LLVM  6.0.0svn
Evaluator.cpp
Go to the documentation of this file.
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 
177 /// Return the value that would be computed by a load from P after the stores
178 /// reflected by 'memory' have been performed. If we can't decide, return null.
179 Constant *Evaluator::ComputeLoadResult(Constant *P) {
180  // If this memory location has been recently stored, use the stored value: it
181  // is the most up-to-date.
182  DenseMap<Constant*, Constant*>::const_iterator I = MutatedMemory.find(P);
183  if (I != MutatedMemory.end()) return I->second;
184 
185  // Access it.
186  if (GlobalVariable *GV = dyn_cast<GlobalVariable>(P)) {
187  if (GV->hasDefinitiveInitializer())
188  return GV->getInitializer();
189  return nullptr;
190  }
191 
192  // Handle a constantexpr getelementptr.
193  if (ConstantExpr *CE = dyn_cast<ConstantExpr>(P))
194  if (CE->getOpcode() == Instruction::GetElementPtr &&
195  isa<GlobalVariable>(CE->getOperand(0))) {
196  GlobalVariable *GV = cast<GlobalVariable>(CE->getOperand(0));
197  if (GV->hasDefinitiveInitializer())
199  }
200 
201  return nullptr; // don't know how to evaluate.
202 }
203 
204 /// Evaluate all instructions in block BB, returning true if successful, false
205 /// if we can't evaluate it. NewBB returns the next BB that control flows into,
206 /// or null upon return.
208  BasicBlock *&NextBB) {
209  // This is the main evaluation loop.
210  while (true) {
211  Constant *InstResult = nullptr;
212 
213  DEBUG(dbgs() << "Evaluating Instruction: " << *CurInst << "\n");
214 
215  if (StoreInst *SI = dyn_cast<StoreInst>(CurInst)) {
216  if (!SI->isSimple()) {
217  DEBUG(dbgs() << "Store is not simple! Can not evaluate.\n");
218  return false; // no volatile/atomic accesses.
219  }
220  Constant *Ptr = getVal(SI->getOperand(1));
221  if (auto *FoldedPtr = ConstantFoldConstant(Ptr, DL, TLI)) {
222  DEBUG(dbgs() << "Folding constant ptr expression: " << *Ptr);
223  Ptr = FoldedPtr;
224  DEBUG(dbgs() << "; To: " << *Ptr << "\n");
225  }
226  if (!isSimpleEnoughPointerToCommit(Ptr)) {
227  // If this is too complex for us to commit, reject it.
228  DEBUG(dbgs() << "Pointer is too complex for us to evaluate store.");
229  return false;
230  }
231 
232  Constant *Val = getVal(SI->getOperand(0));
233 
234  // If this might be too difficult for the backend to handle (e.g. the addr
235  // of one global variable divided by another) then we can't commit it.
236  if (!isSimpleEnoughValueToCommit(Val, SimpleConstants, DL)) {
237  DEBUG(dbgs() << "Store value is too complex to evaluate store. " << *Val
238  << "\n");
239  return false;
240  }
241 
242  if (ConstantExpr *CE = dyn_cast<ConstantExpr>(Ptr)) {
243  if (CE->getOpcode() == Instruction::BitCast) {
244  DEBUG(dbgs() << "Attempting to resolve bitcast on constant ptr.\n");
245  // If we're evaluating a store through a bitcast, then we need
246  // to pull the bitcast off the pointer type and push it onto the
247  // stored value.
248  Ptr = CE->getOperand(0);
249 
250  Type *NewTy = cast<PointerType>(Ptr->getType())->getElementType();
251 
252  // In order to push the bitcast onto the stored value, a bitcast
253  // from NewTy to Val's type must be legal. If it's not, we can try
254  // introspecting NewTy to find a legal conversion.
255  while (!Val->getType()->canLosslesslyBitCastTo(NewTy)) {
256  // If NewTy is a struct, we can convert the pointer to the struct
257  // into a pointer to its first member.
258  // FIXME: This could be extended to support arrays as well.
259  if (StructType *STy = dyn_cast<StructType>(NewTy)) {
260  NewTy = STy->getTypeAtIndex(0U);
261 
262  IntegerType *IdxTy = IntegerType::get(NewTy->getContext(), 32);
263  Constant *IdxZero = ConstantInt::get(IdxTy, 0, false);
264  Constant * const IdxList[] = {IdxZero, IdxZero};
265 
266  Ptr = ConstantExpr::getGetElementPtr(nullptr, Ptr, IdxList);
267  if (auto *FoldedPtr = ConstantFoldConstant(Ptr, DL, TLI))
268  Ptr = FoldedPtr;
269 
270  // If we can't improve the situation by introspecting NewTy,
271  // we have to give up.
