lib/Analysis/Lint.cpp

   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"
  56 using namespace llvm;
  57
  58 namespace {
  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                               const 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
 149 char Lint::ID = 0;
 150 INITIALIZE_PASS_BEGIN(Lint, "lint", "Statically lint-checks LLVM IR",
 151                       false, true)
 152 INITIALIZE_PASS_DEPENDENCY(DominatorTree)
 153 INITIALIZE_AG_DEPENDENCY(AliasAnalysis)
 154 INITIALIZE_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 //
 172 bool 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
 183 void 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
 192 void 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     const 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           const 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
 342 void Lint::visitCallInst(CallInst &I) {
 343   return visitCallSite(&I);
 344 }
 345
 346 void Lint::visitInvokeInst(InvokeInst &I) {
 347   return visitCallSite(&I);
 348 }
 349
 350 void 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.
 365 void Lint::visitMemoryReference(Instruction &I,
 366                                 Value *Ptr, uint64_t Size, unsigned Align,
 367                                 const 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
 423 void Lint::visitLoadInst(LoadInst &I) {
 424   visitMemoryReference(I, I.getPointerOperand(),
 425                        AA->getTypeStoreSize(I.getType()), I.getAlignment(),
 426                        I.getType(), MemRef::Read);
 427 }
 428
 429 void 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
 436 void 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
 442 void 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
 448 void 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
 455 void 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
 462 void 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
 469 static 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
 480 void Lint::visitSDiv(BinaryOperator &I) {
 481   Assert1(!isZero(I.getOperand(1), TD),
 482           "Undefined behavior: Division by zero", &I);
 483 }
 484
 485 void Lint::visitUDiv(BinaryOperator &I) {
 486   Assert1(!isZero(I.getOperand(1), TD),
 487           "Undefined behavior: Division by zero", &I);
 488 }
 489
 490 void Lint::visitSRem(BinaryOperator &I) {
 491   Assert1(!isZero(I.getOperand(1), TD),
 492           "Undefined behavior: Division by zero", &I);
 493 }
 494
 495 void Lint::visitURem(BinaryOperator &I) {
 496   Assert1(!isZero(I.getOperand(1), TD),
 497           "Undefined behavior: Division by zero", &I);
 498 }
 499
 500 void 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
 509 void Lint::visitVAArgInst(VAArgInst &I) {
 510   visitMemoryReference(I, I.getOperand(0), AliasAnalysis::UnknownSize, 0, 0,
 511                        MemRef::Read | MemRef::Write);
 512 }
 513
 514 void 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
 522 void 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
 530 void 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
 538 void 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.
 553 Value *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.
 559 Value *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->idx_begin(),
 596                                      Ex->idx_end()))
 597       if (W != V)
 598         return findValueImpl(W, OffsetOk, Visited);
 599   } else if (ConstantExpr *CE = dyn_cast<ConstantExpr>(V)) {
 600     // Same as above, but for ConstantExpr instead of Instruction.
 601     if (Instruction::isCast(CE->getOpcode())) {
 602       if (CastInst::isNoopCast(Instruction::CastOps(CE->getOpcode()),
 603                                CE->getOperand(0)->getType(),
 604                                CE->getType(),
 605                                TD ? TD->getIntPtrType(V->getContext()) :
 606                                     Type::getInt64Ty(V->getContext())))
 607         return findValueImpl(CE->getOperand(0), OffsetOk, Visited);
 608     } else if (CE->getOpcode() == Instruction::ExtractValue) {
 609       ArrayRef<unsigned> Indices = CE->getIndices();
 610       if (Value *W = FindInsertedValue(CE->getOperand(0),
 611                                        Indices.begin(),
 612                                        Indices.end()))
 613         if (W != V)
 614           return findValueImpl(W, OffsetOk, Visited);
 615     }
 616   }
 617
 618   // As a last resort, try SimplifyInstruction or constant folding.
 619   if (Instruction *Inst = dyn_cast<Instruction>(V)) {
 620     if (Value *W = SimplifyInstruction(Inst, TD, DT))
 621       return findValueImpl(W, OffsetOk, Visited);
 622   } else if (ConstantExpr *CE = dyn_cast<ConstantExpr>(V)) {
 623     if (Value *W = ConstantFoldConstantExpression(CE, TD))
 624       if (W != V)
 625         return findValueImpl(W, OffsetOk, Visited);
 626   }
 627
 628   return V;
 629 }
 630
 631 //===----------------------------------------------------------------------===//
 632 //  Implement the public interfaces to this file...
 633 //===----------------------------------------------------------------------===//
 634
 635 FunctionPass *llvm::createLintPass() {
 636   return new Lint();
 637 }
 638
 639 /// lintFunction - Check a function for errors, printing messages on stderr.
 640 ///
 641 void llvm::lintFunction(const Function &f) {
 642   Function &F = const_cast<Function&>(f);
 643   assert(!F.isDeclaration() && "Cannot lint external functions");
 644
 645   FunctionPassManager FPM(F.getParent());
 646   Lint *V = new Lint();
 647   FPM.add(V);
 648   FPM.run(F);
 649 }
 650
 651 /// lintModule - Check a module for errors, printing messages on stderr.
 652 ///
 653 void llvm::lintModule(const Module &M) {
 654   PassManager PM;
 655   Lint *V = new Lint();
 656   PM.add(V);
 657   PM.run(const_cast<Module&>(M));
 658 }