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/Lint.h"
  38 #include "llvm/ADT/APInt.h"
  39 #include "llvm/ADT/ArrayRef.h"
  40 #include "llvm/ADT/SmallPtrSet.h"
  41 #include "llvm/ADT/Twine.h"
  42 #include "llvm/Analysis/AliasAnalysis.h"
  43 #include "llvm/Analysis/AssumptionCache.h"
  44 #include "llvm/Analysis/ConstantFolding.h"
  45 #include "llvm/Analysis/InstructionSimplify.h"
  46 #include "llvm/Analysis/Loads.h"
  47 #include "llvm/Analysis/MemoryLocation.h"
  48 #include "llvm/Analysis/Passes.h"
  49 #include "llvm/Analysis/TargetLibraryInfo.h"
  50 #include "llvm/Analysis/ValueTracking.h"
  51 #include "llvm/IR/Argument.h"
  52 #include "llvm/IR/BasicBlock.h"
  53 #include "llvm/IR/CallSite.h"
  54 #include "llvm/IR/Constant.h"
  55 #include "llvm/IR/Constants.h"
  56 #include "llvm/IR/DataLayout.h"
  57 #include "llvm/IR/DerivedTypes.h"
  58 #include "llvm/IR/Dominators.h"
  59 #include "llvm/IR/Function.h"
  60 #include "llvm/IR/GlobalVariable.h"
  61 #include "llvm/IR/InstVisitor.h"
  62 #include "llvm/IR/InstrTypes.h"
  63 #include "llvm/IR/Instruction.h"
  64 #include "llvm/IR/Instructions.h"
  65 #include "llvm/IR/IntrinsicInst.h"
  66 #include "llvm/IR/LegacyPassManager.h"
  67 #include "llvm/IR/Module.h"
  68 #include "llvm/IR/Type.h"
  69 #include "llvm/IR/Value.h"
  70 #include "llvm/Pass.h"
  71 #include "llvm/Support/Casting.h"
  72 #include "llvm/Support/Debug.h"
  73 #include "llvm/Support/KnownBits.h"
  74 #include "llvm/Support/MathExtras.h"
  75 #include "llvm/Support/raw_ostream.h"
  76 #include <cassert>
  77 #include <cstdint>
  78 #include <iterator>
  79 #include <string>
  80
  81 using namespace llvm;
  82
  83 namespace {
  84   namespace MemRef {
  85     static const unsigned Read     = 1;
  86     static const unsigned Write    = 2;
  87     static const unsigned Callee   = 4;
  88     static const unsigned Branchee = 8;
  89   } // end namespace MemRef
  90
  91   class Lint : public FunctionPass, public InstVisitor<Lint> {
  92     friend class InstVisitor<Lint>;
  93
  94     void visitFunction(Function &F);
  95
  96     void visitCallSite(CallSite CS);
  97     void visitMemoryReference(Instruction &I, Value *Ptr,
  98                               uint64_t Size, unsigned Align,
  99                               Type *Ty, unsigned Flags);
 100     void visitEHBeginCatch(IntrinsicInst *II);
 101     void visitEHEndCatch(IntrinsicInst *II);
 102
 103     void visitCallInst(CallInst &I);
 104     void visitInvokeInst(InvokeInst &I);
 105     void visitReturnInst(ReturnInst &I);
 106     void visitLoadInst(LoadInst &I);
 107     void visitStoreInst(StoreInst &I);
 108     void visitXor(BinaryOperator &I);
 109     void visitSub(BinaryOperator &I);
 110     void visitLShr(BinaryOperator &I);
 111     void visitAShr(BinaryOperator &I);
 112     void visitShl(BinaryOperator &I);
 113     void visitSDiv(BinaryOperator &I);
 114     void visitUDiv(BinaryOperator &I);
 115     void visitSRem(BinaryOperator &I);
 116     void visitURem(BinaryOperator &I);
 117     void visitAllocaInst(AllocaInst &I);
 118     void visitVAArgInst(VAArgInst &I);
 119     void visitIndirectBrInst(IndirectBrInst &I);
 120     void visitExtractElementInst(ExtractElementInst &I);
 121     void visitInsertElementInst(InsertElementInst &I);
 122     void visitUnreachableInst(UnreachableInst &I);
 123
 124     Value *findValue(Value *V, bool OffsetOk) const;
 125     Value *findValueImpl(Value *V, bool OffsetOk,
 126                          SmallPtrSetImpl<Value *> &Visited) const;
 127
 128   public:
 129     Module *Mod;
 130     const DataLayout *DL;