272  } else {
273  DEBUG(dbgs() << "Failed to bitcast constant ptr, can not "
274  "evaluate.\n");
275  return false;
276  }
277  }
278 
279  // If we found compatible types, go ahead and push the bitcast
280  // onto the stored value.
281  Val = ConstantExpr::getBitCast(Val, NewTy);
282 
283  DEBUG(dbgs() << "Evaluated bitcast: " << *Val << "\n");
284  }
285  }
286 
287  MutatedMemory[Ptr] = Val;
288  } else if (BinaryOperator *BO = dyn_cast<BinaryOperator>(CurInst)) {
289  InstResult = ConstantExpr::get(BO->getOpcode(),
290  getVal(BO->getOperand(0)),
291  getVal(BO->getOperand(1)));
292  DEBUG(dbgs() << "Found a BinaryOperator! Simplifying: " << *InstResult
293  << "\n");
294  } else if (CmpInst *CI = dyn_cast<CmpInst>(CurInst)) {
295  InstResult = ConstantExpr::getCompare(CI->getPredicate(),
296  getVal(CI->getOperand(0)),
297  getVal(CI->getOperand(1)));
298  DEBUG(dbgs() << "Found a CmpInst! Simplifying: " << *InstResult
299  << "\n");
300  } else if (CastInst *CI = dyn_cast<CastInst>(CurInst)) {
301  InstResult = ConstantExpr::getCast(CI->getOpcode(),
302  getVal(CI->getOperand(0)),
303  CI->getType());
304  DEBUG(dbgs() << "Found a Cast! Simplifying: " << *InstResult
305  << "\n");
306  } else if (SelectInst *SI = dyn_cast<SelectInst>(CurInst)) {
307  InstResult = ConstantExpr::getSelect(getVal(SI->getOperand(0)),
308  getVal(SI->getOperand(1)),
309  getVal(SI->getOperand(2)));
310  DEBUG(dbgs() << "Found a Select! Simplifying: " << *InstResult
311  << "\n");
312  } else if (auto *EVI = dyn_cast<ExtractValueInst>(CurInst)) {
313  InstResult = ConstantExpr::getExtractValue(
314  getVal(EVI->getAggregateOperand()), EVI->getIndices());
315  DEBUG(dbgs() << "Found an ExtractValueInst! Simplifying: " << *InstResult
316  << "\n");
317  } else if (auto *IVI = dyn_cast<InsertValueInst>(CurInst)) {
318  InstResult = ConstantExpr::getInsertValue(
319  getVal(IVI->getAggregateOperand()),
320  getVal(IVI->getInsertedValueOperand()), IVI->getIndices());
321  DEBUG(dbgs() << "Found an InsertValueInst! Simplifying: " << *InstResult
322  << "\n");
323  } else if (GetElementPtrInst *GEP = dyn_cast<GetElementPtrInst>(CurInst)) {
324  Constant *P = getVal(GEP->getOperand(0));
326  for (User::op_iterator i = GEP->op_begin() + 1, e = GEP->op_end();
327  i != e; ++i)
328  GEPOps.push_back(getVal(*i));
329  InstResult =
330  ConstantExpr::getGetElementPtr(GEP->getSourceElementType(), P, GEPOps,
331  cast<GEPOperator>(GEP)->isInBounds());
332  DEBUG(dbgs() << "Found a GEP! Simplifying: " << *InstResult
333  << "\n");
334  } else if (LoadInst *LI = dyn_cast<LoadInst>(CurInst)) {
335  if (!LI->isSimple()) {
336  DEBUG(dbgs() << "Found a Load! Not a simple load, can not evaluate.\n");
337  return false; // no volatile/atomic accesses.
338  }
339 
340  Constant *Ptr = getVal(LI->getOperand(0));
341  if (auto *FoldedPtr = ConstantFoldConstant(Ptr, DL, TLI)) {
342  Ptr = FoldedPtr;
343  DEBUG(dbgs() << "Found a constant pointer expression, constant "
344  "folding: " << *Ptr << "\n");
345  }
346  InstResult = ComputeLoadResult(Ptr);
347  if (!InstResult) {
348  DEBUG(dbgs() << "Failed to compute load result. Can not evaluate load."
349  "\n");
350  return false; // Could not evaluate load.
