1//===-- Lint.cpp - Check for common errors in LLVM IR ---------------------===//
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// This pass statically checks for common and easily-identified constructs
11// which produce undefined or likely unintended behavior in LLVM IR.
12//
13// It is not a guarantee of correctness, in two ways. First, it isn't
14// comprehensive. There are checks which could be done statically which are
15// not yet implemented. Some of these are indicated by TODO comments, but
16// those aren't comprehensive either. Second, many conditions cannot be
17// checked statically. This pass does no dynamic instrumentation, so it
18// can't check for all possible problems.
19//
20// Another limitation is that it assumes all code will be executed. A store
21// through a null pointer in a basic block which is never reached is harmless,
22// but this pass will warn about it anyway. This is the main reason why most
23// of these checks live here instead of in the Verifier pass.
24//
25// Optimization passes may make conditions that this pass checks for more or
26// less obvious. If an optimization pass appears to be introducing a warning,
27// it may be that the optimization pass is merely exposing an existing
28// condition in the code.
29//
30// This code may be run before instcombine. In many cases, instcombine checks
31// for the same kinds of things and turns instructions with undefined behavior
32// into unreachable (or equivalent). Because of this, this pass makes some
33// effort to look through bitcasts and so on.
34//
35//===----------------------------------------------------------------------===//
36
37#include "llvm/Analysis/Passes.h"
38#include "llvm/Analysis/AliasAnalysis.h"
39#include "llvm/Analysis/InstructionSimplify.h"
40#include "llvm/Analysis/ConstantFolding.h"
41#include "llvm/Analysis/Dominators.h"
42#include "llvm/Analysis/Lint.h"
43#include "llvm/Analysis/Loads.h"
44#include "llvm/Analysis/ValueTracking.h"
45#include "llvm/Assembly/Writer.h"
46#include "llvm/Target/TargetData.h"
47#include "llvm/Pass.h"
48#include "llvm/PassManager.h"
49#include "llvm/IntrinsicInst.h"
50#include "llvm/Function.h"
51#include "llvm/Support/CallSite.h"
52#include "llvm/Support/Debug.h"
53#include "llvm/Support/InstVisitor.h"
54#include "llvm/Support/raw_ostream.h"
55#include "llvm/ADT/STLExtras.h"
56using namespace llvm;
57
58namespace {
59  namespace MemRef {
60    static unsigned Read     = 1;
61    static unsigned Write    = 2;
62    static unsigned Callee   = 4;
63    static unsigned Branchee = 8;
64  }
65
66  class Lint : public FunctionPass, public InstVisitor<Lint> {
67    friend class InstVisitor<Lint>;
68
69    void visitFunction(Function &F);
70
71    void visitCallSite(CallSite CS);
72    void visitMemoryReference(Instruction &I, Value *Ptr,
73                              uint64_t Size, unsigned Align,
74                              Type *Ty, unsigned Flags);
75
76    void visitCallInst(CallInst &I);
77    void visitInvokeInst(InvokeInst &I);
78    void visitReturnInst(ReturnInst &I);
79    void visitLoadInst(LoadInst &I);
80    void visitStoreInst(StoreInst &I);
81    void visitXor(BinaryOperator &I);
82    void visitSub(BinaryOperator &I);
83    void visitLShr(BinaryOperator &I);
84    void visitAShr(BinaryOperator &I);
85    void visitShl(BinaryOperator &I);
86    void visitSDiv(BinaryOperator &I);
87    void visitUDiv(BinaryOperator &I);
88    void visitSRem(BinaryOperator &I);
89    void visitURem(BinaryOperator &I);
90    void visitAllocaInst(AllocaInst &I);
91    void visitVAArgInst(VAArgInst &I);
92    void visitIndirectBrInst(IndirectBrInst &I);
93    void visitExtractElementInst(ExtractElementInst &I);
94    void visitInsertElementInst(InsertElementInst &I);
95    void visitUnreachableInst(UnreachableInst &I);
96
97    Value *findValue(Value *V, bool OffsetOk) const;
98    Value *findValueImpl(Value *V, bool OffsetOk,
99                         SmallPtrSet<Value *, 4> &Visited) const;
100
101  public:
102    Module *Mod;
103    AliasAnalysis *AA;
104    DominatorTree *DT;
105    TargetData *TD;
106
107    std::string Messages;
108    raw_string_ostream MessagesStr;
109
110    static char ID; // Pass identification, replacement for typeid
111    Lint() : FunctionPass(ID), MessagesStr(Messages) {
112      initializeLintPass(*PassRegistry::getPassRegistry());
113    }
114
115    virtual bool runOnFunction(Function &F);
116
117    virtual void getAnalysisUsage(AnalysisUsage &AU) const {
118      AU.setPreservesAll();
119      AU.addRequired<AliasAnalysis>();
120      AU.addRequired<DominatorTree>();
121    }
122    virtual void print(raw_ostream &O, const Module *M) const {}
123
124    void WriteValue(const Value *V) {
125      if (!V) return;
126      if (isa<Instruction>(V)) {
127        MessagesStr << *V << '\n';
128      } else {
129        WriteAsOperand(MessagesStr, V, true, Mod);
130        MessagesStr << '\n';
131      }
132    }
133
134    // CheckFailed - A check failed, so print out the condition and the message
135    // that failed.  This provides a nice place to put a breakpoint if you want
136    // to see why something is not correct.
