1 //===-- Lint.cpp - Check for common errors in LLVM IR ---------------------===//
3 // The LLVM Compiler Infrastructure
5 // This file is distributed under the University of Illinois Open Source
6 // License. See LICENSE.TXT for details.
8 //===----------------------------------------------------------------------===//
10 // This pass statically checks for common and easily-identified constructs
11 // which produce undefined or likely unintended behavior in LLVM IR.
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.
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.
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.
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.
35 //===----------------------------------------------------------------------===//
37 #include "llvm/Analysis/Lint.h"
38 #include "llvm/ADT/STLExtras.h"
39 #include "llvm/ADT/SmallSet.h"
40 #include "llvm/Analysis/AliasAnalysis.h"
41 #include "llvm/Analysis/AssumptionCache.h"
42 #include "llvm/Analysis/ConstantFolding.h"
43 #include "llvm/Analysis/InstructionSimplify.h"
44 #include "llvm/Analysis/Loads.h"
45 #include "llvm/Analysis/Passes.h"
46 #include "llvm/Analysis/TargetLibraryInfo.h"
47 #include "llvm/Analysis/ValueTracking.h"
48 #include "llvm/IR/CallSite.h"
49 #include "llvm/IR/DataLayout.h"
50 #include "llvm/IR/Dominators.h"
51 #include "llvm/IR/Function.h"
52 #include "llvm/IR/InstVisitor.h"
53 #include "llvm/IR/IntrinsicInst.h"
54 #include "llvm/IR/LegacyPassManager.h"
55 #include "llvm/Pass.h"
56 #include "llvm/Support/Debug.h"
57 #include "llvm/Support/raw_ostream.h"
62 static const unsigned Read = 1;
63 static const unsigned Write = 2;
64 static const unsigned Callee = 4;
65 static const unsigned Branchee = 8;
68 class Lint : public FunctionPass, public InstVisitor<Lint> {
69 friend class InstVisitor<Lint>;
71 void visitFunction(Function &F);
73 void visitCallSite(CallSite CS);
74 void visitMemoryReference(Instruction &I, Value *Ptr,
75 uint64_t Size, unsigned Align,
76 Type *Ty, unsigned Flags);
77 void visitEHBeginCatch(IntrinsicInst *II);
78 void visitEHEndCatch(IntrinsicInst *II);
80 void visitCallInst(CallInst &I);
81 void visitInvokeInst(InvokeInst &I);
82 void visitReturnInst(ReturnInst &I);
83 void visitLoadInst(LoadInst &I);
84 void visitStoreInst(StoreInst &I);
85 void visitXor(BinaryOperator &I);
86 void visitSub(BinaryOperator &I);
87 void visitLShr(BinaryOperator &I);
88 void visitAShr(BinaryOperator &I);
89 void visitShl(BinaryOperator &I);
90 void visitSDiv(BinaryOperator &I);
91 void visitUDiv(BinaryOperator &I);
92 void visitSRem(BinaryOperator &I);
93 void visitURem(BinaryOperator &I);
94 void visitAllocaInst(AllocaInst &I);
95 void visitVAArgInst(VAArgInst &I);
96 void visitIndirectBrInst(IndirectBrInst &I);
97 void visitExtractElementInst(ExtractElementInst &I);
98 void visitInsertElementInst(InsertElementInst &I);
99 void visitUnreachableInst(UnreachableInst &I);
101 Value *findValue(Value *V, const DataLayout &DL, bool OffsetOk) const;
102 Value *findValueImpl(Value *V, const DataLayout &DL, bool OffsetOk,
103 SmallPtrSetImpl<Value *> &Visited) const;
110 TargetLibraryInfo *TLI;
112 std::string Messages;
113 raw_string_ostream MessagesStr;
115 static char ID; // Pass identification, replacement for typeid
116 Lint() : FunctionPass(ID), MessagesStr(Messages) {
117 initializeLintPass(*PassRegistry::getPassRegistry());
120 bool runOnFunction(Function &F) override;
122 void getAnalysisUsage(AnalysisUsage &AU) const override {
123 AU.setPreservesAll();
124 AU.addRequired<AliasAnalysis>();
125 AU.addRequired<AssumptionCacheTracker>();
126 AU.addRequired<TargetLibraryInfoWrapperPass>();
127 AU.addRequired<DominatorTreeWrapperPass>();
129 void print(raw_ostream &O, const Module *M) const override {}
131 void WriteValues(ArrayRef<const Value *> Vs) {
132 for (const Value *V : Vs) {
135 if (isa<Instruction>(V)) {
136 MessagesStr << *V << '\n';
138 V->printAsOperand(MessagesStr, true, Mod);
144 /// \brief A check failed, so printout out the condition and the message.
