| //===- Evaluator.cpp - LLVM IR evaluator ----------------------------------===// |
| // |
| // 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 |
| // |
| //===----------------------------------------------------------------------===// |
| // |
| // Function evaluator for LLVM IR. |
| // |
| //===----------------------------------------------------------------------===// |
| |
| #include "llvm/Transforms/Utils/Evaluator.h" |
| #include "llvm/ADT/DenseMap.h" |
| #include "llvm/ADT/STLExtras.h" |
| #include "llvm/ADT/SmallPtrSet.h" |
| #include "llvm/ADT/SmallVector.h" |
| #include "llvm/Analysis/ConstantFolding.h" |
| #include "llvm/IR/BasicBlock.h" |
| #include "llvm/IR/CallSite.h" |
| #include "llvm/IR/Constant.h" |
| #include "llvm/IR/Constants.h" |
| #include "llvm/IR/DataLayout.h" |
| #include "llvm/IR/DerivedTypes.h" |
| #include "llvm/IR/Function.h" |
| #include "llvm/IR/GlobalAlias.h" |
| #include "llvm/IR/GlobalValue.h" |
| #include "llvm/IR/GlobalVariable.h" |
| #include "llvm/IR/InstrTypes.h" |
| #include "llvm/IR/Instruction.h" |
| #include "llvm/IR/Instructions.h" |
| #include "llvm/IR/IntrinsicInst.h" |
| #include "llvm/IR/Intrinsics.h" |
| #include "llvm/IR/Operator.h" |
| #include "llvm/IR/Type.h" |
| #include "llvm/IR/User.h" |
| #include "llvm/IR/Value.h" |
| #include "llvm/Support/Casting.h" |
| #include "llvm/Support/Debug.h" |
| #include "llvm/Support/raw_ostream.h" |
| #include <iterator> |
| |
| #define DEBUG_TYPE "evaluator" |
| |
| using namespace llvm; |
| |
| static inline bool |
| isSimpleEnoughValueToCommit(Constant *C, |
| SmallPtrSetImpl<Constant *> &SimpleConstants, |
| const DataLayout &DL); |
| |
| /// Return true if the specified constant can be handled by the code generator. |
| /// We don't want to generate something like: |
| /// void *X = &X/42; |
| /// because the code generator doesn't have a relocation that can handle that. |
| /// |
| /// This function should be called if C was not found (but just got inserted) |
| /// in SimpleConstants to avoid having to rescan the same constants all the |
| /// time. |
| static bool |
| isSimpleEnoughValueToCommitHelper(Constant *C, |
| SmallPtrSetImpl<Constant *> &SimpleConstants, |
| const DataLayout &DL) { |
| // Simple global addresses are supported, do not allow dllimport or |
| // thread-local globals. |
| if (auto *GV = dyn_cast<GlobalValue>(C)) |
| return !GV->hasDLLImportStorageClass() && !GV->isThreadLocal(); |
| |
| // Simple integer, undef, constant aggregate zero, etc are all supported. |
| if (C->getNumOperands() == 0 || isa<BlockAddress>(C)) |
| return true; |
| |
| // Aggregate values are safe if all their elements are. |
| if (isa<ConstantAggregate>(C)) { |
| for (Value *Op : C->operands()) |
| if (!isSimpleEnoughValueToCommit(cast<Constant>(Op), SimpleConstants, DL)) |
| return false; |
| return true; |
| } |
| |
| // We don't know exactly what relocations are allowed in constant expressions, |
| // so we allow &global+constantoffset, which is safe and uniformly supported |
| // across targets. |
| ConstantExpr *CE = cast<ConstantExpr>(C); |
| switch (CE->getOpcode()) { |
| case Instruction::BitCast: |
| // Bitcast is fine if the casted value is fine. |
| return isSimpleEnoughValueToCommit(CE->getOperand(0), SimpleConstants, DL); |
| |
| case Instruction::IntToPtr: |
| case Instruction::PtrToInt: |
