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 unsigned Read = 1;
63 static unsigned Write = 2;
64 static unsigned Callee = 4;
65 static 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, bool OffsetOk) const;
102 Value *findValueImpl(Value *V, bool OffsetOk,
103 SmallPtrSetImpl<Value *> &Visited) const;
110 const DataLayout *DL;
111 TargetLibraryInfo *TLI;
113 std::string Messages;
114 raw_string_ostream MessagesStr;
116 static char ID; // Pass identification, replacement for typeid
117 Lint() : FunctionPass(ID), MessagesStr(Messages) {
118 initializeLintPass(*PassRegistry::getPassRegistry());
121 bool runOnFunction(Function &F) override;
123 void getAnalysisUsage(AnalysisUsage &AU) const override {
124 AU.setPreservesAll();
125 AU.addRequired<AliasAnalysis>();
126 AU.addRequired<AssumptionCacheTracker>();
127 AU.addRequired<TargetLibraryInfoWrapperPass>();
128 AU.addRequired<DominatorTreeWrapperPass>();
130 void print(raw_ostream &O, const Module *M) const override {}
132 void WriteValues(ArrayRef<const Value *> Vs) {
133 for (const Value *V : Vs) {
136 if (isa<Instruction>(V)) {
137 MessagesStr << *V << '\n';
139 V->printAsOperand(MessagesStr, true, Mod);
145 // CheckFailed - A check failed, so print out the condition and the message
146 // that failed. This provides a nice place to put a breakpoint if you want
147 // to see why something is not correct.
148 template <typename... Ts>
149 void CheckFailed(const Twine &Message, const Ts &...Vs) {
150 MessagesStr << Message << '\n';
151 WriteValues({Vs...});
157 INITIALIZE_PASS_BEGIN(Lint, "lint", "Statically lint-checks LLVM IR",
159 INITIALIZE_PASS_DEPENDENCY(AssumptionCacheTracker)
160 INITIALIZE_PASS_DEPENDENCY(TargetLibraryInfoWrapperPass)
161 INITIALIZE_PASS_DEPENDENCY(DominatorTreeWrapperPass)
162 INITIALIZE_AG_DEPENDENCY(AliasAnalysis)
163 INITIALIZE_PASS_END(Lint, "lint", "Statically lint-checks LLVM IR",
166 // Assert - We know that cond should be true, if not print an error message.
167 #define Assert(C, ...) \
168 do { if (!(C)) { CheckFailed(__VA_ARGS__); return; } } while (0)
170 // Lint::run - This is the main Analysis entry point for a
173 bool Lint::runOnFunction(Function &F) {
175 AA = &getAnalysis<AliasAnalysis>();
176 AC = &getAnalysis<AssumptionCacheTracker>().getAssumptionCache(F);
177 DT = &getAnalysis<DominatorTreeWrapperPass>().getDomTree();
178 DL = &F.getParent()->getDataLayout();
179 TLI = &getAnalysis<TargetLibraryInfoWrapperPass>().getTLI();
181 dbgs() << MessagesStr.str();
186 void Lint::visitFunction(Function &F) {
187 // This isn't undefined behavior, it's just a little unusual, and it's a
188 // fairly common mistake to neglect to name a function.
189 Assert(F.hasName() || F.hasLocalLinkage(),
190 "Unusual: Unnamed function with non-local linkage", &F);
192 // TODO: Check for irreducible control flow.
195 void Lint::visitCallSite(CallSite CS) {
196 Instruction &I = *CS.getInstruction();
197 Value *Callee = CS.getCalledValue();
199 visitMemoryReference(I, Callee, AliasAnalysis::UnknownSize,
200 0, nullptr, MemRef::Callee);
202 if (Function *F = dyn_cast<Function>(findValue(Callee, /*OffsetOk=*/false))) {
203 Assert(CS.getCallingConv() == F->getCallingConv(),
204 "Undefined behavior: Caller and callee calling convention differ",
207 FunctionType *FT = F->getFunctionType();
208 unsigned NumActualArgs = CS.arg_size();
210 Assert(FT->isVarArg() ? FT->getNumParams() <= NumActualArgs
211 : FT->getNumParams() == NumActualArgs,
212 "Undefined behavior: Call argument count mismatches callee "
216 Assert(FT->getReturnType() == I.getType(),
217 "Undefined behavior: Call return type mismatches "
218 "callee return type",
221 // Check argument types (in case the callee was casted) and attributes.
222 // TODO: Verify that caller and callee attributes are compatible.
