aboutsummaryrefslogtreecommitdiffstats
path: root/contrib/libs/llvm12/lib/Transforms/Utils/Evaluator.cpp
blob: f21a60673ad42c7ec5006d868c5cc5eac3c6472c (plain) (blame)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
570
571
572
573
574
575
576
577
578
579
580
581
582
583
584
585
586
587
588
589
590
591
592
593
594
595
596
597
598
599
600
601
602
603
604
605
606
607
608
609
610
611
612
613
614
615
616
617
618
619
620
621
622
623
624
625
626
627
628
629
630
631
632
633
634
635
636
637
638
639
640
641
642
643
644
645
646
647
648
649
650
651
652
653
654
655
656
657
658
659
660
661
662
663
664
665
666
667
668
669
670
671
672
673
674
675
676
677
678
679
680
681
682
683
684
685
686
687
688
689
690
691
692
693
694
695
696
697
698
699
700
701
702
703
704
705
706
707
708
709
710
711
712
713
714
715
716
717
718
719
720
721
722
723
724
725
726
727
728
//===- Evaluator.cpp - LLVM IR evaluator ----------------------------------===//
//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See https://llvm.org/LICENSE.txt for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
//
//===----------------------------------------------------------------------===//
//
// Function evaluator for LLVM IR.
//
//===----------------------------------------------------------------------===//

#include "llvm/Transforms/Utils/Evaluator.h"
#include "llvm/ADT/DenseMap.h"
#include "llvm/ADT/STLExtras.h"
#include "llvm/ADT/SmallPtrSet.h"
#include "llvm/ADT/SmallVector.h"
#include "llvm/Analysis/ConstantFolding.h"
#include "llvm/IR/BasicBlock.h"
#include "llvm/IR/Constant.h"
#include "llvm/IR/Constants.h"
#include "llvm/IR/DataLayout.h"
#include "llvm/IR/DerivedTypes.h"
#include "llvm/IR/Function.h"
#include "llvm/IR/GlobalAlias.h"
#include "llvm/IR/GlobalValue.h"
#include "llvm/IR/GlobalVariable.h"
#include "llvm/IR/InstrTypes.h"
#include "llvm/IR/Instruction.h"
#include "llvm/IR/Instructions.h"
#include "llvm/IR/IntrinsicInst.h"
#include "llvm/IR/Intrinsics.h"
#include "llvm/IR/Operator.h"
#include "llvm/IR/Type.h"
#include "llvm/IR/User.h"
#include "llvm/IR/Value.h"
#include "llvm/Support/Casting.h"
#include "llvm/Support/Debug.h"
#include "llvm/Support/raw_ostream.h"
#include <iterator>

#define DEBUG_TYPE "evaluator"

using namespace llvm;

static inline bool
isSimpleEnoughValueToCommit(Constant *C,
                            SmallPtrSetImpl<Constant *> &SimpleConstants,
                            const DataLayout &DL);

/// Return true if the specified constant can be handled by the code generator.
/// We don't want to generate something like:
///   void *X = &X/42;
/// because the code generator doesn't have a relocation that can handle that.
///
/// This function should be called if C was not found (but just got inserted)
/// in SimpleConstants to avoid having to rescan the same constants all the
/// time.
static bool
isSimpleEnoughValueToCommitHelper(Constant *C,
                                  SmallPtrSetImpl<Constant *> &SimpleConstants,
                                  const DataLayout &DL) {
  // Simple global addresses are supported, do not allow dllimport or
  // thread-local globals.
  if (auto *GV = dyn_cast<GlobalValue>(C))
    return !GV->hasDLLImportStorageClass() && !GV->isThreadLocal();

  // Simple integer, undef, constant aggregate zero, etc are all supported.
  if (C->getNumOperands() == 0 || isa<BlockAddress>(C))
    return true;

  // Aggregate values are safe if all their elements are.
  if (isa<ConstantAggregate>(C)) {
    for (Value *Op : C->operands())
      if (!isSimpleEnoughValueToCommit(cast<Constant>(Op), SimpleConstants, DL))
        return false;
    return true;
  }