 131     AliasAnalysis *AA;
 132     AssumptionCache *AC;
 133     DominatorTree *DT;
 134     TargetLibraryInfo *TLI;
 135
 136     std::string Messages;
 137     raw_string_ostream MessagesStr;
 138
 139     static char ID; // Pass identification, replacement for typeid
 140     Lint() : FunctionPass(ID), MessagesStr(Messages) {
 141       initializeLintPass(*PassRegistry::getPassRegistry());
 142     }
 143
 144     bool runOnFunction(Function &F) override;
 145
 146     void getAnalysisUsage(AnalysisUsage &AU) const override {
 147       AU.setPreservesAll();
 148       AU.addRequired<AAResultsWrapperPass>();
 149       AU.addRequired<AssumptionCacheTracker>();
 150       AU.addRequired<TargetLibraryInfoWrapperPass>();
 151       AU.addRequired<DominatorTreeWrapperPass>();
 152     }
 153     void print(raw_ostream &O, const Module *M) const override {}
 154
 155     void WriteValues(ArrayRef<const Value *> Vs) {
 156       for (const Value *V : Vs) {
 157         if (!V)
 158           continue;
 159         if (isa<Instruction>(V)) {
 160           MessagesStr << *V << '\n';
 161         } else {
 162           V->printAsOperand(MessagesStr, true, Mod);
 163           MessagesStr << '\n';
 164         }
 165       }
 166     }
 167
 168     /// A check failed, so printout out the condition and the message.
 169     ///
 170     /// This provides a nice place to put a breakpoint if you want to see why
 171     /// something is not correct.
 172     void CheckFailed(const Twine &Message) { MessagesStr << Message << '\n'; }
 173
 174     /// A check failed (with values to print).
 175     ///
 176     /// This calls the Message-only version so that the above is easier to set
 177     /// a breakpoint on.
 178     template <typename T1, typename... Ts>
 179     void CheckFailed(const Twine &Message, const T1 &V1, const Ts &...Vs) {
 180       CheckFailed(Message);
 181       WriteValues({V1, Vs...});
 182     }
 183   };
 184 } // end anonymous namespace
 185
 186 char Lint::ID = 0;
 187 INITIALIZE_PASS_BEGIN(Lint, "lint", "Statically lint-checks LLVM IR",
 188                       false, true)
 189 INITIALIZE_PASS_DEPENDENCY(AssumptionCacheTracker)
 190 INITIALIZE_PASS_DEPENDENCY(TargetLibraryInfoWrapperPass)
 191 INITIALIZE_PASS_DEPENDENCY(DominatorTreeWrapperPass)
 192 INITIALIZE_PASS_DEPENDENCY(AAResultsWrapperPass)
 193 INITIALIZE_PASS_END(Lint, "lint", "Statically lint-checks LLVM IR",
 194                     false, true)
 195
 196 // Assert - We know that cond should be true, if not print an error message.
 197 #define Assert(C, ...) \
 198     do { if (!(C)) { CheckFailed(__VA_ARGS__); return; } } while (false)
 199
 200 // Lint::run - This is the main Analysis entry point for a
 201 // function.
 202 //
 203 bool Lint::runOnFunction(Function &F) {
 204   Mod = F.getParent();
 205   DL = &F.getParent()->getDataLayout();
 206   AA = &getAnalysis<AAResultsWrapperPass>().getAAResults();
 207   AC = &getAnalysis<AssumptionCacheTracker>().getAssumptionCache(F);
 208   DT = &getAnalysis<DominatorTreeWrapperPass>().getDomTree();
 209   TLI = &getAnalysis<TargetLibraryInfoWrapperPass>().getTLI();
 210   visit(F);
 211   dbgs() << MessagesStr.str();
 212   Messages.clear();
 213   return false;
 214 }
 215
 216 void Lint::visitFunction(Function &F) {
 217   // This isn't undefined behavior, it's just a little unusual, and it's a
 218   // fairly common mistake to neglect to name a function.
 219   Assert(F.hasName() || F.hasLocalLinkage(),
 220          "Unusual: Unnamed function with non-local linkage", &F);
 221
 222   // TODO: Check for irreducible control flow.