351  }
352 
353  DEBUG(dbgs() << "Evaluated load: " << *InstResult << "\n");
354  } else if (AllocaInst *AI = dyn_cast<AllocaInst>(CurInst)) {
355  if (AI->isArrayAllocation()) {
356  DEBUG(dbgs() << "Found an array alloca. Can not evaluate.\n");
357  return false; // Cannot handle array allocs.
358  }
359  Type *Ty = AI->getAllocatedType();
360  AllocaTmps.push_back(llvm::make_unique<GlobalVariable>(
362  AI->getName()));
363  InstResult = AllocaTmps.back().get();
364  DEBUG(dbgs() << "Found an alloca. Result: " << *InstResult << "\n");
365  } else if (isa<CallInst>(CurInst) || isa<InvokeInst>(CurInst)) {
366  CallSite CS(&*CurInst);
367 
368  // Debug info can safely be ignored here.
369  if (isa<DbgInfoIntrinsic>(CS.getInstruction())) {
370  DEBUG(dbgs() << "Ignoring debug info.\n");
371  ++CurInst;
372  continue;
373  }
374 
375  // Cannot handle inline asm.
376  if (isa<InlineAsm>(CS.getCalledValue())) {
377  DEBUG(dbgs() << "Found inline asm, can not evaluate.\n");
378  return false;
379  }
380 
381  if (IntrinsicInst *II = dyn_cast<IntrinsicInst>(CS.getInstruction())) {
382  if (MemSetInst *MSI = dyn_cast<MemSetInst>(II)) {
383  if (MSI->isVolatile()) {
384  DEBUG(dbgs() << "Can not optimize a volatile memset " <<
385  "intrinsic.\n");
386  return false;
387  }
388  Constant *Ptr = getVal(MSI->getDest());
389  Constant *Val = getVal(MSI->getValue());
390  Constant *DestVal = ComputeLoadResult(getVal(Ptr));
391  if (Val->isNullValue() && DestVal && DestVal->isNullValue()) {
392  // This memset is a no-op.
393  DEBUG(dbgs() << "Ignoring no-op memset.\n");
394  ++CurInst;
395  continue;
396  }
397  }
398 
399  if (II->getIntrinsicID() == Intrinsic::lifetime_start ||
400  II->getIntrinsicID() == Intrinsic::lifetime_end) {
401  DEBUG(dbgs() << "Ignoring lifetime intrinsic.\n");
402  ++CurInst;
403  continue;
404  }
405 
406  if (II->getIntrinsicID() == Intrinsic::invariant_start) {
407  // We don't insert an entry into Values, as it doesn't have a
408  // meaningful return value.
409  if (!II->use_empty()) {
410  DEBUG(dbgs() << "Found unused invariant_start. Can't evaluate.\n");
411  return false;
412  }
413  ConstantInt *Size = cast<ConstantInt>(II->getArgOperand(0));
414  Value *PtrArg = getVal(II->getArgOperand(1));
415  Value *Ptr = PtrArg->stripPointerCasts();
416  if (GlobalVariable *GV = dyn_cast<GlobalVariable>(Ptr)) {
417  Type *ElemTy = GV->getValueType();
418  if (!Size->isMinusOne() &&
419  Size->getValue().getLimitedValue() >=
420  DL.getTypeStoreSize(ElemTy)) {
421  Invariants.insert(GV);
422  DEBUG(dbgs() << "Found a global var that is an invariant: " << *GV
423  << "\n");
424  } else {
425  DEBUG(dbgs() << "Found a global var, but can not treat it as an "
426  "invariant.\n");
427  }
428  }
429  // Continue even if we do nothing.
430  ++CurInst;
431  continue;
432  } else if (II->getIntrinsicID() == Intrinsic::assume) {
433  DEBUG(dbgs() << "Skipping assume intrinsic.\n");
434  ++CurInst;
435  continue;
436  } else if (II->getIntrinsicID() == Intrinsic::sideeffect) {
437  DEBUG(dbgs() << "Skipping sideeffect intrinsic.\n");
438  ++CurInst;
439  continue;
440  }
441 
442  DEBUG(dbgs() << "Unknown intrinsic. Can not evaluate.\n");
443  return false;
444  }
445 
446  // Resolve function pointers.
448  if (!Callee || Callee->isInterposable()) {
449  DEBUG(dbgs() << "Can not resolve function pointer.\n");
450  return false; // Cannot resolve.
