llvm/lib/Analysis/Lint.cpp

   1 //===-- Lint.cpp - Check for common errors in LLVM IR ---------------------===//
   2 //
   3 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
   4 // See https://llvm.org/LICENSE.txt for license information.
   5 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
   6 //
   7 //===----------------------------------------------------------------------===//
   8 //
   9 // This pass statically checks for common and easily-identified constructs
  10 // which produce undefined or likely unintended behavior in LLVM IR.
  11 //
  12 // It is not a guarantee of correctness, in two ways. First, it isn't
  13 // comprehensive. There are checks which could be done statically which are
  14 // not yet implemented. Some of these are indicated by TODO comments, but
  15 // those aren't comprehensive either. Second, many conditions cannot be
  16 // checked statically. This pass does no dynamic instrumentation, so it
  17 // can't check for all possible problems.
  18 //
  19 // Another limitation is that it assumes all code will be executed. A store
  20 // through a null pointer in a basic block which is never reached is harmless,
  21 // but this pass will warn about it anyway. This is the main reason why most
  22 // of these checks live here instead of in the Verifier pass.
  23 //
  24 // Optimization passes may make conditions that this pass checks for more or
  25 // less obvious. If an optimization pass appears to be introducing a warning,
  26 // it may be that the optimization pass is merely exposing an existing
  27 // condition in the code.
  28 //
  29 // This code may be run before instcombine. In many cases, instcombine checks
  30 // for the same kinds of things and turns instructions with undefined behavior
  31 // into unreachable (or equivalent). Because of this, this pass makes some
  32 // effort to look through bitcasts and so on.
  33 //
  34 //===----------------------------------------------------------------------===//
  35
  36 #include "llvm/Analysis/Lint.h"
  37 #include "llvm/ADT/APInt.h"
  38 #include "llvm/ADT/ArrayRef.h"
  39 #include "llvm/ADT/SmallPtrSet.h"
  40 #include "llvm/ADT/Twine.h"
  41 #include "llvm/Analysis/AliasAnalysis.h"
  42 #include "llvm/Analysis/AssumptionCache.h"
  43 #include "llvm/Analysis/BasicAliasAnalysis.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/ScopedNoAliasAA.h"
  49 #include "llvm/Analysis/TargetLibraryInfo.h"
  50 #include "llvm/Analysis/TypeBasedAliasAnalysis.h"
  51 #include "llvm/Analysis/ValueTracking.h"
  52 #include "llvm/IR/Argument.h"
  53 #include "llvm/IR/BasicBlock.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/Module.h"
  67 #include "llvm/IR/PassManager.h"
  68 #include "llvm/IR/Type.h"
  69 #include "llvm/IR/Value.h"
  70 #include "llvm/Support/AMDGPUAddrSpace.h"
  71 #include "llvm/Support/Casting.h"
  72 #include "llvm/Support/KnownBits.h"
  73 #include "llvm/Support/raw_ostream.h"
  74 #include <cassert>
  75 #include <cstdint>
  76 #include <iterator>
  77 #include <string>
  78
  79 using namespace llvm;
  80
  81 static const char LintAbortOnErrorArgName[] = "lint-abort-on-error";
  82 static cl::opt<bool>
  83     LintAbortOnError(LintAbortOnErrorArgName, cl::init(false),
  84                      cl::desc("In the Lint pass, abort on errors."));
  85
  86 namespace {
  87 namespace MemRef {
  88 static const unsigned Read = 1;
  89 static const unsigned Write = 2;
  90 static const unsigned Callee = 4;
  91 static const unsigned Branchee = 8;
  92 } // end namespace MemRef
  93
  94 class Lint : public InstVisitor<Lint> {
  95   friend class InstVisitor<Lint>;
  96
  97   void visitFunction(Function &F);
  98
  99   void visitCallBase(CallBase &CB);
 100   void visitMemoryReference(Instruction &I, const MemoryLocation &Loc,
 101                             MaybeAlign Alignment, Type *Ty, unsigned Flags);
 102
 103   void visitReturnInst(ReturnInst &I);
 104   void visitLoadInst(LoadInst &I);
 105   void visitStoreInst(StoreInst &I);
 106   void visitAtomicCmpXchgInst(AtomicCmpXchgInst &I);
 107   void visitAtomicRMWInst(AtomicRMWInst &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   Triple TT;
 131   const DataLayout *DL;
 132   AliasAnalysis *AA;
 133   AssumptionCache *AC;
 134   DominatorTree *DT;
 135   TargetLibraryInfo *TLI;
 136
 137   std::string Messages;
 138   raw_string_ostream MessagesStr;
 139
 140   Lint(Module *Mod, const DataLayout *DL, AliasAnalysis *AA,
 141        AssumptionCache *AC, DominatorTree *DT, TargetLibraryInfo *TLI)
 142       : Mod(Mod), TT(Triple::normalize(Mod->getTargetTriple())), DL(DL), AA(AA),
 143         AC(AC), DT(DT), TLI(TLI), MessagesStr(Messages) {}
 144
 145   void WriteValues(ArrayRef<const Value *> Vs) {
 146     for (const Value *V : Vs) {
 147       if (!V)
 148         continue;
 149       if (isa<Instruction>(V)) {
 150         MessagesStr << *V << '\n';
 151       } else {
 152         V->printAsOperand(MessagesStr, true, Mod);
 153         MessagesStr << '\n';
 154       }
 155     }
 156   }
 157
 158   /// A check failed, so printout out the condition and the message.