146 /// This provides a nice place to put a breakpoint if you want to see why
147 /// something is not correct.
148 void CheckFailed(const Twine &Message) { MessagesStr << Message << '\n'; }
150 /// \brief A check failed (with values to print).
152 /// This calls the Message-only version so that the above is easier to set
154 template <typename T1, typename... Ts>
155 void CheckFailed(const Twine &Message, const T1 &V1, const Ts &...Vs) {
156 CheckFailed(Message);
157 WriteValues({V1, Vs...});
163 INITIALIZE_PASS_BEGIN(Lint, "lint", "Statically lint-checks LLVM IR",
165 INITIALIZE_PASS_DEPENDENCY(AssumptionCacheTracker)
166 INITIALIZE_PASS_DEPENDENCY(TargetLibraryInfoWrapperPass)
167 INITIALIZE_PASS_DEPENDENCY(DominatorTreeWrapperPass)
168 INITIALIZE_AG_DEPENDENCY(AliasAnalysis)
169 INITIALIZE_PASS_END(Lint, "lint", "Statically lint-checks LLVM IR",
172 // Assert - We know that cond should be true, if not print an error message.
173 #define Assert(C, ...) \
174 do { if (!(C)) { CheckFailed(__VA_ARGS__); return; } } while (0)
176 // Lint::run - This is the main Analysis entry point for a
179 bool Lint::runOnFunction(Function &F) {
181 AA = &getAnalysis<AliasAnalysis>();
182 AC = &getAnalysis<AssumptionCacheTracker>().getAssumptionCache(F);
183 DT = &getAnalysis<DominatorTreeWrapperPass>().getDomTree();
184 TLI = &getAnalysis<TargetLibraryInfoWrapperPass>().getTLI();
186 dbgs() << MessagesStr.str();
191 void Lint::visitFunction(Function &F) {
192 // This isn't undefined behavior, it's just a little unusual, and it's a
193 // fairly common mistake to neglect to name a function.
194 Assert(F.hasName() || F.hasLocalLinkage(),
195 "Unusual: Unnamed function with non-local linkage", &F);
197 // TODO: Check for irreducible control flow.
200 void Lint::visitCallSite(CallSite CS) {
201 Instruction &I = *CS.getInstruction();
202 Value *Callee = CS.getCalledValue();
203 const DataLayout &DL = CS->getModule()->getDataLayout();
205 visitMemoryReference(I, Callee, AliasAnalysis::UnknownSize,
206 0, nullptr, MemRef::Callee);
208 if (Function *F = dyn_cast<Function>(findValue(Callee, DL,
209 /*OffsetOk=*/false))) {
210 Assert(CS.getCallingConv() == F->getCallingConv(),
211 "Undefined behavior: Caller and callee calling convention differ",
214 FunctionType *FT = F->getFunctionType();
215 unsigned NumActualArgs = CS.arg_size();
217 Assert(FT->isVarArg() ? FT->getNumParams() <= NumActualArgs
218 : FT->getNumParams() == NumActualArgs,
219 "Undefined behavior: Call argument count mismatches callee "
223 Assert(FT->getReturnType() == I.getType(),
224 "Undefined behavior: Call return type mismatches "
225 "callee return type",
228 // Check argument types (in case the callee was casted) and attributes.
229 // TODO: Verify that caller and callee attributes are compatible.
230 Function::arg_iterator PI = F->arg_begin(), PE = F->arg_end();
231 CallSite::arg_iterator AI = CS.arg_begin(), AE = CS.arg_end();
232 for (; AI != AE; ++AI) {
235 Argument *Formal = PI++;
236 Assert(Formal->getType() == Actual->getType(),
237 "Undefined behavior: Call argument type mismatches "
238 "callee parameter type",
241 // Check that noalias arguments don't alias other arguments. This is
242 // not fully precise because we don't know the sizes of the dereferenced
244 if (Formal->hasNoAliasAttr() && Actual->getType()->isPointerTy())
245 for (CallSite::arg_iterator BI = CS.arg_begin(); BI != AE; ++BI)
246 if (AI != BI && (*BI)->getType()->isPointerTy()) {
247 AliasAnalysis::AliasResult Result = AA->alias(*AI, *BI);
248 Assert(Result != AliasAnalysis::MustAlias &&
249 Result != AliasAnalysis::PartialAlias,
250 "Unusual: noalias argument aliases another argument", &I);
253 // Check that an sret argument points to valid memory.