223 Function::arg_iterator PI = F->arg_begin(), PE = F->arg_end();
224 CallSite::arg_iterator AI = CS.arg_begin(), AE = CS.arg_end();
225 for (; AI != AE; ++AI) {
228 Argument *Formal = PI++;
229 Assert(Formal->getType() == Actual->getType(),
230 "Undefined behavior: Call argument type mismatches "
231 "callee parameter type",
234 // Check that noalias arguments don't alias other arguments. This is
235 // not fully precise because we don't know the sizes of the dereferenced
237 if (Formal->hasNoAliasAttr() && Actual->getType()->isPointerTy())
238 for (CallSite::arg_iterator BI = CS.arg_begin(); BI != AE; ++BI)
239 if (AI != BI && (*BI)->getType()->isPointerTy()) {
240 AliasAnalysis::AliasResult Result = AA->alias(*AI, *BI);
241 Assert(Result != AliasAnalysis::MustAlias &&
242 Result != AliasAnalysis::PartialAlias,
243 "Unusual: noalias argument aliases another argument", &I);
246 // Check that an sret argument points to valid memory.
247 if (Formal->hasStructRetAttr() && Actual->getType()->isPointerTy()) {
249 cast<PointerType>(Formal->getType())->getElementType();
250 visitMemoryReference(I, Actual, AA->getTypeStoreSize(Ty),
251 DL ? DL->getABITypeAlignment(Ty) : 0,
252 Ty, MemRef::Read | MemRef::Write);
258 if (CS.isCall() && cast<CallInst>(CS.getInstruction())->isTailCall())
259 for (CallSite::arg_iterator AI = CS.arg_begin(), AE = CS.arg_end();
261 Value *Obj = findValue(*AI, /*OffsetOk=*/true);
262 Assert(!isa<AllocaInst>(Obj),
263 "Undefined behavior: Call with \"tail\" keyword references alloca",
268 if (IntrinsicInst *II = dyn_cast<IntrinsicInst>(&I))
269 switch (II->getIntrinsicID()) {
272 // TODO: Check more intrinsics
274 case Intrinsic::memcpy: {
275 MemCpyInst *MCI = cast<MemCpyInst>(&I);
276 // TODO: If the size is known, use it.
277 visitMemoryReference(I, MCI->getDest(), AliasAnalysis::UnknownSize,
278 MCI->getAlignment(), nullptr,
280 visitMemoryReference(I, MCI->getSource(), AliasAnalysis::UnknownSize,
281 MCI->getAlignment(), nullptr,
284 // Check that the memcpy arguments don't overlap. The AliasAnalysis API
285 // isn't expressive enough for what we really want to do. Known partial
286 // overlap is not distinguished from the case where nothing is known.
288 if (const ConstantInt *Len =
289 dyn_cast<ConstantInt>(findValue(MCI->getLength(),
290 /*OffsetOk=*/false)))
291 if (Len->getValue().isIntN(32))
292 Size = Len->getValue().getZExtValue();
293 Assert(AA->alias(MCI->getSource(), Size, MCI->getDest(), Size) !=
294 AliasAnalysis::MustAlias,
295 "Undefined behavior: memcpy source and destination overlap", &I);
298 case Intrinsic::memmove: {
299 MemMoveInst *MMI = cast<MemMoveInst>(&I);
300 // TODO: If the size is known, use it.
301 visitMemoryReference(I, MMI->getDest(), AliasAnalysis::UnknownSize,
302 MMI->getAlignment(), nullptr,
304 visitMemoryReference(I, MMI->getSource(), AliasAnalysis::UnknownSize,
305 MMI->getAlignment(), nullptr,
309 case Intrinsic::memset: {
310 MemSetInst *MSI = cast<MemSetInst>(&I);
311 // TODO: If the size is known, use it.
312 visitMemoryReference(I, MSI->getDest(), AliasAnalysis::UnknownSize,
313 MSI->getAlignment(), nullptr,
318 case Intrinsic::vastart:
319 Assert(I.getParent()->getParent()->isVarArg(),
320 "Undefined behavior: va_start called in a non-varargs function",
323 visitMemoryReference(I, CS.getArgument(0), AliasAnalysis::UnknownSize,
324 0, nullptr, MemRef::Read | MemRef::Write);
326 case Intrinsic::vacopy:
327 visitMemoryReference(I, CS.getArgument(0), AliasAnalysis::UnknownSize,
328 0, nullptr, MemRef::Write);
329 visitMemoryReference(I, CS.getArgument(1), AliasAnalysis::UnknownSize,
330 0, nullptr, MemRef::Read);
332 case Intrinsic::vaend:
333 visitMemoryReference(I, CS.getArgument(0), AliasAnalysis::UnknownSize,
334 0, nullptr, MemRef::Read | MemRef::Write);
337 case Intrinsic::stackrestore:
338 // Stackrestore doesn't read or write memory, but it sets the
339 // stack pointer, which the compiler may read from or write to
340 // at any time, so check it for both readability and writeability.