 159   ///
 160   /// This provides a nice place to put a breakpoint if you want to see why
 161   /// something is not correct.
 162   void CheckFailed(const Twine &Message) { MessagesStr << Message << '\n'; }
 163
 164   /// A check failed (with values to print).
 165   ///
 166   /// This calls the Message-only version so that the above is easier to set
 167   /// a breakpoint on.
 168   template <typename T1, typename... Ts>
 169   void CheckFailed(const Twine &Message, const T1 &V1, const Ts &... Vs) {
 170     CheckFailed(Message);
 171     WriteValues({V1, Vs...});
 172   }
 173 };
 174 } // end anonymous namespace
 175
 176 // Check - We know that cond should be true, if not print an error message.
 177 #define Check(C, ...)                                                          \
 178   do {                                                                         \
 179     if (!(C)) {                                                                \
 180       CheckFailed(__VA_ARGS__);                                                \
 181       return;                                                                  \
 182     }                                                                          \
 183   } while (false)
 184
 185 void Lint::visitFunction(Function &F) {
 186   // This isn't undefined behavior, it's just a little unusual, and it's a
 187   // fairly common mistake to neglect to name a function.
 188   Check(F.hasName() || F.hasLocalLinkage(),
 189         "Unusual: Unnamed function with non-local linkage", &F);
 190
 191   // TODO: Check for irreducible control flow.
 192 }
 193
 194 void Lint::visitCallBase(CallBase &I) {
 195   Value *Callee = I.getCalledOperand();
 196
 197   visitMemoryReference(I, MemoryLocation::getAfter(Callee), std::nullopt,
 198                        nullptr, MemRef::Callee);
 199
 200   if (Function *F = dyn_cast<Function>(findValue(Callee,
 201                                                  /*OffsetOk=*/false))) {
 202     Check(I.getCallingConv() == F->getCallingConv(),
 203           "Undefined behavior: Caller and callee calling convention differ",
 204           &I);
 205
 206     FunctionType *FT = F->getFunctionType();
 207     unsigned NumActualArgs = I.arg_size();
 208
 209     Check(FT->isVarArg() ? FT->getNumParams() <= NumActualArgs
 210                          : FT->getNumParams() == NumActualArgs,
 211           "Undefined behavior: Call argument count mismatches callee "
 212           "argument count",
 213           &I);
 214
 215     Check(FT->getReturnType() == I.getType(),
 216           "Undefined behavior: Call return type mismatches "
 217           "callee return type",
 218           &I);
 219
 220     // Check argument types (in case the callee was casted) and attributes.
 221     // TODO: Verify that caller and callee attributes are compatible.
 222     Function::arg_iterator PI = F->arg_begin(), PE = F->arg_end();
 223     auto AI = I.arg_begin(), AE = I.arg_end();
 224     for (; AI != AE; ++AI) {
 225       Value *Actual = *AI;
 226       if (PI != PE) {
 227         Argument *Formal = &*PI++;
 228         Check(Formal->getType() == Actual->getType(),
 229               "Undefined behavior: Call argument type mismatches "
 230               "callee parameter type",
 231               &I);
 232
 233         // Check that noalias arguments don't alias other arguments. This is
 234         // not fully precise because we don't know the sizes of the dereferenced
 235         // memory regions.