| // int <=> ptr is fine if the int type is the same size as the |
| // pointer type. |
| if (DL.getTypeSizeInBits(CE->getType()) != |
| DL.getTypeSizeInBits(CE->getOperand(0)->getType())) |
| return false; |
| return isSimpleEnoughValueToCommit(CE->getOperand(0), SimpleConstants, DL); |
| |
| // GEP is fine if it is simple + constant offset. |
| case Instruction::GetElementPtr: |
| for (unsigned i = 1, e = CE->getNumOperands(); i != e; ++i) |
| if (!isa<ConstantInt>(CE->getOperand(i))) |
| return false; |
| return isSimpleEnoughValueToCommit(CE->getOperand(0), SimpleConstants, DL); |
| |
| case Instruction::Add: |
| // We allow simple+cst. |
| if (!isa<ConstantInt>(CE->getOperand(1))) |
| return false; |
| return isSimpleEnoughValueToCommit(CE->getOperand(0), SimpleConstants, DL); |
| } |
| return false; |
| } |
| |
| static inline bool |
| isSimpleEnoughValueToCommit(Constant *C, |
| SmallPtrSetImpl<Constant *> &SimpleConstants, |
| const DataLayout &DL) { |
| // If we already checked this constant, we win. |
| if (!SimpleConstants.insert(C).second) |
| return true; |
| // Check the constant. |
| return isSimpleEnoughValueToCommitHelper(C, SimpleConstants, DL); |
| } |
| |
| /// Return true if this constant is simple enough for us to understand. In |
| /// particular, if it is a cast to anything other than from one pointer type to |
| /// another pointer type, we punt. We basically just support direct accesses to |
| /// globals and GEP's of globals. This should be kept up to date with |
| /// CommitValueTo. |
| static bool isSimpleEnoughPointerToCommit(Constant *C) { |
| // Conservatively, avoid aggregate types. This is because we don't |
| // want to worry about them partially overlapping other stores. |
| if (!cast<PointerType>(C->getType())->getElementType()->isSingleValueType()) |
| return false; |
| |
| if (GlobalVariable *GV = dyn_cast<GlobalVariable>(C)) |
| // Do not allow weak/*_odr/linkonce linkage or external globals. |
| return GV->hasUniqueInitializer(); |
| |
| if (ConstantExpr *CE = dyn_cast<ConstantExpr>(C)) { |
| // Handle a constantexpr gep. |
| if (CE->getOpcode() == Instruction::GetElementPtr && |
| isa<GlobalVariable>(CE->getOperand(0)) && |
| cast<GEPOperator>(CE)->isInBounds()) { |
| GlobalVariable *GV = cast<GlobalVariable>(CE->getOperand(0)); |
| // Do not allow weak/*_odr/linkonce/dllimport/dllexport linkage or |
| // external globals. |
| if (!GV->hasUniqueInitializer()) |
| return false; |
| |
| // The first index must be zero. |
| ConstantInt *CI = dyn_cast<ConstantInt>(*std::next(CE->op_begin())); |
| if (!CI || !CI->isZero()) return false; |
| |
| // The remaining indices must be compile-time known integers within the |
| // notional bounds of the corresponding static array types. |
| if (!CE->isGEPWithNoNotionalOverIndexing()) |
| return false; |
| |
| return ConstantFoldLoadThroughGEPConstantExpr(GV->getInitializer(), CE); |
| |
| // A constantexpr bitcast from a pointer to another pointer is a no-op, |
| // and we know how to evaluate it by moving the bitcast from the pointer |
| // operand to the value operand. |
| } else if (CE->getOpcode() == Instruction::BitCast && |
| isa<GlobalVariable>(CE->getOperand(0))) { |
| // Do not allow weak/*_odr/linkonce/dllimport/dllexport linkage or |
| // external globals. |
| return cast<GlobalVariable>(CE->getOperand(0))->hasUniqueInitializer(); |
| } |
