LLVM  9.0.0svn
Evaluator.cpp
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1 //===- Evaluator.cpp - LLVM IR evaluator ----------------------------------===//
2 //
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
6 //
7 //===----------------------------------------------------------------------===//
8 //
9 // Function evaluator for LLVM IR.
10 //
11 //===----------------------------------------------------------------------===//
12 
14 #include "llvm/ADT/DenseMap.h"
15 #include "llvm/ADT/STLExtras.h"
16 #include "llvm/ADT/SmallPtrSet.h"
17 #include "llvm/ADT/SmallVector.h"
19 #include "llvm/IR/BasicBlock.h"
20 #include "llvm/IR/CallSite.h"
21 #include "llvm/IR/Constant.h"
22 #include "llvm/IR/Constants.h"
23 #include "llvm/IR/DataLayout.h"
24 #include "llvm/IR/DerivedTypes.h"
25 #include "llvm/IR/Function.h"
26 #include "llvm/IR/GlobalAlias.h"
27 #include "llvm/IR/GlobalValue.h"
28 #include "llvm/IR/GlobalVariable.h"
29 #include "llvm/IR/InstrTypes.h"
30 #include "llvm/IR/Instruction.h"
31 #include "llvm/IR/Instructions.h"
32 #include "llvm/IR/IntrinsicInst.h"
33 #include "llvm/IR/Intrinsics.h"
34 #include "llvm/IR/Operator.h"
35 #include "llvm/IR/Type.h"
36 #include "llvm/IR/User.h"
37 #include "llvm/IR/Value.h"
38 #include "llvm/Support/Casting.h"
39 #include "llvm/Support/Debug.h"
41 #include <iterator>
42 
43 #define DEBUG_TYPE "evaluator"
44 
45 using namespace llvm;
46 
47 static inline bool
49  SmallPtrSetImpl<Constant *> &SimpleConstants,
50  const DataLayout &DL);
51 
52 /// Return true if the specified constant can be handled by the code generator.
53 /// We don't want to generate something like:
54 /// void *X = &X/42;
55 /// because the code generator doesn't have a relocation that can handle that.
56 ///
57 /// This function should be called if C was not found (but just got inserted)
58 /// in SimpleConstants to avoid having to rescan the same constants all the
59 /// time.
60 static bool
62  SmallPtrSetImpl<Constant *> &SimpleConstants,
63  const DataLayout &DL) {
64  // Simple global addresses are supported, do not allow dllimport or
65  // thread-local globals.
66  if (auto *GV = dyn_cast<GlobalValue>(C))
67  return !GV->hasDLLImportStorageClass() && !GV->isThreadLocal();
68 
69  // Simple integer, undef, constant aggregate zero, etc are all supported.
70  if (C->getNumOperands() == 0 || isa<BlockAddress>(C))
71  return true;
72 
73  // Aggregate values are safe if all their elements are.
74  if (isa<ConstantAggregate>(C)) {
75  for (Value *Op : C->operands())
76  if (!isSimpleEnoughValueToCommit(cast<Constant>(Op), SimpleConstants, DL))
77  return false;
78  return true;
79  }
80 
81  // We don't know exactly what relocations are allowed in constant expressions,
82  // so we allow &global+constantoffset, which is safe and uniformly supported
83  // across targets.
84  ConstantExpr *CE = cast<ConstantExpr>(C);
85  switch (CE->getOpcode()) {
86  case Instruction::BitCast:
87  // Bitcast is fine if the casted value is fine.
88  return isSimpleEnoughValueToCommit(CE->getOperand(0), SimpleConstants, DL);
89 
90  case Instruction::IntToPtr:
91  case Instruction::PtrToInt:
92  // int <=> ptr is fine if the int type is the same size as the
93  // pointer type.
94  if (DL.getTypeSizeInBits(CE->getType()) !=
95  DL.getTypeSizeInBits(CE->getOperand(0)->getType()))
96  return false;
97  return isSimpleEnoughValueToCommit(CE->getOperand(0), SimpleConstants, DL);
98 
99  // GEP is fine if it is simple + constant offset.
100  case Instruction::GetElementPtr:
101  for (unsigned i = 1, e = CE->getNumOperands(); i != e; ++i)
102  if (!isa<ConstantInt>(CE->getOperand(i)))
103  return false;
104  return isSimpleEnoughValueToCommit(CE->getOperand(0), SimpleConstants, DL);
105 
106  case Instruction::Add:
107  // We allow simple+cst.
108  if (!isa<ConstantInt>(CE->getOperand(1)))
109  return false;
110  return isSimpleEnoughValueToCommit(CE->getOperand(0), SimpleConstants, DL);
111  }
112  return false;
113 }
114 
115 static inline bool
117  SmallPtrSetImpl<Constant *> &SimpleConstants,
118  const DataLayout &DL) {
119  // If we already checked this constant, we win.
120  if (!SimpleConstants.insert(C).second)
121  return true;
122  // Check the constant.
123  return isSimpleEnoughValueToCommitHelper(C, SimpleConstants, DL);
124 }
125 
126 /// Return true if this constant is simple enough for us to understand. In
127 /// particular, if it is a cast to anything other than from one pointer type to
128 /// another pointer type, we punt. We basically just support direct accesses to
129 /// globals and GEP's of globals. This should be kept up to date with
130 /// CommitValueTo.