 236         if (Formal->hasNoAliasAttr() && Actual->getType()->isPointerTy()) {
 237           AttributeList PAL = I.getAttributes();
 238           unsigned ArgNo = 0;
 239           for (auto *BI = I.arg_begin(); BI != AE; ++BI, ++ArgNo) {
 240             // Skip ByVal arguments since they will be memcpy'd to the callee's
 241             // stack so we're not really passing the pointer anyway.
 242             if (PAL.hasParamAttr(ArgNo, Attribute::ByVal))
 243               continue;
 244             // If both arguments are readonly, they have no dependence.
 245             if (Formal->onlyReadsMemory() && I.onlyReadsMemory(ArgNo))
 246               continue;
 247             // Skip readnone arguments since those are guaranteed not to be
 248             // dereferenced anyway.
 249             if (I.doesNotAccessMemory(ArgNo))
 250               continue;
 251             if (AI != BI && (*BI)->getType()->isPointerTy() &&
 252                 !isa<ConstantPointerNull>(*BI)) {
 253               AliasResult Result = AA->alias(*AI, *BI);
 254               Check(Result != AliasResult::MustAlias &&
 255                         Result != AliasResult::PartialAlias,
 256                     "Unusual: noalias argument aliases another argument", &I);
 257             }
 258           }
 259         }
 260
 261         // Check that an sret argument points to valid memory.
 262         if (Formal->hasStructRetAttr() && Actual->getType()->isPointerTy()) {
 263           Type *Ty = Formal->getParamStructRetType();
 264           MemoryLocation Loc(
 265               Actual, LocationSize::precise(DL->getTypeStoreSize(Ty)));
 266           visitMemoryReference(I, Loc, DL->getABITypeAlign(Ty), Ty,
 267                                MemRef::Read | MemRef::Write);
 268         }
 269
 270         // Check that ABI attributes for the function and call-site match.
 271         unsigned ArgNo = AI->getOperandNo();
 272         Attribute::AttrKind ABIAttributes[] = {
 273             Attribute::ZExt,         Attribute::SExt,     Attribute::InReg,
 274             Attribute::ByVal,        Attribute::ByRef,    Attribute::InAlloca,
 275             Attribute::Preallocated, Attribute::StructRet};
 276         AttributeList CallAttrs = I.getAttributes();
 277         for (Attribute::AttrKind Attr : ABIAttributes) {
 278           Attribute CallAttr = CallAttrs.getParamAttr(ArgNo, Attr);
 279           Attribute FnAttr = F->getParamAttribute(ArgNo, Attr);
 280           Check(CallAttr.isValid() == FnAttr.isValid(),
 281                 Twine("Undefined behavior: ABI attribute ") +
 282                     Attribute::getNameFromAttrKind(Attr) +
 283                     " not present on both function and call-site",
 284                 &I);
 285           if (CallAttr.isValid() && FnAttr.isValid()) {
 286             Check(CallAttr == FnAttr,
 287                   Twine("Undefined behavior: ABI attribute ") +
 288                       Attribute::getNameFromAttrKind(Attr) +
 289                       " does not have same argument for function and call-site",
 290                   &I);
 291           }
 292         }
 293       }
 294     }
 295   }
 296
 297   if (const auto *CI = dyn_cast<CallInst>(&I)) {
 298     if (CI->isTailCall()) {
 299       const AttributeList &PAL = CI->getAttributes();
 300       unsigned ArgNo = 0;
 301       for (Value *Arg : I.args()) {
 302         // Skip ByVal arguments since they will be memcpy'd to the callee's
 303         // stack anyway.