254 if (Formal->hasStructRetAttr() && Actual->getType()->isPointerTy()) {
256 cast<PointerType>(Formal->getType())->getElementType();
257 visitMemoryReference(I, Actual, AA->getTypeStoreSize(Ty),
258 DL.getABITypeAlignment(Ty), Ty,
259 MemRef::Read | MemRef::Write);
265 if (CS.isCall() && cast<CallInst>(CS.getInstruction())->isTailCall())
266 for (CallSite::arg_iterator AI = CS.arg_begin(), AE = CS.arg_end();
268 Value *Obj = findValue(*AI, DL, /*OffsetOk=*/true);
269 Assert(!isa<AllocaInst>(Obj),
270 "Undefined behavior: Call with \"tail\" keyword references "
276 if (IntrinsicInst *II = dyn_cast<IntrinsicInst>(&I))
277 switch (II->getIntrinsicID()) {
280 // TODO: Check more intrinsics
282 case Intrinsic::memcpy: {
283 MemCpyInst *MCI = cast<MemCpyInst>(&I);
284 // TODO: If the size is known, use it.
285 visitMemoryReference(I, MCI->getDest(), AliasAnalysis::UnknownSize,
286 MCI->getAlignment(), nullptr,
288 visitMemoryReference(I, MCI->getSource(), AliasAnalysis::UnknownSize,
289 MCI->getAlignment(), nullptr,
292 // Check that the memcpy arguments don't overlap. The AliasAnalysis API
293 // isn't expressive enough for what we really want to do. Known partial
294 // overlap is not distinguished from the case where nothing is known.
296 if (const ConstantInt *Len =
297 dyn_cast<ConstantInt>(findValue(MCI->getLength(), DL,
298 /*OffsetOk=*/false)))
299 if (Len->getValue().isIntN(32))
300 Size = Len->getValue().getZExtValue();
301 Assert(AA->alias(MCI->getSource(), Size, MCI->getDest(), Size) !=
302 AliasAnalysis::MustAlias,
303 "Undefined behavior: memcpy source and destination overlap", &I);
306 case Intrinsic::memmove: {
307 MemMoveInst *MMI = cast<MemMoveInst>(&I);
308 // TODO: If the size is known, use it.
309 visitMemoryReference(I, MMI->getDest(), AliasAnalysis::UnknownSize,
310 MMI->getAlignment(), nullptr,
312 visitMemoryReference(I, MMI->getSource(), AliasAnalysis::UnknownSize,
313 MMI->getAlignment(), nullptr,
317 case Intrinsic::memset: {
318 MemSetInst *MSI = cast<MemSetInst>(&I);
319 // TODO: If the size is known, use it.
320 visitMemoryReference(I, MSI->getDest(), AliasAnalysis::UnknownSize,
321 MSI->getAlignment(), nullptr,
326 case Intrinsic::vastart:
327 Assert(I.getParent()->getParent()->isVarArg(),
328 "Undefined behavior: va_start called in a non-varargs function",
331 visitMemoryReference(I, CS.getArgument(0), AliasAnalysis::UnknownSize,
332 0, nullptr, MemRef::Read | MemRef::Write);
334 case Intrinsic::vacopy:
335 visitMemoryReference(I, CS.getArgument(0), AliasAnalysis::UnknownSize,
336 0, nullptr, MemRef::Write);
337 visitMemoryReference(I, CS.getArgument(1), AliasAnalysis::UnknownSize,
338 0, nullptr, MemRef::Read);
340 case Intrinsic::vaend:
341 visitMemoryReference(I, CS.getArgument(0), AliasAnalysis::UnknownSize,
342 0, nullptr, MemRef::Read | MemRef::Write);
345 case Intrinsic::stackrestore:
346 // Stackrestore doesn't read or write memory, but it sets the
347 // stack pointer, which the compiler may read from or write to
348 // at any time, so check it for both readability and writeability.
349 visitMemoryReference(I, CS.getArgument(0), AliasAnalysis::UnknownSize,
350 0, nullptr, MemRef::Read | MemRef::Write);
353 case Intrinsic::eh_begincatch:
354 visitEHBeginCatch(II);
356 case Intrinsic::eh_endcatch:
362 void Lint::visitCallInst(CallInst &I) {
363 return visitCallSite(&I);
366 void Lint::visitInvokeInst(InvokeInst &I) {
367 return visitCallSite(&I);
370 void Lint::visitReturnInst(ReturnInst &I) {
371 Function *F = I.getParent()->getParent();
372 Assert(!F->doesNotReturn(),
373 "Unusual: Return statement in function with noreturn attribute", &I);
375 if (Value *V = I.getReturnValue()) {
377 findValue(V, F->getParent()->getDataLayout(), /*OffsetOk=*/true);
378 Assert(!isa<AllocaInst>(Obj), "Unusual: Returning alloca value", &I);
382 // TODO: Check that the reference is in bounds.
