1 //===- Evaluator.cpp - LLVM IR evaluator ----------------------------------===//
3 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
4 // See https://llvm.org/LICENSE.txt for license information.
5 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
7 //===----------------------------------------------------------------------===//
9 // Function evaluator for LLVM IR.
11 //===----------------------------------------------------------------------===//
13 #include "llvm/Transforms/Utils/Evaluator.h"
14 #include "llvm/ADT/DenseMap.h"
15 #include "llvm/ADT/STLExtras.h"
16 #include "llvm/ADT/SmallPtrSet.h"
17 #include "llvm/ADT/SmallVector.h"
18 #include "llvm/Analysis/ConstantFolding.h"
19 #include "llvm/IR/BasicBlock.h"
20 #include "llvm/IR/Constant.h"
21 #include "llvm/IR/Constants.h"
22 #include "llvm/IR/DataLayout.h"
23 #include "llvm/IR/DerivedTypes.h"
24 #include "llvm/IR/Function.h"
25 #include "llvm/IR/GlobalAlias.h"
26 #include "llvm/IR/GlobalValue.h"
27 #include "llvm/IR/GlobalVariable.h"
28 #include "llvm/IR/InstrTypes.h"
29 #include "llvm/IR/Instruction.h"
30 #include "llvm/IR/Instructions.h"
31 #include "llvm/IR/IntrinsicInst.h"
32 #include "llvm/IR/Intrinsics.h"
33 #include "llvm/IR/Operator.h"
34 #include "llvm/IR/Type.h"
35 #include "llvm/IR/User.h"
36 #include "llvm/IR/Value.h"
37 #include "llvm/Support/Casting.h"
38 #include "llvm/Support/Debug.h"
39 #include "llvm/Support/raw_ostream.h"
42 #define DEBUG_TYPE "evaluator"
47 isSimpleEnoughValueToCommit(Constant *C,
48 SmallPtrSetImpl<Constant *> &SimpleConstants,
49 const DataLayout &DL);
51 /// Return true if the specified constant can be handled by the code generator.
52 /// We don't want to generate something like:
54 /// because the code generator doesn't have a relocation that can handle that.
56 /// This function should be called if C was not found (but just got inserted)
57 /// in SimpleConstants to avoid having to rescan the same constants all the
60 isSimpleEnoughValueToCommitHelper(Constant *C,
61 SmallPtrSetImpl<Constant *> &SimpleConstants,
62 const DataLayout &DL) {
63 // Simple global addresses are supported, do not allow dllimport or
64 // thread-local globals.
65 if (auto *GV = dyn_cast<GlobalValue>(C))
66 return !GV->hasDLLImportStorageClass() && !GV->isThreadLocal();
68 // Simple integer, undef, constant aggregate zero, etc are all supported.
69 if (C->getNumOperands() == 0 || isa<BlockAddress>(C))
72 // Aggregate values are safe if all their elements are.
73 if (isa<ConstantAggregate>(C)) {
74 for (Value *Op : C->operands())
75 if (!isSimpleEnoughValueToCommit(cast<Constant>(Op), SimpleConstants, DL))
80 // We don't know exactly what relocations are allowed in constant expressions,
81 // so we allow &global+constantoffset, which is safe and uniformly supported
83 ConstantExpr *CE = cast<ConstantExpr>(C);
84 switch (CE->getOpcode()) {
85 case Instruction::BitCast:
86 // Bitcast is fine if the casted value is fine.
87 return isSimpleEnoughValueToCommit(CE->getOperand(0), SimpleConstants, DL);
89 case Instruction::IntToPtr:
90 case Instruction::PtrToInt:
91 // int <=> ptr is fine if the int type is the same size as the
93 if (DL.getTypeSizeInBits(CE->getType()) !=
94 DL.getTypeSizeInBits(CE->getOperand(0)->getType()))
96 return isSimpleEnoughValueToCommit(CE->getOperand(0), SimpleConstants, DL);
98 // GEP is fine if it is simple + constant offset.