 304         if (PAL.hasParamAttr(ArgNo++, Attribute::ByVal))
 305           continue;
 306         Value *Obj = findValue(Arg, /*OffsetOk=*/true);
 307         Check(!isa<AllocaInst>(Obj),
 308               "Undefined behavior: Call with \"tail\" keyword references "
 309               "alloca",
 310               &I);
 311       }
 312     }
 313   }
 314
 315   if (IntrinsicInst *II = dyn_cast<IntrinsicInst>(&I))
 316     switch (II->getIntrinsicID()) {
 317     default:
 318       break;
 319
 320       // TODO: Check more intrinsics
 321
 322     case Intrinsic::memcpy:
 323     case Intrinsic::memcpy_inline: {
 324       MemCpyInst *MCI = cast<MemCpyInst>(&I);
 325       visitMemoryReference(I, MemoryLocation::getForDest(MCI),
 326                            MCI->getDestAlign(), nullptr, MemRef::Write);
 327       visitMemoryReference(I, MemoryLocation::getForSource(MCI),
 328                            MCI->getSourceAlign(), 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       auto Size = LocationSize::afterPointer();
 334       if (const ConstantInt *Len =
 335               dyn_cast<ConstantInt>(findValue(MCI->getLength(),
 336                                               /*OffsetOk=*/false)))
 337         if (Len->getValue().isIntN(32))
 338           Size = LocationSize::precise(Len->getValue().getZExtValue());
 339       Check(AA->alias(MCI->getSource(), Size, MCI->getDest(), Size) !=
 340                 AliasResult::MustAlias,
 341             "Undefined behavior: memcpy source and destination overlap", &I);
 342       break;
 343     }
 344     case Intrinsic::memmove: {
 345       MemMoveInst *MMI = cast<MemMoveInst>(&I);
 346       visitMemoryReference(I, MemoryLocation::getForDest(MMI),
 347                            MMI->getDestAlign(), nullptr, MemRef::Write);
 348       visitMemoryReference(I, MemoryLocation::getForSource(MMI),
 349                            MMI->getSourceAlign(), nullptr, MemRef::Read);
 350       break;
 351     }
 352     case Intrinsic::memset: {
 353       MemSetInst *MSI = cast<MemSetInst>(&I);
 354       visitMemoryReference(I, MemoryLocation::getForDest(MSI),
 355                            MSI->getDestAlign(), nullptr, MemRef::Write);
 356       break;
 357     }
 358     case Intrinsic::memset_inline: {
 359       MemSetInlineInst *MSII = cast<MemSetInlineInst>(&I);
 360       visitMemoryReference(I, MemoryLocation::getForDest(MSII),
 361                            MSII->getDestAlign(), nullptr, MemRef::Write);
 362       break;
 363     }
 364
 365     case Intrinsic::vastart:
 366       // vastart in non-varargs function is rejected by the verifier
 367       visitMemoryReference(I, MemoryLocation::getForArgument(&I, 0, TLI),
 368                            std::nullopt, nullptr, MemRef::Read | MemRef::Write);
 369       break;
 370     case Intrinsic::vacopy:
 371       visitMemoryReference(I, MemoryLocation::getForArgument(&I, 0, TLI),
 372                            std::nullopt, nullptr, MemRef::Write);
 373       visitMemoryReference(I, MemoryLocation::getForArgument(&I, 1, TLI),
 374                            std::nullopt, nullptr, MemRef::Read);
 375       break;
 376     case Intrinsic::vaend:
 377       visitMemoryReference(I, MemoryLocation::getForArgument(&I, 0, TLI),
 378                            std::nullopt, nullptr, MemRef::Read | MemRef::Write);
 379       break;
 380
 381     case Intrinsic::stackrestore:
 382       // Stackrestore doesn't read or write memory, but it sets the
 383       // stack pointer, which the compiler may read from or write to
 384       // at any time, so check it for both readability and writeability.
 385       visitMemoryReference(I, MemoryLocation::getForArgument(&I, 0, TLI),
 386                            std::nullopt, nullptr, MemRef::Read | MemRef::Write);
 387       break;
 388     case Intrinsic::get_active_lane_mask:
 389       if (auto *TripCount = dyn_cast<ConstantInt>(I.getArgOperand(1)))
 390         Check(!TripCount->isZero(),
 391               "get_active_lane_mask: operand #2 "
 392               "must be greater than 0",
 393               &I);
 394       break;
 395     }
 396 }
 397
 398 void Lint::visitReturnInst(ReturnInst &I) {
 399   Function *F = I.getParent()->getParent();
 400   Check(!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     Check(!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, const MemoryLocation &Loc,
 412                                 MaybeAlign Align, Type *Ty, unsigned Flags) {
 413   // If no memory is being referenced, it doesn't matter if the pointer
 414   // is valid.
