--- /dev/null
+//===-- Evaluator.h - LLVM IR evaluator -------------------------*- C++ -*-===//
+//
+// The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+//
+// Function evaluator for LLVM IR.
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef LLVM_TRANSFORMS_UTILS_EVALUATOR_H
+#define LLVM_TRANSFORMS_UTILS_EVALUATOR_H
+
+#include "llvm/ADT/DenseMap.h"
+#include "llvm/ADT/SmallPtrSet.h"
+#include "llvm/ADT/SmallVector.h"
+#include "llvm/IR/BasicBlock.h"
+#include "llvm/IR/Constant.h"
+#include "llvm/IR/GlobalVariable.h"
+
+#include <deque>
+#include <memory>
+
+namespace llvm {
+
+class DataLayout;
+class Function;
+class TargetLibraryInfo;
+
+/// This class evaluates LLVM IR, producing the Constant representing each SSA
+/// instruction. Changes to global variables are stored in a mapping that can
+/// be iterated over after the evaluation is complete. Once an evaluation call
+/// fails, the evaluation object should not be reused.
+class Evaluator {
+public:
+ Evaluator(const DataLayout &DL, const TargetLibraryInfo *TLI)
+ : DL(DL), TLI(TLI) {
+ ValueStack.emplace_back();
+ }
+
+ ~Evaluator() {
+ for (auto &Tmp : AllocaTmps)
+ // If there are still users of the alloca, the program is doing something
+ // silly, e.g. storing the address of the alloca somewhere and using it
+ // later. Since this is undefined, we'll just make it be null.
+ if (!Tmp->use_empty())
+ Tmp->replaceAllUsesWith(Constant::getNullValue(Tmp->getType()));
+ }
+
+ /// 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 EvaluateFunction(Function *F, Constant *&RetVal,
+ const SmallVectorImpl<Constant*> &ActualArgs);
+
+ /// 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 EvaluateBlock(BasicBlock::iterator CurInst, BasicBlock *&NextBB);
+
+ Constant *getVal(Value *V) {
+ if (Constant *CV = dyn_cast<Constant>(V)) return CV;
+ Constant *R = ValueStack.back().lookup(V);
+ assert(R && "Reference to an uncomputed value!");
+ return R;
+ }
+
+ void setVal(Value *V, Constant *C) {
+ ValueStack.back()[V] = C;
+ }
+
+ const DenseMap<Constant*, Constant*> &getMutatedMemory() const {
+ return MutatedMemory;
+ }
+
+ const SmallPtrSetImpl<GlobalVariable*> &getInvariants() const {
+ return Invariants;
+ }
+
+private:
+ Constant *ComputeLoadResult(Constant *P);
+
+ /// As we compute SSA register values, we store their contents here. The back
+ /// of the deque contains the current function and the stack contains the
+ /// values in the calling frames.
+ std::deque<DenseMap<Value*, Constant*>> ValueStack;
+
+ /// This is used to detect recursion. In pathological situations we could hit
+ /// exponential behavior, but at least there is nothing unbounded.
+ SmallVector<Function*, 4> CallStack;
+
+ /// For each store we execute, we update this map. Loads check this to get
+ /// the most up-to-date value. If evaluation is successful, this state is
+ /// committed to the process.
+ DenseMap<Constant*, Constant*> MutatedMemory;
+
+ /// To 'execute' an alloca, we create a temporary global variable to represent
+ /// its body. This vector is needed so we can delete the temporary globals
+ /// when we are done.
+ SmallVector<std::unique_ptr<GlobalVariable>, 32> AllocaTmps;
+
+ /// These global variables have been marked invariant by the static
+ /// constructor.
+ SmallPtrSet<GlobalVariable*, 8> Invariants;
+
+ /// These are constants we have checked and know to be simple enough to live
+ /// in a static initializer of a global.