| } |
| |
| return false; |
| } |
| |
| /// Apply 'Func' to Ptr. If this returns nullptr, introspect the pointer's |
| /// type and walk down through the initial elements to obtain additional |
| /// pointers to try. Returns the first non-null return value from Func, or |
| /// nullptr if the type can't be introspected further. |
| static Constant * |
| evaluateBitcastFromPtr(Constant *Ptr, const DataLayout &DL, |
| const TargetLibraryInfo *TLI, |
| std::function<Constant *(Constant *)> Func) { |
| Constant *Val; |
| while (!(Val = Func(Ptr))) { |
| // If Ty is a struct, we can convert the pointer to the struct |
| // into a pointer to its first member. |
| // FIXME: This could be extended to support arrays as well. |
| Type *Ty = cast<PointerType>(Ptr->getType())->getElementType(); |
| if (!isa<StructType>(Ty)) |
| break; |
| |
| IntegerType *IdxTy = IntegerType::get(Ty->getContext(), 32); |
| Constant *IdxZero = ConstantInt::get(IdxTy, 0, false); |
| Constant *const IdxList[] = {IdxZero, IdxZero}; |
| |
| Ptr = ConstantExpr::getGetElementPtr(Ty, Ptr, IdxList); |
| if (auto *FoldedPtr = ConstantFoldConstant(Ptr, DL, TLI)) |
| Ptr = FoldedPtr; |
| } |
| return Val; |
| } |
| |
| static Constant *getInitializer(Constant *C) { |
| auto *GV = dyn_cast<GlobalVariable>(C); |
| return GV && GV->hasDefinitiveInitializer() ? GV->getInitializer() : nullptr; |
| } |
| |
| /// Return the value that would be computed by a load from P after the stores |
| /// reflected by 'memory' have been performed. If we can't decide, return null. |
| Constant *Evaluator::ComputeLoadResult(Constant *P) { |
| // If this memory location has been recently stored, use the stored value: it |
| // is the most up-to-date. |
| auto findMemLoc = [this](Constant *Ptr) { |
| DenseMap<Constant *, Constant *>::const_iterator I = |
| MutatedMemory.find(Ptr); |
| return I != MutatedMemory.end() ? I->second : nullptr; |
| }; |
| |
| if (Constant *Val = findMemLoc(P)) |
| return Val; |
| |
| // Access it. |
| if (GlobalVariable *GV = dyn_cast<GlobalVariable>(P)) { |
| if (GV->hasDefinitiveInitializer()) |
| return GV->getInitializer(); |
| return nullptr; |
| } |
| |
| if (ConstantExpr *CE = dyn_cast<ConstantExpr>(P)) { |
| switch (CE->getOpcode()) { |
| // Handle a constantexpr getelementptr. |
| case Instruction::GetElementPtr: |
| if (auto *I = getInitializer(CE->getOperand(0))) |
| return ConstantFoldLoadThroughGEPConstantExpr(I, CE); |
| break; |
| // Handle a constantexpr bitcast. |
| case Instruction::BitCast: |
| // We're evaluating a load through a pointer that was bitcast to a |
| // different type. See if the "from" pointer has recently been stored. |
| // If it hasn't, we may still be able to find a stored pointer by |
| // introspecting the type. |
| Constant *Val = |
| evaluateBitcastFromPtr(CE->getOperand(0), DL, TLI, findMemLoc); |
| if (!Val) |
| Val = getInitializer(CE->getOperand(0)); |
| if (Val) |
| return ConstantFoldLoadThroughBitcast( |
| Val, P->getType()->getPointerElementType(), DL); |
| break; |
| } |
| } |
| |
| return nullptr; // don't know how to evaluate. |
| } |
| |
| static Function *getFunction(Constant *C) { |
| if (auto *Fn = dyn_cast<Function>(C)) |
| return Fn; |
| |
| if (auto *Alias = dyn_cast<GlobalAlias>(C)) |
| if (auto *Fn = dyn_cast<Function>(Alias->getAliasee())) |
| return Fn; |
| return nullptr; |
| } |
| |