 415   if (Loc.Size.isZero())
 416     return;
 417
 418   Value *Ptr = const_cast<Value *>(Loc.Ptr);
 419   Value *UnderlyingObject = findValue(Ptr, /*OffsetOk=*/true);
 420   Check(!isa<ConstantPointerNull>(UnderlyingObject),
 421         "Undefined behavior: Null pointer dereference", &I);
 422   Check(!isa<UndefValue>(UnderlyingObject),
 423         "Undefined behavior: Undef pointer dereference", &I);
 424   Check(!isa<ConstantInt>(UnderlyingObject) ||
 425             !cast<ConstantInt>(UnderlyingObject)->isMinusOne(),
 426         "Unusual: All-ones pointer dereference", &I);
 427   Check(!isa<ConstantInt>(UnderlyingObject) ||
 428             !cast<ConstantInt>(UnderlyingObject)->isOne(),
 429         "Unusual: Address one pointer dereference", &I);
 430
 431   if (Flags & MemRef::Write) {
 432     if (TT.isAMDGPU())
 433       Check(!AMDGPU::isConstantAddressSpace(
 434                 UnderlyingObject->getType()->getPointerAddressSpace()),
 435             "Undefined behavior: Write to memory in const addrspace", &I);
 436
 437     if (const GlobalVariable *GV = dyn_cast<GlobalVariable>(UnderlyingObject))
 438       Check(!GV->isConstant(), "Undefined behavior: Write to read-only memory",
 439             &I);
 440     Check(!isa<Function>(UnderlyingObject) &&
 441               !isa<BlockAddress>(UnderlyingObject),
 442           "Undefined behavior: Write to text section", &I);
 443   }
 444   if (Flags & MemRef::Read) {
 445     Check(!isa<Function>(UnderlyingObject), "Unusual: Load from function body",
 446           &I);
 447     Check(!isa<BlockAddress>(UnderlyingObject),
 448           "Undefined behavior: Load from block address", &I);
 449   }
 450   if (Flags & MemRef::Callee) {
 451     Check(!isa<BlockAddress>(UnderlyingObject),
 452           "Undefined behavior: Call to block address", &I);
 453   }
 454   if (Flags & MemRef::Branchee) {
 455     Check(!isa<Constant>(UnderlyingObject) ||
 456               isa<BlockAddress>(UnderlyingObject),
 457           "Undefined behavior: Branch to non-blockaddress", &I);
 458   }
 459
 460   // Check for buffer overflows and misalignment.
 461   // Only handles memory references that read/write something simple like an
 462   // alloca instruction or a global variable.
 463   int64_t Offset = 0;
 464   if (Value *Base = GetPointerBaseWithConstantOffset(Ptr, Offset, *DL)) {
 465     // OK, so the access is to a constant offset from Ptr.  Check that Ptr is
 466     // something we can handle and if so extract the size of this base object
 467     // along with its alignment.
 468     uint64_t BaseSize = MemoryLocation::UnknownSize;
 469     MaybeAlign BaseAlign;
 470
 471     if (AllocaInst *AI = dyn_cast<AllocaInst>(Base)) {
 472       Type *ATy = AI->getAllocatedType();
 473       if (!AI->isArrayAllocation() && ATy->isSized() && !ATy->isScalableTy())
 474         BaseSize = DL->getTypeAllocSize(ATy).getFixedValue();
 475       BaseAlign = AI->getAlign();
 476     } else if (GlobalVariable *GV = dyn_cast<GlobalVariable>(Base)) {
 477       // If the global may be defined differently in another compilation unit
 478       // then don't warn about funky memory accesses.
 479       if (GV->hasDefinitiveInitializer()) {
 480         Type *GTy = GV->getValueType();
 481         if (GTy->isSized())
 482           BaseSize = DL->getTypeAllocSize(GTy);
 483         BaseAlign = GV->getAlign();
 484         if (!BaseAlign && GTy->isSized())
 485           BaseAlign = DL->getABITypeAlign(GTy);
 486       }
 487     }
 488
 489     // Accesses from before the start or after the end of the object are not
 490     // defined.
 491     Check(!Loc.Size.hasValue() || Loc.Size.isScalable() ||
 492               BaseSize == MemoryLocation::UnknownSize ||
 493               (Offset >= 0 && Offset + Loc.Size.getValue() <= BaseSize),
 494           "Undefined behavior: Buffer overflow", &I);
 495
 496     // Accesses that say that the memory is more aligned than it is are not
 497     // defined.