99 case Instruction::GetElementPtr:
100 for (unsigned i = 1, e = CE->getNumOperands(); i != e; ++i)
101 if (!isa<ConstantInt>(CE->getOperand(i)))
103 return isSimpleEnoughValueToCommit(CE->getOperand(0), SimpleConstants, DL);
105 case Instruction::Add:
106 // We allow simple+cst.
107 if (!isa<ConstantInt>(CE->getOperand(1)))
109 return isSimpleEnoughValueToCommit(CE->getOperand(0), SimpleConstants, DL);
115 isSimpleEnoughValueToCommit(Constant *C,
116 SmallPtrSetImpl<Constant *> &SimpleConstants,
117 const DataLayout &DL) {
118 // If we already checked this constant, we win.
119 if (!SimpleConstants.insert(C).second)
121 // Check the constant.
122 return isSimpleEnoughValueToCommitHelper(C, SimpleConstants, DL);
125 /// Return true if this constant is simple enough for us to understand. In
126 /// particular, if it is a cast to anything other than from one pointer type to
127 /// another pointer type, we punt. We basically just support direct accesses to
128 /// globals and GEP's of globals. This should be kept up to date with
130 static bool isSimpleEnoughPointerToCommit(Constant *C, const DataLayout &DL) {
131 if (GlobalVariable *GV = dyn_cast<GlobalVariable>(C))
132 // Do not allow weak/*_odr/linkonce linkage or external globals.
133 return GV->hasUniqueInitializer();
135 if (ConstantExpr *CE = dyn_cast<ConstantExpr>(C)) {
136 // Handle a constantexpr gep.
137 if (CE->getOpcode() == Instruction::GetElementPtr &&
138 isa<GlobalVariable>(CE->getOperand(0)) &&
139 cast<GEPOperator>(CE)->isInBounds()) {
140 GlobalVariable *GV = cast<GlobalVariable>(CE->getOperand(0));
141 // Do not allow weak/*_odr/linkonce/dllimport/dllexport linkage or
143 if (!GV->hasUniqueInitializer())
146 // The first index must be zero.
147 ConstantInt *CI = dyn_cast<ConstantInt>(*std::next(CE->op_begin()));
148 if (!CI || !CI->isZero()) return false;
150 // The remaining indices must be compile-time known integers within the
151 // notional bounds of the corresponding static array types.
152 if (!CE->isGEPWithNoNotionalOverIndexing())
155 return ConstantFoldLoadThroughGEPConstantExpr(
156 GV->getInitializer(), CE,
157 cast<GEPOperator>(CE)->getResultElementType(), DL);
158 } else if (CE->getOpcode() == Instruction::BitCast &&
159 isa<GlobalVariable>(CE->getOperand(0))) {
160 // A constantexpr bitcast from a pointer to another pointer is a no-op,
161 // and we know how to evaluate it by moving the bitcast from the pointer
162 // operand to the value operand.
163 // Do not allow weak/*_odr/linkonce/dllimport/dllexport linkage or
165 return cast<GlobalVariable>(CE->getOperand(0))->hasUniqueInitializer();
172 /// Apply \p TryLoad to Ptr. If this returns \p nullptr, introspect the
173 /// pointer's type and walk down through the initial elements to obtain
174 /// additional pointers to try. Returns the first non-null return value from
175 /// \p TryLoad, or \p nullptr if the type can't be introspected further.
177 evaluateBitcastFromPtr(Constant *Ptr, const DataLayout &DL,
178 const TargetLibraryInfo *TLI,
179 std::function<Constant *(Constant *)> TryLoad) {
181 while (!(Val = TryLoad(Ptr))) {
182 // If Ty is a non-opaque struct, we can convert the pointer to the struct
183 // into a pointer to its first member.
184 // FIXME: This could be extended to support arrays as well.