| Function * |
| Evaluator::getCalleeWithFormalArgs(CallSite &CS, |
| SmallVector<Constant *, 8> &Formals) { |
| auto *V = CS.getCalledValue(); |
| if (auto *Fn = getFunction(getVal(V))) |
| return getFormalParams(CS, Fn, Formals) ? Fn : nullptr; |
| |
| auto *CE = dyn_cast<ConstantExpr>(V); |
| if (!CE || CE->getOpcode() != Instruction::BitCast || |
| !getFormalParams(CS, getFunction(CE->getOperand(0)), Formals)) |
| return nullptr; |
| |
| return dyn_cast<Function>( |
| ConstantFoldLoadThroughBitcast(CE, CE->getOperand(0)->getType(), DL)); |
| } |
| |
| bool Evaluator::getFormalParams(CallSite &CS, Function *F, |
| SmallVector<Constant *, 8> &Formals) { |
| if (!F) |
| return false; |
| |
| auto *FTy = F->getFunctionType(); |
| if (FTy->getNumParams() > CS.getNumArgOperands()) { |
| LLVM_DEBUG(dbgs() << "Too few arguments for function.\n"); |
| return false; |
| } |
| |
| auto ArgI = CS.arg_begin(); |
| for (auto ParI = FTy->param_begin(), ParE = FTy->param_end(); ParI != ParE; |
| ++ParI) { |
| auto *ArgC = ConstantFoldLoadThroughBitcast(getVal(*ArgI), *ParI, DL); |
| if (!ArgC) { |
| LLVM_DEBUG(dbgs() << "Can not convert function argument.\n"); |
| return false; |
| } |
| Formals.push_back(ArgC); |
| ++ArgI; |
| } |
| return true; |
| } |
| |
| /// If call expression contains bitcast then we may need to cast |
| /// evaluated return value to a type of the call expression. |
| Constant *Evaluator::castCallResultIfNeeded(Value *CallExpr, Constant *RV) { |
| ConstantExpr *CE = dyn_cast<ConstantExpr>(CallExpr); |
| if (!RV || !CE || CE->getOpcode() != Instruction::BitCast) |
| return RV; |
| |
| if (auto *FT = |
| dyn_cast<FunctionType>(CE->getType()->getPointerElementType())) { |
| RV = ConstantFoldLoadThroughBitcast(RV, FT->getReturnType(), DL); |
| if (!RV) |
| LLVM_DEBUG(dbgs() << "Failed to fold bitcast call expr\n"); |
| } |
| return RV; |
| } |
| |
| /// Evaluate all instructions in block BB, returning true if successful, false |
| /// if we can't evaluate it. NewBB returns the next BB that control flows into, |
| /// or null upon return. |
| bool Evaluator::EvaluateBlock(BasicBlock::iterator CurInst, |
| BasicBlock *&NextBB) { |
| // This is the main evaluation loop. |
| while (true) { |
| Constant *InstResult = nullptr; |
| |
| LLVM_DEBUG(dbgs() << "Evaluating Instruction: " << *CurInst << "\n"); |
| |
| if (StoreInst *SI = dyn_cast<StoreInst>(CurInst)) { |
| if (!SI->isSimple()) { |
| LLVM_DEBUG(dbgs() << "Store is not simple! Can not evaluate.\n"); |
| return false; // no volatile/atomic accesses. |
| } |
| Constant *Ptr = getVal(SI->getOperand(1)); |
| if (auto *FoldedPtr = ConstantFoldConstant(Ptr, DL, TLI)) { |
| LLVM_DEBUG(dbgs() << "Folding constant ptr expression: " << *Ptr); |
| Ptr = FoldedPtr; |
| LLVM_DEBUG(dbgs() << "; To: " << *Ptr << "\n"); |
| } |
| if (!isSimpleEnoughPointerToCommit(Ptr)) { |
| // If this is too complex for us to commit, reject it. |
| LLVM_DEBUG( |
| dbgs() << "Pointer is too complex for us to evaluate store."); |
| return false; |
| } |
| |
| Constant *Val = getVal(SI->getOperand(0)); |
| |
| // If this might be too difficult for the backend to handle (e.g. the addr |
| // of one global variable divided by another) then we can't commit it. |
| if (!isSimpleEnoughValueToCommit(Val, SimpleConstants, DL)) { |
| LLVM_DEBUG(dbgs() << "Store value is too complex to evaluate store. " |
