LLVM  7.0.0svn
Evaluator.cpp
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1 //===- Evaluator.cpp - LLVM IR evaluator ----------------------------------===//
2 //
3 // The LLVM Compiler Infrastructure
4 //
5 // This file is distributed under the University of Illinois Open Source
6 // License. See LICENSE.TXT for details.
7 //
8 //===----------------------------------------------------------------------===//
9 //
10 // Function evaluator for LLVM IR.
11 //
12 //===----------------------------------------------------------------------===//
13 
15 #include "llvm/ADT/DenseMap.h"
16 #include "llvm/ADT/STLExtras.h"
17 #include "llvm/ADT/SmallPtrSet.h"
18 #include "llvm/ADT/SmallVector.h"
20 #include "llvm/IR/BasicBlock.h"
21 #include "llvm/IR/CallSite.h"
22 #include "llvm/IR/Constant.h"
23 #include "llvm/IR/Constants.h"
24 #include "llvm/IR/DataLayout.h"
25 #include "llvm/IR/DerivedTypes.h"
26 #include "llvm/IR/Function.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 
220 /// Evaluate all instructions in block BB, returning true if successful, false
221 /// if we can't evaluate it. NewBB returns the next BB that control flows into,
222 /// or null upon return.
224  BasicBlock *&NextBB) {
225  // This is the main evaluation loop.
226  while (true) {
227  Constant *InstResult = nullptr;
228 
229  LLVM_DEBUG(dbgs() << "Evaluating Instruction: " << *CurInst << "\n");
230 
231  if (StoreInst *SI = dyn_cast<StoreInst>(CurInst)) {
232  if (!SI->isSimple()) {
233  LLVM_DEBUG(dbgs() << "Store is not simple! Can not evaluate.\n");
234  return false; // no volatile/atomic accesses.
235  }
236  Constant *Ptr = getVal(SI->getOperand(1));
237  if (auto *FoldedPtr = ConstantFoldConstant(Ptr, DL, TLI)) {
238  LLVM_DEBUG(dbgs() << "Folding constant ptr expression: " << *Ptr);
239  Ptr = FoldedPtr;
240  LLVM_DEBUG(dbgs() << "; To: " << *Ptr << "\n");
241  }
242  if (!isSimpleEnoughPointerToCommit(Ptr)) {
243  // If this is too complex for us to commit, reject it.
244  LLVM_DEBUG(
245  dbgs() << "Pointer is too complex for us to evaluate store.");
246  return false;
247  }
248 
249  Constant *Val = getVal(SI->getOperand(0));
250 
251  // If this might be too difficult for the backend to handle (e.g. the addr
252  // of one global variable divided by another) then we can't commit it.
253  if (!isSimpleEnoughValueToCommit(Val, SimpleConstants, DL)) {
254  LLVM_DEBUG(dbgs() << "Store value is too complex to evaluate store. "
255  << *Val << "\n");
256  return false;
257  }
258 
259  if (ConstantExpr *CE = dyn_cast<ConstantExpr>(Ptr)) {
260  if (CE->getOpcode() == Instruction::BitCast) {
261  LLVM_DEBUG(dbgs()
262  << "Attempting to resolve bitcast on constant ptr.\n");
263  // If we're evaluating a store through a bitcast, then we need
264  // to pull the bitcast off the pointer type and push it onto the
265  // stored value.
266  Ptr = CE->getOperand(0);
267 
268  Type *NewTy = cast<PointerType>(Ptr->getType())->getElementType();
269 
270  // In order to push the bitcast onto the stored value, a bitcast
271  // from NewTy to Val's type must be legal. If it's not, we can try
272  // introspecting NewTy to find a legal conversion.
273  Constant *NewVal;
274  while (!(NewVal = ConstantFoldLoadThroughBitcast(Val, NewTy, DL))) {
275  // If NewTy is a struct, we can convert the pointer to the struct
276  // into a pointer to its first member.