383 // TODO: Check readnone/readonly function attributes.
384 void Lint::visitMemoryReference(Instruction &I,
385 Value *Ptr, uint64_t Size, unsigned Align,
386 Type *Ty, unsigned Flags) {
387 // If no memory is being referenced, it doesn't matter if the pointer
392 Value *UnderlyingObject =
393 findValue(Ptr, I.getModule()->getDataLayout(), /*OffsetOk=*/true);
394 Assert(!isa<ConstantPointerNull>(UnderlyingObject),
395 "Undefined behavior: Null pointer dereference", &I);
396 Assert(!isa<UndefValue>(UnderlyingObject),
397 "Undefined behavior: Undef pointer dereference", &I);
398 Assert(!isa<ConstantInt>(UnderlyingObject) ||
399 !cast<ConstantInt>(UnderlyingObject)->isAllOnesValue(),
400 "Unusual: All-ones pointer dereference", &I);
401 Assert(!isa<ConstantInt>(UnderlyingObject) ||
402 !cast<ConstantInt>(UnderlyingObject)->isOne(),
403 "Unusual: Address one pointer dereference", &I);
405 if (Flags & MemRef::Write) {
406 if (const GlobalVariable *GV = dyn_cast<GlobalVariable>(UnderlyingObject))
407 Assert(!GV->isConstant(), "Undefined behavior: Write to read-only memory",
409 Assert(!isa<Function>(UnderlyingObject) &&
410 !isa<BlockAddress>(UnderlyingObject),
411 "Undefined behavior: Write to text section", &I);
413 if (Flags & MemRef::Read) {
414 Assert(!isa<Function>(UnderlyingObject), "Unusual: Load from function body",
416 Assert(!isa<BlockAddress>(UnderlyingObject),
417 "Undefined behavior: Load from block address", &I);
419 if (Flags & MemRef::Callee) {
420 Assert(!isa<BlockAddress>(UnderlyingObject),
421 "Undefined behavior: Call to block address", &I);
423 if (Flags & MemRef::Branchee) {
424 Assert(!isa<Constant>(UnderlyingObject) ||
425 isa<BlockAddress>(UnderlyingObject),
426 "Undefined behavior: Branch to non-blockaddress", &I);
429 // Check for buffer overflows and misalignment.
430 // Only handles memory references that read/write something simple like an
431 // alloca instruction or a global variable.
432 auto &DL = I.getModule()->getDataLayout();
434 if (Value *Base = GetPointerBaseWithConstantOffset(Ptr, Offset, DL)) {
435 // OK, so the access is to a constant offset from Ptr. Check that Ptr is
436 // something we can handle and if so extract the size of this base object
437 // along with its alignment.
438 uint64_t BaseSize = AliasAnalysis::UnknownSize;
439 unsigned BaseAlign = 0;
441 if (AllocaInst *AI = dyn_cast<AllocaInst>(Base)) {
442 Type *ATy = AI->getAllocatedType();
443 if (!AI->isArrayAllocation() && ATy->isSized())
444 BaseSize = DL.getTypeAllocSize(ATy);
445 BaseAlign = AI->getAlignment();
446 if (BaseAlign == 0 && ATy->isSized())
447 BaseAlign = DL.getABITypeAlignment(ATy);
448 } else if (GlobalVariable *GV = dyn_cast<GlobalVariable>(Base)) {
449 // If the global may be defined differently in another compilation unit
450 // then don't warn about funky memory accesses.