  // We don't know exactly what relocations are allowed in constant expressions,
  // so we allow &global+constantoffset, which is safe and uniformly supported
  // across targets.
  ConstantExpr *CE = cast<ConstantExpr>(C);
  switch (CE->getOpcode()) {
  case Instruction::BitCast:
    // Bitcast is fine if the casted value is fine.
    return isSimpleEnoughValueToCommit(CE->getOperand(0), SimpleConstants, DL);

  case Instruction::IntToPtr:
  case Instruction::PtrToInt:
    // int <=> ptr is fine if the int type is the same size as the
    // pointer type.
    if (DL.getTypeSizeInBits(CE->getType()) !=
        DL.getTypeSizeInBits(CE->getOperand(0)->getType()))
      return false;
    return isSimpleEnoughValueToCommit(CE->getOperand(0), SimpleConstants, DL);

  // GEP is fine if it is simple + constant offset.
  case Instruction::GetElementPtr:
    for (unsigned i = 1, e = CE->getNumOperands(); i != e; ++i)
      if (!isa<ConstantInt>(CE->getOperand(i)))
        return false;
    return isSimpleEnoughValueToCommit(CE->getOperand(0), SimpleConstants, DL);

  case Instruction::Add:
    // We allow simple+cst.
    if (!isa<ConstantInt>(CE->getOperand(1)))
      return false;
    return isSimpleEnoughValueToCommit(CE->getOperand(0), SimpleConstants, DL);
  }
  return false;
}

static inline bool
isSimpleEnoughValueToCommit(Constant *C,
                            SmallPtrSetImpl<Constant *> &SimpleConstants,
                            const DataLayout &DL) {
  // If we already checked this constant, we win.
  if (!SimpleConstants.insert(C).second)
    return true;
  // Check the constant.
  return isSimpleEnoughValueToCommitHelper(C, SimpleConstants, DL);
}

/// Return true if this constant is simple enough for us to understand.  In
/// particular, if it is a cast to anything other than from one pointer type to
/// another pointer type, we punt.  We basically just support direct accesses to
/// globals and GEP's of globals.  This should be kept up to date with
/// CommitValueTo.
static bool isSimpleEnoughPointerToCommit(Constant *C) {
  // Conservatively, avoid aggregate types. This is because we don't
  // want to worry about them partially overlapping other stores.
  if (!cast<PointerType>(C->getType())->getElementType()->isSingleValueType())
    return false;

  if (GlobalVariable *GV = dyn_cast<GlobalVariable>(C))
    // Do not allow weak/*_odr/linkonce linkage or external globals.
    return GV->hasUniqueInitializer();

  if (ConstantExpr *CE = dyn_cast<ConstantExpr>(C)) {
    // Handle a constantexpr gep.
    if (CE->getOpcode() == Instruction::GetElementPtr &&
        isa<GlobalVariable>(CE->getOperand(0)) &&
        cast<GEPOperator>(CE)->isInBounds()) {
      GlobalVariable *GV = cast<GlobalVariable>(CE->getOperand(0));
      // Do not allow weak/*_odr/linkonce/dllimport/dllexport linkage or
      // external globals.
      if (!GV->hasUniqueInitializer())
        return false;

      // The first index must be zero.
      ConstantInt *CI = dyn_cast<ConstantInt>(*std::next(CE->op_begin()));
      if (!CI || !CI->isZero()) return false;

      // The remaining indices must be compile-time known integers within the
      // notional bounds of the corresponding static array types.
      if (!CE->isGEPWithNoNotionalOverIndexing())
        return false;

      return ConstantFoldLoadThroughGEPConstantExpr(GV->getInitializer(), CE);