132  // Conservatively, avoid aggregate types. This is because we don't
133  // want to worry about them partially overlapping other stores.
134  if (!cast<PointerType>(C->getType())->getElementType()->isSingleValueType())
135  return false;
136 
137  if (GlobalVariable *GV = dyn_cast<GlobalVariable>(C))
138  // Do not allow weak/*_odr/linkonce linkage or external globals.
139  return GV->hasUniqueInitializer();
140 
141  if (ConstantExpr *CE = dyn_cast<ConstantExpr>(C)) {
142  // Handle a constantexpr gep.
143  if (CE->getOpcode() == Instruction::GetElementPtr &&
144  isa<GlobalVariable>(CE->getOperand(0)) &&
145  cast<GEPOperator>(CE)->isInBounds()) {
146  GlobalVariable *GV = cast<GlobalVariable>(CE->getOperand(0));
147  // Do not allow weak/*_odr/linkonce/dllimport/dllexport linkage or
148  // external globals.
149  if (!GV->hasUniqueInitializer())
150  return false;
151 
152  // The first index must be zero.
153  ConstantInt *CI = dyn_cast<ConstantInt>(*std::next(CE->op_begin()));
154  if (!CI || !CI->isZero()) return false;
155 
156  // The remaining indices must be compile-time known integers within the
157  // notional bounds of the corresponding static array types.
158  if (!CE->isGEPWithNoNotionalOverIndexing())
159  return false;
160 
162 
163  // A constantexpr bitcast from a pointer to another pointer is a no-op,
164  // and we know how to evaluate it by moving the bitcast from the pointer
165  // operand to the value operand.
166  } else if (CE->getOpcode() == Instruction::BitCast &&
167  isa<GlobalVariable>(CE->getOperand(0))) {
168  // Do not allow weak/*_odr/linkonce/dllimport/dllexport linkage or
169  // external globals.
170  return cast<GlobalVariable>(CE->getOperand(0))->hasUniqueInitializer();
171  }
172  }
173 
174  return false;
175 }
176 
178  auto *GV = dyn_cast<GlobalVariable>(C);
179  return GV && GV->hasDefinitiveInitializer() ? GV->getInitializer() : nullptr;
180 }
181 
182 /// Return the value that would be computed by a load from P after the stores
183 /// reflected by 'memory' have been performed. If we can't decide, return null.
184 Constant *Evaluator::ComputeLoadResult(Constant *P) {
185  // If this memory location has been recently stored, use the stored value: it
186  // is the most up-to-date.
187  DenseMap<Constant*, Constant*>::const_iterator I = MutatedMemory.find(P);
188  if (I != MutatedMemory.end()) return I->second;
189 
190  // Access it.
191  if (GlobalVariable *GV = dyn_cast<GlobalVariable>(P)) {
192  if (GV->hasDefinitiveInitializer())
193  return GV->getInitializer();
194  return nullptr;
195  }
196 
197  if (ConstantExpr *CE = dyn_cast<ConstantExpr>(P)) {
198  switch (CE->getOpcode()) {
199  // Handle a constantexpr getelementptr.
200  case Instruction::GetElementPtr:
201  if (auto *I = getInitializer(CE->getOperand(0)))
203  break;
204  // Handle a constantexpr bitcast.
205  case Instruction::BitCast:
206  Constant *Val = getVal(CE->getOperand(0));
207  auto MM = MutatedMemory.find(Val);
208  auto *I = (MM != MutatedMemory.end()) ? MM->second
209  : getInitializer(CE->getOperand(0));
210  if (I)
212  I, P->getType()->getPointerElementType(), DL);
213  break;
214  }
215  }
216 
217  return nullptr; // don't know how to evaluate.
218 }
219 
221  if (auto *Fn = dyn_cast<Function>(C))
222  return Fn;
223 
224  if (auto *Alias = dyn_cast<GlobalAlias>(C))
225  if (auto *Fn = dyn_cast<Function>(Alias->getAliasee()))
226  return Fn;
227  return nullptr;
228 }
229 
230 Function *
232  SmallVector<Constant *, 8> &Formals) {
233  auto *V = CS.getCalledValue();
234  if (auto *Fn = getFunction(getVal(V)))
235  return getFormalParams(CS, Fn, Formals) ? Fn : nullptr;
236 
237  auto *CE = dyn_cast<ConstantExpr>(V);
238  if (!CE || CE->getOpcode() != Instruction::BitCast ||
239  !getFormalParams(CS, getFunction(CE->getOperand(0)), Formals))
240  return nullptr;
241 
242  return dyn_cast<Function>(
243  ConstantFoldLoadThroughBitcast(CE, CE->getOperand(0)->getType(), DL));
244 }
245 
247  SmallVector<Constant *, 8> &Formals) {
248  if (!F)
249  return false;
250 
251  auto *FTy = F->getFunctionType();
252  if (FTy->getNumParams() > CS.getNumArgOperands()) {
253  LLVM_DEBUG(dbgs() << "Too few arguments for function.\n");
254  return false;
255  }
256 
257  auto ArgI = CS.arg_begin();
258  for (auto ParI = FTy->param_begin(), ParE = FTy->param_end(); ParI != ParE;
259  ++ParI) {
260  auto *ArgC = ConstantFoldLoadThroughBitcast(getVal(*ArgI), *ParI, DL);
261  if (!ArgC) {
262  LLVM_DEBUG(dbgs() << "Can not convert function argument.\n");
263  return false;
264  }
265  Formals.push_back(ArgC);
266  ++ArgI;
267  }
268  return true;
269 }
270 
271 /// If call expression contains bitcast then we may need to cast
272 /// evaluated return value to a type of the call expression.