| << *Val << "\n"); |
| return false; |
| } |
| |
| if (ConstantExpr *CE = dyn_cast<ConstantExpr>(Ptr)) { |
| if (CE->getOpcode() == Instruction::BitCast) { |
| LLVM_DEBUG(dbgs() |
| << "Attempting to resolve bitcast on constant ptr.\n"); |
| // If we're evaluating a store through a bitcast, then we need |
| // to pull the bitcast off the pointer type and push it onto the |
| // stored value. In order to push the bitcast onto the stored value, |
| // a bitcast from the pointer's element type to Val's type must be |
| // legal. If it's not, we can try introspecting the type to find a |
| // legal conversion. |
| |
| auto castValTy = [&](Constant *P) -> Constant * { |
| Type *Ty = cast<PointerType>(P->getType())->getElementType(); |
| if (Constant *FV = ConstantFoldLoadThroughBitcast(Val, Ty, DL)) { |
| Ptr = P; |
| return FV; |
| } |
| return nullptr; |
| }; |
| |
| Constant *NewVal = |
| evaluateBitcastFromPtr(CE->getOperand(0), DL, TLI, castValTy); |
| if (!NewVal) { |
| LLVM_DEBUG(dbgs() << "Failed to bitcast constant ptr, can not " |
| "evaluate.\n"); |
| return false; |
| } |
| |
| Val = NewVal; |
| LLVM_DEBUG(dbgs() << "Evaluated bitcast: " << *Val << "\n"); |
| } |
| } |
| |
| MutatedMemory[Ptr] = Val; |
| } else if (BinaryOperator *BO = dyn_cast<BinaryOperator>(CurInst)) { |
| InstResult = ConstantExpr::get(BO->getOpcode(), |
| getVal(BO->getOperand(0)), |
| getVal(BO->getOperand(1))); |
| LLVM_DEBUG(dbgs() << "Found a BinaryOperator! Simplifying: " |
| << *InstResult << "\n"); |
| } else if (CmpInst *CI = dyn_cast<CmpInst>(CurInst)) { |
| InstResult = ConstantExpr::getCompare(CI->getPredicate(), |
| getVal(CI->getOperand(0)), |
| getVal(CI->getOperand(1))); |
| LLVM_DEBUG(dbgs() << "Found a CmpInst! Simplifying: " << *InstResult |
| << "\n"); |
| } else if (CastInst *CI = dyn_cast<CastInst>(CurInst)) { |
| InstResult = ConstantExpr::getCast(CI->getOpcode(), |
| getVal(CI->getOperand(0)), |
| CI->getType()); |
| LLVM_DEBUG(dbgs() << "Found a Cast! Simplifying: " << *InstResult |
| << "\n"); |
| } else if (SelectInst *SI = dyn_cast<SelectInst>(CurInst)) { |
| InstResult = ConstantExpr::getSelect(getVal(SI->getOperand(0)), |
| getVal(SI->getOperand(1)), |
| getVal(SI->getOperand(2))); |
| LLVM_DEBUG(dbgs() << "Found a Select! Simplifying: " << *InstResult |
| << "\n"); |
| } else if (auto *EVI = dyn_cast<ExtractValueInst>(CurInst)) { |
| InstResult = ConstantExpr::getExtractValue( |
| getVal(EVI->getAggregateOperand()), EVI->getIndices()); |
| LLVM_DEBUG(dbgs() << "Found an ExtractValueInst! Simplifying: " |
| << *InstResult << "\n"); |
| } else if (auto *IVI = dyn_cast<InsertValueInst>(CurInst)) { |
| InstResult = ConstantExpr::getInsertValue( |
| getVal(IVI->getAggregateOperand()), |
| getVal(IVI->getInsertedValueOperand()), IVI->getIndices()); |
| LLVM_DEBUG(dbgs() << "Found an InsertValueInst! Simplifying: " |
| << *InstResult << "\n"); |
| } else if (GetElementPtrInst *GEP = dyn_cast<GetElementPtrInst>(CurInst)) { |
| Constant *P = getVal(GEP->getOperand(0)); |
| SmallVector<Constant*, 8> GEPOps; |
| for (User::op_iterator i = GEP->op_begin() + 1, e = GEP->op_end(); |
| i != e; ++i) |
| GEPOps.push_back(getVal(*i)); |
| InstResult = |
| ConstantExpr::getGetElementPtr(GEP->getSourceElementType(), P, GEPOps, |
| cast<GEPOperator>(GEP)->isInBounds()); |
| LLVM_DEBUG(dbgs() << "Found a GEP! Simplifying: " << *InstResult << "\n"); |