 223 }
 224
 225 void Lint::visitCallSite(CallSite CS) {
 226   Instruction &I = *CS.getInstruction();
 227   Value *Callee = CS.getCalledValue();
 228
 229   visitMemoryReference(I, Callee, MemoryLocation::UnknownSize, 0, nullptr,
 230                        MemRef::Callee);
 231
 232   if (Function *F = dyn_cast<Function>(findValue(Callee,
 233                                                  /*OffsetOk=*/false))) {
 234     Assert(CS.getCallingConv() == F->getCallingConv(),
 235            "Undefined behavior: Caller and callee calling convention differ",
 236            &I);
 237
 238     FunctionType *FT = F->getFunctionType();
 239     unsigned NumActualArgs = CS.arg_size();
 240
 241     Assert(FT->isVarArg() ? FT->getNumParams() <= NumActualArgs
 242                           : FT->getNumParams() == NumActualArgs,
 243            "Undefined behavior: Call argument count mismatches callee "
 244            "argument count",
 245            &I);
 246
 247     Assert(FT->getReturnType() == I.getType(),
 248            "Undefined behavior: Call return type mismatches "
 249            "callee return type",
 250            &I);
 251
 252     // Check argument types (in case the callee was casted) and attributes.
 253     // TODO: Verify that caller and callee attributes are compatible.
 254     Function::arg_iterator PI = F->arg_begin(), PE = F->arg_end();
 255     CallSite::arg_iterator AI = CS.arg_begin(), AE = CS.arg_end();
 256     for (; AI != AE; ++AI) {
 257       Value *Actual = *AI;
 258       if (PI != PE) {
 259         Argument *Formal = &*PI++;
 260         Assert(Formal->getType() == Actual->getType(),
 261                "Undefined behavior: Call argument type mismatches "
 262                "callee parameter type",
 263                &I);
 264
 265         // Check that noalias arguments don't alias other arguments. This is
 266         // not fully precise because we don't know the sizes of the dereferenced
 267         // memory regions.
 268         if (Formal->hasNoAliasAttr() && Actual->getType()->isPointerTy()) {
 269           AttributeList PAL = CS.getAttributes();
 270           unsigned ArgNo = 0;
 271           for (CallSite::arg_iterator BI = CS.arg_begin(); BI != AE; ++BI) {
 272             // Skip ByVal arguments since they will be memcpy'd to the callee's
 273             // stack so we're not really passing the pointer anyway.
 274             if (PAL.hasParamAttribute(ArgNo++, Attribute::ByVal))
 275               continue;
 276             if (AI != BI && (*BI)->getType()->isPointerTy()) {
 277               AliasResult Result = AA->alias(*AI, *BI);
 278               Assert(Result != MustAlias && Result != PartialAlias,
 279                      "Unusual: noalias argument aliases another argument", &I);
 280             }
 281           }
 282         }
 283
 284         // Check that an sret argument points to valid memory.
 285         if (Formal->hasStructRetAttr() && Actual->getType()->isPointerTy()) {
 286           Type *Ty =
 287             cast<PointerType>(Formal->getType())->getElementType();
 288           visitMemoryReference(I, Actual, DL->getTypeStoreSize(Ty),
 289                                DL->getABITypeAlignment(Ty), Ty,
 290                                MemRef::Read | MemRef::Write);
 291         }
 292       }
 293     }
 294   }
 295
 296   if (CS.isCall()) {
 297     const CallInst *CI = cast<CallInst>(CS.getInstruction());
 298     if (CI->isTailCall()) {
 299       const AttributeList &PAL = CI->getAttributes();
 300       unsigned ArgNo = 0;
 301       for (Value *Arg : CS.args()) {
 302         // Skip ByVal arguments since they will be memcpy'd to the callee's
 303         // stack anyway.
 304         if (PAL.hasParamAttribute(ArgNo++, Attribute::ByVal))
 305           continue;
 306         Value *Obj = findValue(Arg, /*OffsetOk=*/true);
 307         Assert(!isa<AllocaInst>(Obj),
 308                "Undefined behavior: Call with \"tail\" keyword references "
 309                "alloca",
 310                &I);
 311       }
 312     }
 313   }
 314
 315
 316   if (IntrinsicInst *II = dyn_cast<IntrinsicInst>(&I))
 317     switch (II->getIntrinsicID()) {
 318     default: break;
 319
 320     // TODO: Check more intrinsics
 321
 322     case Intrinsic::memcpy: {
 323       MemCpyInst *MCI = cast<MemCpyInst>(&I);
 324       // TODO: If the size is known, use it.