    // A constantexpr bitcast from a pointer to another pointer is a no-op,
    // and we know how to evaluate it by moving the bitcast from the pointer
    // operand to the value operand.
    } else if (CE->getOpcode() == Instruction::BitCast &&
               isa<GlobalVariable>(CE->getOperand(0))) {
      // Do not allow weak/*_odr/linkonce/dllimport/dllexport linkage or
      // external globals.
      return cast<GlobalVariable>(CE->getOperand(0))->hasUniqueInitializer();
    }
  }

  return false;
}

/// Apply 'Func' to Ptr. If this returns nullptr, introspect the pointer's
/// type and walk down through the initial elements to obtain additional
/// pointers to try. Returns the first non-null return value from Func, or
/// nullptr if the type can't be introspected further.
static Constant *
evaluateBitcastFromPtr(Constant *Ptr, const DataLayout &DL,
                       const TargetLibraryInfo *TLI,
                       std::function<Constant *(Constant *)> Func) {
  Constant *Val;
  while (!(Val = Func(Ptr))) {
    // If Ty is a non-opaque struct, we can convert the pointer to the struct 
    // into a pointer to its first member.
    // FIXME: This could be extended to support arrays as well.
    Type *Ty = cast<PointerType>(Ptr->getType())->getElementType();
    if (!isa<StructType>(Ty) || cast<StructType>(Ty)->isOpaque()) 
      break;

    IntegerType *IdxTy = IntegerType::get(Ty->getContext(), 32);
    Constant *IdxZero = ConstantInt::get(IdxTy, 0, false);
    Constant *const IdxList[] = {IdxZero, IdxZero};

    Ptr = ConstantExpr::getGetElementPtr(Ty, Ptr, IdxList);
    Ptr = ConstantFoldConstant(Ptr, DL, TLI);
  }
  return Val;
}

static Constant *getInitializer(Constant *C) {
  auto *GV = dyn_cast<GlobalVariable>(C);
  return GV && GV->hasDefinitiveInitializer() ? GV->getInitializer() : nullptr;
}

/// Return the value that would be computed by a load from P after the stores
/// reflected by 'memory' have been performed.  If we can't decide, return null.
Constant *Evaluator::ComputeLoadResult(Constant *P) {
  // If this memory location has been recently stored, use the stored value: it
  // is the most up-to-date.
  auto findMemLoc = [this](Constant *Ptr) { return MutatedMemory.lookup(Ptr); }; 

  if (Constant *Val = findMemLoc(P))
    return Val;

  // Access it.
  if (GlobalVariable *GV = dyn_cast<GlobalVariable>(P)) {
    if (GV->hasDefinitiveInitializer())
      return GV->getInitializer();
    return nullptr;
  }

  if (ConstantExpr *CE = dyn_cast<ConstantExpr>(P)) {
    switch (CE->getOpcode()) {
    // Handle a constantexpr getelementptr.
    case Instruction::GetElementPtr:
      if (auto *I = getInitializer(CE->getOperand(0)))
        return ConstantFoldLoadThroughGEPConstantExpr(I, CE);
      break;
    // Handle a constantexpr bitcast.
    case Instruction::BitCast:
      // We're evaluating a load through a pointer that was bitcast to a
      // different type. See if the "from" pointer has recently been stored.
      // If it hasn't, we may still be able to find a stored pointer by
      // introspecting the type.
      Constant *Val =
          evaluateBitcastFromPtr(CE->getOperand(0), DL, TLI, findMemLoc);
      if (!Val)
        Val = getInitializer(CE->getOperand(0));
      if (Val)
        return ConstantFoldLoadThroughBitcast(
            Val, P->getType()->getPointerElementType(), DL);
      break;
    }
  }

  return nullptr;  // don't know how to evaluate.
}

static Function *getFunction(Constant *C) {
  if (auto *Fn = dyn_cast<Function>(C))
    return Fn;

  if (auto *Alias = dyn_cast<GlobalAlias>(C))
    if (auto *Fn = dyn_cast<Function>(Alias->getAliasee()))
      return Fn;
  return nullptr;
}