451 if (GV->hasDefinitiveInitializer()) {
452 Type *GTy = GV->getType()->getElementType();
454 BaseSize = DL.getTypeAllocSize(GTy);
455 BaseAlign = GV->getAlignment();
456 if (BaseAlign == 0 && GTy->isSized())
457 BaseAlign = DL.getABITypeAlignment(GTy);
461 // Accesses from before the start or after the end of the object are not
463 Assert(Size == AliasAnalysis::UnknownSize ||
464 BaseSize == AliasAnalysis::UnknownSize ||
465 (Offset >= 0 && Offset + Size <= BaseSize),
466 "Undefined behavior: Buffer overflow", &I);
468 // Accesses that say that the memory is more aligned than it is are not
470 if (Align == 0 && Ty && Ty->isSized())
471 Align = DL.getABITypeAlignment(Ty);
472 Assert(!BaseAlign || Align <= MinAlign(BaseAlign, Offset),
473 "Undefined behavior: Memory reference address is misaligned", &I);
477 void Lint::visitLoadInst(LoadInst &I) {
478 visitMemoryReference(I, I.getPointerOperand(),
479 AA->getTypeStoreSize(I.getType()), I.getAlignment(),
480 I.getType(), MemRef::Read);
483 void Lint::visitStoreInst(StoreInst &I) {
484 visitMemoryReference(I, I.getPointerOperand(),
485 AA->getTypeStoreSize(I.getOperand(0)->getType()),
487 I.getOperand(0)->getType(), MemRef::Write);
490 void Lint::visitXor(BinaryOperator &I) {
491 Assert(!isa<UndefValue>(I.getOperand(0)) || !isa<UndefValue>(I.getOperand(1)),
492 "Undefined result: xor(undef, undef)", &I);
495 void Lint::visitSub(BinaryOperator &I) {
496 Assert(!isa<UndefValue>(I.getOperand(0)) || !isa<UndefValue>(I.getOperand(1)),
497 "Undefined result: sub(undef, undef)", &I);
500 void Lint::visitLShr(BinaryOperator &I) {
501 if (ConstantInt *CI = dyn_cast<ConstantInt>(
502 findValue(I.getOperand(1), I.getModule()->getDataLayout(),
503 /*OffsetOk=*/false)))
504 Assert(CI->getValue().ult(cast<IntegerType>(I.getType())->getBitWidth()),
505 "Undefined result: Shift count out of range", &I);
508 void Lint::visitAShr(BinaryOperator &I) {
509 if (ConstantInt *CI = dyn_cast<ConstantInt>(findValue(
510 I.getOperand(1), I.getModule()->getDataLayout(), /*OffsetOk=*/false)))
511 Assert(CI->getValue().ult(cast<IntegerType>(I.getType())->getBitWidth()),
512 "Undefined result: Shift count out of range", &I);
515 void Lint::visitShl(BinaryOperator &I) {
516 if (ConstantInt *CI = dyn_cast<ConstantInt>(findValue(
517 I.getOperand(1), I.getModule()->getDataLayout(), /*OffsetOk=*/false)))
518 Assert(CI->getValue().ult(cast<IntegerType>(I.getType())->getBitWidth()),
519 "Undefined result: Shift count out of range", &I);
523 allPredsCameFromLandingPad(BasicBlock *BB,
524 SmallSet<BasicBlock *, 4> &VisitedBlocks) {
525 VisitedBlocks.insert(BB);
526 if (BB->isLandingPad())
528 // If we find a block with no predecessors, the search failed.
531 for (BasicBlock *Pred : predecessors(BB)) {
532 if (VisitedBlocks.count(Pred))
534 if (!allPredsCameFromLandingPad(Pred, VisitedBlocks))
541 allSuccessorsReachEndCatch(BasicBlock *BB, BasicBlock::iterator InstBegin,
542 IntrinsicInst **SecondBeginCatch,
543 SmallSet<BasicBlock *, 4> &VisitedBlocks) {
544 VisitedBlocks.insert(BB);
545 for (BasicBlock::iterator I = InstBegin, E = BB->end(); I != E; ++I) {
546 IntrinsicInst *IC = dyn_cast<IntrinsicInst>(I);
547 if (IC && IC->getIntrinsicID() == Intrinsic::eh_endcatch)
549 // If we find another begincatch while looking for an endcatch,
550 // that's also an error.
551 if (IC && IC->getIntrinsicID() == Intrinsic::eh_begincatch) {
552 *SecondBeginCatch = IC;
557 // If we reach a block with no successors while searching, the
558 // search has failed.
561 // Otherwise, search all of the successors.
562 for (BasicBlock *Succ : successors(BB)) {
563 if (VisitedBlocks.count(Succ))
565 if (!allSuccessorsReachEndCatch(Succ, Succ->begin(), SecondBeginCatch,
572 void Lint::visitEHBeginCatch(IntrinsicInst *II) {
573 // The checks in this function make a potentially dubious assumption about
574 // the CFG, namely that any block involved in a catch is only used for the
575 // catch. This will very likely be true of IR generated by a front end,
576 // but it may cease to be true, for example, if the IR is run through a
577 // pass which combines similar blocks.
579 // In general, if we encounter a block the isn't dominated by the catch
580 // block while we are searching the catch block's successors for a call
581 // to end catch intrinsic, then it is possible that it will be legal for
582 // a path through this block to never reach a call to llvm.eh.endcatch.
583 // An analogous statement could be made about our search for a landing
584 // pad among the catch block's predecessors.