185 Type *Ty = cast<PointerType>(Ptr->getType())->getElementType();
186 if (!isa<StructType>(Ty) || cast<StructType>(Ty)->isOpaque())
189 IntegerType *IdxTy = IntegerType::get(Ty->getContext(), 32);
190 Constant *IdxZero = ConstantInt::get(IdxTy, 0, false);
191 Constant *const IdxList[] = {IdxZero, IdxZero};
193 Ptr = ConstantExpr::getGetElementPtr(Ty, Ptr, IdxList);
194 Ptr = ConstantFoldConstant(Ptr, DL, TLI);
199 static Constant *getInitializer(Constant *C) {
200 auto *GV = dyn_cast<GlobalVariable>(C);
201 return GV && GV->hasDefinitiveInitializer() ? GV->getInitializer() : nullptr;
204 /// Return the value that would be computed by a load from P after the stores
205 /// reflected by 'memory' have been performed. If we can't decide, return null.
206 Constant *Evaluator::ComputeLoadResult(Constant *P, Type *Ty) {
207 // If this memory location has been recently stored, use the stored value: it
208 // is the most up-to-date.
209 auto TryFindMemLoc = [this](Constant *Ptr) {
210 return MutatedMemory.lookup(Ptr);
213 if (Constant *Val = TryFindMemLoc(P))
217 if (GlobalVariable *GV = dyn_cast<GlobalVariable>(P)) {
218 if (GV->hasDefinitiveInitializer())
219 return GV->getInitializer();
223 if (ConstantExpr *CE = dyn_cast<ConstantExpr>(P)) {
224 switch (CE->getOpcode()) {
225 // Handle a constantexpr getelementptr.
226 case Instruction::GetElementPtr:
227 if (auto *I = getInitializer(CE->getOperand(0)))
228 return ConstantFoldLoadThroughGEPConstantExpr(I, CE, Ty, DL);
230 // Handle a constantexpr bitcast.
231 case Instruction::BitCast:
232 // We're evaluating a load through a pointer that was bitcast to a
233 // different type. See if the "from" pointer has recently been stored.
234 // If it hasn't, we may still be able to find a stored pointer by
235 // introspecting the type.
237 evaluateBitcastFromPtr(CE->getOperand(0), DL, TLI, TryFindMemLoc);
239 Val = getInitializer(CE->getOperand(0));
241 return ConstantFoldLoadThroughBitcast(
242 Val, P->getType()->getPointerElementType(), DL);
247 return nullptr; // don't know how to evaluate.
250 static Function *getFunction(Constant *C) {
251 if (auto *Fn = dyn_cast<Function>(C))
254 if (auto *Alias = dyn_cast<GlobalAlias>(C))
255 if (auto *Fn = dyn_cast<Function>(Alias->getAliasee()))
261 Evaluator::getCalleeWithFormalArgs(CallBase &CB,
262 SmallVectorImpl<Constant *> &Formals) {
263 auto *V = CB.getCalledOperand();
264 if (auto *Fn = getFunction(getVal(V)))
265 return getFormalParams(CB, Fn, Formals) ? Fn : nullptr;
267 auto *CE = dyn_cast<ConstantExpr>(V);
268 if (!CE || CE->getOpcode() != Instruction::BitCast ||
269 !getFormalParams(CB, getFunction(CE->getOperand(0)), Formals))
272 return dyn_cast<Function>(
273 ConstantFoldLoadThroughBitcast(CE, CE->getOperand(0)->getType(), DL));
276 bool Evaluator::getFormalParams(CallBase &CB, Function *F,
277 SmallVectorImpl<Constant *> &Formals) {
281 auto *FTy = F->getFunctionType();
282 if (FTy->getNumParams() > CB.arg_size()) {
283 LLVM_DEBUG(dbgs() << "Too few arguments for function.\n");
287 auto ArgI = CB.arg_begin();
288 for (auto ParI = FTy->param_begin(), ParE = FTy->param_end(); ParI != ParE;
290 auto *ArgC = ConstantFoldLoadThroughBitcast(getVal(*ArgI), *ParI, DL);
292 LLVM_DEBUG(dbgs() << "Can not convert function argument.\n");
295 Formals.push_back(ArgC);
301 /// If call expression contains bitcast then we may need to cast
302 /// evaluated return value to a type of the call expression.