137    void CheckFailed(const Twine &Message,
138                     const Value *V1 = 0, const Value *V2 = 0,
139                     const Value *V3 = 0, const Value *V4 = 0) {
140      MessagesStr << Message.str() << "\n";
141      WriteValue(V1);
142      WriteValue(V2);
143      WriteValue(V3);
144      WriteValue(V4);
145    }
146  };
147}
148
149char Lint::ID = 0;
150INITIALIZE_PASS_BEGIN(Lint, "lint", "Statically lint-checks LLVM IR",
151                      false, true)
152INITIALIZE_PASS_DEPENDENCY(DominatorTree)
153INITIALIZE_AG_DEPENDENCY(AliasAnalysis)
154INITIALIZE_PASS_END(Lint, "lint", "Statically lint-checks LLVM IR",
155                    false, true)
156
157// Assert - We know that cond should be true, if not print an error message.
158#define Assert(C, M) \
159    do { if (!(C)) { CheckFailed(M); return; } } while (0)
160#define Assert1(C, M, V1) \
161    do { if (!(C)) { CheckFailed(M, V1); return; } } while (0)
162#define Assert2(C, M, V1, V2) \
163    do { if (!(C)) { CheckFailed(M, V1, V2); return; } } while (0)
164#define Assert3(C, M, V1, V2, V3) \
165    do { if (!(C)) { CheckFailed(M, V1, V2, V3); return; } } while (0)
166#define Assert4(C, M, V1, V2, V3, V4) \
167    do { if (!(C)) { CheckFailed(M, V1, V2, V3, V4); return; } } while (0)
168
169// Lint::run - This is the main Analysis entry point for a
170// function.
171//
172bool Lint::runOnFunction(Function &F) {
173  Mod = F.getParent();
174  AA = &getAnalysis<AliasAnalysis>();
175  DT = &getAnalysis<DominatorTree>();
176  TD = getAnalysisIfAvailable<TargetData>();
177  visit(F);
178  dbgs() << MessagesStr.str();
179  Messages.clear();
180  return false;
181}
182
183void Lint::visitFunction(Function &F) {
184  // This isn't undefined behavior, it's just a little unusual, and it's a
185  // fairly common mistake to neglect to name a function.
186  Assert1(F.hasName() || F.hasLocalLinkage(),
187          "Unusual: Unnamed function with non-local linkage", &F);
188
189  // TODO: Check for irreducible control flow.
190}
191
192void Lint::visitCallSite(CallSite CS) {
193  Instruction &I = *CS.getInstruction();
194  Value *Callee = CS.getCalledValue();
195
196  visitMemoryReference(I, Callee, AliasAnalysis::UnknownSize,
197                       0, 0, MemRef::Callee);
198
199  if (Function *F = dyn_cast<Function>(findValue(Callee, /*OffsetOk=*/false))) {
200    Assert1(CS.getCallingConv() == F->getCallingConv(),
201            "Undefined behavior: Caller and callee calling convention differ",
202            &I);
203
204    FunctionType *FT = F->getFunctionType();
205    unsigned NumActualArgs = unsigned(CS.arg_end()-CS.arg_begin());
206
207    Assert1(FT->isVarArg() ?
208              FT->getNumParams() <= NumActualArgs :
209              FT->getNumParams() == NumActualArgs,
210            "Undefined behavior: Call argument count mismatches callee "
211            "argument count", &I);
212
213    Assert1(FT->getReturnType() == I.getType(),
214            "Undefined behavior: Call return type mismatches "
215            "callee return type", &I);
216
217    // Check argument types (in case the callee was casted) and attributes.