Function *
Evaluator::getCalleeWithFormalArgs(CallBase &CB,
                                   SmallVectorImpl<Constant *> &Formals) {
  auto *V = CB.getCalledOperand();
  if (auto *Fn = getFunction(getVal(V)))
    return getFormalParams(CB, Fn, Formals) ? Fn : nullptr;

  auto *CE = dyn_cast<ConstantExpr>(V);
  if (!CE || CE->getOpcode() != Instruction::BitCast ||
      !getFormalParams(CB, getFunction(CE->getOperand(0)), Formals))
    return nullptr;

  return dyn_cast<Function>(
      ConstantFoldLoadThroughBitcast(CE, CE->getOperand(0)->getType(), DL));
}

bool Evaluator::getFormalParams(CallBase &CB, Function *F,
                                SmallVectorImpl<Constant *> &Formals) {
  if (!F)
    return false;

  auto *FTy = F->getFunctionType();
  if (FTy->getNumParams() > CB.getNumArgOperands()) {
    LLVM_DEBUG(dbgs() << "Too few arguments for function.\n");
    return false;
  }

  auto ArgI = CB.arg_begin();
  for (auto ParI = FTy->param_begin(), ParE = FTy->param_end(); ParI != ParE;
       ++ParI) {
    auto *ArgC = ConstantFoldLoadThroughBitcast(getVal(*ArgI), *ParI, DL);
    if (!ArgC) {
      LLVM_DEBUG(dbgs() << "Can not convert function argument.\n");
      return false;
    }
    Formals.push_back(ArgC);
    ++ArgI;
  }
  return true;
}

/// If call expression contains bitcast then we may need to cast
/// evaluated return value to a type of the call expression.
Constant *Evaluator::castCallResultIfNeeded(Value *CallExpr, Constant *RV) {
  ConstantExpr *CE = dyn_cast<ConstantExpr>(CallExpr);
  if (!RV || !CE || CE->getOpcode() != Instruction::BitCast)
    return RV;

  if (auto *FT =
          dyn_cast<FunctionType>(CE->getType()->getPointerElementType())) {
    RV = ConstantFoldLoadThroughBitcast(RV, FT->getReturnType(), DL);
    if (!RV)
      LLVM_DEBUG(dbgs() << "Failed to fold bitcast call expr\n");
  }
  return RV;
}

/// Evaluate all instructions in block BB, returning true if successful, false
/// if we can't evaluate it.  NewBB returns the next BB that control flows into,
/// or null upon return.
bool Evaluator::EvaluateBlock(BasicBlock::iterator CurInst,
                              BasicBlock *&NextBB) {
  // This is the main evaluation loop.
  while (true) {
    Constant *InstResult = nullptr;

    LLVM_DEBUG(dbgs() << "Evaluating Instruction: " << *CurInst << "\n");

    if (StoreInst *SI = dyn_cast<StoreInst>(CurInst)) {
      if (!SI->isSimple()) {
        LLVM_DEBUG(dbgs() << "Store is not simple! Can not evaluate.\n");
        return false;  // no volatile/atomic accesses.
      }
      Constant *Ptr = getVal(SI->getOperand(1));
      Constant *FoldedPtr = ConstantFoldConstant(Ptr, DL, TLI);
      if (Ptr != FoldedPtr) {
        LLVM_DEBUG(dbgs() << "Folding constant ptr expression: " << *Ptr);
        Ptr = FoldedPtr;
        LLVM_DEBUG(dbgs() << "; To: " << *Ptr << "\n");
      }
      if (!isSimpleEnoughPointerToCommit(Ptr)) {
        // If this is too complex for us to commit, reject it.
        LLVM_DEBUG(
            dbgs() << "Pointer is too complex for us to evaluate store.");
        return false;
      }

      Constant *Val = getVal(SI->getOperand(0));

      // If this might be too difficult for the backend to handle (e.g. the addr
      // of one global variable divided by another) then we can't commit it.
      if (!isSimpleEnoughValueToCommit(Val, SimpleConstants, DL)) {
        LLVM_DEBUG(dbgs() << "Store value is too complex to evaluate store. "
                          << *Val << "\n");
        return false;
      }

      if (ConstantExpr *CE = dyn_cast<ConstantExpr>(Ptr)) {
        if (CE->getOpcode() == Instruction::BitCast) {
          LLVM_DEBUG(dbgs()
                     << "Attempting to resolve bitcast on constant ptr.\n");
          // If we're evaluating a store through a bitcast, then we need
          // to pull the bitcast off the pointer type and push it onto the
          // stored value. In order to push the bitcast onto the stored value,
          // a bitcast from the pointer's element type to Val's type must be
          // legal. If it's not, we can try introspecting the type to find a
          // legal conversion.