277  // FIXME: This could be extended to support arrays as well.
278  if (StructType *STy = dyn_cast<StructType>(NewTy)) {
279  NewTy = STy->getTypeAtIndex(0U);
280 
281  IntegerType *IdxTy = IntegerType::get(NewTy->getContext(), 32);
282  Constant *IdxZero = ConstantInt::get(IdxTy, 0, false);
283  Constant * const IdxList[] = {IdxZero, IdxZero};
284 
285  Ptr = ConstantExpr::getGetElementPtr(nullptr, Ptr, IdxList);
286  if (auto *FoldedPtr = ConstantFoldConstant(Ptr, DL, TLI))
287  Ptr = FoldedPtr;
288 
289  // If we can't improve the situation by introspecting NewTy,
290  // we have to give up.
291  } else {
292  LLVM_DEBUG(dbgs() << "Failed to bitcast constant ptr, can not "
293  "evaluate.\n");
294  return false;
295  }
296  }
297 
298  Val = NewVal;
299  LLVM_DEBUG(dbgs() << "Evaluated bitcast: " << *Val << "\n");
300  }
301  }
302 
303  MutatedMemory[Ptr] = Val;
304  } else if (BinaryOperator *BO = dyn_cast<BinaryOperator>(CurInst)) {
305  InstResult = ConstantExpr::get(BO->getOpcode(),
306  getVal(BO->getOperand(0)),
307  getVal(BO->getOperand(1)));
308  LLVM_DEBUG(dbgs() << "Found a BinaryOperator! Simplifying: "
309  << *InstResult << "\n");
310  } else if (CmpInst *CI = dyn_cast<CmpInst>(CurInst)) {
311  InstResult = ConstantExpr::getCompare(CI->getPredicate(),
312  getVal(CI->getOperand(0)),
313  getVal(CI->getOperand(1)));
314  LLVM_DEBUG(dbgs() << "Found a CmpInst! Simplifying: " << *InstResult
315  << "\n");
316  } else if (CastInst *CI = dyn_cast<CastInst>(CurInst)) {
317  InstResult = ConstantExpr::getCast(CI->getOpcode(),
318  getVal(CI->getOperand(0)),
319  CI->getType());
320  LLVM_DEBUG(dbgs() << "Found a Cast! Simplifying: " << *InstResult
321  << "\n");
322  } else if (SelectInst *SI = dyn_cast<SelectInst>(CurInst)) {
323  InstResult = ConstantExpr::getSelect(getVal(SI->getOperand(0)),
324  getVal(SI->getOperand(1)),
325  getVal(SI->getOperand(2)));
326  LLVM_DEBUG(dbgs() << "Found a Select! Simplifying: " << *InstResult
327  << "\n");
328  } else if (auto *EVI = dyn_cast<ExtractValueInst>(CurInst)) {
329  InstResult = ConstantExpr::getExtractValue(
330  getVal(EVI->getAggregateOperand()), EVI->getIndices());
331  LLVM_DEBUG(dbgs() << "Found an ExtractValueInst! Simplifying: "
332  << *InstResult << "\n");
333  } else if (auto *IVI = dyn_cast<InsertValueInst>(CurInst)) {
334  InstResult = ConstantExpr::getInsertValue(
335  getVal(IVI->getAggregateOperand()),
336  getVal(IVI->getInsertedValueOperand()), IVI->getIndices());
337  LLVM_DEBUG(dbgs() << "Found an InsertValueInst! Simplifying: "
338  << *InstResult << "\n");
339  } else if (GetElementPtrInst *GEP = dyn_cast<GetElementPtrInst>(CurInst)) {
340  Constant *P = getVal(GEP->getOperand(0));
342  for (User::op_iterator i = GEP->op_begin() + 1, e = GEP->op_end();
343  i != e; ++i)
344  GEPOps.push_back(getVal(*i));
345  InstResult =
346  ConstantExpr::getGetElementPtr(GEP->getSourceElementType(), P, GEPOps,
347  cast<GEPOperator>(GEP)->isInBounds());
348  LLVM_DEBUG(dbgs() << "Found a GEP! Simplifying: " << *InstResult << "\n");
349  } else if (LoadInst *LI = dyn_cast<LoadInst>(CurInst)) {
350  if (!LI->isSimple()) {
351  LLVM_DEBUG(
352  dbgs() << "Found a Load! Not a simple load, can not evaluate.\n");
353  return false; // no volatile/atomic accesses.