218    // TODO: Verify that caller and callee attributes are compatible.
219    Function::arg_iterator PI = F->arg_begin(), PE = F->arg_end();
220    CallSite::arg_iterator AI = CS.arg_begin(), AE = CS.arg_end();
221    for (; AI != AE; ++AI) {
222      Value *Actual = *AI;
223      if (PI != PE) {
224        Argument *Formal = PI++;
225        Assert1(Formal->getType() == Actual->getType(),
226                "Undefined behavior: Call argument type mismatches "
227                "callee parameter type", &I);
228
229        // Check that noalias arguments don't alias other arguments. This is
230        // not fully precise because we don't know the sizes of the dereferenced
231        // memory regions.
232        if (Formal->hasNoAliasAttr() && Actual->getType()->isPointerTy())
233          for (CallSite::arg_iterator BI = CS.arg_begin(); BI != AE; ++BI)
234            if (AI != BI && (*BI)->getType()->isPointerTy()) {
235              AliasAnalysis::AliasResult Result = AA->alias(*AI, *BI);
236              Assert1(Result != AliasAnalysis::MustAlias &&
237                      Result != AliasAnalysis::PartialAlias,
238                      "Unusual: noalias argument aliases another argument", &I);
239            }
240
241        // Check that an sret argument points to valid memory.
242        if (Formal->hasStructRetAttr() && Actual->getType()->isPointerTy()) {
243          Type *Ty =
244            cast<PointerType>(Formal->getType())->getElementType();
245          visitMemoryReference(I, Actual, AA->getTypeStoreSize(Ty),
246                               TD ? TD->getABITypeAlignment(Ty) : 0,
247                               Ty, MemRef::Read | MemRef::Write);
248        }
249      }
250    }
251  }
252
253  if (CS.isCall() && cast<CallInst>(CS.getInstruction())->isTailCall())
254    for (CallSite::arg_iterator AI = CS.arg_begin(), AE = CS.arg_end();
255         AI != AE; ++AI) {
256      Value *Obj = findValue(*AI, /*OffsetOk=*/true);
257      Assert1(!isa<AllocaInst>(Obj),
258              "Undefined behavior: Call with \"tail\" keyword references "
259              "alloca", &I);
260    }
261
262
263  if (IntrinsicInst *II = dyn_cast<IntrinsicInst>(&I))
264    switch (II->getIntrinsicID()) {
265    default: break;
266
267    // TODO: Check more intrinsics
268
269    case Intrinsic::memcpy: {
270      MemCpyInst *MCI = cast<MemCpyInst>(&I);
271      // TODO: If the size is known, use it.
272      visitMemoryReference(I, MCI->getDest(), AliasAnalysis::UnknownSize,
273                           MCI->getAlignment(), 0,
274                           MemRef::Write);
275      visitMemoryReference(I, MCI->getSource(), AliasAnalysis::UnknownSize,
276                           MCI->getAlignment(), 0,
277                           MemRef::Read);
278
279      // Check that the memcpy arguments don't overlap. The AliasAnalysis API
280      // isn't expressive enough for what we really want to do. Known partial
281      // overlap is not distinguished from the case where nothing is known.
282      uint64_t Size = 0;
283      if (const ConstantInt *Len =
284            dyn_cast<ConstantInt>(findValue(MCI->getLength(),
285                                            /*OffsetOk=*/false)))
286        if (Len->getValue().isIntN(32))
287          Size = Len->getValue().getZExtValue();
288      Assert1(AA->alias(MCI->getSource(), Size, MCI->getDest(), Size) !=
289              AliasAnalysis::MustAlias,
290              "Undefined behavior: memcpy source and destination overlap", &I);
291      break;
292    }
293    case Intrinsic::memmove: {
294      MemMoveInst *MMI = cast<MemMoveInst>(&I);
295      // TODO: If the size is known, use it.