          auto castValTy = [&](Constant *P) -> Constant * {
            Type *Ty = cast<PointerType>(P->getType())->getElementType();
            if (Constant *FV = ConstantFoldLoadThroughBitcast(Val, Ty, DL)) {
              Ptr = P;
              return FV;
            }
            return nullptr;
          };

          Constant *NewVal =
              evaluateBitcastFromPtr(CE->getOperand(0), DL, TLI, castValTy);
          if (!NewVal) {
            LLVM_DEBUG(dbgs() << "Failed to bitcast constant ptr, can not "
                                 "evaluate.\n");
            return false;
          }

          Val = NewVal;
          LLVM_DEBUG(dbgs() << "Evaluated bitcast: " << *Val << "\n");
        }
      }

      MutatedMemory[Ptr] = Val;
    } else if (BinaryOperator *BO = dyn_cast<BinaryOperator>(CurInst)) {
      InstResult = ConstantExpr::get(BO->getOpcode(),
                                     getVal(BO->getOperand(0)),
                                     getVal(BO->getOperand(1)));
      LLVM_DEBUG(dbgs() << "Found a BinaryOperator! Simplifying: "
                        << *InstResult << "\n");
    } else if (CmpInst *CI = dyn_cast<CmpInst>(CurInst)) {
      InstResult = ConstantExpr::getCompare(CI->getPredicate(),
                                            getVal(CI->getOperand(0)),
                                            getVal(CI->getOperand(1)));
      LLVM_DEBUG(dbgs() << "Found a CmpInst! Simplifying: " << *InstResult
                        << "\n");
    } else if (CastInst *CI = dyn_cast<CastInst>(CurInst)) {
      InstResult = ConstantExpr::getCast(CI->getOpcode(),
                                         getVal(CI->getOperand(0)),
                                         CI->getType());
      LLVM_DEBUG(dbgs() << "Found a Cast! Simplifying: " << *InstResult
                        << "\n");
    } else if (SelectInst *SI = dyn_cast<SelectInst>(CurInst)) {
      InstResult = ConstantExpr::getSelect(getVal(SI->getOperand(0)),
                                           getVal(SI->getOperand(1)),
                                           getVal(SI->getOperand(2)));
      LLVM_DEBUG(dbgs() << "Found a Select! Simplifying: " << *InstResult
                        << "\n");
    } else if (auto *EVI = dyn_cast<ExtractValueInst>(CurInst)) {
      InstResult = ConstantExpr::getExtractValue(
          getVal(EVI->getAggregateOperand()), EVI->getIndices());
      LLVM_DEBUG(dbgs() << "Found an ExtractValueInst! Simplifying: "
                        << *InstResult << "\n");
    } else if (auto *IVI = dyn_cast<InsertValueInst>(CurInst)) {
      InstResult = ConstantExpr::getInsertValue(
          getVal(IVI->getAggregateOperand()),
          getVal(IVI->getInsertedValueOperand()), IVI->getIndices());
      LLVM_DEBUG(dbgs() << "Found an InsertValueInst! Simplifying: "
                        << *InstResult << "\n");
    } else if (GetElementPtrInst *GEP = dyn_cast<GetElementPtrInst>(CurInst)) {
      Constant *P = getVal(GEP->getOperand(0));
      SmallVector<Constant*, 8> GEPOps;
      for (User::op_iterator i = GEP->op_begin() + 1, e = GEP->op_end();
           i != e; ++i)
        GEPOps.push_back(getVal(*i));
      InstResult =
          ConstantExpr::getGetElementPtr(GEP->getSourceElementType(), P, GEPOps,
                                         cast<GEPOperator>(GEP)->isInBounds());
      LLVM_DEBUG(dbgs() << "Found a GEP! Simplifying: " << *InstResult << "\n");
    } else if (LoadInst *LI = dyn_cast<LoadInst>(CurInst)) {
      if (!LI->isSimple()) {
        LLVM_DEBUG(
            dbgs() << "Found a Load! Not a simple load, can not evaluate.\n");
        return false;  // no volatile/atomic accesses.
      }