354  }
355 
356  Constant *Ptr = getVal(LI->getOperand(0));
357  if (auto *FoldedPtr = ConstantFoldConstant(Ptr, DL, TLI)) {
358  Ptr = FoldedPtr;
359  LLVM_DEBUG(dbgs() << "Found a constant pointer expression, constant "
360  "folding: "
361  << *Ptr << "\n");
362  }
363  InstResult = ComputeLoadResult(Ptr);
364  if (!InstResult) {
365  LLVM_DEBUG(
366  dbgs() << "Failed to compute load result. Can not evaluate load."
367  "\n");
368  return false; // Could not evaluate load.
369  }
370 
371  LLVM_DEBUG(dbgs() << "Evaluated load: " << *InstResult << "\n");
372  } else if (AllocaInst *AI = dyn_cast<AllocaInst>(CurInst)) {
373  if (AI->isArrayAllocation()) {
374  LLVM_DEBUG(dbgs() << "Found an array alloca. Can not evaluate.\n");
375  return false; // Cannot handle array allocs.
376  }
377  Type *Ty = AI->getAllocatedType();
378  AllocaTmps.push_back(llvm::make_unique<GlobalVariable>(
380  AI->getName(), /*TLMode=*/GlobalValue::NotThreadLocal,
381  AI->getType()->getPointerAddressSpace()));
382  InstResult = AllocaTmps.back().get();
383  LLVM_DEBUG(dbgs() << "Found an alloca. Result: " << *InstResult << "\n");
384  } else if (isa<CallInst>(CurInst) || isa<InvokeInst>(CurInst)) {
385  CallSite CS(&*CurInst);
386 
387  // Debug info can safely be ignored here.
388  if (isa<DbgInfoIntrinsic>(CS.getInstruction())) {
389  LLVM_DEBUG(dbgs() << "Ignoring debug info.\n");
390  ++CurInst;
391  continue;
392  }
393 
394  // Cannot handle inline asm.
395  if (isa<InlineAsm>(CS.getCalledValue())) {
396  LLVM_DEBUG(dbgs() << "Found inline asm, can not evaluate.\n");
397  return false;
398  }
399 
400  if (IntrinsicInst *II = dyn_cast<IntrinsicInst>(CS.getInstruction())) {
401  if (MemSetInst *MSI = dyn_cast<MemSetInst>(II)) {
402  if (MSI->isVolatile()) {
403  LLVM_DEBUG(dbgs() << "Can not optimize a volatile memset "
404  << "intrinsic.\n");
405  return false;
406  }
407  Constant *Ptr = getVal(MSI->getDest());
408  Constant *Val = getVal(MSI->getValue());
409  Constant *DestVal = ComputeLoadResult(getVal(Ptr));
410  if (Val->isNullValue() && DestVal && DestVal->isNullValue()) {
411  // This memset is a no-op.
412  LLVM_DEBUG(dbgs() << "Ignoring no-op memset.\n");
413  ++CurInst;
414  continue;
415  }
416  }
417 
418  if (II->getIntrinsicID() == Intrinsic::lifetime_start ||
419  II->getIntrinsicID() == Intrinsic::lifetime_end) {
420  LLVM_DEBUG(dbgs() << "Ignoring lifetime intrinsic.\n");
421  ++CurInst;
422  continue;
423  }
424 
425  if (II->getIntrinsicID() == Intrinsic::invariant_start) {
426  // We don't insert an entry into Values, as it doesn't have a
427  // meaningful return value.