274  ConstantExpr *CE = dyn_cast<ConstantExpr>(CallExpr);
275  if (!RV || !CE || CE->getOpcode() != Instruction::BitCast)
276  return RV;
277 
278  if (auto *FT =
279  dyn_cast<FunctionType>(CE->getType()->getPointerElementType())) {
280  RV = ConstantFoldLoadThroughBitcast(RV, FT->getReturnType(), DL);
281  if (!RV)
282  LLVM_DEBUG(dbgs() << "Failed to fold bitcast call expr\n");
283  }
284  return RV;
285 }
286 
287 /// Evaluate all instructions in block BB, returning true if successful, false
288 /// if we can't evaluate it. NewBB returns the next BB that control flows into,
289 /// or null upon return.
291  BasicBlock *&NextBB) {
292  // This is the main evaluation loop.
293  while (true) {
294  Constant *InstResult = nullptr;
295 
296  LLVM_DEBUG(dbgs() << "Evaluating Instruction: " << *CurInst << "\n");
297 
298  if (StoreInst *SI = dyn_cast<StoreInst>(CurInst)) {
299  if (!SI->isSimple()) {
300  LLVM_DEBUG(dbgs() << "Store is not simple! Can not evaluate.\n");
301  return false; // no volatile/atomic accesses.
302  }
303  Constant *Ptr = getVal(SI->getOperand(1));
304  if (auto *FoldedPtr = ConstantFoldConstant(Ptr, DL, TLI)) {
305  LLVM_DEBUG(dbgs() << "Folding constant ptr expression: " << *Ptr);
306  Ptr = FoldedPtr;
307  LLVM_DEBUG(dbgs() << "; To: " << *Ptr << "\n");
308  }
309  if (!isSimpleEnoughPointerToCommit(Ptr)) {
310  // If this is too complex for us to commit, reject it.
311  LLVM_DEBUG(
312  dbgs() << "Pointer is too complex for us to evaluate store.");
313  return false;
314  }
315 
316  Constant *Val = getVal(SI->getOperand(0));
317 
318  // If this might be too difficult for the backend to handle (e.g. the addr
319  // of one global variable divided by another) then we can't commit it.
320  if (!isSimpleEnoughValueToCommit(Val, SimpleConstants, DL)) {
321  LLVM_DEBUG(dbgs() << "Store value is too complex to evaluate store. "
322  << *Val << "\n");
323  return false;
324  }
325 
326  if (ConstantExpr *CE = dyn_cast<ConstantExpr>(Ptr)) {
327  if (CE->getOpcode() == Instruction::BitCast) {
328  LLVM_DEBUG(dbgs()
329  << "Attempting to resolve bitcast on constant ptr.\n");
330  // If we're evaluating a store through a bitcast, then we need
331  // to pull the bitcast off the pointer type and push it onto the
332  // stored value.
333  Ptr = CE->getOperand(0);
334 
335  Type *NewTy = cast<PointerType>(Ptr->getType())->getElementType();
336 
337  // In order to push the bitcast onto the stored value, a bitcast
338  // from NewTy to Val's type must be legal. If it's not, we can try
339  // introspecting NewTy to find a legal conversion.
340  Constant *NewVal;
341  while (!(NewVal = ConstantFoldLoadThroughBitcast(Val, NewTy, DL))) {
342  // If NewTy is a struct, we can convert the pointer to the struct
343  // into a pointer to its first member.
344  // FIXME: This could be extended to support arrays as well.
345  if (StructType *STy = dyn_cast<StructType>(NewTy)) {
346 
347  IntegerType *IdxTy = IntegerType::get(NewTy->getContext(), 32);
348  Constant *IdxZero = ConstantInt::get(IdxTy, 0, false);
349  Constant * const IdxList[] = {IdxZero, IdxZero};
350 
351  Ptr = ConstantExpr::getGetElementPtr(NewTy, Ptr, IdxList);
352  if (auto *FoldedPtr = ConstantFoldConstant(Ptr, DL, TLI))
353  Ptr = FoldedPtr;
354  NewTy = STy->getTypeAtIndex(0U);
355 
356  // If we can't improve the situation by introspecting NewTy,
357  // we have to give up.