      Constant *Ptr = getVal(LI->getOperand(0));
      Constant *FoldedPtr = ConstantFoldConstant(Ptr, DL, TLI);
      if (Ptr != FoldedPtr) {
        Ptr = FoldedPtr;
        LLVM_DEBUG(dbgs() << "Found a constant pointer expression, constant "
                             "folding: "
                          << *Ptr << "\n");
      }
      InstResult = ComputeLoadResult(Ptr);
      if (!InstResult) {
        LLVM_DEBUG(
            dbgs() << "Failed to compute load result. Can not evaluate load."
                      "\n");
        return false; // Could not evaluate load.
      }

      LLVM_DEBUG(dbgs() << "Evaluated load: " << *InstResult << "\n");
    } else if (AllocaInst *AI = dyn_cast<AllocaInst>(CurInst)) {
      if (AI->isArrayAllocation()) {
        LLVM_DEBUG(dbgs() << "Found an array alloca. Can not evaluate.\n");
        return false;  // Cannot handle array allocs.
      }
      Type *Ty = AI->getAllocatedType();
      AllocaTmps.push_back(std::make_unique<GlobalVariable>(
          Ty, false, GlobalValue::InternalLinkage, UndefValue::get(Ty),
          AI->getName(), /*TLMode=*/GlobalValue::NotThreadLocal,
          AI->getType()->getPointerAddressSpace()));
      InstResult = AllocaTmps.back().get();
      LLVM_DEBUG(dbgs() << "Found an alloca. Result: " << *InstResult << "\n");
    } else if (isa<CallInst>(CurInst) || isa<InvokeInst>(CurInst)) {
      CallBase &CB = *cast<CallBase>(&*CurInst);

      // Debug info can safely be ignored here.
      if (isa<DbgInfoIntrinsic>(CB)) {
        LLVM_DEBUG(dbgs() << "Ignoring debug info.\n");
        ++CurInst;
        continue;
      }

      // Cannot handle inline asm.
      if (CB.isInlineAsm()) {
        LLVM_DEBUG(dbgs() << "Found inline asm, can not evaluate.\n");
        return false;
      }

      if (IntrinsicInst *II = dyn_cast<IntrinsicInst>(&CB)) {
        if (MemSetInst *MSI = dyn_cast<MemSetInst>(II)) {
          if (MSI->isVolatile()) {
            LLVM_DEBUG(dbgs() << "Can not optimize a volatile memset "
                              << "intrinsic.\n");
            return false;
          }
          Constant *Ptr = getVal(MSI->getDest());
          Constant *Val = getVal(MSI->getValue());
          Constant *DestVal = ComputeLoadResult(getVal(Ptr));
          if (Val->isNullValue() && DestVal && DestVal->isNullValue()) {
            // This memset is a no-op.
            LLVM_DEBUG(dbgs() << "Ignoring no-op memset.\n");
            ++CurInst;
            continue;
          }
        }

        if (II->isLifetimeStartOrEnd()) {
          LLVM_DEBUG(dbgs() << "Ignoring lifetime intrinsic.\n");
          ++CurInst;
          continue;
        }