 498     if (!Align && Ty && Ty->isSized())
 499       Align = DL->getABITypeAlign(Ty);
 500     if (BaseAlign && Align)
 501       Check(*Align <= commonAlignment(*BaseAlign, Offset),
 502             "Undefined behavior: Memory reference address is misaligned", &I);
 503   }
 504 }
 505
 506 void Lint::visitLoadInst(LoadInst &I) {
 507   visitMemoryReference(I, MemoryLocation::get(&I), I.getAlign(), I.getType(),
 508                        MemRef::Read);
 509 }
 510
 511 void Lint::visitStoreInst(StoreInst &I) {
 512   visitMemoryReference(I, MemoryLocation::get(&I), I.getAlign(),
 513                        I.getOperand(0)->getType(), MemRef::Write);
 514 }
 515
 516 void Lint::visitAtomicCmpXchgInst(AtomicCmpXchgInst &I) {
 517   visitMemoryReference(I, MemoryLocation::get(&I), I.getAlign(),
 518                        I.getOperand(0)->getType(), MemRef::Write);
 519 }
 520
 521 void Lint::visitAtomicRMWInst(AtomicRMWInst &I) {
 522   visitMemoryReference(I, MemoryLocation::get(&I), I.getAlign(),
 523                        I.getOperand(0)->getType(), MemRef::Write);
 524 }
 525
 526 void Lint::visitXor(BinaryOperator &I) {
 527   Check(!isa<UndefValue>(I.getOperand(0)) || !isa<UndefValue>(I.getOperand(1)),
 528         "Undefined result: xor(undef, undef)", &I);
 529 }
 530
 531 void Lint::visitSub(BinaryOperator &I) {
 532   Check(!isa<UndefValue>(I.getOperand(0)) || !isa<UndefValue>(I.getOperand(1)),
 533         "Undefined result: sub(undef, undef)", &I);
 534 }
 535
 536 void Lint::visitLShr(BinaryOperator &I) {
 537   if (ConstantInt *CI = dyn_cast<ConstantInt>(findValue(I.getOperand(1),
 538                                                         /*OffsetOk=*/false)))
 539     Check(CI->getValue().ult(cast<IntegerType>(I.getType())->getBitWidth()),
 540           "Undefined result: Shift count out of range", &I);
 541 }
 542
 543 void Lint::visitAShr(BinaryOperator &I) {
 544   if (ConstantInt *CI =
 545           dyn_cast<ConstantInt>(findValue(I.getOperand(1), /*OffsetOk=*/false)))
 546     Check(CI->getValue().ult(cast<IntegerType>(I.getType())->getBitWidth()),
 547           "Undefined result: Shift count out of range", &I);
 548 }
 549
 550 void Lint::visitShl(BinaryOperator &I) {
 551   if (ConstantInt *CI =
 552           dyn_cast<ConstantInt>(findValue(I.getOperand(1), /*OffsetOk=*/false)))
 553     Check(CI->getValue().ult(cast<IntegerType>(I.getType())->getBitWidth()),
 554           "Undefined result: Shift count out of range", &I);
 555 }
 556
 557 static bool isZero(Value *V, const DataLayout &DL, DominatorTree *DT,
 558                    AssumptionCache *AC) {
 559   // Assume undef could be zero.
 560   if (isa<UndefValue>(V))
 561     return true;
 562
 563   VectorType *VecTy = dyn_cast<VectorType>(V->getType());
 564   if (!VecTy) {
 565     KnownBits Known =
 566         computeKnownBits(V, DL, 0, AC, dyn_cast<Instruction>(V), DT);
 567     return Known.isZero();
 568   }
 569
 570   // Per-component check doesn't work with zeroinitializer
 571   Constant *C = dyn_cast<Constant>(V);
 572   if (!C)
 573     return false;
 574
 575   if (C->isZeroValue())
 576     return true;
 577
 578   // For a vector, KnownZero will only be true if all values are zero, so check
 579   // this per component
 580   for (unsigned I = 0, N = cast<FixedVectorType>(VecTy)->getNumElements();
 581        I != N; ++I) {
 582     Constant *Elem = C->getAggregateElement(I);
 583     if (isa<UndefValue>(Elem))
 584       return true;
 585
 586     KnownBits Known = computeKnownBits(Elem, DL);
 587     if (Known.isZero())
 588       return true;
 589   }
 590
 591   return false;
 592 }
 593
 594 void Lint::visitSDiv(BinaryOperator &I) {
 595   Check(!isZero(I.getOperand(1), I.getDataLayout(), DT, AC),
 596         "Undefined behavior: Division by zero", &I);
 597 }
 598
 599 void Lint::visitUDiv(BinaryOperator &I) {
 600   Check(!isZero(I.getOperand(1), I.getDataLayout(), DT, AC),
 601         "Undefined behavior: Division by zero", &I);
 602 }
 603
 604 void Lint::visitSRem(BinaryOperator &I) {
 605   Check(!isZero(I.getOperand(1), I.getDataLayout(), DT, AC),
 606         "Undefined behavior: Division by zero", &I);
 607 }
 608
 609 void Lint::visitURem(BinaryOperator &I) {
 610   Check(!isZero(I.getOperand(1), I.getDataLayout(), DT, AC),
 611         "Undefined behavior: Division by zero", &I);
 612 }
 613
 614 void Lint::visitAllocaInst(AllocaInst &I) {
 615   if (isa<ConstantInt>(I.getArraySize()))
 616     // This isn't undefined behavior, it's just an obvious pessimization.