303 Constant *Evaluator::castCallResultIfNeeded(Value *CallExpr, Constant *RV) {
304 ConstantExpr *CE = dyn_cast<ConstantExpr>(CallExpr);
305 if (!RV || !CE || CE->getOpcode() != Instruction::BitCast)
309 dyn_cast<FunctionType>(CE->getType()->getPointerElementType())) {
310 RV = ConstantFoldLoadThroughBitcast(RV, FT->getReturnType(), DL);
312 LLVM_DEBUG(dbgs() << "Failed to fold bitcast call expr\n");
317 /// Evaluate all instructions in block BB, returning true if successful, false
318 /// if we can't evaluate it. NewBB returns the next BB that control flows into,
319 /// or null upon return. StrippedPointerCastsForAliasAnalysis is set to true if
320 /// we looked through pointer casts to evaluate something.
321 bool Evaluator::EvaluateBlock(BasicBlock::iterator CurInst, BasicBlock *&NextBB,
322 bool &StrippedPointerCastsForAliasAnalysis) {
323 // This is the main evaluation loop.
325 Constant *InstResult = nullptr;
327 LLVM_DEBUG(dbgs() << "Evaluating Instruction: " << *CurInst << "\n");
329 if (StoreInst *SI = dyn_cast<StoreInst>(CurInst)) {
330 if (!SI->isSimple()) {
331 LLVM_DEBUG(dbgs() << "Store is not simple! Can not evaluate.\n");
332 return false; // no volatile/atomic accesses.
334 Constant *Ptr = getVal(SI->getOperand(1));
335 Constant *FoldedPtr = ConstantFoldConstant(Ptr, DL, TLI);
336 if (Ptr != FoldedPtr) {
337 LLVM_DEBUG(dbgs() << "Folding constant ptr expression: " << *Ptr);
339 LLVM_DEBUG(dbgs() << "; To: " << *Ptr << "\n");
341 // Conservatively, avoid aggregate types. This is because we don't
342 // want to worry about them partially overlapping other stores.
343 if (!SI->getValueOperand()->getType()->isSingleValueType() ||
344 !isSimpleEnoughPointerToCommit(Ptr, DL)) {
345 // If this is too complex for us to commit, reject it.
347 dbgs() << "Pointer is too complex for us to evaluate store.");
351 Constant *Val = getVal(SI->getOperand(0));
353 // If this might be too difficult for the backend to handle (e.g. the addr
354 // of one global variable divided by another) then we can't commit it.
355 if (!isSimpleEnoughValueToCommit(Val, SimpleConstants, DL)) {
356 LLVM_DEBUG(dbgs() << "Store value is too complex to evaluate store. "
361 if (ConstantExpr *CE = dyn_cast<ConstantExpr>(Ptr)) {
362 if (CE->getOpcode() == Instruction::BitCast) {
364 << "Attempting to resolve bitcast on constant ptr.\n");
365 // If we're evaluating a store through a bitcast, then we need
366 // to pull the bitcast off the pointer type and push it onto the
367 // stored value. In order to push the bitcast onto the stored value,
368 // a bitcast from the pointer's element type to Val's type must be
369 // legal. If it's not, we can try introspecting the type to find a
372 auto TryCastValTy = [&](Constant *P) -> Constant * {
373 // The conversion is illegal if the store is wider than the
374 // pointee proposed by `evaluateBitcastFromPtr`, since that would
375 // drop stores to other struct elements when the caller attempts to
376 // look through a struct's 0th element.