586 // What is actually required is that no path is possible at runtime that
587 // reaches a call to llvm.eh.begincatch without having previously visited
588 // a landingpad instruction and that no path is possible at runtime that
589 // calls llvm.eh.begincatch and does not subsequently call llvm.eh.endcatch
590 // (mentally adjusting for the fact that in reality these calls will be
591 // removed before code generation).
593 // Because this is a lint check, we take a pessimistic approach and warn if
594 // the control flow is potentially incorrect.
596 SmallSet<BasicBlock *, 4> VisitedBlocks;
597 BasicBlock *CatchBB = II->getParent();
599 // The begin catch must occur in a landing pad block or all paths
600 // to it must have come from a landing pad.
601 Assert(allPredsCameFromLandingPad(CatchBB, VisitedBlocks),
602 "llvm.eh.begincatch may be reachable without passing a landingpad",
605 // Reset the visited block list.
606 VisitedBlocks.clear();
608 IntrinsicInst *SecondBeginCatch = nullptr;
610 // This has to be called before it is asserted. Otherwise, the first assert
611 // below can never be hit.
612 bool EndCatchFound = allSuccessorsReachEndCatch(
613 CatchBB, std::next(static_cast<BasicBlock::iterator>(II)),
614 &SecondBeginCatch, VisitedBlocks);
616 SecondBeginCatch == nullptr,
617 "llvm.eh.begincatch may be called a second time before llvm.eh.endcatch",
618 II, SecondBeginCatch);
619 Assert(EndCatchFound,
620 "Some paths from llvm.eh.begincatch may not reach llvm.eh.endcatch",
624 static bool allPredCameFromBeginCatch(
625 BasicBlock *BB, BasicBlock::reverse_iterator InstRbegin,
626 IntrinsicInst **SecondEndCatch, SmallSet<BasicBlock *, 4> &VisitedBlocks) {
627 VisitedBlocks.insert(BB);
628 // Look for a begincatch in this block.
629 for (BasicBlock::reverse_iterator RI = InstRbegin, RE = BB->rend(); RI != RE;
631 IntrinsicInst *IC = dyn_cast<IntrinsicInst>(&*RI);
632 if (IC && IC->getIntrinsicID() == Intrinsic::eh_begincatch)
634 // If we find another end catch before we find a begin catch, that's
636 if (IC && IC->getIntrinsicID() == Intrinsic::eh_endcatch) {
637 *SecondEndCatch = IC;
640 // If we encounter a landingpad instruction, the search failed.
641 if (isa<LandingPadInst>(*RI))
644 // If while searching we find a block with no predeccesors,
645 // the search failed.
648 // Search any predecessors we haven't seen before.
649 for (BasicBlock *Pred : predecessors(BB)) {
650 if (VisitedBlocks.count(Pred))
652 if (!allPredCameFromBeginCatch(Pred, Pred->rbegin(), SecondEndCatch,
659 void Lint::visitEHEndCatch(IntrinsicInst *II) {
660 // The check in this function makes a potentially dubious assumption about
661 // the CFG, namely that any block involved in a catch is only used for the
662 // catch. This will very likely be true of IR generated by a front end,
663 // but it may cease to be true, for example, if the IR is run through a
664 // pass which combines similar blocks.
666 // In general, if we encounter a block the isn't post-dominated by the
667 // end catch block while we are searching the end catch block's predecessors
668 // for a call to the begin catch intrinsic, then it is possible that it will
669 // be legal for a path to reach the end catch block without ever having
670 // called llvm.eh.begincatch.
672 // What is actually required is that no path is possible at runtime that
673 // reaches a call to llvm.eh.endcatch without having previously visited
674 // a call to llvm.eh.begincatch (mentally adjusting for the fact that in
675 // reality these calls will be removed before code generation).
677 // Because this is a lint check, we take a pessimistic approach and warn if
678 // the control flow is potentially incorrect.
680 BasicBlock *EndCatchBB = II->getParent();
682 // Alls paths to the end catch call must pass through a begin catch call.
684 // If llvm.eh.begincatch wasn't called in the current block, we'll use this
685 // lambda to recursively look for it in predecessors.
686 SmallSet<BasicBlock *, 4> VisitedBlocks;
687 IntrinsicInst *SecondEndCatch = nullptr;
689 // This has to be called before it is asserted. Otherwise, the first assert
690 // below can never be hit.
691 bool BeginCatchFound =
692 allPredCameFromBeginCatch(EndCatchBB, BasicBlock::reverse_iterator(II),
693 &SecondEndCatch, VisitedBlocks);
695 SecondEndCatch == nullptr,
696 "llvm.eh.endcatch may be called a second time after llvm.eh.begincatch",
698 Assert(BeginCatchFound,
699 "llvm.eh.endcatch may be reachable without passing llvm.eh.begincatch",
703 static bool isZero(Value *V, const DataLayout &DL, DominatorTree *DT,
704 AssumptionCache *AC) {
705 // Assume undef could be zero.