        if (II->getIntrinsicID() == Intrinsic::invariant_start) {
          // We don't insert an entry into Values, as it doesn't have a
          // meaningful return value.
          if (!II->use_empty()) {
            LLVM_DEBUG(dbgs()
                       << "Found unused invariant_start. Can't evaluate.\n");
            return false;
          }
          ConstantInt *Size = cast<ConstantInt>(II->getArgOperand(0));
          Value *PtrArg = getVal(II->getArgOperand(1));
          Value *Ptr = PtrArg->stripPointerCasts();
          if (GlobalVariable *GV = dyn_cast<GlobalVariable>(Ptr)) {
            Type *ElemTy = GV->getValueType();
            if (!Size->isMinusOne() &&
                Size->getValue().getLimitedValue() >=
                    DL.getTypeStoreSize(ElemTy)) {
              Invariants.insert(GV);
              LLVM_DEBUG(dbgs() << "Found a global var that is an invariant: "
                                << *GV << "\n");
            } else {
              LLVM_DEBUG(dbgs()
                         << "Found a global var, but can not treat it as an "
                            "invariant.\n");
            }
          }
          // Continue even if we do nothing.
          ++CurInst;
          continue;
        } else if (II->getIntrinsicID() == Intrinsic::assume) {
          LLVM_DEBUG(dbgs() << "Skipping assume intrinsic.\n");
          ++CurInst;
          continue;
        } else if (II->getIntrinsicID() == Intrinsic::sideeffect) {
          LLVM_DEBUG(dbgs() << "Skipping sideeffect intrinsic.\n");
          ++CurInst;
          continue;
        } else if (II->getIntrinsicID() == Intrinsic::pseudoprobe) { 
          LLVM_DEBUG(dbgs() << "Skipping pseudoprobe intrinsic.\n"); 
          ++CurInst; 
          continue; 
        }

        LLVM_DEBUG(dbgs() << "Unknown intrinsic. Can not evaluate.\n");
        return false;
      }

      // Resolve function pointers.
      SmallVector<Constant *, 8> Formals;
      Function *Callee = getCalleeWithFormalArgs(CB, Formals);
      if (!Callee || Callee->isInterposable()) {
        LLVM_DEBUG(dbgs() << "Can not resolve function pointer.\n");
        return false;  // Cannot resolve.
      }

      if (Callee->isDeclaration()) {
        // If this is a function we can constant fold, do it.
        if (Constant *C = ConstantFoldCall(&CB, Callee, Formals, TLI)) {
          InstResult = castCallResultIfNeeded(CB.getCalledOperand(), C);
          if (!InstResult)
            return false;
          LLVM_DEBUG(dbgs() << "Constant folded function call. Result: "
                            << *InstResult << "\n");
        } else {
          LLVM_DEBUG(dbgs() << "Can not constant fold function call.\n");
          return false;
        }
      } else {
        if (Callee->getFunctionType()->isVarArg()) {
          LLVM_DEBUG(dbgs() << "Can not constant fold vararg function call.\n");
          return false;
        }

        Constant *RetVal = nullptr;
        // Execute the call, if successful, use the return value.
        ValueStack.emplace_back();
        if (!EvaluateFunction(Callee, RetVal, Formals)) {
          LLVM_DEBUG(dbgs() << "Failed to evaluate function.\n");
          return false;
        }
        ValueStack.pop_back();
        InstResult = castCallResultIfNeeded(CB.getCalledOperand(), RetVal);
        if (RetVal && !InstResult)
          return false;

        if (InstResult) {
          LLVM_DEBUG(dbgs() << "Successfully evaluated function. Result: "
                            << *InstResult << "\n\n");
        } else {
          LLVM_DEBUG(dbgs()
                     << "Successfully evaluated function. Result: 0\n\n");
        }
      }
    } else if (CurInst->isTerminator()) {
      LLVM_DEBUG(dbgs() << "Found a terminator instruction.\n");

      if (BranchInst *BI = dyn_cast<BranchInst>(CurInst)) {
        if (BI->isUnconditional()) {
          NextBB = BI->getSuccessor(0);
        } else {
          ConstantInt *Cond =
            dyn_cast<ConstantInt>(getVal(BI->getCondition()));
          if (!Cond) return false;  // Cannot determine.

