat (limited to 'llvm/lib/Transforms/Utils/SCCPSolver.cpp')
| -rw-r--r-- | llvm/lib/Transforms/Utils/SCCPSolver.cpp | 1713 |
1 files changed, 1713 insertions, 0 deletions
diff --git a/llvm/lib/Transforms/Utils/SCCPSolver.cpp b/llvm/lib/Transforms/Utils/SCCPSolver.cpp new file mode 100644 index 000000000000..4cf99abcc10f --- /dev/null +++ b/llvm/lib/Transforms/Utils/SCCPSolver.cpp @@ -0,0 +1,1713 @@ +//===- 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)) { + ValueState[J] = ValueState[I]; + pushToWorkList(ValueState[J], 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 (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 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 (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 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); } |