358  } else {
359  LLVM_DEBUG(dbgs() << "Failed to bitcast constant ptr, can not "
360  "evaluate.\n");
361  return false;
362  }
363  }
364 
365  Val = NewVal;
366  LLVM_DEBUG(dbgs() << "Evaluated bitcast: " << *Val << "\n");
367  }
368  }
369 
370  MutatedMemory[Ptr] = Val;
371  } else if (BinaryOperator *BO = dyn_cast<BinaryOperator>(CurInst)) {
372  InstResult = ConstantExpr::get(BO->getOpcode(),
373  getVal(BO->getOperand(0)),
374  getVal(BO->getOperand(1)));
375  LLVM_DEBUG(dbgs() << "Found a BinaryOperator! Simplifying: "
376  << *InstResult << "\n");
377  } else if (CmpInst *CI = dyn_cast<CmpInst>(CurInst)) {
378  InstResult = ConstantExpr::getCompare(CI->getPredicate(),
379  getVal(CI->getOperand(0)),
380  getVal(CI->getOperand(1)));
381  LLVM_DEBUG(dbgs() << "Found a CmpInst! Simplifying: " << *InstResult
382  << "\n");
383  } else if (CastInst *CI = dyn_cast<CastInst>(CurInst)) {
384  InstResult = ConstantExpr::getCast(CI->getOpcode(),
385  getVal(CI->getOperand(0)),
386  CI->getType());
387  LLVM_DEBUG(dbgs() << "Found a Cast! Simplifying: " << *InstResult
388  << "\n");
389  } else if (SelectInst *SI = dyn_cast<SelectInst>(CurInst)) {
390  InstResult = ConstantExpr::getSelect(getVal(SI->getOperand(0)),
391  getVal(SI->getOperand(1)),
392  getVal(SI->getOperand(2)));
393  LLVM_DEBUG(dbgs() << "Found a Select! Simplifying: " << *InstResult
394  << "\n");
395  } else if (auto *EVI = dyn_cast<ExtractValueInst>(CurInst)) {
396  InstResult = ConstantExpr::getExtractValue(
397  getVal(EVI->getAggregateOperand()), EVI->getIndices());
398  LLVM_DEBUG(dbgs() << "Found an ExtractValueInst! Simplifying: "
399  << *InstResult << "\n");
400  } else if (auto *IVI = dyn_cast<InsertValueInst>(CurInst)) {
401  InstResult = ConstantExpr::getInsertValue(
402  getVal(IVI->getAggregateOperand()),
403  getVal(IVI->getInsertedValueOperand()), IVI->getIndices());
404  LLVM_DEBUG(dbgs() << "Found an InsertValueInst! Simplifying: "
405  << *InstResult << "\n");
406  } else if (GetElementPtrInst *GEP = dyn_cast<GetElementPtrInst>(CurInst)) {
407  Constant *P = getVal(GEP->getOperand(0));
409  for (User::op_iterator i = GEP->op_begin() + 1, e = GEP->op_end();
410  i != e; ++i)
411  GEPOps.push_back(getVal(*i));
412  InstResult =
413  ConstantExpr::getGetElementPtr(GEP->getSourceElementType(), P, GEPOps,
414  cast<GEPOperator>(GEP)->isInBounds());
415  LLVM_DEBUG(dbgs() << "Found a GEP! Simplifying: " << *InstResult << "\n");
416  } else if (LoadInst *LI = dyn_cast<LoadInst>(CurInst)) {
417  if (!LI->isSimple()) {
418  LLVM_DEBUG(
419  dbgs() << "Found a Load! Not a simple load, can not evaluate.\n");
420  return false; // no volatile/atomic accesses.
421  }
422 
423  Constant *Ptr = getVal(LI->getOperand(0));
424  if (auto *FoldedPtr = ConstantFoldConstant(Ptr, DL, TLI)) {
425  Ptr = FoldedPtr;
426  LLVM_DEBUG(dbgs() << "Found a constant pointer expression, constant "
427  "folding: "
428  << *Ptr << "\n");
429  }
430  InstResult = ComputeLoadResult(Ptr);
431  if (!InstResult) {
432  LLVM_DEBUG(
433  dbgs() << "Failed to compute load result. Can not evaluate load."
434  "\n");
435  return false; // Could not evaluate load.
436  }
437 
438  LLVM_DEBUG(dbgs() << "Evaluated load: " << *InstResult << "\n");
439  } else if (AllocaInst *AI = dyn_cast<AllocaInst>(CurInst)) {
440  if (AI->isArrayAllocation()) {
441  LLVM_DEBUG(dbgs() << "Found an array alloca. Can not evaluate.\n");
442  return false; // Cannot handle array allocs.
443  }
444  Type *Ty = AI->getAllocatedType();
445  AllocaTmps.push_back(llvm::make_unique<GlobalVariable>(
447  AI->getName(), /*TLMode=*/GlobalValue::NotThreadLocal,
448  AI->getType()->getPointerAddressSpace()));
449  InstResult = AllocaTmps.back().get();
450  LLVM_DEBUG(dbgs() << "Found an alloca. Result: " << *InstResult << "\n");
451  } else if (isa<CallInst>(CurInst) || isa<InvokeInst>(CurInst)) {
452  CallSite CS(&*CurInst);
453 
454  // Debug info can safely be ignored here.
455  if (isa<DbgInfoIntrinsic>(CS.getInstruction())) {
456  LLVM_DEBUG(dbgs() << "Ignoring debug info.\n");
457  ++CurInst;
458  continue;
459  }
460 
461  // Cannot handle inline asm.
462  if (isa<InlineAsm>(CS.getCalledValue())) {
463  LLVM_DEBUG(dbgs() << "Found inline asm, can not evaluate.\n");
464  return false;
465  }
466 
467  if (IntrinsicInst *II = dyn_cast<IntrinsicInst>(CS.getInstruction())) {
468  if (MemSetInst *MSI = dyn_cast<MemSetInst>(II)) {
469  if (MSI->isVolatile()) {
470  LLVM_DEBUG(dbgs() << "Can not optimize a volatile memset "
471  << "intrinsic.\n");
472  return false;
473  }
474  Constant *Ptr = getVal(MSI->getDest());
475  Constant *Val = getVal(MSI->getValue());
476  Constant *DestVal = ComputeLoadResult(getVal(Ptr));
477  if (Val->isNullValue() && DestVal && DestVal->isNullValue()) {
478  // This memset is a no-op.