377 Type *NewTy = cast<PointerType>(P->getType())->getElementType();
378 Type *STy = Val->getType();
379 if (DL.getTypeSizeInBits(NewTy) < DL.getTypeSizeInBits(STy))
382 if (Constant *FV = ConstantFoldLoadThroughBitcast(Val, NewTy, DL)) {
390 evaluateBitcastFromPtr(CE->getOperand(0), DL, TLI, TryCastValTy);
392 LLVM_DEBUG(dbgs() << "Failed to bitcast constant ptr, can not "
398 LLVM_DEBUG(dbgs() << "Evaluated bitcast: " << *Val << "\n");
402 MutatedMemory[Ptr] = Val;
403 } else if (BinaryOperator *BO = dyn_cast<BinaryOperator>(CurInst)) {
404 InstResult = ConstantExpr::get(BO->getOpcode(),
405 getVal(BO->getOperand(0)),
406 getVal(BO->getOperand(1)));
407 LLVM_DEBUG(dbgs() << "Found a BinaryOperator! Simplifying: "
408 << *InstResult << "\n");
409 } else if (CmpInst *CI = dyn_cast<CmpInst>(CurInst)) {
410 InstResult = ConstantExpr::getCompare(CI->getPredicate(),
411 getVal(CI->getOperand(0)),
412 getVal(CI->getOperand(1)));
413 LLVM_DEBUG(dbgs() << "Found a CmpInst! Simplifying: " << *InstResult
415 } else if (CastInst *CI = dyn_cast<CastInst>(CurInst)) {
416 InstResult = ConstantExpr::getCast(CI->getOpcode(),
417 getVal(CI->getOperand(0)),
419 LLVM_DEBUG(dbgs() << "Found a Cast! Simplifying: " << *InstResult
421 } else if (SelectInst *SI = dyn_cast<SelectInst>(CurInst)) {
422 InstResult = ConstantExpr::getSelect(getVal(SI->getOperand(0)),
423 getVal(SI->getOperand(1)),
424 getVal(SI->getOperand(2)));
425 LLVM_DEBUG(dbgs() << "Found a Select! Simplifying: " << *InstResult
427 } else if (auto *EVI = dyn_cast<ExtractValueInst>(CurInst)) {
428 InstResult = ConstantExpr::getExtractValue(
429 getVal(EVI->getAggregateOperand()), EVI->getIndices());
430 LLVM_DEBUG(dbgs() << "Found an ExtractValueInst! Simplifying: "
431 << *InstResult << "\n");
432 } else if (auto *IVI = dyn_cast<InsertValueInst>(CurInst)) {
433 InstResult = ConstantExpr::getInsertValue(
434 getVal(IVI->getAggregateOperand()),
435 getVal(IVI->getInsertedValueOperand()), IVI->getIndices());
436 LLVM_DEBUG(dbgs() << "Found an InsertValueInst! Simplifying: "
437 << *InstResult << "\n");
438 } else if (GetElementPtrInst *GEP = dyn_cast<GetElementPtrInst>(CurInst)) {
439 Constant *P = getVal(GEP->getOperand(0));
440 SmallVector<Constant*, 8> GEPOps;
441 for (Use &Op : llvm::drop_begin(GEP->operands()))
442 GEPOps.push_back(getVal(Op));
444 ConstantExpr::getGetElementPtr(GEP->getSourceElementType(), P, GEPOps,
445 cast<GEPOperator>(GEP)->isInBounds());
446 LLVM_DEBUG(dbgs() << "Found a GEP! Simplifying: " << *InstResult << "\n");
447 } else if (LoadInst *LI = dyn_cast<LoadInst>(CurInst)) {
448 if (!LI->isSimple()) {
450 dbgs() << "Found a Load! Not a simple load, can not evaluate.\n");
451 return false; // no volatile/atomic accesses.