+ SmallPtrSet<Constant*, 8> SimpleConstants;
+
+ const DataLayout &DL;
+ const TargetLibraryInfo *TLI;
+};
+
+}
+
+#endif
#include "llvm/Support/MathExtras.h"
#include "llvm/Support/raw_ostream.h"
#include "llvm/Transforms/Utils/CtorUtils.h"
+#include "llvm/Transforms/Utils/Evaluator.h"
#include "llvm/Transforms/Utils/GlobalStatus.h"
#include "llvm/Transforms/Utils/ModuleUtils.h"
#include <algorithm>
return Changed;
}
-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<ConstantArray>(C) || isa<ConstantStruct>(C) ||
- isa<ConstantVector>(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;
-}
-
/// Evaluate a piece of a constantexpr store into a global initializer. This
/// returns 'Init' modified to reflect 'Val' stored into it. At this point, the
/// GEP operands of Addr [0, OpNo) have been stepped into.
GV->setInitializer(EvaluateStoreInto(GV->getInitializer(), Val, CE, 2));
}
-namespace {
-
-/// This class evaluates LLVM IR, producing the Constant representing each SSA
-/// instruction. Changes to global variables are stored in a mapping that can
-/// be iterated over after the evaluation is complete. Once an evaluation call
-/// fails, the evaluation object should not be reused.
-class Evaluator {
-public:
- Evaluator(const DataLayout &DL, const TargetLibraryInfo *TLI)
- : DL(DL), TLI(TLI) {
- ValueStack.emplace_back();
- }
-
- ~Evaluator() {
- for (auto &Tmp : AllocaTmps)
- // If there are still users of the alloca, the program is doing something
- // silly, e.g. storing the address of the alloca somewhere and using it
- // later. Since this is undefined, we'll just make it be null.
- if (!Tmp->use_empty())
- Tmp->replaceAllUsesWith(Constant::getNullValue(Tmp->getType()));
- }
-
- /// 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 EvaluateFunction(Function *F, Constant *&RetVal,
- const SmallVectorImpl<Constant*> &ActualArgs);
-
- /// 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 EvaluateBlock(BasicBlock::iterator CurInst, BasicBlock *&NextBB);
-
- Constant *getVal(Value *V) {
- if (Constant *CV = dyn_cast<Constant>(V)) return CV;
- Constant *R = ValueStack.back().lookup(V);
- assert(R && "Reference to an uncomputed value!");
- return R;
- }
-
- void setVal(Value *V, Constant *C) {
- ValueStack.back()[V] = C;
- }
-
- const DenseMap<Constant*, Constant*> &getMutatedMemory() const {
- return MutatedMemory;
- }
-
- const SmallPtrSetImpl<GlobalVariable*> &getInvariants() const {
- return Invariants;
- }
-
-private:
- Constant *ComputeLoadResult(Constant *P);
-
- /// As we compute SSA register values, we store their contents here. The back
- /// of the deque contains the current function and the stack contains the
- /// values in the calling frames.
- std::deque<DenseMap<Value*, Constant*>> ValueStack;
-
- /// This is used to detect recursion. In pathological situations we could hit
- /// exponential behavior, but at least there is nothing unbounded.
- SmallVector<Function*, 4> CallStack;
-
- /// For each store we execute, we update this map. Loads check this to get
- /// the most up-to-date value. If evaluation is successful, this state is
- /// committed to the process.
- DenseMap<Constant*, Constant*> MutatedMemory;
-
- /// To 'execute' an alloca, we create a temporary global variable to represent
- /// its body. This vector is needed so we can delete the temporary globals
- /// when we are done.
- SmallVector<std::unique_ptr<GlobalVariable>, 32> AllocaTmps;
-
- /// These global variables have been marked invariant by the static
- /// constructor.
- SmallPtrSet<GlobalVariable*, 8> Invariants;
-
- /// These are constants we have checked and know to be simple enough to live
- /// in a static initializer of a global.
- SmallPtrSet<Constant*, 8> SimpleConstants;
-
- const DataLayout &DL;
- const TargetLibraryInfo *TLI;
-};
-
-} // anonymous namespace
-
-/// 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.