479  LLVM_DEBUG(dbgs() << "Ignoring no-op memset.\n");
480  ++CurInst;
481  continue;
482  }
483  }
484 
485  if (II->isLifetimeStartOrEnd()) {
486  LLVM_DEBUG(dbgs() << "Ignoring lifetime intrinsic.\n");
487  ++CurInst;
488  continue;
489  }
490 
491  if (II->getIntrinsicID() == Intrinsic::invariant_start) {
492  // We don't insert an entry into Values, as it doesn't have a
493  // meaningful return value.
494  if (!II->use_empty()) {
495  LLVM_DEBUG(dbgs()
496  << "Found unused invariant_start. Can't evaluate.\n");
497  return false;
498  }
499  ConstantInt *Size = cast<ConstantInt>(II->getArgOperand(0));
500  Value *PtrArg = getVal(II->getArgOperand(1));
501  Value *Ptr = PtrArg->stripPointerCasts();
502  if (GlobalVariable *GV = dyn_cast<GlobalVariable>(Ptr)) {
503  Type *ElemTy = GV->getValueType();
504  if (!Size->isMinusOne() &&
505  Size->getValue().getLimitedValue() >=
506  DL.getTypeStoreSize(ElemTy)) {
507  Invariants.insert(GV);
508  LLVM_DEBUG(dbgs() << "Found a global var that is an invariant: "
509  << *GV << "\n");
510  } else {
511  LLVM_DEBUG(dbgs()
512  << "Found a global var, but can not treat it as an "
513  "invariant.\n");
514  }
515  }
516  // Continue even if we do nothing.
517  ++CurInst;
518  continue;
519  } else if (II->getIntrinsicID() == Intrinsic::assume) {
520  LLVM_DEBUG(dbgs() << "Skipping assume intrinsic.\n");
521  ++CurInst;
522  continue;
523  } else if (II->getIntrinsicID() == Intrinsic::sideeffect) {
524  LLVM_DEBUG(dbgs() << "Skipping sideeffect intrinsic.\n");
525  ++CurInst;
526  continue;
527  }
528 
529  LLVM_DEBUG(dbgs() << "Unknown intrinsic. Can not evaluate.\n");
530  return false;
531  }
532 
533  // Resolve function pointers.
535  Function *Callee = getCalleeWithFormalArgs(CS, Formals);
536  if (!Callee || Callee->isInterposable()) {
537  LLVM_DEBUG(dbgs() << "Can not resolve function pointer.\n");
538  return false; // Cannot resolve.
539  }
540 
541  if (Callee->isDeclaration()) {
542  // If this is a function we can constant fold, do it.
543  if (Constant *C = ConstantFoldCall(cast<CallBase>(CS.getInstruction()),
544  Callee, Formals, TLI)) {
545  InstResult = castCallResultIfNeeded(CS.getCalledValue(), C);
546  if (!InstResult)
547  return false;
548  LLVM_DEBUG(dbgs() << "Constant folded function call. Result: "
549  << *InstResult << "\n");
550  } else {
551  LLVM_DEBUG(dbgs() << "Can not constant fold function call.\n");
552  return false;
553  }
554  } else {
555  if (Callee->getFunctionType()->isVarArg()) {
556  LLVM_DEBUG(dbgs() << "Can not constant fold vararg function call.\n");
557  return false;
558  }
559 
560  Constant *RetVal = nullptr;
561  // Execute the call, if successful, use the return value.
562  ValueStack.emplace_back();
563  if (!EvaluateFunction(Callee, RetVal, Formals)) {
564  LLVM_DEBUG(dbgs() << "Failed to evaluate function.\n");
565  return false;
566  }
567  ValueStack.pop_back();
568  InstResult = castCallResultIfNeeded(CS.getCalledValue(), RetVal);
569  if (RetVal && !InstResult)
570  return false;
571 
572  if (InstResult) {
573  LLVM_DEBUG(dbgs() << "Successfully evaluated function. Result: "
574  << *InstResult << "\n\n");
575  } else {
576  LLVM_DEBUG(dbgs()
577  << "Successfully evaluated function. Result: 0\n\n");
578  }
579  }
580  } else if (CurInst->isTerminator()) {
581  LLVM_DEBUG(dbgs() << "Found a terminator instruction.\n");
582 
583  if (BranchInst *BI = dyn_cast<BranchInst>(CurInst)) {
584  if (BI->isUnconditional()) {
585  NextBB = BI->getSuccessor(0);
586  } else {
587  ConstantInt *Cond =
588  dyn_cast<ConstantInt>(getVal(BI->getCondition()));
589  if (!Cond) return false; // Cannot determine.
590 
591  NextBB = BI->getSuccessor(!Cond->getZExtValue());
592  }
593  } else if (SwitchInst *SI = dyn_cast<SwitchInst>(CurInst)) {
594  ConstantInt *Val =
595  dyn_cast<ConstantInt>(getVal(SI->getCondition()));
596  if (!Val) return false; // Cannot determine.