 325       visitMemoryReference(I, MCI->getDest(), MemoryLocation::UnknownSize,
 326                            MCI->getDestAlignment(), nullptr, MemRef::Write);
 327       visitMemoryReference(I, MCI->getSource(), MemoryLocation::UnknownSize,
 328                            MCI->getSourceAlignment(), nullptr, MemRef::Read);
 329
 330       // Check that the memcpy arguments don't overlap. The AliasAnalysis API
 331       // isn't expressive enough for what we really want to do. Known partial
 332       // overlap is not distinguished from the case where nothing is known.
 333       uint64_t Size = 0;
 334       if (const ConstantInt *Len =
 335               dyn_cast<ConstantInt>(findValue(MCI->getLength(),
 336                                               /*OffsetOk=*/false)))
 337         if (Len->getValue().isIntN(32))
 338           Size = Len->getValue().getZExtValue();
 339       Assert(AA->alias(MCI->getSource(), Size, MCI->getDest(), Size) !=
 340                  MustAlias,
 341              "Undefined behavior: memcpy source and destination overlap", &I);
 342       break;
 343     }
 344     case Intrinsic::memmove: {
 345       MemMoveInst *MMI = cast<MemMoveInst>(&I);
 346       // TODO: If the size is known, use it.
 347       visitMemoryReference(I, MMI->getDest(), MemoryLocation::UnknownSize,
 348                            MMI->getDestAlignment(), nullptr, MemRef::Write);
 349       visitMemoryReference(I, MMI->getSource(), MemoryLocation::UnknownSize,
 350                            MMI->getSourceAlignment(), nullptr, MemRef::Read);
 351       break;
 352     }
 353     case Intrinsic::memset: {
 354       MemSetInst *MSI = cast<MemSetInst>(&I);
 355       // TODO: If the size is known, use it.
 356       visitMemoryReference(I, MSI->getDest(), MemoryLocation::UnknownSize,
 357                            MSI->getDestAlignment(), nullptr, MemRef::Write);
 358       break;
 359     }
 360
 361     case Intrinsic::vastart:
 362       Assert(I.getParent()->getParent()->isVarArg(),
 363              "Undefined behavior: va_start called in a non-varargs function",
 364              &I);
 365
 366       visitMemoryReference(I, CS.getArgument(0), MemoryLocation::UnknownSize, 0,
 367                            nullptr, MemRef::Read | MemRef::Write);
 368       break;
 369     case Intrinsic::vacopy:
 370       visitMemoryReference(I, CS.getArgument(0), MemoryLocation::UnknownSize, 0,
 371                            nullptr, MemRef::Write);
 372       visitMemoryReference(I, CS.getArgument(1), MemoryLocation::UnknownSize, 0,
 373                            nullptr, MemRef::Read);
 374       break;
 375     case Intrinsic::vaend:
 376       visitMemoryReference(I, CS.getArgument(0), MemoryLocation::UnknownSize, 0,
 377                            nullptr, MemRef::Read | MemRef::Write);
 378       break;
 379
 380     case Intrinsic::stackrestore:
 381       // Stackrestore doesn't read or write memory, but it sets the
 382       // stack pointer, which the compiler may read from or write to
 383       // at any time, so check it for both readability and writeability.
 384       visitMemoryReference(I, CS.getArgument(0), MemoryLocation::UnknownSize, 0,
 385                            nullptr, MemRef::Read | MemRef::Write);
 386       break;
 387     }
 388 }
 389
 390 void Lint::visitCallInst(CallInst &I) {
 391   return visitCallSite(&I);
 392 }
 393
 394 void Lint::visitInvokeInst(InvokeInst &I) {
 395   return visitCallSite(&I);
 396 }
 397
 398 void Lint::visitReturnInst(ReturnInst &I) {
 399   Function *F = I.getParent()->getParent();
 400   Assert(!F->doesNotReturn(),
 401          "Unusual: Return statement in function with noreturn attribute", &I);
 402
 403   if (Value *V = I.getReturnValue()) {
 404     Value *Obj = findValue(V, /*OffsetOk=*/true);
 405     Assert(!isa<AllocaInst>(Obj), "Unusual: Returning alloca value", &I);
 406   }
 407 }
 408
 409 // TODO: Check that the reference is in bounds.