| } else if (LoadInst *LI = dyn_cast<LoadInst>(CurInst)) { |
| if (!LI->isSimple()) { |
| LLVM_DEBUG( |
| dbgs() << "Found a Load! Not a simple load, can not evaluate.\n"); |
| return false; // no volatile/atomic accesses. |
| } |
| |
| Constant *Ptr = getVal(LI->getOperand(0)); |
| if (auto *FoldedPtr = ConstantFoldConstant(Ptr, DL, TLI)) { |
| Ptr = FoldedPtr; |
| LLVM_DEBUG(dbgs() << "Found a constant pointer expression, constant " |
| "folding: " |
| << *Ptr << "\n"); |
| } |
| InstResult = ComputeLoadResult(Ptr); |
| if (!InstResult) { |
| LLVM_DEBUG( |
| dbgs() << "Failed to compute load result. Can not evaluate load." |
| "\n"); |
| return false; // Could not evaluate load. |
| } |
| |
| LLVM_DEBUG(dbgs() << "Evaluated load: " << *InstResult << "\n"); |
| } else if (AllocaInst *AI = dyn_cast<AllocaInst>(CurInst)) { |
| if (AI->isArrayAllocation()) { |
| LLVM_DEBUG(dbgs() << "Found an array alloca. Can not evaluate.\n"); |
| return false; // Cannot handle array allocs. |
| } |
| Type *Ty = AI->getAllocatedType(); |
| AllocaTmps.push_back(std::make_unique<GlobalVariable>( |
| Ty, false, GlobalValue::InternalLinkage, UndefValue::get(Ty), |
| AI->getName(), /*TLMode=*/GlobalValue::NotThreadLocal, |
| AI->getType()->getPointerAddressSpace())); |
| InstResult = AllocaTmps.back().get(); |
| LLVM_DEBUG(dbgs() << "Found an alloca. Result: " << *InstResult << "\n"); |
| } else if (isa<CallInst>(CurInst) || isa<InvokeInst>(CurInst)) { |
| CallSite CS(&*CurInst); |
| |
| // Debug info can safely be ignored here. |
| if (isa<DbgInfoIntrinsic>(CS.getInstruction())) { |
| LLVM_DEBUG(dbgs() << "Ignoring debug info.\n"); |
| ++CurInst; |
| continue; |
| } |
| |
| // Cannot handle inline asm. |
| if (isa<InlineAsm>(CS.getCalledValue())) { |
| LLVM_DEBUG(dbgs() << "Found inline asm, can not evaluate.\n"); |
| return false; |
| } |
| |
| if (IntrinsicInst *II = dyn_cast<IntrinsicInst>(CS.getInstruction())) { |
| if (MemSetInst *MSI = dyn_cast<MemSetInst>(II)) { |
| if (MSI->isVolatile()) { |
| LLVM_DEBUG(dbgs() << "Can not optimize a volatile memset " |
| << "intrinsic.\n"); |
| return false; |
| } |
| Constant *Ptr = getVal(MSI->getDest()); |
| Constant *Val = getVal(MSI->getValue()); |
| Constant *DestVal = ComputeLoadResult(getVal(Ptr)); |
| if (Val->isNullValue() && DestVal && DestVal->isNullValue()) { |
| // This memset is a no-op. |
| LLVM_DEBUG(dbgs() << "Ignoring no-op memset.\n"); |
| ++CurInst; |
| continue; |
| } |
| } |
| |
| if (II->isLifetimeStartOrEnd()) { |
| LLVM_DEBUG(dbgs() << "Ignoring lifetime intrinsic.\n"); |
| ++CurInst; |
| continue; |
| } |
| |
| if (II->getIntrinsicID() == Intrinsic::invariant_start) { |
| // We don't insert an entry into Values, as it doesn't have a |
| // meaningful return value. |
| if (!II->use_empty()) { |
| LLVM_DEBUG(dbgs() |
| << "Found unused invariant_start. Can't evaluate.\n"); |
| return false; |
| } |
| ConstantInt *Size = cast<ConstantInt>(II->getArgOperand(0)); |
| Value *PtrArg = getVal(II->getArgOperand(1)); |
| Value *Ptr = PtrArg->stripPointerCasts(); |
| if (GlobalVariable *GV = dyn_cast<GlobalVariable>(Ptr)) { |
| Type *ElemTy = GV->getValueType(); |
| if (!Size->isMinusOne() && |
| Size->getValue().getLimitedValue() >= |
| DL.getTypeStoreSize(ElemTy)) { |
| Invariants.insert(GV); |
| LLVM_DEBUG(dbgs() << "Found a global var that is an invariant: " |