296      visitMemoryReference(I, MMI->getDest(), AliasAnalysis::UnknownSize,
297                           MMI->getAlignment(), 0,
298                           MemRef::Write);
299      visitMemoryReference(I, MMI->getSource(), AliasAnalysis::UnknownSize,
300                           MMI->getAlignment(), 0,
301                           MemRef::Read);
302      break;
303    }
304    case Intrinsic::memset: {
305      MemSetInst *MSI = cast<MemSetInst>(&I);
306      // TODO: If the size is known, use it.
307      visitMemoryReference(I, MSI->getDest(), AliasAnalysis::UnknownSize,
308                           MSI->getAlignment(), 0,
309                           MemRef::Write);
310      break;
311    }
312
313    case Intrinsic::vastart:
314      Assert1(I.getParent()->getParent()->isVarArg(),
315              "Undefined behavior: va_start called in a non-varargs function",
316              &I);
317
318      visitMemoryReference(I, CS.getArgument(0), AliasAnalysis::UnknownSize,
319                           0, 0, MemRef::Read | MemRef::Write);
320      break;
321    case Intrinsic::vacopy:
322      visitMemoryReference(I, CS.getArgument(0), AliasAnalysis::UnknownSize,
323                           0, 0, MemRef::Write);
324      visitMemoryReference(I, CS.getArgument(1), AliasAnalysis::UnknownSize,
325                           0, 0, MemRef::Read);
326      break;
327    case Intrinsic::vaend:
328      visitMemoryReference(I, CS.getArgument(0), AliasAnalysis::UnknownSize,
329                           0, 0, MemRef::Read | MemRef::Write);
330      break;
331
332    case Intrinsic::stackrestore:
333      // Stackrestore doesn't read or write memory, but it sets the
334      // stack pointer, which the compiler may read from or write to
335      // at any time, so check it for both readability and writeability.
336      visitMemoryReference(I, CS.getArgument(0), AliasAnalysis::UnknownSize,
337                           0, 0, MemRef::Read | MemRef::Write);
338      break;
339    }
340}
341
342void Lint::visitCallInst(CallInst &I) {
343  return visitCallSite(&I);
344}
345
346void Lint::visitInvokeInst(InvokeInst &I) {
347  return visitCallSite(&I);
348}
349
350void Lint::visitReturnInst(ReturnInst &I) {
351  Function *F = I.getParent()->getParent();
352  Assert1(!F->doesNotReturn(),
353          "Unusual: Return statement in function with noreturn attribute",
354          &I);
355
356  if (Value *V = I.getReturnValue()) {
357    Value *Obj = findValue(V, /*OffsetOk=*/true);
358    Assert1(!isa<AllocaInst>(Obj),
359            "Unusual: Returning alloca value", &I);
360  }
361}
362
363// TODO: Check that the reference is in bounds.
364// TODO: Check readnone/readonly function attributes.
365void Lint::visitMemoryReference(Instruction &I,
366                                Value *Ptr, uint64_t Size, unsigned Align,
367                                Type *Ty, unsigned Flags) {
368  // If no memory is being referenced, it doesn't matter if the pointer
369  // is valid.