 410 // TODO: Check readnone/readonly function attributes.
 411 void Lint::visitMemoryReference(Instruction &I,
 412                                 Value *Ptr, uint64_t Size, unsigned Align,
 413                                 Type *Ty, unsigned Flags) {
 414   // If no memory is being referenced, it doesn't matter if the pointer
 415   // is valid.
 416   if (Size == 0)
 417     return;
 418
 419   Value *UnderlyingObject = findValue(Ptr, /*OffsetOk=*/true);
 420   Assert(!isa<ConstantPointerNull>(UnderlyingObject),
 421          "Undefined behavior: Null pointer dereference", &I);
 422   Assert(!isa<UndefValue>(UnderlyingObject),
 423          "Undefined behavior: Undef pointer dereference", &I);
 424   Assert(!isa<ConstantInt>(UnderlyingObject) ||
 425              !cast<ConstantInt>(UnderlyingObject)->isMinusOne(),
 426          "Unusual: All-ones pointer dereference", &I);
 427   Assert(!isa<ConstantInt>(UnderlyingObject) ||
 428              !cast<ConstantInt>(UnderlyingObject)->isOne(),
 429          "Unusual: Address one pointer dereference", &I);
 430
 431   if (Flags & MemRef::Write) {
 432     if (const GlobalVariable *GV = dyn_cast<GlobalVariable>(UnderlyingObject))
 433       Assert(!GV->isConstant(), "Undefined behavior: Write to read-only memory",
 434              &I);
 435     Assert(!isa<Function>(UnderlyingObject) &&
 436                !isa<BlockAddress>(UnderlyingObject),
 437            "Undefined behavior: Write to text section", &I);
 438   }
 439   if (Flags & MemRef::Read) {
 440     Assert(!isa<Function>(UnderlyingObject), "Unusual: Load from function body",
 441            &I);
 442     Assert(!isa<BlockAddress>(UnderlyingObject),
 443            "Undefined behavior: Load from block address", &I);
 444   }
 445   if (Flags & MemRef::Callee) {
 446     Assert(!isa<BlockAddress>(UnderlyingObject),
 447            "Undefined behavior: Call to block address", &I);
 448   }
 449   if (Flags & MemRef::Branchee) {
 450     Assert(!isa<Constant>(UnderlyingObject) ||
 451                isa<BlockAddress>(UnderlyingObject),
 452            "Undefined behavior: Branch to non-blockaddress", &I);
 453   }
 454
 455   // Check for buffer overflows and misalignment.
 456   // Only handles memory references that read/write something simple like an
 457   // alloca instruction or a global variable.
 458   int64_t Offset = 0;
 459   if (Value *Base = GetPointerBaseWithConstantOffset(Ptr, Offset, *DL)) {
 460     // OK, so the access is to a constant offset from Ptr.  Check that Ptr is
 461     // something we can handle and if so extract the size of this base object
 462     // along with its alignment.
 463     uint64_t BaseSize = MemoryLocation::UnknownSize;
 464     unsigned BaseAlign = 0;
 465
 466     if (AllocaInst *AI = dyn_cast<AllocaInst>(Base)) {
 467       Type *ATy = AI->getAllocatedType();
 468       if (!AI->isArrayAllocation() && ATy->isSized())
 469         BaseSize = DL->getTypeAllocSize(ATy);
 470       BaseAlign = AI->getAlignment();
 471       if (BaseAlign == 0 && ATy->isSized())
 472         BaseAlign = DL->getABITypeAlignment(ATy);
 473     } else if (GlobalVariable *GV = dyn_cast<GlobalVariable>(Base)) {
 474       // If the global may be defined differently in another compilation unit
 475       // then don't warn about funky memory accesses.
 476       if (GV->hasDefinitiveInitializer()) {
 477         Type *GTy = GV->getValueType();
 478         if (GTy->isSized())
 479           BaseSize = DL->getTypeAllocSize(GTy);
 480         BaseAlign = GV->getAlignment();
 481         if (BaseAlign == 0 && GTy->isSized())
 482           BaseAlign = DL->getABITypeAlignment(GTy);
 483       }
 484     }
 485
 486     // Accesses from before the start or after the end of the object are not
 487     // defined.