706 if (isa<UndefValue>(V))
709 VectorType *VecTy = dyn_cast<VectorType>(V->getType());
711 unsigned BitWidth = V->getType()->getIntegerBitWidth();
712 APInt KnownZero(BitWidth, 0), KnownOne(BitWidth, 0);
713 computeKnownBits(V, KnownZero, KnownOne, DL, 0, AC,
714 dyn_cast<Instruction>(V), DT);
715 return KnownZero.isAllOnesValue();
718 // Per-component check doesn't work with zeroinitializer
719 Constant *C = dyn_cast<Constant>(V);
723 if (C->isZeroValue())
726 // For a vector, KnownZero will only be true if all values are zero, so check
727 // this per component
728 unsigned BitWidth = VecTy->getElementType()->getIntegerBitWidth();
729 for (unsigned I = 0, N = VecTy->getNumElements(); I != N; ++I) {
730 Constant *Elem = C->getAggregateElement(I);
731 if (isa<UndefValue>(Elem))
734 APInt KnownZero(BitWidth, 0), KnownOne(BitWidth, 0);
735 computeKnownBits(Elem, KnownZero, KnownOne, DL);
736 if (KnownZero.isAllOnesValue())
743 void Lint::visitSDiv(BinaryOperator &I) {
744 Assert(!isZero(I.getOperand(1), I.getModule()->getDataLayout(), DT, AC),
745 "Undefined behavior: Division by zero", &I);
748 void Lint::visitUDiv(BinaryOperator &I) {
749 Assert(!isZero(I.getOperand(1), I.getModule()->getDataLayout(), DT, AC),
750 "Undefined behavior: Division by zero", &I);
753 void Lint::visitSRem(BinaryOperator &I) {
754 Assert(!isZero(I.getOperand(1), I.getModule()->getDataLayout(), DT, AC),
755 "Undefined behavior: Division by zero", &I);
758 void Lint::visitURem(BinaryOperator &I) {
759 Assert(!isZero(I.getOperand(1), I.getModule()->getDataLayout(), DT, AC),
760 "Undefined behavior: Division by zero", &I);
763 void Lint::visitAllocaInst(AllocaInst &I) {
764 if (isa<ConstantInt>(I.getArraySize()))
765 // This isn't undefined behavior, it's just an obvious pessimization.
766 Assert(&I.getParent()->getParent()->getEntryBlock() == I.getParent(),
767 "Pessimization: Static alloca outside of entry block", &I);
769 // TODO: Check for an unusual size (MSB set?)
772 void Lint::visitVAArgInst(VAArgInst &I) {
773 visitMemoryReference(I, I.getOperand(0), AliasAnalysis::UnknownSize, 0,
774 nullptr, MemRef::Read | MemRef::Write);
777 void Lint::visitIndirectBrInst(IndirectBrInst &I) {
778 visitMemoryReference(I, I.getAddress(), AliasAnalysis::UnknownSize, 0,
779 nullptr, MemRef::Branchee);
781 Assert(I.getNumDestinations() != 0,
782 "Undefined behavior: indirectbr with no destinations", &I);
785 void Lint::visitExtractElementInst(ExtractElementInst &I) {
786 if (ConstantInt *CI = dyn_cast<ConstantInt>(
787 findValue(I.getIndexOperand(), I.getModule()->getDataLayout(),
788 /*OffsetOk=*/false)))
789 Assert(CI->getValue().ult(I.getVectorOperandType()->getNumElements()),
790 "Undefined result: extractelement index out of range", &I);
793 void Lint::visitInsertElementInst(InsertElementInst &I) {
794 if (ConstantInt *CI = dyn_cast<ConstantInt>(
795 findValue(I.getOperand(2), I.getModule()->getDataLayout(),
796 /*OffsetOk=*/false)))
797 Assert(CI->getValue().ult(I.getType()->getNumElements()),
798 "Undefined result: insertelement index out of range", &I);
801 void Lint::visitUnreachableInst(UnreachableInst &I) {
802 // This isn't undefined behavior, it's merely suspicious.
803 Assert(&I == I.getParent()->begin() ||
804 std::prev(BasicBlock::iterator(&I))->mayHaveSideEffects(),
805 "Unusual: unreachable immediately preceded by instruction without "
810 /// findValue - Look through bitcasts and simple memory reference patterns
811 /// to identify an equivalent, but more informative, value. If OffsetOk
812 /// is true, look through getelementptrs with non-zero offsets too.