597  NextBB = SI->findCaseValue(Val)->getCaseSuccessor();
598  } else if (IndirectBrInst *IBI = dyn_cast<IndirectBrInst>(CurInst)) {
599  Value *Val = getVal(IBI->getAddress())->stripPointerCasts();
600  if (BlockAddress *BA = dyn_cast<BlockAddress>(Val))
601  NextBB = BA->getBasicBlock();
602  else
603  return false; // Cannot determine.
604  } else if (isa<ReturnInst>(CurInst)) {
605  NextBB = nullptr;
606  } else {
607  // invoke, unwind, resume, unreachable.
608  LLVM_DEBUG(dbgs() << "Can not handle terminator.");
609  return false; // Cannot handle this terminator.
610  }
611 
612  // We succeeded at evaluating this block!
613  LLVM_DEBUG(dbgs() << "Successfully evaluated block.\n");
614  return true;
615  } else {
616  // Did not know how to evaluate this!
617  LLVM_DEBUG(
618  dbgs() << "Failed to evaluate block due to unhandled instruction."
619  "\n");
620  return false;
621  }
622 
623  if (!CurInst->use_empty()) {
624  if (auto *FoldedInstResult = ConstantFoldConstant(InstResult, DL, TLI))
625  InstResult = FoldedInstResult;
626 
627  setVal(&*CurInst, InstResult);
628  }
629 
630  // If we just processed an invoke, we finished evaluating the block.
631  if (InvokeInst *II = dyn_cast<InvokeInst>(CurInst)) {
632  NextBB = II->getNormalDest();
633  LLVM_DEBUG(dbgs() << "Found an invoke instruction. Finished Block.\n\n");
634  return true;
635  }
636 
637  // Advance program counter.
638  ++CurInst;
639  }
640 }
641 
642 /// Evaluate a call to function F, returning true if successful, false if we
643 /// can't evaluate it. ActualArgs contains the formal arguments for the
644 /// function.
646  const SmallVectorImpl<Constant*> &ActualArgs) {
647  // Check to see if this function is already executing (recursion). If so,
648  // bail out. TODO: we might want to accept limited recursion.
649  if (is_contained(CallStack, F))
650  return false;
651 
652  CallStack.push_back(F);
653 
654  // Initialize arguments to the incoming values specified.
655  unsigned ArgNo = 0;
656  for (Function::arg_iterator AI = F->arg_begin(), E = F->arg_end(); AI != E;
657  ++AI, ++ArgNo)
658  setVal(&*AI, ActualArgs[ArgNo]);
659 
660  // ExecutedBlocks - We only handle non-looping, non-recursive code. As such,
661  // we can only evaluate any one basic block at most once. This set keeps
662  // track of what we have executed so we can detect recursive cases etc.
663  SmallPtrSet<BasicBlock*, 32> ExecutedBlocks;
664 
665  // CurBB - The current basic block we're evaluating.
666  BasicBlock *CurBB = &F->front();
667 
668  BasicBlock::iterator CurInst = CurBB->begin();
669 
670  while (true) {
671  BasicBlock *NextBB = nullptr; // Initialized to avoid compiler warnings.
672  LLVM_DEBUG(dbgs() << "Trying to evaluate BB: " << *CurBB << "\n");
673 
674  if (!EvaluateBlock(CurInst, NextBB))
675  return false;
676 
677  if (!NextBB) {
678  // Successfully running until there's no next block means that we found
679  // the return. Fill it the return value and pop the call stack.
680  ReturnInst *RI = cast<ReturnInst>(CurBB->getTerminator());
681  if (RI->getNumOperands())
682  RetVal = getVal(RI->getOperand(0));
683  CallStack.pop_back();
684  return true;
685  }
686 
687  // Okay, we succeeded in evaluating this control flow. See if we have
688  // executed the new block before. If so, we have a looping function,
689  // which we cannot evaluate in reasonable time.
690  if (!ExecutedBlocks.insert(NextBB).second)
691  return false; // looped!
692 
693  // Okay, we have never been in this block before. Check to see if there
694  // are any PHI nodes. If so, evaluate them with information about where
695  // we came from.
696  PHINode *PN = nullptr;
697  for (CurInst = NextBB->begin();
698  (PN = dyn_cast<PHINode>(CurInst)); ++CurInst)
699  setVal(PN, getVal(PN->getIncomingValueForBlock(CurBB)));
700 
701  // Advance to the next block.
702  CurBB = NextBB;
703  }
704 }
uint64_t CallInst * C
Return a value (possibly void), from a function.
A parsed version of the target data layout string in and methods for querying it. ...
Definition: DataLayout.h:110
This class is the base class for the comparison instructions.
Definition: InstrTypes.h:636
bool hasDefinitiveInitializer() const
hasDefinitiveInitializer - Whether the global variable has an initializer, and any other instances of...
unsigned getOpcode() const
Return the opcode at the root of this constant expression.
Definition: Constants.h:1209
This class represents an incoming formal argument to a Function.
Definition: Argument.h:29
const Constant * getInitializer() const
getInitializer - Return the initializer for this global variable.
IterTy arg_begin() const
Definition: CallSite.h:579
This class represents lattice values for constants.
Definition: AllocatorList.h:23
Constant * ConstantFoldLoadThroughGEPConstantExpr(Constant *C, ConstantExpr *CE)
ConstantFoldLoadThroughGEPConstantExpr - Given a constant and a getelementptr constantexpr, return the constant value being addressed by the constant expression, or null if something is funny and we can&#39;t decide.
static Constant * getGetElementPtr(Type *Ty, Constant *C, ArrayRef< Constant *> IdxList, bool InBounds=false, Optional< unsigned > InRangeIndex=None, Type *OnlyIfReducedTy=nullptr)
Getelementptr form.