 488     Assert(Size == MemoryLocation::UnknownSize ||
 489                BaseSize == MemoryLocation::UnknownSize ||
 490                (Offset >= 0 && Offset + Size <= BaseSize),
 491            "Undefined behavior: Buffer overflow", &I);
 492
 493     // Accesses that say that the memory is more aligned than it is are not
 494     // defined.
 495     if (Align == 0 && Ty && Ty->isSized())
 496       Align = DL->getABITypeAlignment(Ty);
 497     Assert(!BaseAlign || Align <= MinAlign(BaseAlign, Offset),
 498            "Undefined behavior: Memory reference address is misaligned", &I);
 499   }
 500 }
 501
 502 void Lint::visitLoadInst(LoadInst &I) {
 503   visitMemoryReference(I, I.getPointerOperand(),
 504                        DL->getTypeStoreSize(I.getType()), I.getAlignment(),
 505                        I.getType(), MemRef::Read);
 506 }
 507
 508 void Lint::visitStoreInst(StoreInst &I) {
 509   visitMemoryReference(I, I.getPointerOperand(),
 510                        DL->getTypeStoreSize(I.getOperand(0)->getType()),
 511                        I.getAlignment(),
 512                        I.getOperand(0)->getType(), MemRef::Write);
 513 }
 514
 515 void Lint::visitXor(BinaryOperator &I) {
 516   Assert(!isa<UndefValue>(I.getOperand(0)) || !isa<UndefValue>(I.getOperand(1)),
 517          "Undefined result: xor(undef, undef)", &I);
 518 }
 519
 520 void Lint::visitSub(BinaryOperator &I) {
 521   Assert(!isa<UndefValue>(I.getOperand(0)) || !isa<UndefValue>(I.getOperand(1)),
 522          "Undefined result: sub(undef, undef)", &I);
 523 }
 524
 525 void Lint::visitLShr(BinaryOperator &I) {
 526   if (ConstantInt *CI = dyn_cast<ConstantInt>(findValue(I.getOperand(1),
 527                                                         /*OffsetOk=*/false)))
 528     Assert(CI->getValue().ult(cast<IntegerType>(I.getType())->getBitWidth()),
 529            "Undefined result: Shift count out of range", &I);
 530 }
 531
 532 void Lint::visitAShr(BinaryOperator &I) {
 533   if (ConstantInt *CI =
 534           dyn_cast<ConstantInt>(findValue(I.getOperand(1), /*OffsetOk=*/false)))
 535     Assert(CI->getValue().ult(cast<IntegerType>(I.getType())->getBitWidth()),
 536            "Undefined result: Shift count out of range", &I);
 537 }
 538
 539 void Lint::visitShl(BinaryOperator &I) {
 540   if (ConstantInt *CI =
 541           dyn_cast<ConstantInt>(findValue(I.getOperand(1), /*OffsetOk=*/false)))
 542     Assert(CI->getValue().ult(cast<IntegerType>(I.getType())->getBitWidth()),
 543            "Undefined result: Shift count out of range", &I);
 544 }
 545
 546 static bool isZero(Value *V, const DataLayout &DL, DominatorTree *DT,
 547                    AssumptionCache *AC) {
 548   // Assume undef could be zero.