814 /// Most analysis passes don't require this logic, because instcombine
815 /// will simplify most of these kinds of things away. But it's a goal of
816 /// this Lint pass to be useful even on non-optimized IR.
817 Value *Lint::findValue(Value *V, const DataLayout &DL, bool OffsetOk) const {
818 SmallPtrSet<Value *, 4> Visited;
819 return findValueImpl(V, DL, OffsetOk, Visited);
822 /// findValueImpl - Implementation helper for findValue.
823 Value *Lint::findValueImpl(Value *V, const DataLayout &DL, bool OffsetOk,
824 SmallPtrSetImpl<Value *> &Visited) const {
825 // Detect self-referential values.
826 if (!Visited.insert(V).second)
827 return UndefValue::get(V->getType());
829 // TODO: Look through sext or zext cast, when the result is known to
830 // be interpreted as signed or unsigned, respectively.
831 // TODO: Look through eliminable cast pairs.
832 // TODO: Look through calls with unique return values.
833 // TODO: Look through vector insert/extract/shuffle.
834 V = OffsetOk ? GetUnderlyingObject(V, DL) : V->stripPointerCasts();
835 if (LoadInst *L = dyn_cast<LoadInst>(V)) {
836 BasicBlock::iterator BBI = L;
837 BasicBlock *BB = L->getParent();
838 SmallPtrSet<BasicBlock *, 4> VisitedBlocks;
840 if (!VisitedBlocks.insert(BB).second)
842 if (Value *U = FindAvailableLoadedValue(L->getPointerOperand(),
844 return findValueImpl(U, DL, OffsetOk, Visited);
845 if (BBI != BB->begin()) break;
846 BB = BB->getUniquePredecessor();
850 } else if (PHINode *PN = dyn_cast<PHINode>(V)) {
851 if (Value *W = PN->hasConstantValue())
853 return findValueImpl(W, DL, OffsetOk, Visited);
854 } else if (CastInst *CI = dyn_cast<CastInst>(V)) {
855 if (CI->isNoopCast(DL))
856 return findValueImpl(CI->getOperand(0), DL, OffsetOk, Visited);
857 } else if (ExtractValueInst *Ex = dyn_cast<ExtractValueInst>(V)) {
858 if (Value *W = FindInsertedValue(Ex->getAggregateOperand(),
861 return findValueImpl(W, DL, OffsetOk, Visited);
862 } else if (ConstantExpr *CE = dyn_cast<ConstantExpr>(V)) {
863 // Same as above, but for ConstantExpr instead of Instruction.
864 if (Instruction::isCast(CE->getOpcode())) {
865 if (CastInst::isNoopCast(Instruction::CastOps(CE->getOpcode()),
866 CE->getOperand(0)->getType(), CE->getType(),
867 DL.getIntPtrType(V->getType())))
868 return findValueImpl(CE->getOperand(0), DL, OffsetOk, Visited);
869 } else if (CE->getOpcode() == Instruction::ExtractValue) {
870 ArrayRef<unsigned> Indices = CE->getIndices();
871 if (Value *W = FindInsertedValue(CE->getOperand(0), Indices))
873 return findValueImpl(W, DL, OffsetOk, Visited);
877 // As a last resort, try SimplifyInstruction or constant folding.
878 if (Instruction *Inst = dyn_cast<Instruction>(V)) {
879 if (Value *W = SimplifyInstruction(Inst, DL, TLI, DT, AC))
880 return findValueImpl(W, DL, OffsetOk, Visited);
881 } else if (ConstantExpr *CE = dyn_cast<ConstantExpr>(V)) {
882 if (Value *W = ConstantFoldConstantExpression(CE, DL, TLI))
884 return findValueImpl(W, DL, OffsetOk, Visited);
890 //===----------------------------------------------------------------------===//
891 // Implement the public interfaces to this file...
892 //===----------------------------------------------------------------------===//
894 FunctionPass *llvm::createLintPass() {
898 /// lintFunction - Check a function for errors, printing messages on stderr.
900 void llvm::lintFunction(const Function &f) {
901 Function &F = const_cast<Function&>(f);
902 assert(!F.isDeclaration() && "Cannot lint external functions");
904 legacy::FunctionPassManager FPM(F.getParent());
905 Lint *V = new Lint();
910 /// lintModule - Check a module for errors, printing messages on stderr.
912 void llvm::lintModule(const Module &M) {
913 legacy::PassManager PM;
914 Lint *V = new Lint();
916 PM.run(const_cast<Module&>(M));