Definition: Constants.h:1153
Constant * ConstantFoldCall(const CallBase *Call, Function *F, ArrayRef< Constant *> Operands, const TargetLibraryInfo *TLI=nullptr)
ConstantFoldCall - Attempt to constant fold a call to the specified function with the specified argum...
bool EvaluateBlock(BasicBlock::iterator CurInst, BasicBlock *&NextBB)
Evaluate all instructions in block BB, returning true if successful, false if we can&#39;t evaluate it...
Definition: Evaluator.cpp:290
bool getFormalParams(CallSite &CS, Function *F, SmallVector< Constant *, 8 > &Formals)
Given call site and callee returns list of callee formal argument values converting them when necessa...
Definition: Evaluator.cpp:246
bool isInterposable() const
Return true if this global&#39;s definition can be substituted with an arbitrary definition at link time...
Definition: GlobalValue.h:419
This class wraps the llvm.memset intrinsic.
arg_iterator arg_end()
Definition: Function.h:682
F(f)
An instruction for reading from memory.
Definition: Instructions.h:167
static Constant * getCompare(unsigned short pred, Constant *C1, Constant *C2, bool OnlyIfReduced=false)
Return an ICmp or FCmp comparison operator constant expression.
Definition: Constants.cpp:1965
Hexagon Common GEP
const Instruction * getTerminator() const LLVM_READONLY
Returns the terminator instruction if the block is well formed or null if the block is not well forme...
Definition: BasicBlock.cpp:137
bool EvaluateFunction(Function *F, Constant *&RetVal, const SmallVectorImpl< Constant *> &ActualArgs)
Evaluate a call to function F, returning true if successful, false if we can&#39;t evaluate it...
Definition: Evaluator.cpp:645
LLVMContext & getContext() const
Return the LLVMContext in which this type was uniqued.
Definition: Type.h:129
A templated base class for SmallPtrSet which provides the typesafe interface that is common across al...
Definition: SmallPtrSet.h:343
iterator begin()
Instruction iterator methods.
Definition: BasicBlock.h:268
The address of a basic block.
Definition: Constants.h:839
This class represents the LLVM &#39;select&#39; instruction.
Type * getPointerElementType() const
Definition: Type.h:375
This is the base class for all instructions that perform data casts.
Definition: InstrTypes.h:353
Class to represent struct types.
Definition: DerivedTypes.h:232
A Use represents the edge between a Value definition and its users.
Definition: Use.h:55
ValTy * getCalledValue() const
Return the pointer to function that is being called.
Definition: CallSite.h:104
This class consists of common code factored out of the SmallVector class to reduce code duplication b...
Definition: APFloat.h:41
InstrTy * getInstruction() const
Definition: CallSite.h:96
Constant * ConstantFoldConstant(const Constant *C, const DataLayout &DL, const TargetLibraryInfo *TLI=nullptr)
ConstantFoldConstant - Attempt to fold the constant using the specified DataLayout.
A constant value that is initialized with an expression using other constant values.
Definition: Constants.h:888
Type * getType() const
All values are typed, get the type of this value.
Definition: Value.h:244
static Constant * getSelect(Constant *C, Constant *V1, Constant *V2, Type *OnlyIfReducedTy=nullptr)
Select constant expr.
Definition: Constants.cpp:1987
bool isVarArg() const
Definition: DerivedTypes.h:122
const APInt & getValue() const
Return the constant as an APInt value reference.
Definition: Constants.h:137
An instruction for storing to memory.
Definition: Instructions.h:320
bool isMinusOne() const
This function will return true iff every bit in this constant is set to true.
Definition: Constants.h:208
static Function * getFunction(Constant *C)
Definition: Evaluator.cpp:220
Value * getOperand(unsigned i) const
Definition: User.h:169
an instruction for type-safe pointer arithmetic to access elements of arrays and structs ...
Definition: Instructions.h:873
static Constant * getInsertValue(Constant *Agg, Constant *Val, ArrayRef< unsigned > Idxs, Type *OnlyIfReducedTy=nullptr)
Definition: Constants.cpp:2180
#define P(N)
uint64_t getZExtValue() const
Return the constant as a 64-bit unsigned integer value after it has been zero extended as appropriate...
Definition: Constants.h:148
* if(!EatIfPresent(lltok::kw_thread_local)) return false
ParseOptionalThreadLocal := /*empty.
unsigned getNumArgOperands() const
Definition: CallSite.h:303
LLVM Basic Block Representation.
Definition: BasicBlock.h:57
The instances of the Type class are immutable: once they are created, they are never changed...
Definition: Type.h:45
Conditional or Unconditional Branch instruction.
static GCRegistry::Add< CoreCLRGC > E("coreclr", "CoreCLR-compatible GC")
This is an important base class in LLVM.
Definition: Constant.h:41
void setVal(Value *V, Constant *C)
Definition: Evaluator.h:72
Value * getIncomingValueForBlock(const BasicBlock *BB) const
This file contains the declarations for the subclasses of Constant, which represent the different fla...
Indirect Branch Instruction.
std::pair< iterator, bool > insert(PtrType Ptr)
Inserts Ptr if and only if there is no element in the container equal to Ptr.