| << *GV << "\n"); |
| } else { |
| LLVM_DEBUG(dbgs() |
| << "Found a global var, but can not treat it as an " |
| "invariant.\n"); |
| } |
| } |
| // Continue even if we do nothing. |
| ++CurInst; |
| continue; |
| } else if (II->getIntrinsicID() == Intrinsic::assume) { |
| LLVM_DEBUG(dbgs() << "Skipping assume intrinsic.\n"); |
| ++CurInst; |
| continue; |
| } else if (II->getIntrinsicID() == Intrinsic::sideeffect) { |
| LLVM_DEBUG(dbgs() << "Skipping sideeffect intrinsic.\n"); |
| ++CurInst; |
| continue; |
| } |
| |
| LLVM_DEBUG(dbgs() << "Unknown intrinsic. Can not evaluate.\n"); |
| return false; |
| } |
| |
| // Resolve function pointers. |
| SmallVector<Constant *, 8> Formals; |
| Function *Callee = getCalleeWithFormalArgs(CS, Formals); |
| if (!Callee || Callee->isInterposable()) { |
| LLVM_DEBUG(dbgs() << "Can not resolve function pointer.\n"); |
| return false; // Cannot resolve. |
| } |
| |
| if (Callee->isDeclaration()) { |
| // If this is a function we can constant fold, do it. |
| if (Constant *C = ConstantFoldCall(cast<CallBase>(CS.getInstruction()), |
| Callee, Formals, TLI)) { |
| InstResult = castCallResultIfNeeded(CS.getCalledValue(), C); |
| if (!InstResult) |
| return false; |
| LLVM_DEBUG(dbgs() << "Constant folded function call. Result: " |
| << *InstResult << "\n"); |
| } else { |
| LLVM_DEBUG(dbgs() << "Can not constant fold function call.\n"); |
| return false; |
| } |
| } else { |
| if (Callee->getFunctionType()->isVarArg()) { |
| LLVM_DEBUG(dbgs() << "Can not constant fold vararg function call.\n"); |
| return false; |
| } |
| |
| Constant *RetVal = nullptr; |
| // Execute the call, if successful, use the return value. |
| ValueStack.emplace_back(); |
| if (!EvaluateFunction(Callee, RetVal, Formals)) { |
| LLVM_DEBUG(dbgs() << "Failed to evaluate function.\n"); |
| return false; |
| } |
| ValueStack.pop_back(); |
| InstResult = castCallResultIfNeeded(CS.getCalledValue(), RetVal); |
| if (RetVal && !InstResult) |
| return false; |
| |
| if (InstResult) { |
| LLVM_DEBUG(dbgs() << "Successfully evaluated function. Result: " |
| << *InstResult << "\n\n"); |
| } else { |
| LLVM_DEBUG(dbgs() |
| << "Successfully evaluated function. Result: 0\n\n"); |
| } |
| } |
| } else if (CurInst->isTerminator()) { |
| LLVM_DEBUG(dbgs() << "Found a terminator instruction.\n"); |
| |
| if (BranchInst *BI = dyn_cast<BranchInst>(CurInst)) { |
| if (BI->isUnconditional()) { |
| NextBB = BI->getSuccessor(0); |
| } else { |
| ConstantInt *Cond = |
| dyn_cast<ConstantInt>(getVal(BI->getCondition())); |
| if (!Cond) return false; // Cannot determine. |
| |
| NextBB = BI->getSuccessor(!Cond->getZExtValue()); |
| } |
| } else if (SwitchInst *SI = dyn_cast<SwitchInst>(CurInst)) { |
| ConstantInt *Val = |
| dyn_cast<ConstantInt>(getVal(SI->getCondition())); |
| if (!Val) return false; // Cannot determine. |
| NextBB = SI->findCaseValue(Val)->getCaseSuccessor(); |
| } else if (IndirectBrInst *IBI = dyn_cast<IndirectBrInst>(CurInst)) { |
| Value *Val = getVal(IBI->getAddress())->stripPointerCasts(); |
| if (BlockAddress *BA = dyn_cast<BlockAddress>(Val)) |
| NextBB = BA->getBasicBlock(); |
| else |
| return false; // Cannot determine. |
| } else if (isa<ReturnInst>(CurInst)) { |
| NextBB = nullptr; |
| } else { |
| // invoke, unwind, resume, unreachable. |
| LLVM_DEBUG(dbgs() << "Can not handle terminator."); |