370  if (Size == 0)
371    return;
372
373  Value *UnderlyingObject = findValue(Ptr, /*OffsetOk=*/true);
374  Assert1(!isa<ConstantPointerNull>(UnderlyingObject),
375          "Undefined behavior: Null pointer dereference", &I);
376  Assert1(!isa<UndefValue>(UnderlyingObject),
377          "Undefined behavior: Undef pointer dereference", &I);
378  Assert1(!isa<ConstantInt>(UnderlyingObject) ||
379          !cast<ConstantInt>(UnderlyingObject)->isAllOnesValue(),
380          "Unusual: All-ones pointer dereference", &I);
381  Assert1(!isa<ConstantInt>(UnderlyingObject) ||
382          !cast<ConstantInt>(UnderlyingObject)->isOne(),
383          "Unusual: Address one pointer dereference", &I);
384
385  if (Flags & MemRef::Write) {
386    if (const GlobalVariable *GV = dyn_cast<GlobalVariable>(UnderlyingObject))
387      Assert1(!GV->isConstant(),
388              "Undefined behavior: Write to read-only memory", &I);
389    Assert1(!isa<Function>(UnderlyingObject) &&
390            !isa<BlockAddress>(UnderlyingObject),
391            "Undefined behavior: Write to text section", &I);
392  }
393  if (Flags & MemRef::Read) {
394    Assert1(!isa<Function>(UnderlyingObject),
395            "Unusual: Load from function body", &I);
396    Assert1(!isa<BlockAddress>(UnderlyingObject),
397            "Undefined behavior: Load from block address", &I);
398  }
399  if (Flags & MemRef::Callee) {
400    Assert1(!isa<BlockAddress>(UnderlyingObject),
401            "Undefined behavior: Call to block address", &I);
402  }
403  if (Flags & MemRef::Branchee) {
404    Assert1(!isa<Constant>(UnderlyingObject) ||
405            isa<BlockAddress>(UnderlyingObject),
406            "Undefined behavior: Branch to non-blockaddress", &I);
407  }
408
409  if (TD) {
410    if (Align == 0 && Ty) Align = TD->getABITypeAlignment(Ty);
411
412    if (Align != 0) {
413      unsigned BitWidth = TD->getTypeSizeInBits(Ptr->getType());
414      APInt Mask = APInt::getAllOnesValue(BitWidth),
415                   KnownZero(BitWidth, 0), KnownOne(BitWidth, 0);
416      ComputeMaskedBits(Ptr, Mask, KnownZero, KnownOne, TD);
417      Assert1(!(KnownOne & APInt::getLowBitsSet(BitWidth, Log2_32(Align))),
418              "Undefined behavior: Memory reference address is misaligned", &I);
419    }
420  }
421}
422
423void Lint::visitLoadInst(LoadInst &I) {
424  visitMemoryReference(I, I.getPointerOperand(),
425                       AA->getTypeStoreSize(I.getType()), I.getAlignment(),
426                       I.getType(), MemRef::Read);
427}
428
429void Lint::visitStoreInst(StoreInst &I) {
430  visitMemoryReference(I, I.getPointerOperand(),
431                       AA->getTypeStoreSize(I.getOperand(0)->getType()),
432                       I.getAlignment(),
433                       I.getOperand(0)->getType(), MemRef::Write);
434}
435
436void Lint::visitXor(BinaryOperator &I) {
437  Assert1(!isa<UndefValue>(I.getOperand(0)) ||
438          !isa<UndefValue>(I.getOperand(1)),
439          "Undefined result: xor(undef, undef)", &I);
440}
441
442void Lint::visitSub(BinaryOperator &I) {
443  Assert1(!isa<UndefValue>(I.getOperand(0)) ||
444          !isa<UndefValue>(I.getOperand(1)),
445          "Undefined result: sub(undef, undef)", &I);
446}
447
448void Lint::visitLShr(BinaryOperator &I) {
449  if (ConstantInt *CI =
450        dyn_cast<ConstantInt>(findValue(I.getOperand(1), /*OffsetOk=*/false)))
451    Assert1(CI->getValue().ult(cast<IntegerType>(I.getType())->getBitWidth()),
452            "Undefined result: Shift count out of range", &I);
453}
454
455void Lint::visitAShr(BinaryOperator &I) {
456  if (ConstantInt *CI =
457        dyn_cast<ConstantInt>(findValue(I.getOperand(1), /*OffsetOk=*/false)))
458    Assert1(CI->getValue().ult(cast<IntegerType>(I.getType())->getBitWidth()),
459            "Undefined result: Shift count out of range", &I);
460}
461
462void Lint::visitShl(BinaryOperator &I) {
463  if (ConstantInt *CI =
464        dyn_cast<ConstantInt>(findValue(I.getOperand(1), /*OffsetOk=*/false)))
465    Assert1(CI->getValue().ult(cast<IntegerType>(I.getType())->getBitWidth()),
466            "Undefined result: Shift count out of range", &I);
467}
468
469static bool isZero(Value *V, TargetData *TD) {
470  // Assume undef could be zero.