451  }
452 
454  for (User::op_iterator i = CS.arg_begin(), e = CS.arg_end(); i != e; ++i)
455  Formals.push_back(getVal(*i));
456 
457  if (Callee->isDeclaration()) {
458  // If this is a function we can constant fold, do it.
459  if (Constant *C = ConstantFoldCall(CS, Callee, Formals, TLI)) {
460  InstResult = C;
461  DEBUG(dbgs() << "Constant folded function call. Result: " <<
462  *InstResult << "\n");
463  } else {
464  DEBUG(dbgs() << "Can not constant fold function call.\n");
465  return false;
466  }
467  } else {
468  if (Callee->getFunctionType()->isVarArg()) {
469  DEBUG(dbgs() << "Can not constant fold vararg function call.\n");
470  return false;
471  }
472 
473  Constant *RetVal = nullptr;
474  // Execute the call, if successful, use the return value.
475  ValueStack.emplace_back();
476  if (!EvaluateFunction(Callee, RetVal, Formals)) {
477  DEBUG(dbgs() << "Failed to evaluate function.\n");
478  return false;
479  }
480  ValueStack.pop_back();
481  InstResult = RetVal;
482 
483  if (InstResult) {
484  DEBUG(dbgs() << "Successfully evaluated function. Result: "
485  << *InstResult << "\n\n");
486  } else {
487  DEBUG(dbgs() << "Successfully evaluated function. Result: 0\n\n");
488  }
489  }
490  } else if (isa<TerminatorInst>(CurInst)) {
491  DEBUG(dbgs() << "Found a terminator instruction.\n");
492 
493  if (BranchInst *BI = dyn_cast<BranchInst>(CurInst)) {
494  if (BI->isUnconditional()) {
495  NextBB = BI->getSuccessor(0);
496  } else {
497  ConstantInt *Cond =
498  dyn_cast<ConstantInt>(getVal(BI->getCondition()));
499  if (!Cond) return false; // Cannot determine.
500 
501  NextBB = BI->getSuccessor(!Cond->getZExtValue());
502  }
503  } else if (SwitchInst *SI = dyn_cast<SwitchInst>(CurInst)) {
504  ConstantInt *Val =
505  dyn_cast<ConstantInt>(getVal(SI->getCondition()));
506  if (!Val) return false; // Cannot determine.
507  NextBB = SI->findCaseValue(Val)->getCaseSuccessor();
508  } else if (IndirectBrInst *IBI = dyn_cast<IndirectBrInst>(CurInst)) {
509  Value *Val = getVal(IBI->getAddress())->stripPointerCasts();
510  if (BlockAddress *BA = dyn_cast<BlockAddress>(Val))
511  NextBB = BA->getBasicBlock();
512  else
513  return false; // Cannot determine.
514  } else if (isa<ReturnInst>(CurInst)) {
515  NextBB = nullptr;
516  } else {
517  // invoke, unwind, resume, unreachable.
518  DEBUG(dbgs() << "Can not handle terminator.");
519  return false; // Cannot handle this terminator.
520  }
521 
522  // We succeeded at evaluating this block!
523  DEBUG(dbgs() << "Successfully evaluated block.\n");
524  return true;
525  } else {
526  // Did not know how to evaluate this!
527  DEBUG(dbgs() << "Failed to evaluate block due to unhandled instruction."
528  "\n");
529  return false;
530  }
531 
532  if (!CurInst->use_empty()) {
533  if (auto *FoldedInstResult = ConstantFoldConstant(InstResult, DL, TLI))
534  InstResult = FoldedInstResult;
535 
536  setVal(&*CurInst, InstResult);
537  }
538 
539  // If we just processed an invoke, we finished evaluating the block.
540  if (InvokeInst *II = dyn_cast<InvokeInst>(CurInst)) {
541  NextBB = II->getNormalDest();
542  DEBUG(dbgs() << "Found an invoke instruction. Finished Block.\n\n");
543  return true;
544  }
545 
546  // Advance program counter.
547  ++CurInst;
548  }
549 }
550 
551 /// Evaluate a call to function F, returning true if successful, false if we
552 /// can't evaluate it. ActualArgs contains the formal arguments for the
553 /// function.
555  const SmallVectorImpl<Constant*> &ActualArgs) {
556  // Check to see if this function is already executing (recursion). If so,
557  // bail out. TODO: we might want to accept limited recursion.