454 Constant *Ptr = getVal(LI->getOperand(0));
455 Constant *FoldedPtr = ConstantFoldConstant(Ptr, DL, TLI);
456 if (Ptr != FoldedPtr) {
458 LLVM_DEBUG(dbgs() << "Found a constant pointer expression, constant "
462 InstResult = ComputeLoadResult(Ptr, LI->getType());
465 dbgs() << "Failed to compute load result. Can not evaluate load."
467 return false; // Could not evaluate load.
470 LLVM_DEBUG(dbgs() << "Evaluated load: " << *InstResult << "\n");
471 } else if (AllocaInst *AI = dyn_cast<AllocaInst>(CurInst)) {
472 if (AI->isArrayAllocation()) {
473 LLVM_DEBUG(dbgs() << "Found an array alloca. Can not evaluate.\n");
474 return false; // Cannot handle array allocs.
476 Type *Ty = AI->getAllocatedType();
477 AllocaTmps.push_back(std::make_unique<GlobalVariable>(
478 Ty, false, GlobalValue::InternalLinkage, UndefValue::get(Ty),
479 AI->getName(), /*TLMode=*/GlobalValue::NotThreadLocal,
480 AI->getType()->getPointerAddressSpace()));
481 InstResult = AllocaTmps.back().get();
482 LLVM_DEBUG(dbgs() << "Found an alloca. Result: " << *InstResult << "\n");
483 } else if (isa<CallInst>(CurInst) || isa<InvokeInst>(CurInst)) {
484 CallBase &CB = *cast<CallBase>(&*CurInst);
486 // Debug info can safely be ignored here.
487 if (isa<DbgInfoIntrinsic>(CB)) {
488 LLVM_DEBUG(dbgs() << "Ignoring debug info.\n");
493 // Cannot handle inline asm.
494 if (CB.isInlineAsm()) {
495 LLVM_DEBUG(dbgs() << "Found inline asm, can not evaluate.\n");
499 if (IntrinsicInst *II = dyn_cast<IntrinsicInst>(&CB)) {
500 if (MemSetInst *MSI = dyn_cast<MemSetInst>(II)) {
501 if (MSI->isVolatile()) {
502 LLVM_DEBUG(dbgs() << "Can not optimize a volatile memset "
506 Constant *Ptr = getVal(MSI->getDest());
507 Constant *Val = getVal(MSI->getValue());
509 ComputeLoadResult(getVal(Ptr), MSI->getValue()->getType());
510 if (Val->isNullValue() && DestVal && DestVal->isNullValue()) {
511 // This memset is a no-op.
512 LLVM_DEBUG(dbgs() << "Ignoring no-op memset.\n");
518 if (II->isLifetimeStartOrEnd()) {
519 LLVM_DEBUG(dbgs() << "Ignoring lifetime intrinsic.\n");
524 if (II->getIntrinsicID() == Intrinsic::invariant_start) {
525 // We don't insert an entry into Values, as it doesn't have a
526 // meaningful return value.
527 if (!II->use_empty()) {
529 << "Found unused invariant_start. Can't evaluate.\n");
532 ConstantInt *Size = cast<ConstantInt>(II->getArgOperand(0));
533 Value *PtrArg = getVal(II->getArgOperand(1));
534 Value *Ptr = PtrArg->stripPointerCasts();
535 if (GlobalVariable *GV = dyn_cast<GlobalVariable>(Ptr)) {
536 Type *ElemTy = GV->getValueType();
537 if (!Size->isMinusOne() &&
538 Size->getValue().getLimitedValue() >=
539 DL.getTypeStoreSize(ElemTy)) {
540 Invariants.insert(GV);
541 LLVM_DEBUG(dbgs() << "Found a global var that is an invariant: "
545 << "Found a global var, but can not treat it as an "
549 // Continue even if we do nothing.