 549   if (isa<UndefValue>(V))
 550     return true;
 551
 552   VectorType *VecTy = dyn_cast<VectorType>(V->getType());
 553   if (!VecTy) {
 554     KnownBits Known = computeKnownBits(V, DL, 0, AC, dyn_cast<Instruction>(V), DT);
 555     return Known.isZero();
 556   }
 557
 558   // Per-component check doesn't work with zeroinitializer
 559   Constant *C = dyn_cast<Constant>(V);
 560   if (!C)
 561     return false;
 562
 563   if (C->isZeroValue())
 564     return true;
 565
 566   // For a vector, KnownZero will only be true if all values are zero, so check
 567   // this per component
 568   for (unsigned I = 0, N = VecTy->getNumElements(); I != N; ++I) {
 569     Constant *Elem = C->getAggregateElement(I);
 570     if (isa<UndefValue>(Elem))
 571       return true;
 572
 573     KnownBits Known = computeKnownBits(Elem, DL);
 574     if (Known.isZero())
 575       return true;
 576   }
 577
 578   return false;
 579 }
 580
 581 void Lint::visitSDiv(BinaryOperator &I) {
 582   Assert(!isZero(I.getOperand(1), I.getModule()->getDataLayout(), DT, AC),
 583          "Undefined behavior: Division by zero", &I);
 584 }
 585
 586 void Lint::visitUDiv(BinaryOperator &I) {
 587   Assert(!isZero(I.getOperand(1), I.getModule()->getDataLayout(), DT, AC),
 588          "Undefined behavior: Division by zero", &I);
 589 }
 590
 591 void Lint::visitSRem(BinaryOperator &I) {
 592   Assert(!isZero(I.getOperand(1), I.getModule()->getDataLayout(), DT, AC),
 593          "Undefined behavior: Division by zero", &I);
 594 }
 595
 596 void Lint::visitURem(BinaryOperator &I) {
 597   Assert(!isZero(I.getOperand(1), I.getModule()->getDataLayout(), DT, AC),
 598          "Undefined behavior: Division by zero", &I);
 599 }
 600
 601 void Lint::visitAllocaInst(AllocaInst &I) {
 602   if (isa<ConstantInt>(I.getArraySize()))
 603     // This isn't undefined behavior, it's just an obvious pessimization.
 604     Assert(&I.getParent()->getParent()->getEntryBlock() == I.getParent(),
 605            "Pessimization: Static alloca outside of entry block", &I);
 606
 607   // TODO: Check for an unusual size (MSB set?)
 608 }
 609
 610 void Lint::visitVAArgInst(VAArgInst &I) {
 611   visitMemoryReference(I, I.getOperand(0), MemoryLocation::UnknownSize, 0,
 612                        nullptr, MemRef::Read | MemRef::Write);
 613 }
 614
 615 void Lint::visitIndirectBrInst(IndirectBrInst &I) {
 616   visitMemoryReference(I, I.getAddress(), MemoryLocation::UnknownSize, 0,
 617                        nullptr, MemRef::Branchee);
 618
 619   Assert(I.getNumDestinations() != 0,
 620          "Undefined behavior: indirectbr with no destinations", &I);
 621 }
 622
 623 void Lint::visitExtractElementInst(ExtractElementInst &I) {
 624   if (ConstantInt *CI = dyn_cast<ConstantInt>(findValue(I.getIndexOperand(),
 625                                                         /*OffsetOk=*/false)))
 626     Assert(CI->getValue().ult(I.getVectorOperandType()->getNumElements()),
 627            "Undefined result: extractelement index out of range", &I);
 628 }
 629
 630 void Lint::visitInsertElementInst(InsertElementInst &I) {
 631   if (ConstantInt *CI = dyn_cast<ConstantInt>(findValue(I.getOperand(2),
 632                                                         /*OffsetOk=*/false)))
 633     Assert(CI->getValue().ult(I.getType()->getNumElements()),
 634            "Undefined result: insertelement index out of range", &I);
 635 }
 636
 637 void Lint::visitUnreachableInst(UnreachableInst &I) {
 638   // This isn't undefined behavior, it's merely suspicious.
 639   Assert(&I == &I.getParent()->front() ||
 640              std::prev(I.getIterator())->mayHaveSideEffects(),
 641          "Unusual: unreachable immediately preceded by instruction without "
 642          "side effects",
 643          &I);
 644 }
 645
 646 /// findValue - Look through bitcasts and simple memory reference patterns
 647 /// to identify an equivalent, but more informative, value.  If OffsetOk
 648 /// is true, look through getelementptrs with non-zero offsets too.
 649 ///
 650 /// Most analysis passes don't require this logic, because instcombine
 651 /// will simplify most of these kinds of things away. But it's a goal of
 652 /// this Lint pass to be useful even on non-optimized IR.
 653 Value *Lint::findValue(Value *V, bool OffsetOk) const {
 654   SmallPtrSet<Value *, 4> Visited;
 655   return findValueImpl(V, OffsetOk, Visited);
 656 }
 657
 658 /// findValueImpl - Implementation helper for findValue.
 659 Value *Lint::findValueImpl(Value *V, bool OffsetOk,
 660                            SmallPtrSetImpl<Value *> &Visited) const {
 661   // Detect self-referential values.
 662   if (!Visited.insert(V).second)
 663     return UndefValue::get(V->getType());
 664
 665   // TODO: Look through sext or zext cast, when the result is known to
 666   // be interpreted as signed or unsigned, respectively.