 617     Check(&I.getParent()->getParent()->getEntryBlock() == I.getParent(),
 618           "Pessimization: Static alloca outside of entry block", &I);
 619
 620   // TODO: Check for an unusual size (MSB set?)
 621 }
 622
 623 void Lint::visitVAArgInst(VAArgInst &I) {
 624   visitMemoryReference(I, MemoryLocation::get(&I), std::nullopt, nullptr,
 625                        MemRef::Read | MemRef::Write);
 626 }
 627
 628 void Lint::visitIndirectBrInst(IndirectBrInst &I) {
 629   visitMemoryReference(I, MemoryLocation::getAfter(I.getAddress()),
 630                        std::nullopt, nullptr, MemRef::Branchee);
 631
 632   Check(I.getNumDestinations() != 0,
 633         "Undefined behavior: indirectbr with no destinations", &I);
 634 }
 635
 636 void Lint::visitExtractElementInst(ExtractElementInst &I) {
 637   if (ConstantInt *CI = dyn_cast<ConstantInt>(findValue(I.getIndexOperand(),
 638                                                         /*OffsetOk=*/false))) {
 639     ElementCount EC = I.getVectorOperandType()->getElementCount();
 640     Check(EC.isScalable() || CI->getValue().ult(EC.getFixedValue()),
 641           "Undefined result: extractelement index out of range", &I);
 642   }
 643 }
 644
 645 void Lint::visitInsertElementInst(InsertElementInst &I) {
 646   if (ConstantInt *CI = dyn_cast<ConstantInt>(findValue(I.getOperand(2),
 647                                                         /*OffsetOk=*/false))) {
 648     ElementCount EC = I.getType()->getElementCount();
 649     Check(EC.isScalable() || CI->getValue().ult(EC.getFixedValue()),
 650           "Undefined result: insertelement index out of range", &I);
 651   }
 652 }
 653
 654 void Lint::visitUnreachableInst(UnreachableInst &I) {
 655   // This isn't undefined behavior, it's merely suspicious.
 656   Check(&I == &I.getParent()->front() ||
 657             std::prev(I.getIterator())->mayHaveSideEffects(),
 658         "Unusual: unreachable immediately preceded by instruction without "
 659         "side effects",
 660         &I);
 661 }
 662
 663 /// findValue - Look through bitcasts and simple memory reference patterns
 664 /// to identify an equivalent, but more informative, value.  If OffsetOk
 665 /// is true, look through getelementptrs with non-zero offsets too.
 666 ///
 667 /// Most analysis passes don't require this logic, because instcombine
 668 /// will simplify most of these kinds of things away. But it's a goal of
 669 /// this Lint pass to be useful even on non-optimized IR.
 670 Value *Lint::findValue(Value *V, bool OffsetOk) const {
 671   SmallPtrSet<Value *, 4> Visited;
 672   return findValueImpl(V, OffsetOk, Visited);
 673 }
 674
 675 /// findValueImpl - Implementation helper for findValue.
 676 Value *Lint::findValueImpl(Value *V, bool OffsetOk,
 677                            SmallPtrSetImpl<Value *> &Visited) const {
 678   // Detect self-referential values.
 679   if (!Visited.insert(V).second)
 680     return PoisonValue::get(V->getType());
 681
 682   // TODO: Look through sext or zext cast, when the result is known to
 683   // be interpreted as signed or unsigned, respectively.
 684   // TODO: Look through eliminable cast pairs.
 685   // TODO: Look through calls with unique return values.
 686   // TODO: Look through vector insert/extract/shuffle.