552 } else if (II->getIntrinsicID() == Intrinsic::assume) {
553 LLVM_DEBUG(dbgs() << "Skipping assume intrinsic.\n");
556 } else if (II->getIntrinsicID() == Intrinsic::sideeffect) {
557 LLVM_DEBUG(dbgs() << "Skipping sideeffect intrinsic.\n");
560 } else if (II->getIntrinsicID() == Intrinsic::pseudoprobe) {
561 LLVM_DEBUG(dbgs() << "Skipping pseudoprobe intrinsic.\n");
565 Value *Stripped = CurInst->stripPointerCastsForAliasAnalysis();
566 // Only attempt to getVal() if we've actually managed to strip
567 // anything away, or else we'll call getVal() on the current
569 if (Stripped != &*CurInst) {
570 InstResult = getVal(Stripped);
574 << "Stripped pointer casts for alias analysis for "
575 "intrinsic call.\n");
576 StrippedPointerCastsForAliasAnalysis = true;
577 InstResult = ConstantExpr::getBitCast(InstResult, II->getType());
579 LLVM_DEBUG(dbgs() << "Unknown intrinsic. Cannot evaluate.\n");
586 // Resolve function pointers.
587 SmallVector<Constant *, 8> Formals;
588 Function *Callee = getCalleeWithFormalArgs(CB, Formals);
589 if (!Callee || Callee->isInterposable()) {
590 LLVM_DEBUG(dbgs() << "Can not resolve function pointer.\n");
591 return false; // Cannot resolve.
594 if (Callee->isDeclaration()) {
595 // If this is a function we can constant fold, do it.
596 if (Constant *C = ConstantFoldCall(&CB, Callee, Formals, TLI)) {
597 InstResult = castCallResultIfNeeded(CB.getCalledOperand(), C);
600 LLVM_DEBUG(dbgs() << "Constant folded function call. Result: "
601 << *InstResult << "\n");
603 LLVM_DEBUG(dbgs() << "Can not constant fold function call.\n");
607 if (Callee->getFunctionType()->isVarArg()) {
609 << "Can not constant fold vararg function call.\n");
613 Constant *RetVal = nullptr;
614 // Execute the call, if successful, use the return value.
615 ValueStack.emplace_back();
616 if (!EvaluateFunction(Callee, RetVal, Formals)) {
617 LLVM_DEBUG(dbgs() << "Failed to evaluate function.\n");
620 ValueStack.pop_back();
621 InstResult = castCallResultIfNeeded(CB.getCalledOperand(), RetVal);
622 if (RetVal && !InstResult)
626 LLVM_DEBUG(dbgs() << "Successfully evaluated function. Result: "
627 << *InstResult << "\n\n");
630 << "Successfully evaluated function. Result: 0\n\n");
634 } else if (CurInst->isTerminator()) {
635 LLVM_DEBUG(dbgs() << "Found a terminator instruction.\n");
637 if (BranchInst *BI = dyn_cast<BranchInst>(CurInst)) {
638 if (BI->isUnconditional()) {
639 NextBB = BI->getSuccessor(0);
642 dyn_cast<ConstantInt>(getVal(BI->getCondition()));
643 if (!Cond) return false; // Cannot determine.
645 NextBB = BI->getSuccessor(!Cond->getZExtValue());
647 } else if (SwitchInst *SI = dyn_cast<SwitchInst>(CurInst)) {
649 dyn_cast<ConstantInt>(getVal(SI->getCondition()));
650 if (!Val) return false; // Cannot determine.
651 NextBB = SI->findCaseValue(Val)->getCaseSuccessor();
652 } else if (IndirectBrInst *IBI = dyn_cast<IndirectBrInst>(CurInst)) {
653 Value *Val = getVal(IBI->getAddress())->stripPointerCasts();
654 if (BlockAddress *BA = dyn_cast<BlockAddress>(Val))
655 NextBB = BA->getBasicBlock();
657 return false; // Cannot determine.