428  if (!II->use_empty()) {
429  LLVM_DEBUG(dbgs()
430  << "Found unused invariant_start. Can't evaluate.\n");
431  return false;
432  }
433  ConstantInt *Size = cast<ConstantInt>(II->getArgOperand(0));
434  Value *PtrArg = getVal(II->getArgOperand(1));
435  Value *Ptr = PtrArg->stripPointerCasts();
436  if (GlobalVariable *GV = dyn_cast<GlobalVariable>(Ptr)) {
437  Type *ElemTy = GV->getValueType();
438  if (!Size->isMinusOne() &&
439  Size->getValue().getLimitedValue() >=
440  DL.getTypeStoreSize(ElemTy)) {
441  Invariants.insert(GV);
442  LLVM_DEBUG(dbgs() << "Found a global var that is an invariant: "
443  << *GV << "\n");
444  } else {
445  LLVM_DEBUG(dbgs()
446  << "Found a global var, but can not treat it as an "
447  "invariant.\n");
448  }
449  }
450  // Continue even if we do nothing.
451  ++CurInst;
452  continue;
453  } else if (II->getIntrinsicID() == Intrinsic::assume) {
454  LLVM_DEBUG(dbgs() << "Skipping assume intrinsic.\n");
455  ++CurInst;
456  continue;
457  } else if (II->getIntrinsicID() == Intrinsic::sideeffect) {
458  LLVM_DEBUG(dbgs() << "Skipping sideeffect intrinsic.\n");
459  ++CurInst;
460  continue;
461  }
462 
463  LLVM_DEBUG(dbgs() << "Unknown intrinsic. Can not evaluate.\n");
464  return false;
465  }
466 
467  // Resolve function pointers.
469  if (!Callee || Callee->isInterposable()) {
470  LLVM_DEBUG(dbgs() << "Can not resolve function pointer.\n");
471  return false; // Cannot resolve.
472  }
473 
475  for (User::op_iterator i = CS.arg_begin(), e = CS.arg_end(); i != e; ++i)
476  Formals.push_back(getVal(*i));
477 
478  if (Callee->isDeclaration()) {
479  // If this is a function we can constant fold, do it.
480  if (Constant *C = ConstantFoldCall(CS, Callee, Formals, TLI)) {
481  InstResult = C;
482  LLVM_DEBUG(dbgs() << "Constant folded function call. Result: "
483  << *InstResult << "\n");
484  } else {
485  LLVM_DEBUG(dbgs() << "Can not constant fold function call.\n");
486  return false;
487  }
488  } else {
489  if (Callee->getFunctionType()->isVarArg()) {
490  LLVM_DEBUG(dbgs() << "Can not constant fold vararg function call.\n");
491  return false;
492  }
493 
494  Constant *RetVal = nullptr;
495  // Execute the call, if successful, use the return value.
496  ValueStack.emplace_back();
497  if (!EvaluateFunction(Callee, RetVal, Formals)) {
498  LLVM_DEBUG(dbgs() << "Failed to evaluate function.\n");
499  return false;
500  }
501  ValueStack.pop_back();
502  InstResult = RetVal;
503 
504  if (InstResult) {
505  LLVM_DEBUG(dbgs() << "Successfully evaluated function. Result: "
506  << *InstResult << "\n\n");
507  } else {
508  LLVM_DEBUG(dbgs()
509  << "Successfully evaluated function. Result: 0\n\n");
510  }
511  }
512  } else if (isa<TerminatorInst>(CurInst)) {
513  LLVM_DEBUG(dbgs() << "Found a terminator instruction.\n");
514 
515  if (BranchInst *BI = dyn_cast<BranchInst>(CurInst)) {
516  if (BI->isUnconditional()) {
517  NextBB = BI->getSuccessor(0);
518  } else {
519  ConstantInt *Cond =
520  dyn_cast<ConstantInt>(getVal(BI->getCondition()));
521  if (!Cond) return false; // Cannot determine.