 687   V = OffsetOk ? getUnderlyingObject(V) : V->stripPointerCasts();
 688   if (LoadInst *L = dyn_cast<LoadInst>(V)) {
 689     BasicBlock::iterator BBI = L->getIterator();
 690     BasicBlock *BB = L->getParent();
 691     SmallPtrSet<BasicBlock *, 4> VisitedBlocks;
 692     BatchAAResults BatchAA(*AA);
 693     for (;;) {
 694       if (!VisitedBlocks.insert(BB).second)
 695         break;
 696       if (Value *U =
 697               FindAvailableLoadedValue(L, BB, BBI, DefMaxInstsToScan, &BatchAA))
 698         return findValueImpl(U, OffsetOk, Visited);
 699       if (BBI != BB->begin())
 700         break;
 701       BB = BB->getUniquePredecessor();
 702       if (!BB)
 703         break;
 704       BBI = BB->end();
 705     }
 706   } else if (PHINode *PN = dyn_cast<PHINode>(V)) {
 707     if (Value *W = PN->hasConstantValue())
 708       return findValueImpl(W, OffsetOk, Visited);
 709   } else if (CastInst *CI = dyn_cast<CastInst>(V)) {
 710     if (CI->isNoopCast(*DL))
 711       return findValueImpl(CI->getOperand(0), OffsetOk, Visited);
 712   } else if (ExtractValueInst *Ex = dyn_cast<ExtractValueInst>(V)) {
 713     if (Value *W =
 714             FindInsertedValue(Ex->getAggregateOperand(), Ex->getIndices()))
 715       if (W != V)
 716         return findValueImpl(W, OffsetOk, Visited);
 717   } else if (ConstantExpr *CE = dyn_cast<ConstantExpr>(V)) {
 718     // Same as above, but for ConstantExpr instead of Instruction.
 719     if (Instruction::isCast(CE->getOpcode())) {
 720       if (CastInst::isNoopCast(Instruction::CastOps(CE->getOpcode()),
 721                                CE->getOperand(0)->getType(), CE->getType(),
 722                                *DL))
 723         return findValueImpl(CE->getOperand(0), OffsetOk, Visited);
 724     }
 725   }
 726
 727   // As a last resort, try SimplifyInstruction or constant folding.
 728   if (Instruction *Inst = dyn_cast<Instruction>(V)) {
 729     if (Value *W = simplifyInstruction(Inst, {*DL, TLI, DT, AC}))
 730       return findValueImpl(W, OffsetOk, Visited);
 731   } else if (auto *C = dyn_cast<Constant>(V)) {
 732     Value *W = ConstantFoldConstant(C, *DL, TLI);
 733     if (W != V)
 734       return findValueImpl(W, OffsetOk, Visited);
 735   }
 736
 737   return V;
 738 }
 739
 740 PreservedAnalyses LintPass::run(Function &F, FunctionAnalysisManager &AM) {
 741   auto *Mod = F.getParent();
 742   auto *DL = &F.getDataLayout();
 743   auto *AA = &AM.getResult<AAManager>(F);
 744   auto *AC = &AM.getResult<AssumptionAnalysis>(F);
 745   auto *DT = &AM.getResult<DominatorTreeAnalysis>(F);
 746   auto *TLI = &AM.getResult<TargetLibraryAnalysis>(F);
 747   Lint L(Mod, DL, AA, AC, DT, TLI);
 748   L.visit(F);
 749   dbgs() << L.MessagesStr.str();
 750   if (LintAbortOnError && !L.MessagesStr.str().empty())
 751     report_fatal_error(Twine("Linter found errors, aborting. (enabled by --") +
 752                            LintAbortOnErrorArgName + ")",
 753                        false);
 754   return PreservedAnalyses::all();
 755 }
 756
 757 //===----------------------------------------------------------------------===//
 758 //  Implement the public interfaces to this file...
 759 //===----------------------------------------------------------------------===//
 760
 761 /// lintFunction - Check a function for errors, printing messages on stderr.
 762 ///
 763 void llvm::lintFunction(const Function &f) {
 764   Function &F = const_cast<Function &>(f);
 765   assert(!F.isDeclaration() && "Cannot lint external functions");
 766
 767   FunctionAnalysisManager FAM;
 768   FAM.registerPass([&] { return TargetLibraryAnalysis(); });
 769   FAM.registerPass([&] { return DominatorTreeAnalysis(); });
 770   FAM.registerPass([&] { return AssumptionAnalysis(); });
 771   FAM.registerPass([&] {
 772     AAManager AA;
 773     AA.registerFunctionAnalysis<BasicAA>();
 774     AA.registerFunctionAnalysis<ScopedNoAliasAA>();
 775     AA.registerFunctionAnalysis<TypeBasedAA>();
 776     return AA;
 777   });
 778   LintPass().run(F, FAM);
 779 }
 780
 781 /// lintModule - Check a module for errors, printing messages on stderr.
 782 ///
 783 void llvm::lintModule(const Module &M) {
 784   for (const Function &F : M) {
 785     if (!F.isDeclaration())
 786       lintFunction(F);
 787   }
 788 }