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+//===- 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;
+ }
+}
generated by cgit v1.2.3 (git 2.25.1) at 2025-10-30 23:09:24 +0000