| return false; // Cannot handle this terminator. |
| } |
| |
| // We succeeded at evaluating this block! |
| LLVM_DEBUG(dbgs() << "Successfully evaluated block.\n"); |
| return true; |
| } else { |
| // Did not know how to evaluate this! |
| LLVM_DEBUG( |
| dbgs() << "Failed to evaluate block due to unhandled instruction." |
| "\n"); |
| return false; |
| } |
| |
| if (!CurInst->use_empty()) { |
| if (auto *FoldedInstResult = ConstantFoldConstant(InstResult, DL, TLI)) |
| InstResult = FoldedInstResult; |
| |
| setVal(&*CurInst, InstResult); |
| } |
| |
| // If we just processed an invoke, we finished evaluating the block. |
| if (InvokeInst *II = dyn_cast<InvokeInst>(CurInst)) { |
| NextBB = II->getNormalDest(); |
| LLVM_DEBUG(dbgs() << "Found an invoke instruction. Finished Block.\n\n"); |
| return true; |
| } |
| |
| // Advance program counter. |
| ++CurInst; |
| } |
| } |
| |
| /// Evaluate a call to function F, returning true if successful, false if we |
| /// can't evaluate it. ActualArgs contains the formal arguments for the |
| /// function. |
| bool Evaluator::EvaluateFunction(Function *F, Constant *&RetVal, |
| const SmallVectorImpl<Constant*> &ActualArgs) { |
| // Check to see if this function is already executing (recursion). If so, |
| // bail out. TODO: we might want to accept limited recursion. |
| if (is_contained(CallStack, F)) |
| return false; |
| |
| CallStack.push_back(F); |
| |
| // Initialize arguments to the incoming values specified. |
| unsigned ArgNo = 0; |
| for (Function::arg_iterator AI = F->arg_begin(), E = F->arg_end(); AI != E; |
| ++AI, ++ArgNo) |
| setVal(&*AI, ActualArgs[ArgNo]); |
| |
| // ExecutedBlocks - We only handle non-looping, non-recursive code. As such, |
| // we can only evaluate any one basic block at most once. This set keeps |
| // track of what we have executed so we can detect recursive cases etc. |
| SmallPtrSet<BasicBlock*, 32> ExecutedBlocks; |
| |
| // CurBB - The current basic block we're evaluating. |
| BasicBlock *CurBB = &F->front(); |
| |
| BasicBlock::iterator CurInst = CurBB->begin(); |
| |
| while (true) { |
| BasicBlock *NextBB = nullptr; // Initialized to avoid compiler warnings. |
| LLVM_DEBUG(dbgs() << "Trying to evaluate BB: " << *CurBB << "\n"); |
| |
| if (!EvaluateBlock(CurInst, NextBB)) |
| return false; |
| |
| if (!NextBB) { |
| // Successfully running until there's no next block means that we found |
| // the return. Fill it the return value and pop the call stack. |
| ReturnInst *RI = cast<ReturnInst>(CurBB->getTerminator()); |
| if (RI->getNumOperands()) |
| RetVal = getVal(RI->getOperand(0)); |
| CallStack.pop_back(); |
| return true; |
| } |
| |
| // Okay, we succeeded in evaluating this control flow. See if we have |
| // executed the new block before. If so, we have a looping function, |
| // which we cannot evaluate in reasonable time. |
| if (!ExecutedBlocks.insert(NextBB).second) |
| return false; // looped! |
| |
| // Okay, we have never been in this block before. Check to see if there |
| // are any PHI nodes. If so, evaluate them with information about where |
| // we came from. |
| PHINode *PN = nullptr; |
| for (CurInst = NextBB->begin(); |
| (PN = dyn_cast<PHINode>(CurInst)); ++CurInst) |
| setVal(PN, getVal(PN->getIncomingValueForBlock(CurBB))); |
| |
| // Advance to the next block. |
| CurBB = NextBB; |
| } |
| } |