658 } else if (isa<ReturnInst>(CurInst)) {
661 // invoke, unwind, resume, unreachable.
662 LLVM_DEBUG(dbgs() << "Can not handle terminator.");
663 return false; // Cannot handle this terminator.
666 // We succeeded at evaluating this block!
667 LLVM_DEBUG(dbgs() << "Successfully evaluated block.\n");
670 // Did not know how to evaluate this!
672 dbgs() << "Failed to evaluate block due to unhandled instruction."
677 if (!CurInst->use_empty()) {
678 InstResult = ConstantFoldConstant(InstResult, DL, TLI);
679 setVal(&*CurInst, InstResult);
682 // If we just processed an invoke, we finished evaluating the block.
683 if (InvokeInst *II = dyn_cast<InvokeInst>(CurInst)) {
684 NextBB = II->getNormalDest();
685 LLVM_DEBUG(dbgs() << "Found an invoke instruction. Finished Block.\n\n");
689 // Advance program counter.
694 /// Evaluate a call to function F, returning true if successful, false if we
695 /// can't evaluate it. ActualArgs contains the formal arguments for the
697 bool Evaluator::EvaluateFunction(Function *F, Constant *&RetVal,
698 const SmallVectorImpl<Constant*> &ActualArgs) {
699 // Check to see if this function is already executing (recursion). If so,
700 // bail out. TODO: we might want to accept limited recursion.
701 if (is_contained(CallStack, F))
704 CallStack.push_back(F);
706 // Initialize arguments to the incoming values specified.
708 for (Function::arg_iterator AI = F->arg_begin(), E = F->arg_end(); AI != E;
710 setVal(&*AI, ActualArgs[ArgNo]);
712 // ExecutedBlocks - We only handle non-looping, non-recursive code. As such,
713 // we can only evaluate any one basic block at most once. This set keeps
714 // track of what we have executed so we can detect recursive cases etc.
715 SmallPtrSet<BasicBlock*, 32> ExecutedBlocks;
717 // CurBB - The current basic block we're evaluating.
718 BasicBlock *CurBB = &F->front();
720 BasicBlock::iterator CurInst = CurBB->begin();
723 BasicBlock *NextBB = nullptr; // Initialized to avoid compiler warnings.
724 LLVM_DEBUG(dbgs() << "Trying to evaluate BB: " << *CurBB << "\n");
726 bool StrippedPointerCastsForAliasAnalysis = false;
728 if (!EvaluateBlock(CurInst, NextBB, StrippedPointerCastsForAliasAnalysis))
732 // Successfully running until there's no next block means that we found
733 // the return. Fill it the return value and pop the call stack.
734 ReturnInst *RI = cast<ReturnInst>(CurBB->getTerminator());
735 if (RI->getNumOperands()) {
736 // The Evaluator can look through pointer casts as long as alias
737 // analysis holds because it's just a simple interpreter and doesn't
738 // skip memory accesses due to invariant group metadata, but we can't
739 // let users of Evaluator use a value that's been gleaned looking
740 // through stripping pointer casts.
741 if (StrippedPointerCastsForAliasAnalysis &&
742 !RI->getReturnValue()->getType()->isVoidTy()) {
745 RetVal = getVal(RI->getOperand(0));
747 CallStack.pop_back();
751 // Okay, we succeeded in evaluating this control flow. See if we have
752 // executed the new block before. If so, we have a looping function,
753 // which we cannot evaluate in reasonable time.
754 if (!ExecutedBlocks.insert(NextBB).second)
755 return false; // looped!
757 // Okay, we have never been in this block before. Check to see if there
758 // are any PHI nodes. If so, evaluate them with information about where
760 PHINode *PN = nullptr;
761 for (CurInst = NextBB->begin();
762 (PN = dyn_cast<PHINode>(CurInst)); ++CurInst)
763 setVal(PN, getVal(PN->getIncomingValueForBlock(CurBB)));
765 // Advance to the next block.