- DenseMap<Constant*, Constant*>::const_iterator I = MutatedMemory.find(P);
- if (I != MutatedMemory.end()) return I->second;
-
- // Access it.
- if (GlobalVariable *GV = dyn_cast<GlobalVariable>(P)) {
- if (GV->hasDefinitiveInitializer())
- return GV->getInitializer();
- return nullptr;
- }
-
- // Handle a constantexpr getelementptr.
- if (ConstantExpr *CE = dyn_cast<ConstantExpr>(P))
- if (CE->getOpcode() == Instruction::GetElementPtr &&
- isa<GlobalVariable>(CE->getOperand(0))) {
- GlobalVariable *GV = cast<GlobalVariable>(CE->getOperand(0));
- if (GV->hasDefinitiveInitializer())
- return ConstantFoldLoadThroughGEPConstantExpr(GV->getInitializer(), CE);
- }
-
- return nullptr; // don't know how to evaluate.
-}
-
-/// 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 (1) {
- Constant *InstResult = nullptr;
-
- DEBUG(dbgs() << "Evaluating Instruction: " << *CurInst << "\n");
-
- if (StoreInst *SI = dyn_cast<StoreInst>(CurInst)) {
- if (!SI->isSimple()) {
- DEBUG(dbgs() << "Store is not simple! Can not evaluate.\n");
- return false; // no volatile/atomic accesses.
- }
- Constant *Ptr = getVal(SI->getOperand(1));
- if (ConstantExpr *CE = dyn_cast<ConstantExpr>(Ptr)) {
- DEBUG(dbgs() << "Folding constant ptr expression: " << *Ptr);
- Ptr = ConstantFoldConstantExpression(CE, DL, TLI);
- DEBUG(dbgs() << "; To: " << *Ptr << "\n");
- }
- if (!isSimpleEnoughPointerToCommit(Ptr)) {
- // If this is too complex for us to commit, reject it.
- 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)) {
- 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) {
- 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.
- Ptr = CE->getOperand(0);
-
- Type *NewTy = cast<PointerType>(Ptr->getType())->getElementType();
-
- // In order to push the bitcast onto the stored value, a bitcast
- // from NewTy to Val's type must be legal. If it's not, we can try
- // introspecting NewTy to find a legal conversion.
- while (!Val->getType()->canLosslesslyBitCastTo(NewTy)) {
- // If NewTy 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.
- if (StructType *STy = dyn_cast<StructType>(NewTy)) {
- NewTy = STy->getTypeAtIndex(0U);
-
- IntegerType *IdxTy = IntegerType::get(NewTy->getContext(), 32);
- Constant *IdxZero = ConstantInt::get(IdxTy, 0, false);
- Constant * const IdxList[] = {IdxZero, IdxZero};
-
- Ptr = ConstantExpr::getGetElementPtr(nullptr, Ptr, IdxList);
- if (ConstantExpr *CE = dyn_cast<ConstantExpr>(Ptr))
- Ptr = ConstantFoldConstantExpression(CE, DL, TLI);
-
- // If we can't improve the situation by introspecting NewTy,
- // we have to give up.
- } else {
- DEBUG(dbgs() << "Failed to bitcast constant ptr, can not "
- "evaluate.\n");
- return false;
- }
- }
-
- // If we found compatible types, go ahead and push the bitcast
- // onto the stored value.
- Val = ConstantExpr::getBitCast(Val, NewTy);
-
- 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)));
- 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)));
- 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());
- 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)));
- DEBUG(dbgs() << "Found a Select! Simplifying: " << *InstResult
- << "\n");
- } else if (auto *EVI = dyn_cast<ExtractValueInst>(CurInst)) {
- InstResult = ConstantExpr::getExtractValue(
- getVal(EVI->getAggregateOperand()), EVI->getIndices());
- 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());
- 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());
- DEBUG(dbgs() << "Found a GEP! Simplifying: " << *InstResult
- << "\n");
- } else if (LoadInst *LI = dyn_cast<LoadInst>(CurInst)) {
-
- if (!LI->isSimple()) {
- 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 (ConstantExpr *CE = dyn_cast<ConstantExpr>(Ptr)) {
- Ptr = ConstantFoldConstantExpression(CE, DL, TLI);
- DEBUG(dbgs() << "Found a constant pointer expression, constant "
- "folding: " << *Ptr << "\n");
- }
- InstResult = ComputeLoadResult(Ptr);
- if (!InstResult) {
- DEBUG(dbgs() << "Failed to compute load result. Can not evaluate load."