522 
523  NextBB = BI->getSuccessor(!Cond->getZExtValue());
524  }
525  } else if (SwitchInst *SI = dyn_cast<SwitchInst>(CurInst)) {
526  ConstantInt *Val =
527  dyn_cast<ConstantInt>(getVal(SI->getCondition()));
528  if (!Val) return false; // Cannot determine.
529  NextBB = SI->findCaseValue(Val)->getCaseSuccessor();
530  } else if (IndirectBrInst *IBI = dyn_cast<IndirectBrInst>(CurInst)) {
531  Value *Val = getVal(IBI->getAddress())->stripPointerCasts();
532  if (BlockAddress *BA = dyn_cast<BlockAddress>(Val))
533  NextBB = BA->getBasicBlock();
534  else
535  return false; // Cannot determine.
536  } else if (isa<ReturnInst>(CurInst)) {
537  NextBB = nullptr;
538  } else {
539  // invoke, unwind, resume, unreachable.
540  LLVM_DEBUG(dbgs() << "Can not handle terminator.");
541  return false; // Cannot handle this terminator.
542  }
543 
544  // We succeeded at evaluating this block!
545  LLVM_DEBUG(dbgs() << "Successfully evaluated block.\n");
546  return true;
547  } else {
548  // Did not know how to evaluate this!
549  LLVM_DEBUG(
550  dbgs() << "Failed to evaluate block due to unhandled instruction."
551  "\n");
552  return false;
553  }
554 
555  if (!CurInst->use_empty()) {
556  if (auto *FoldedInstResult = ConstantFoldConstant(InstResult, DL, TLI))
557  InstResult = FoldedInstResult;
558 
559  setVal(&*CurInst, InstResult);
560  }
561 
562  // If we just processed an invoke, we finished evaluating the block.
563  if (InvokeInst *II = dyn_cast<InvokeInst>(CurInst)) {
564  NextBB = II->getNormalDest();
565  LLVM_DEBUG(dbgs() << "Found an invoke instruction. Finished Block.\n\n");
566  return true;
567  }
568 
569  // Advance program counter.
570  ++CurInst;
571  }
572 }
573 
574 /// Evaluate a call to function F, returning true if successful, false if we
575 /// can't evaluate it. ActualArgs contains the formal arguments for the
576 /// function.
578  const SmallVectorImpl<Constant*> &ActualArgs) {
579  // Check to see if this function is already executing (recursion). If so,
580  // bail out. TODO: we might want to accept limited recursion.
581  if (is_contained(CallStack, F))
582  return false;
583 
584  CallStack.push_back(F);
585 
586  // Initialize arguments to the incoming values specified.
587  unsigned ArgNo = 0;
588  for (Function::arg_iterator AI = F->arg_begin(), E = F->arg_end(); AI != E;
589  ++AI, ++ArgNo)
590  setVal(&*AI, ActualArgs[ArgNo]);
591 
592  // ExecutedBlocks - We only handle non-looping, non-recursive code. As such,
593  // we can only evaluate any one basic block at most once. This set keeps
594  // track of what we have executed so we can detect recursive cases etc.
595  SmallPtrSet<BasicBlock*, 32> ExecutedBlocks;
596 
597  // CurBB - The current basic block we're evaluating.
598  BasicBlock *CurBB = &F->front();
599 
600  BasicBlock::iterator CurInst = CurBB->begin();
601 
602  while (true) {
603  BasicBlock *NextBB = nullptr; // Initialized to avoid compiler warnings.
604  LLVM_DEBUG(dbgs() << "Trying to evaluate BB: " << *CurBB << "\n");
605 
606  if (!EvaluateBlock(CurInst, NextBB))
607  return false;
608 
609  if (!NextBB) {
610  // Successfully running until there's no next block means that we found
611  // the return. Fill it the return value and pop the call stack.