          NextBB = BI->getSuccessor(!Cond->getZExtValue());
        }
      } else if (SwitchInst *SI = dyn_cast<SwitchInst>(CurInst)) {
        ConstantInt *Val =
          dyn_cast<ConstantInt>(getVal(SI->getCondition()));
        if (!Val) return false;  // Cannot determine.
        NextBB = SI->findCaseValue(Val)->getCaseSuccessor();
      } else if (IndirectBrInst *IBI = dyn_cast<IndirectBrInst>(CurInst)) {
        Value *Val = getVal(IBI->getAddress())->stripPointerCasts();
        if (BlockAddress *BA = dyn_cast<BlockAddress>(Val))
          NextBB = BA->getBasicBlock();
        else
          return false;  // Cannot determine.
      } else if (isa<ReturnInst>(CurInst)) {
        NextBB = nullptr;
      } else {
        // invoke, unwind, resume, unreachable.
        LLVM_DEBUG(dbgs() << "Can not handle terminator.");
        return false;  // Cannot handle this terminator.
      }

      // We succeeded at evaluating this block!
      LLVM_DEBUG(dbgs() << "Successfully evaluated block.\n");
      return true;
    } else {
      // Did not know how to evaluate this!
      LLVM_DEBUG(
          dbgs() << "Failed to evaluate block due to unhandled instruction."
                    "\n");
      return false;
    }

    if (!CurInst->use_empty()) {
      InstResult = ConstantFoldConstant(InstResult, DL, TLI);
      setVal(&*CurInst, InstResult);
    }

    // If we just processed an invoke, we finished evaluating the block.
    if (InvokeInst *II = dyn_cast<InvokeInst>(CurInst)) {
      NextBB = II->getNormalDest();
      LLVM_DEBUG(dbgs() << "Found an invoke instruction. Finished Block.\n\n");
      return true;
    }

    // Advance program counter.
    ++CurInst;
  }
}

/// Evaluate a call to function F, returning true if successful, false if we
/// can't evaluate it.  ActualArgs contains the formal arguments for the
/// function.
bool Evaluator::EvaluateFunction(Function *F, Constant *&RetVal,
                                 const SmallVectorImpl<Constant*> &ActualArgs) {
  // Check to see if this function is already executing (recursion).  If so,
  // bail out.  TODO: we might want to accept limited recursion.
  if (is_contained(CallStack, F))
    return false;

  CallStack.push_back(F);

  // Initialize arguments to the incoming values specified.
  unsigned ArgNo = 0;
  for (Function::arg_iterator AI = F->arg_begin(), E = F->arg_end(); AI != E;
       ++AI, ++ArgNo)
    setVal(&*AI, ActualArgs[ArgNo]);

  // ExecutedBlocks - We only handle non-looping, non-recursive code.  As such,
  // we can only evaluate any one basic block at most once.  This set keeps
  // track of what we have executed so we can detect recursive cases etc.
  SmallPtrSet<BasicBlock*, 32> ExecutedBlocks;

  // CurBB - The current basic block we're evaluating.
  BasicBlock *CurBB = &F->front();

  BasicBlock::iterator CurInst = CurBB->begin();

  while (true) {
    BasicBlock *NextBB = nullptr; // Initialized to avoid compiler warnings.
    LLVM_DEBUG(dbgs() << "Trying to evaluate BB: " << *CurBB << "\n");

    if (!EvaluateBlock(CurInst, NextBB))
      return false;

    if (!NextBB) {
      // Successfully running until there's no next block means that we found
      // the return.  Fill it the return value and pop the call stack.
      ReturnInst *RI = cast<ReturnInst>(CurBB->getTerminator());
      if (RI->getNumOperands())
        RetVal = getVal(RI->getOperand(0));
      CallStack.pop_back();
      return true;
    }

    // Okay, we succeeded in evaluating this control flow.  See if we have
    // executed the new block before.  If so, we have a looping function,
    // which we cannot evaluate in reasonable time.
    if (!ExecutedBlocks.insert(NextBB).second)
      return false;  // looped!

    // Okay, we have never been in this block before.  Check to see if there
    // are any PHI nodes.  If so, evaluate them with information about where
    // we came from.
    PHINode *PN = nullptr;
    for (CurInst = NextBB->begin();
         (PN = dyn_cast<PHINode>(CurInst)); ++CurInst)
      setVal(PN, getVal(PN->getIncomingValueForBlock(CurBB)));

    // Advance to the next block.
    CurBB = NextBB;
  }
}