- "\n");
- return false; // Could not evaluate load.
- }
-
- DEBUG(dbgs() << "Evaluated load: " << *InstResult << "\n");
- } else if (AllocaInst *AI = dyn_cast<AllocaInst>(CurInst)) {
- if (AI->isArrayAllocation()) {
- DEBUG(dbgs() << "Found an array alloca. Can not evaluate.\n");
- return false; // Cannot handle array allocs.
- }
- Type *Ty = AI->getAllocatedType();
- AllocaTmps.push_back(
- make_unique<GlobalVariable>(Ty, false, GlobalValue::InternalLinkage,
- UndefValue::get(Ty), AI->getName()));
- InstResult = AllocaTmps.back().get();
- 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())) {
- DEBUG(dbgs() << "Ignoring debug info.\n");
- ++CurInst;
- continue;
- }
-
- // Cannot handle inline asm.
- if (isa<InlineAsm>(CS.getCalledValue())) {
- 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()) {
- 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.
- DEBUG(dbgs() << "Ignoring no-op memset.\n");
- ++CurInst;
- continue;
- }
- }
-
- if (II->getIntrinsicID() == Intrinsic::lifetime_start ||
- II->getIntrinsicID() == Intrinsic::lifetime_end) {
- 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()) {
- 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->isAllOnesValue() &&
- Size->getValue().getLimitedValue() >=
- DL.getTypeStoreSize(ElemTy)) {
- Invariants.insert(GV);
- DEBUG(dbgs() << "Found a global var that is an invariant: " << *GV
- << "\n");
- } else {
- 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) {
- DEBUG(dbgs() << "Skipping assume intrinsic.\n");
- ++CurInst;
- continue;
- }
-
- DEBUG(dbgs() << "Unknown intrinsic. Can not evaluate.\n");
- return false;
- }
-
- // Resolve function pointers.
- Function *Callee = dyn_cast<Function>(getVal(CS.getCalledValue()));
- if (!Callee || Callee->mayBeOverridden()) {
- DEBUG(dbgs() << "Can not resolve function pointer.\n");
- return false; // Cannot resolve.
- }
-
- SmallVector<Constant*, 8> Formals;
- for (User::op_iterator i = CS.arg_begin(), e = CS.arg_end(); i != e; ++i)
- Formals.push_back(getVal(*i));
-
- if (Callee->isDeclaration()) {
- // If this is a function we can constant fold, do it.
- if (Constant *C = ConstantFoldCall(Callee, Formals, TLI)) {
- InstResult = C;
- DEBUG(dbgs() << "Constant folded function call. Result: " <<
- *InstResult << "\n");
- } else {
- DEBUG(dbgs() << "Can not constant fold function call.\n");
- return false;
- }
- } else {
- if (Callee->getFunctionType()->isVarArg()) {
- 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)) {
- DEBUG(dbgs() << "Failed to evaluate function.\n");
- return false;
- }
- ValueStack.pop_back();
- InstResult = RetVal;
-
- if (InstResult) {
- DEBUG(dbgs() << "Successfully evaluated function. Result: " <<
- InstResult << "\n\n");
- } else {
- DEBUG(dbgs() << "Successfully evaluated function. Result: 0\n\n");
- }
- }
- } else if (isa<TerminatorInst>(CurInst)) {
- 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.
- DEBUG(dbgs() << "Can not handle terminator.");
- return false; // Cannot handle this terminator.