558  if (is_contained(CallStack, F))
559  return false;
560 
561  CallStack.push_back(F);
562 
563  // Initialize arguments to the incoming values specified.
564  unsigned ArgNo = 0;
565  for (Function::arg_iterator AI = F->arg_begin(), E = F->arg_end(); AI != E;
566  ++AI, ++ArgNo)
567  setVal(&*AI, ActualArgs[ArgNo]);
568 
569  // ExecutedBlocks - We only handle non-looping, non-recursive code. As such,
570  // we can only evaluate any one basic block at most once. This set keeps
571  // track of what we have executed so we can detect recursive cases etc.
572  SmallPtrSet<BasicBlock*, 32> ExecutedBlocks;
573 
574  // CurBB - The current basic block we're evaluating.
575  BasicBlock *CurBB = &F->front();
576 
577  BasicBlock::iterator CurInst = CurBB->begin();
578 
579  while (true) {
580  BasicBlock *NextBB = nullptr; // Initialized to avoid compiler warnings.
581  DEBUG(dbgs() << "Trying to evaluate BB: " << *CurBB << "\n");
582 
583  if (!EvaluateBlock(CurInst, NextBB))
584  return false;
585 
586  if (!NextBB) {
587  // Successfully running until there's no next block means that we found
588  // the return. Fill it the return value and pop the call stack.
589  ReturnInst *RI = cast<ReturnInst>(CurBB->getTerminator());
590  if (RI->getNumOperands())
591  RetVal = getVal(RI->getOperand(0));
592  CallStack.pop_back();
593  return true;
594  }
595 
596  // Okay, we succeeded in evaluating this control flow. See if we have
597  // executed the new block before. If so, we have a looping function,
598  // which we cannot evaluate in reasonable time.
599  if (!ExecutedBlocks.insert(NextBB).second)
600  return false; // looped!
601 
602  // Okay, we have never been in this block before. Check to see if there
603  // are any PHI nodes. If so, evaluate them with information about where
604  // we came from.
605  PHINode *PN = nullptr;
606  for (CurInst = NextBB->begin();
607  (PN = dyn_cast<PHINode>(CurInst)); ++CurInst)
608  setVal(PN, getVal(PN->getIncomingValueForBlock(CurBB)));
609 
610  // Advance to the next block.
611  CurBB = NextBB;
612  }
613 }
uint64_t CallInst * C
Return a value (possibly void), from a function.
void push_back(const T &Elt)
Definition: SmallVector.h:212
A parsed version of the target data layout string in and methods for querying it. ...
Definition: DataLayout.h:109
This class is the base class for the comparison instructions.
Definition: InstrTypes.h:843
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:1171
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:1115
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:207
bool isInterposable() const
Return true if this global&#39;s definition can be substituted with an arbitrary definition at link time...
Definition: GlobalValue.h:411
This class wraps the llvm.memset intrinsic.
arg_iterator arg_end()
Definition: Function.h:612
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:1832
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:554
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:252
The address of a basic block.
Definition: Constants.h:813
This class represents the LLVM &#39;select&#39; instruction.
This is the base class for all instructions that perform data casts.
Definition: InstrTypes.h:560
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:1711
A constant value that is initialized with an expression using other constant values.
Definition: Constants.h:862
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:1854
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:154
static Constant * getBitCast(Constant *C, Type *Ty, bool OnlyIfReduced=false)
Definition: Constants.cpp:1678
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:2048
#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:222
arg_iterator arg_begin()
Definition: Function.h:603
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:1320
const Value * stripPointerCasts() const
Strip off pointer casts, all-zero GEPs, and aliases.
Definition: Value.cpp:558
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:176
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:864
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:560
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:145
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:1435
uint64_t getTypeSizeInBits(Type *Ty) const
Size examples:
Definition: DataLayout.h:530
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
bool canLosslesslyBitCastTo(Type *Ty) const
Return true if this type could be converted with a lossless BitCast to type &#39;Ty&#39;. ...
Definition: Type.cpp:61
StringRef getName() const
Return a constant reference to the value&#39;s name.
Definition: Value.cpp:220
#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:595
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:386
constexpr char Size[]
Key for Kernel::Arg::Metadata::mSize.
Invoke instruction.
#define DEBUG(X)
Definition: Debug.h:118
static Constant * getExtractValue(Constant *Agg, ArrayRef< unsigned > Idxs, Type *OnlyIfReducedTy=nullptr)
Definition: Constants.cpp:2072
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:120
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:867