Definition: SmallPtrSet.h:370
bool hasUniqueInitializer() const
hasUniqueInitializer - Whether the global variable has an initializer, and any changes made to the in...
static bool isSimpleEnoughValueToCommit(Constant *C, SmallPtrSetImpl< Constant *> &SimpleConstants, const DataLayout &DL)
Definition: Evaluator.cpp:116
static bool isSimpleEnoughValueToCommitHelper(Constant *C, SmallPtrSetImpl< Constant *> &SimpleConstants, const DataLayout &DL)
Return true if the specified constant can be handled by the code generator.
Definition: Evaluator.cpp:61
op_range operands()
Definition: User.h:237
arg_iterator arg_begin()
Definition: Function.h:673
Class to represent integer types.
Definition: DerivedTypes.h:39
static UndefValue * get(Type *T)
Static factory methods - Return an &#39;undef&#39; object of the specified type.
Definition: Constants.cpp:1424
const Value * stripPointerCasts() const
Strip off pointer casts, all-zero GEPs, and aliases.
Definition: Value.cpp:529
static IntegerType * get(LLVMContext &C, unsigned NumBits)
This static method is the primary way of constructing an IntegerType.
Definition: Type.cpp:239
Iterator for intrusive lists based on ilist_node.
unsigned getNumOperands() const
Definition: User.h:191
SmallPtrSet - This class implements a set which is optimized for holding SmallSize or less elements...
Definition: SmallPtrSet.h:417
This is the shared class of boolean and integer constants.
Definition: Constants.h:83
Constant * getVal(Value *V)
Definition: Evaluator.h:65
This is a &#39;vector&#39; (really, a variable-sized array), optimized for the case when the array is small...
Definition: SmallVector.h:841
static Constant * getInitializer(Constant *C)
Definition: Evaluator.cpp:177
static Constant * get(Type *Ty, uint64_t V, bool isSigned=false)
If Ty is a vector type, return a Constant with a splat of the given value.
Definition: Constants.cpp:631
raw_ostream & dbgs()
dbgs() - This returns a reference to a raw_ostream for debugging messages.
Definition: Debug.cpp:132
FunctionType * getFunctionType() const
Returns the FunctionType for me.
Definition: Function.h:163
amdgpu Simplify well known AMD library false FunctionCallee Callee
static bool isSimpleEnoughPointerToCommit(Constant *C)
Return true if this constant is simple enough for us to understand.
Definition: Evaluator.cpp:131
static Constant * getCast(unsigned ops, Constant *C, Type *Ty, bool OnlyIfReduced=false)
Convenience function for getting a Cast operation.
Definition: Constants.cpp:1539
uint64_t getTypeSizeInBits(Type *Ty) const
Size examples:
Definition: DataLayout.h:593
Function * getCalleeWithFormalArgs(CallSite &CS, SmallVector< Constant *, 8 > &Formals)
Given call site return callee and list of its formal arguments.
Definition: Evaluator.cpp:231
uint64_t getLimitedValue(uint64_t Limit=UINT64_MAX) const
If this value is smaller than the specified limit, return it, otherwise return the limit value...
Definition: APInt.h:481
StringRef getName() const
Return a constant reference to the value&#39;s name.
Definition: Value.cpp:214
#define I(x, y, z)
Definition: MD5.cpp:58
bool isZero() const
This is just a convenience method to make client code smaller for a common code.
Definition: Constants.h:192
Constant * castCallResultIfNeeded(Value *CallExpr, Constant *RV)
Casts call result to a type of bitcast call expression.
Definition: Evaluator.cpp:273
LLVM_NODISCARD std::enable_if<!is_simple_type< Y >::value, typename cast_retty< X, const Y >::ret_type >::type dyn_cast(const Y &Val)
Definition: Casting.h:332
uint32_t Size
Definition: Profile.cpp:46
Rename collisions when linking (static functions).
Definition: GlobalValue.h:55
bool isDeclaration() const
Return true if the primary definition of this global value is outside of the current translation unit...
Definition: Globals.cpp:205
Multiway switch.
const BasicBlock & front() const
Definition: Function.h:665
LLVM Value Representation.
Definition: Value.h:72
uint64_t getTypeStoreSize(Type *Ty) const
Returns the maximum number of bytes that may be overwritten by storing the specified type...
Definition: DataLayout.h:444
Constant * ConstantFoldLoadThroughBitcast(Constant *C, Type *DestTy, const DataLayout &DL)
ConstantFoldLoadThroughBitcast - try to cast constant to destination type returning null if unsuccess...
Invoke instruction.
static Constant * getExtractValue(Constant *Agg, ArrayRef< unsigned > Idxs, Type *OnlyIfReducedTy=nullptr)
Definition: Constants.cpp:2204
#define LLVM_DEBUG(X)
Definition: Debug.h:122
A wrapper class for inspecting calls to intrinsic functions.
Definition: IntrinsicInst.h:43
an instruction to allocate memory on the stack
Definition: Instructions.h:59
static Constant * get(unsigned Opcode, Constant *C1, unsigned Flags=0, Type *OnlyIfReducedTy=nullptr)
get - Return a unary operator constant expression, folding if possible.
Definition: Constants.cpp:1815
bool is_contained(R &&Range, const E &Element)
Wrapper function around std::find to detect if an element exists in a container.
Definition: STLExtras.h:1244