- }
-
- // We succeeded at evaluating this block!
- DEBUG(dbgs() << "Successfully evaluated block.\n");
- return true;
- } else {
- // Did not know how to evaluate this!
- DEBUG(dbgs() << "Failed to evaluate block due to unhandled instruction."
- "\n");
- return false;
- }
-
- if (!CurInst->use_empty()) {
- if (ConstantExpr *CE = dyn_cast<ConstantExpr>(InstResult))
- InstResult = ConstantFoldConstantExpression(CE, DL, TLI);
-
- setVal(&*CurInst, InstResult);
- }
-
- // If we just processed an invoke, we finished evaluating the block.
- if (InvokeInst *II = dyn_cast<InvokeInst>(CurInst)) {
- NextBB = II->getNormalDest();
- 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 (std::find(CallStack.begin(), CallStack.end(), F) != CallStack.end())
- 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 (1) {
- BasicBlock *NextBB = nullptr; // Initialized to avoid compiler warnings.
- 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;
- }
-}
-
/// Evaluate static constructors in the function, if we can. Return true if we
/// can, false otherwise.
static bool EvaluateStaticConstructor(Function *F, const DataLayout &DL,
CodeExtractor.cpp
CtorUtils.cpp
DemoteRegToStack.cpp
+ Evaluator.cpp
FlattenCFG.cpp
GlobalStatus.cpp
InlineFunction.cpp
--- /dev/null
+//===- Evaluator.cpp - LLVM IR evaluator ----------------------------------===//
+//
+// The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+//
+// Function evaluator for LLVM IR.
+//
+//===----------------------------------------------------------------------===//
+
+#include "llvm/Transforms/Utils/Evaluator.h"
+#include "llvm/Analysis/ConstantFolding.h"
+#include "llvm/IR/BasicBlock.h"
+#include "llvm/IR/CallSite.h"
+#include "llvm/IR/Constants.h"
+#include "llvm/IR/DerivedTypes.h"
+#include "llvm/IR/DiagnosticPrinter.h"
+#include "llvm/IR/GlobalVariable.h"
+#include "llvm/IR/IntrinsicInst.h"
+#include "llvm/IR/Instructions.h"
+#include "llvm/IR/Operator.h"
+#include "llvm/Support/Debug.h"
+
+#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<ConstantArray>(C) || isa<ConstantStruct>(C) ||
+ isa<ConstantVector>(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;
+}
+
+/// 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.
+ DenseMap<Constant*, Constant*>::const_iterator I = MutatedMemory.find(P);
+ if (I != MutatedMemory.end()) return I->second;
+
+ // Access it.
+ if (GlobalVariable *GV = dyn_cast<GlobalVariable>(P)) {
+ if (GV->hasDefinitiveInitializer())
+ return GV->getInitializer();
+ return nullptr;
+ }
+
+ // Handle a constantexpr getelementptr.
+ if (ConstantExpr *CE = dyn_cast<ConstantExpr>(P))
+ if (CE->getOpcode() == Instruction::GetElementPtr &&
+ isa<GlobalVariable>(CE->getOperand(0))) {
+ GlobalVariable *GV = cast<GlobalVariable>(CE->getOperand(0));
+ if (GV->hasDefinitiveInitializer())
+ return ConstantFoldLoadThroughGEPConstantExpr(GV->getInitializer(), CE);
+ }
+
+ return nullptr; // don't know how to evaluate.
+}
+
+/// 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 (1) {
+ Constant *InstResult = nullptr;
+
+ DEBUG(dbgs() << "Evaluating Instruction: " << *CurInst << "\n");
+
+ if (StoreInst *SI = dyn_cast<StoreInst>(CurInst)) {
+ if (!SI->isSimple()) {
+ DEBUG(dbgs() << "Store is not simple! Can not evaluate.\n");
+ return false; // no volatile/atomic accesses.