612  ReturnInst *RI = cast<ReturnInst>(CurBB->getTerminator());
613  if (RI->getNumOperands())
614  RetVal = getVal(RI->getOperand(0));
615  CallStack.pop_back();
616  return true;
617  }
618 
619  // Okay, we succeeded in evaluating this control flow. See if we have
620  // executed the new block before. If so, we have a looping function,
621  // which we cannot evaluate in reasonable time.
622  if (!ExecutedBlocks.insert(NextBB).second)
623  return false; // looped!
624 
625  // Okay, we have never been in this block before. Check to see if there
626  // are any PHI nodes. If so, evaluate them with information about where
627  // we came from.
628  PHINode *PN = nullptr;
629  for (CurInst = NextBB->begin();
630  (PN = dyn_cast<PHINode>(CurInst)); ++CurInst)
631  setVal(PN, getVal(PN->getIncomingValueForBlock(CurBB)));
632 
633  // Advance to the next block.
634  CurBB = NextBB;
635  }
636 }
uint64_t CallInst * C
Return a value (possibly void), from a function.
void push_back(const T &Elt)
Definition: SmallVector.h:213
A parsed version of the target data layout string in and methods for querying it. ...
Definition: DataLayout.h:111
This class is the base class for the comparison instructions.
Definition: InstrTypes.h:875
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:1194
This class represents an incoming formal argument to a Function.
Definition: Argument.h:30
const Constant * getInitializer() const
getInitializer - Return the initializer for this global variable.
Compute iterated dominance frontiers using a linear time algorithm.
Definition: AllocatorList.h:24
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:1138
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:223
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:666
F(f)
An instruction for reading from memory.
Definition: Instructions.h:164
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:1894
Hexagon Common GEP
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:577
LLVMContext & getContext() const
Return the LLVMContext in which this type was uniqued.
Definition: Type.h:130
A templated base class for SmallPtrSet which provides the typesafe interface that is common across al...
Definition: SmallPtrSet.h:344
iterator begin()
Instruction iterator methods.
Definition: BasicBlock.h:264
The address of a basic block.
Definition: Constants.h:836
This class represents the LLVM &#39;select&#39; instruction.
Type * getPointerElementType() const
Definition: Type.h:373
This is the base class for all instructions that perform data casts.
Definition: InstrTypes.h:592
Class to represent struct types.
Definition: DerivedTypes.h:201
A Use represents the edge between a Value definition and its users.
Definition: Use.h:56
IterTy arg_end() const
Definition: CallSite.h:575
This class consists of common code factored out of the SmallVector class to reduce code duplication b...
Definition: APFloat.h:42
InstrTy * getInstruction() const
Definition: CallSite.h:92
ValTy * getCalledValue() const
Return the pointer to function that is being called.
Definition: CallSite.h:100
Constant * ConstantFoldConstant(const Constant *C, const DataLayout &DL, const TargetLibraryInfo *TLI=nullptr)
ConstantFoldConstant - Attempt to fold the constant using the specified DataLayout.
static Constant * get(unsigned Opcode, Constant *C1, Constant *C2, unsigned Flags=0, Type *OnlyIfReducedTy=nullptr)
get - Return a binary or shift operator constant expression, folding if possible. ...
Definition: Constants.cpp:1773
A constant value that is initialized with an expression using other constant values.
Definition: Constants.h:885
Type * getType() const
All values are typed, get the type of this value.
Definition: Value.h:245
static Constant * getSelect(Constant *C, Constant *V1, Constant *V2, Type *OnlyIfReducedTy=nullptr)
Select constant expr.
Definition: Constants.cpp:1916
bool isVarArg() const
Definition: DerivedTypes.h:123
const APInt & getValue() const
Return the constant as an APInt value reference.
Definition: Constants.h:138
An instruction for storing to memory.
Definition: Instructions.h:306
bool isMinusOne() const
This function will return true iff every bit in this constant is set to true.