471  if (isa<UndefValue>(V)) return true;
472
473  unsigned BitWidth = cast<IntegerType>(V->getType())->getBitWidth();
474  APInt Mask = APInt::getAllOnesValue(BitWidth),
475               KnownZero(BitWidth, 0), KnownOne(BitWidth, 0);
476  ComputeMaskedBits(V, Mask, KnownZero, KnownOne, TD);
477  return KnownZero.isAllOnesValue();
478}
479
480void Lint::visitSDiv(BinaryOperator &I) {
481  Assert1(!isZero(I.getOperand(1), TD),
482          "Undefined behavior: Division by zero", &I);
483}
484
485void Lint::visitUDiv(BinaryOperator &I) {
486  Assert1(!isZero(I.getOperand(1), TD),
487          "Undefined behavior: Division by zero", &I);
488}
489
490void Lint::visitSRem(BinaryOperator &I) {
491  Assert1(!isZero(I.getOperand(1), TD),
492          "Undefined behavior: Division by zero", &I);
493}
494
495void Lint::visitURem(BinaryOperator &I) {
496  Assert1(!isZero(I.getOperand(1), TD),
497          "Undefined behavior: Division by zero", &I);
498}
499
500void Lint::visitAllocaInst(AllocaInst &I) {
501  if (isa<ConstantInt>(I.getArraySize()))
502    // This isn't undefined behavior, it's just an obvious pessimization.
503    Assert1(&I.getParent()->getParent()->getEntryBlock() == I.getParent(),
504            "Pessimization: Static alloca outside of entry block", &I);
505
506  // TODO: Check for an unusual size (MSB set?)
507}
508
509void Lint::visitVAArgInst(VAArgInst &I) {
510  visitMemoryReference(I, I.getOperand(0), AliasAnalysis::UnknownSize, 0, 0,
511                       MemRef::Read | MemRef::Write);
512}
513
514void Lint::visitIndirectBrInst(IndirectBrInst &I) {
515  visitMemoryReference(I, I.getAddress(), AliasAnalysis::UnknownSize, 0, 0,
516                       MemRef::Branchee);
517
518  Assert1(I.getNumDestinations() != 0,
519          "Undefined behavior: indirectbr with no destinations", &I);
520}
521
522void Lint::visitExtractElementInst(ExtractElementInst &I) {
523  if (ConstantInt *CI =
524        dyn_cast<ConstantInt>(findValue(I.getIndexOperand(),
525                                        /*OffsetOk=*/false)))
526    Assert1(CI->getValue().ult(I.getVectorOperandType()->getNumElements()),
527            "Undefined result: extractelement index out of range", &I);
528}
529
530void Lint::visitInsertElementInst(InsertElementInst &I) {
531  if (ConstantInt *CI =
532        dyn_cast<ConstantInt>(findValue(I.getOperand(2),
533                                        /*OffsetOk=*/false)))
534    Assert1(CI->getValue().ult(I.getType()->getNumElements()),
535            "Undefined result: insertelement index out of range", &I);
536}
537
538void Lint::visitUnreachableInst(UnreachableInst &I) {
539  // This isn't undefined behavior, it's merely suspicious.
540  Assert1(&I == I.getParent()->begin() ||
541          prior(BasicBlock::iterator(&I))->mayHaveSideEffects(),
542          "Unusual: unreachable immediately preceded by instruction without "
543          "side effects", &I);
544}
545
546/// findValue - Look through bitcasts and simple memory reference patterns
547/// to identify an equivalent, but more informative, value.  If OffsetOk
548/// is true, look through getelementptrs with non-zero offsets too.
549///
550/// Most analysis passes don't require this logic, because instcombine
551/// will simplify most of these kinds of things away. But it's a goal of
552/// this Lint pass to be useful even on non-optimized IR.
553Value *Lint::findValue(Value *V, bool OffsetOk) const {
554  SmallPtrSet<Value *, 4> Visited;
555  return findValueImpl(V, OffsetOk, Visited);
556}
557
558/// findValueImpl - Implementation helper for findValue.
559Value *Lint::findValueImpl(Value *V, bool OffsetOk,
560                           SmallPtrSet<Value *, 4> &Visited) const {
561  // Detect self-referential values.
562  if (!Visited.insert(V))
563    return UndefValue::get(V->getType());
564
565  // TODO: Look through sext or zext cast, when the result is known to
566  // be interpreted as signed or unsigned, respectively.