 667   // TODO: Look through eliminable cast pairs.
 668   // TODO: Look through calls with unique return values.
 669   // TODO: Look through vector insert/extract/shuffle.
 670   V = OffsetOk ? GetUnderlyingObject(V, *DL) : V->stripPointerCasts();
 671   if (LoadInst *L = dyn_cast<LoadInst>(V)) {
 672     BasicBlock::iterator BBI = L->getIterator();
 673     BasicBlock *BB = L->getParent();
 674     SmallPtrSet<BasicBlock *, 4> VisitedBlocks;
 675     for (;;) {
 676       if (!VisitedBlocks.insert(BB).second)
 677         break;
 678       if (Value *U =
 679           FindAvailableLoadedValue(L, BB, BBI, DefMaxInstsToScan, AA))
 680         return findValueImpl(U, OffsetOk, Visited);
 681       if (BBI != BB->begin()) break;
 682       BB = BB->getUniquePredecessor();
 683       if (!BB) break;
 684       BBI = BB->end();
 685     }
 686   } else if (PHINode *PN = dyn_cast<PHINode>(V)) {
 687     if (Value *W = PN->hasConstantValue())
 688       if (W != V)
 689         return findValueImpl(W, OffsetOk, Visited);
 690   } else if (CastInst *CI = dyn_cast<CastInst>(V)) {
 691     if (CI->isNoopCast(*DL))
 692       return findValueImpl(CI->getOperand(0), OffsetOk, Visited);
 693   } else if (ExtractValueInst *Ex = dyn_cast<ExtractValueInst>(V)) {
 694     if (Value *W = FindInsertedValue(Ex->getAggregateOperand(),
 695                                      Ex->getIndices()))
 696       if (W != V)
 697         return findValueImpl(W, OffsetOk, Visited);
 698   } else if (ConstantExpr *CE = dyn_cast<ConstantExpr>(V)) {
 699     // Same as above, but for ConstantExpr instead of Instruction.
 700     if (Instruction::isCast(CE->getOpcode())) {
 701       if (CastInst::isNoopCast(Instruction::CastOps(CE->getOpcode()),
 702                                CE->getOperand(0)->getType(), CE->getType(),
 703                                *DL))
 704         return findValueImpl(CE->getOperand(0), OffsetOk, Visited);
 705     } else if (CE->getOpcode() == Instruction::ExtractValue) {
 706       ArrayRef<unsigned> Indices = CE->getIndices();
 707       if (Value *W = FindInsertedValue(CE->getOperand(0), Indices))
 708         if (W != V)
 709           return findValueImpl(W, OffsetOk, Visited);
 710     }
 711   }
 712
 713   // As a last resort, try SimplifyInstruction or constant folding.
 714   if (Instruction *Inst = dyn_cast<Instruction>(V)) {
 715     if (Value *W = SimplifyInstruction(Inst, {*DL, TLI, DT, AC}))
 716       return findValueImpl(W, OffsetOk, Visited);
 717   } else if (auto *C = dyn_cast<Constant>(V)) {
 718     if (Value *W = ConstantFoldConstant(C, *DL, TLI))
 719       if (W && W != V)
 720         return findValueImpl(W, OffsetOk, Visited);
 721   }
 722
 723   return V;
 724 }
 725
 726 //===----------------------------------------------------------------------===//
 727 //  Implement the public interfaces to this file...
 728 //===----------------------------------------------------------------------===//
 729
 730 FunctionPass *llvm::createLintPass() {
 731   return new Lint();
 732 }
 733
 734 /// lintFunction - Check a function for errors, printing messages on stderr.
 735 ///
 736 void llvm::lintFunction(const Function &f) {
 737   Function &F = const_cast<Function&>(f);
 738   assert(!F.isDeclaration() && "Cannot lint external functions");
 739
 740   legacy::FunctionPassManager FPM(F.getParent());
 741   Lint *V = new Lint();
 742   FPM.add(V);
 743   FPM.run(F);
 744 }
 745
 746 /// lintModule - Check a module for errors, printing messages on stderr.
 747 ///
 748 void llvm::lintModule(const Module &M) {
 749   legacy::PassManager PM;
 750   Lint *V = new Lint();
 751   PM.add(V);
 752   PM.run(const_cast<Module&>(M));
 753 }