Definition: Constants.h:209
amdgpu Simplify well known AMD library false Value * Callee
Value * getOperand(unsigned i) const
Definition: User.h:170
an instruction for type-safe pointer arithmetic to access elements of arrays and structs ...
Definition: Instructions.h:837
static Constant * getInsertValue(Constant *Agg, Constant *Val, ArrayRef< unsigned > Idxs, Type *OnlyIfReducedTy=nullptr)
Definition: Constants.cpp:2110
#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:149
* if(!EatIfPresent(lltok::kw_thread_local)) return false
ParseOptionalThreadLocal := /*empty.
LLVM Basic Block Representation.
Definition: BasicBlock.h:59
The instances of the Type class are immutable: once they are created, they are never changed...
Definition: Type.h:46
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:42
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:371
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:238
arg_iterator arg_begin()
Definition: Function.h:657
Class to represent integer types.
Definition: DerivedTypes.h:40
static UndefValue * get(Type *T)
Static factory methods - Return an &#39;undef&#39; object of the specified type.
Definition: Constants.cpp:1382
const Value * stripPointerCasts() const
Strip off pointer casts, all-zero GEPs, and aliases.
Definition: Value.cpp:538
static IntegerType * get(LLVMContext &C, unsigned NumBits)
This static method is the primary way of constructing an IntegerType.
Definition: Type.cpp:240
Iterator for intrusive lists based on ilist_node.
unsigned getNumOperands() const
Definition: User.h:192
SmallPtrSet - This class implements a set which is optimized for holding SmallSize or less elements...
Definition: SmallPtrSet.h:418
This is the shared class of boolean and integer constants.
Definition: Constants.h:84
Constant * getVal(Value *V)
Definition: Evaluator.h:65
IterTy arg_begin() const
Definition: CallSite.h:571
This is a &#39;vector&#39; (really, a variable-sized array), optimized for the case when the array is small...
Definition: SmallVector.h:861
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:611
raw_ostream & dbgs()
dbgs() - This returns a reference to a raw_ostream for debugging messages.
Definition: Debug.cpp:133
FunctionType * getFunctionType() const
Returns the FunctionType for me.
Definition: Function.h:150
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:1497
uint64_t getTypeSizeInBits(Type *Ty) const
Size examples:
Definition: DataLayout.h:560
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:475
StringRef getName() const
Return a constant reference to the value&#39;s name.
Definition: Value.cpp:224
#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:193
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:323
Rename collisions when linking (static functions).
Definition: GlobalValue.h:56
bool isDeclaration() const
Return true if the primary definition of this global value is outside of the current translation unit...
Definition: Globals.cpp:201
Multiway switch.
const BasicBlock & front() const
Definition: Function.h:649
LLVM Value Representation.
Definition: Value.h:73
uint64_t getTypeStoreSize(Type *Ty) const
Returns the maximum number of bytes that may be overwritten by storing the specified type...
Definition: DataLayout.h:411
Constant * ConstantFoldLoadThroughBitcast(Constant *C, Type *DestTy, const DataLayout &DL)
ConstantFoldLoadThroughBitcast - try to cast constant to destination type returning null if unsuccess...
constexpr char Size[]
Key for Kernel::Arg::Metadata::mSize.
Invoke instruction.
static Constant * getExtractValue(Constant *Agg, ArrayRef< unsigned > Idxs, Type *OnlyIfReducedTy=nullptr)
Definition: Constants.cpp:2134
const TerminatorInst * 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:138
#define LLVM_DEBUG(X)
Definition: Debug.h:119
Constant * ConstantFoldCall(ImmutableCallSite CS, Function *F, ArrayRef< Constant *> Operands, const TargetLibraryInfo *TLI=nullptr)
ConstantFoldCall - Attempt to constant fold a call to the specified function with the specified argum...
A wrapper class for inspecting calls to intrinsic functions.
Definition: IntrinsicInst.h:44
an instruction to allocate memory on the stack
Definition: Instructions.h:60
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:967