567  // TODO: Look through eliminable cast pairs.
568  // TODO: Look through calls with unique return values.
569  // TODO: Look through vector insert/extract/shuffle.
570  V = OffsetOk ? GetUnderlyingObject(V, TD) : V->stripPointerCasts();
571  if (LoadInst *L = dyn_cast<LoadInst>(V)) {
572    BasicBlock::iterator BBI = L;
573    BasicBlock *BB = L->getParent();
574    SmallPtrSet<BasicBlock *, 4> VisitedBlocks;
575    for (;;) {
576      if (!VisitedBlocks.insert(BB)) break;
577      if (Value *U = FindAvailableLoadedValue(L->getPointerOperand(),
578                                              BB, BBI, 6, AA))
579        return findValueImpl(U, OffsetOk, Visited);
580      if (BBI != BB->begin()) break;
581      BB = BB->getUniquePredecessor();
582      if (!BB) break;
583      BBI = BB->end();
584    }
585  } else if (PHINode *PN = dyn_cast<PHINode>(V)) {
586    if (Value *W = PN->hasConstantValue())
587      if (W != V)
588        return findValueImpl(W, OffsetOk, Visited);
589  } else if (CastInst *CI = dyn_cast<CastInst>(V)) {
590    if (CI->isNoopCast(TD ? TD->getIntPtrType(V->getContext()) :
591                            Type::getInt64Ty(V->getContext())))
592      return findValueImpl(CI->getOperand(0), OffsetOk, Visited);
593  } else if (ExtractValueInst *Ex = dyn_cast<ExtractValueInst>(V)) {
594    if (Value *W = FindInsertedValue(Ex->getAggregateOperand(),
595                                     Ex->getIndices()))
596      if (W != V)
597        return findValueImpl(W, OffsetOk, Visited);
598  } else if (ConstantExpr *CE = dyn_cast<ConstantExpr>(V)) {
599    // Same as above, but for ConstantExpr instead of Instruction.
600    if (Instruction::isCast(CE->getOpcode())) {
601      if (CastInst::isNoopCast(Instruction::CastOps(CE->getOpcode()),
602                               CE->getOperand(0)->getType(),
603                               CE->getType(),
604                               TD ? TD->getIntPtrType(V->getContext()) :
605                                    Type::getInt64Ty(V->getContext())))
606        return findValueImpl(CE->getOperand(0), OffsetOk, Visited);
607    } else if (CE->getOpcode() == Instruction::ExtractValue) {
608      ArrayRef<unsigned> Indices = CE->getIndices();
609      if (Value *W = FindInsertedValue(CE->getOperand(0), Indices))
610        if (W != V)
611          return findValueImpl(W, OffsetOk, Visited);
612    }
613  }
614
615  // As a last resort, try SimplifyInstruction or constant folding.
616  if (Instruction *Inst = dyn_cast<Instruction>(V)) {
617    if (Value *W = SimplifyInstruction(Inst, TD, DT))
618      return findValueImpl(W, OffsetOk, Visited);
619  } else if (ConstantExpr *CE = dyn_cast<ConstantExpr>(V)) {
620    if (Value *W = ConstantFoldConstantExpression(CE, TD))
621      if (W != V)
622        return findValueImpl(W, OffsetOk, Visited);
623  }
624
625  return V;
626}
627
628//===----------------------------------------------------------------------===//
629//  Implement the public interfaces to this file...
630//===----------------------------------------------------------------------===//
631
632FunctionPass *llvm::createLintPass() {
633  return new Lint();
634}
635
636/// lintFunction - Check a function for errors, printing messages on stderr.
637///
638void llvm::lintFunction(const Function &f) {
639  Function &F = const_cast<Function&>(f);
640  assert(!F.isDeclaration() && "Cannot lint external functions");
641
642  FunctionPassManager FPM(F.getParent());
643  Lint *V = new Lint();
644  FPM.add(V);
645  FPM.run(F);
646}
647
648/// lintModule - Check a module for errors, printing messages on stderr.
649///
650void llvm::lintModule(const Module &M) {
651  PassManager PM;
652  Lint *V = new Lint();
653  PM.add(V);
654  PM.run(const_cast<Module&>(M));
655}
656