+ }
+ Constant *Ptr = getVal(SI->getOperand(1));
+ if (ConstantExpr *CE = dyn_cast<ConstantExpr>(Ptr)) {
+ DEBUG(dbgs() << "Folding constant ptr expression: " << *Ptr);
+ Ptr = ConstantFoldConstantExpression(CE, DL, TLI);
+ DEBUG(dbgs() << "; To: " << *Ptr << "\n");
+ }
+ if (!isSimpleEnoughPointerToCommit(Ptr)) {
+ // If this is too complex for us to commit, reject it.
+ 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)) {
+ 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) {
+ 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.
+ Ptr = CE->getOperand(0);
+
+ Type *NewTy = cast<PointerType>(Ptr->getType())->getElementType();
+
+ // In order to push the bitcast onto the stored value, a bitcast
+ // from NewTy to Val's type must be legal. If it's not, we can try
+ // introspecting NewTy to find a legal conversion.
+ while (!Val->getType()->canLosslesslyBitCastTo(NewTy)) {
+ // If NewTy 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.
+ if (StructType *STy = dyn_cast<StructType>(NewTy)) {
+ NewTy = STy->getTypeAtIndex(0U);
+
+ IntegerType *IdxTy = IntegerType::get(NewTy->getContext(), 32);
+ Constant *IdxZero = ConstantInt::get(IdxTy, 0, false);
+ Constant * const IdxList[] = {IdxZero, IdxZero};
+
+ Ptr = ConstantExpr::getGetElementPtr(nullptr, Ptr, IdxList);
+ if (ConstantExpr *CE = dyn_cast<ConstantExpr>(Ptr))
+ Ptr = ConstantFoldConstantExpression(CE, DL, TLI);
+
+ // If we can't improve the situation by introspecting NewTy,
+ // we have to give up.
+ } else {
+ DEBUG(dbgs() << "Failed to bitcast constant ptr, can not "
+ "evaluate.\n");
+ return false;
+ }
+ }
+
+ // If we found compatible types, go ahead and push the bitcast
+ // onto the stored value.
+ Val = ConstantExpr::getBitCast(Val, NewTy);
+
+ 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)));
+ 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)));
+ 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());
+ 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)));
+ DEBUG(dbgs() << "Found a Select! Simplifying: " << *InstResult
+ << "\n");
+ } else if (auto *EVI = dyn_cast<ExtractValueInst>(CurInst)) {
+ InstResult = ConstantExpr::getExtractValue(
+ getVal(EVI->getAggregateOperand()), EVI->getIndices());
+ 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());
+ 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());
+ DEBUG(dbgs() << "Found a GEP! Simplifying: " << *InstResult
+ << "\n");
+ } else if (LoadInst *LI = dyn_cast<LoadInst>(CurInst)) {
+
+ if (!LI->isSimple()) {
+ 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 (ConstantExpr *CE = dyn_cast<ConstantExpr>(Ptr)) {
+ Ptr = ConstantFoldConstantExpression(CE, DL, TLI);
+ DEBUG(dbgs() << "Found a constant pointer expression, constant "
+ "folding: " << *Ptr << "\n");
+ }
+ InstResult = ComputeLoadResult(Ptr);
+ if (!InstResult) {
+ DEBUG(dbgs() << "Failed to compute load result. Can not evaluate load."
+ "\n");
+ return false; // Could not evaluate load.
+ }
+
+ DEBUG(dbgs() << "Evaluated load: " << *InstResult << "\n");
+ } else if (AllocaInst *AI = dyn_cast<AllocaInst>(CurInst)) {
+ if (AI->isArrayAllocation()) {
+ DEBUG(dbgs() << "Found an array alloca. Can not evaluate.\n");
+ return false; // Cannot handle array allocs.
+ }
+ Type *Ty = AI->getAllocatedType();
+ AllocaTmps.push_back(
+ make_unique<GlobalVariable>(Ty, false, GlobalValue::InternalLinkage,
+ UndefValue::get(Ty), AI->getName()));
+ InstResult = AllocaTmps.back().get();
+ 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())) {
+ DEBUG(dbgs() << "Ignoring debug info.\n");
+ ++CurInst;
+ continue;
+ }
+
+ // Cannot handle inline asm.
+ if (isa<InlineAsm>(CS.getCalledValue())) {
+ 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()) {
+ 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.
+ DEBUG(dbgs() << "Ignoring no-op memset.\n");
+ ++CurInst;
+ continue;
+ }
+ }
+
+ if (II->getIntrinsicID() == Intrinsic::lifetime_start ||
+ II->getIntrinsicID() == Intrinsic::lifetime_end) {
+ 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()) {
+ 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->isAllOnesValue() &&
+ Size->getValue().getLimitedValue() >=
+ DL.getTypeStoreSize(ElemTy)) {
+ Invariants.insert(GV);
+ DEBUG(dbgs() << "Found a global var that is an invariant: " << *GV
+ << "\n");
+ } else {
+ 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) {
+ DEBUG(dbgs() << "Skipping assume intrinsic.\n");
+ ++CurInst;
+ continue;
+ }
+
+ DEBUG(dbgs() << "Unknown intrinsic. Can not evaluate.\n");
+ return false;
+ }
+
+ // Resolve function pointers.
+ Function *Callee = dyn_cast<Function>(getVal(CS.getCalledValue()));
+ if (!Callee || Callee->mayBeOverridden()) {
+ DEBUG(dbgs() << "Can not resolve function pointer.\n");
+ return false; // Cannot resolve.
+ }
+
+ SmallVector<Constant*, 8> Formals;
+ for (User::op_iterator i = CS.arg_begin(), e = CS.arg_end(); i != e; ++i)
+ Formals.push_back(getVal(*i));
+
+ if (Callee->isDeclaration()) {
+ // If this is a function we can constant fold, do it.
+ if (Constant *C = ConstantFoldCall(Callee, Formals, TLI)) {
+ InstResult = C;
+ DEBUG(dbgs() << "Constant folded function call. Result: " <<
+ *InstResult << "\n");
+ } else {
+ DEBUG(dbgs() << "Can not constant fold function call.\n");
+ return false;
+ }
+ } else {
+ if (Callee->getFunctionType()->isVarArg()) {
+ 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)) {
+ DEBUG(dbgs() << "Failed to evaluate function.\n");
+ return false;
+ }
+ ValueStack.pop_back();
+ InstResult = RetVal;
+
+ if (InstResult) {
+ DEBUG(dbgs() << "Successfully evaluated function. Result: "
+ << *InstResult << "\n\n");
+ } else {
+ DEBUG(dbgs() << "Successfully evaluated function. Result: 0\n\n");
+ }
+ }
+ } else if (isa<TerminatorInst>(CurInst)) {
+ 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.
+ DEBUG(dbgs() << "Can not handle terminator.");
+ return false; // Cannot handle this terminator.
+ }
+
+ // We succeeded at evaluating this block!
+ DEBUG(dbgs() << "Successfully evaluated block.\n");
+ return true;
+ } else {
+ // Did not know how to evaluate this!
+ DEBUG(dbgs() << "Failed to evaluate block due to unhandled instruction."
+ "\n");
+ return false;
+ }
+
+ if (!CurInst->use_empty()) {
+ if (ConstantExpr *CE = dyn_cast<ConstantExpr>(InstResult))
+ InstResult = ConstantFoldConstantExpression(CE, DL, TLI);
+
+ setVal(&*CurInst, InstResult);
+ }
+
+ // If we just processed an invoke, we finished evaluating the block.
+ if (InvokeInst *II = dyn_cast<InvokeInst>(CurInst)) {
+ NextBB = II->getNormalDest();
+ 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 (std::find(CallStack.begin(), CallStack.end(), F) != CallStack.end())
+ 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 (1) {
+ BasicBlock *NextBB = nullptr; // Initialized to avoid compiler warnings.
+ 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;
+ }
+}
+
projects / platform / upstream / llvm.git / commitdiff