341 visitMemoryReference(I, CS.getArgument(0), AliasAnalysis::UnknownSize,
342 0, nullptr, MemRef::Read | MemRef::Write);
345 case Intrinsic::eh_begincatch:
346 visitEHBeginCatch(II);
348 case Intrinsic::eh_endcatch:
354 void Lint::visitCallInst(CallInst &I) {
355 return visitCallSite(&I);
358 void Lint::visitInvokeInst(InvokeInst &I) {
359 return visitCallSite(&I);
362 void Lint::visitReturnInst(ReturnInst &I) {
363 Function *F = I.getParent()->getParent();
364 Assert(!F->doesNotReturn(),
365 "Unusual: Return statement in function with noreturn attribute", &I);
367 if (Value *V = I.getReturnValue()) {
368 Value *Obj = findValue(V, /*OffsetOk=*/true);
369 Assert(!isa<AllocaInst>(Obj), "Unusual: Returning alloca value", &I);
373 // TODO: Check that the reference is in bounds.
374 // TODO: Check readnone/readonly function attributes.
375 void Lint::visitMemoryReference(Instruction &I,
376 Value *Ptr, uint64_t Size, unsigned Align,
377 Type *Ty, unsigned Flags) {
378 // If no memory is being referenced, it doesn't matter if the pointer
383 Value *UnderlyingObject = findValue(Ptr, /*OffsetOk=*/true);
384 Assert(!isa<ConstantPointerNull>(UnderlyingObject),
385 "Undefined behavior: Null pointer dereference", &I);
386 Assert(!isa<UndefValue>(UnderlyingObject),
387 "Undefined behavior: Undef pointer dereference", &I);
388 Assert(!isa<ConstantInt>(UnderlyingObject) ||
389 !cast<ConstantInt>(UnderlyingObject)->isAllOnesValue(),
390 "Unusual: All-ones pointer dereference", &I);
391 Assert(!isa<ConstantInt>(UnderlyingObject) ||
392 !cast<ConstantInt>(UnderlyingObject)->isOne(),
393 "Unusual: Address one pointer dereference", &I);
395 if (Flags & MemRef::Write) {
396 if (const GlobalVariable *GV = dyn_cast<GlobalVariable>(UnderlyingObject))
397 Assert(!GV->isConstant(), "Undefined behavior: Write to read-only memory",
399 Assert(!isa<Function>(UnderlyingObject) &&
400 !isa<BlockAddress>(UnderlyingObject),
401 "Undefined behavior: Write to text section", &I);
403 if (Flags & MemRef::Read) {
404 Assert(!isa<Function>(UnderlyingObject), "Unusual: Load from function body",
406 Assert(!isa<BlockAddress>(UnderlyingObject),
407 "Undefined behavior: Load from block address", &I);
409 if (Flags & MemRef::Callee) {
410 Assert(!isa<BlockAddress>(UnderlyingObject),
411 "Undefined behavior: Call to block address", &I);
413 if (Flags & MemRef::Branchee) {
414 Assert(!isa<Constant>(UnderlyingObject) ||
415 isa<BlockAddress>(UnderlyingObject),
416 "Undefined behavior: Branch to non-blockaddress", &I);
419 // Check for buffer overflows and misalignment.
420 // Only handles memory references that read/write something simple like an
421 // alloca instruction or a global variable.
423 if (Value *Base = GetPointerBaseWithConstantOffset(Ptr, Offset, DL)) {
424 // OK, so the access is to a constant offset from Ptr. Check that Ptr is
425 // something we can handle and if so extract the size of this base object
426 // along with its alignment.
427 uint64_t BaseSize = AliasAnalysis::UnknownSize;
428 unsigned BaseAlign = 0;
430 if (AllocaInst *AI = dyn_cast<AllocaInst>(Base)) {
431 Type *ATy = AI->getAllocatedType();
432 if (DL && !AI->isArrayAllocation() && ATy->isSized())
433 BaseSize = DL->getTypeAllocSize(ATy);
434 BaseAlign = AI->getAlignment();
435 if (DL && BaseAlign == 0 && ATy->isSized())
436 BaseAlign = DL->getABITypeAlignment(ATy);
437 } else if (GlobalVariable *GV = dyn_cast<GlobalVariable>(Base)) {
438 // If the global may be defined differently in another compilation unit
439 // then don't warn about funky memory accesses.
440 if (GV->hasDefinitiveInitializer()) {
441 Type *GTy = GV->getType()->getElementType();
442 if (DL && GTy->isSized())
443 BaseSize = DL->getTypeAllocSize(GTy);
444 BaseAlign = GV->getAlignment();
445 if (DL && BaseAlign == 0 && GTy->isSized())
446 BaseAlign = DL->getABITypeAlignment(GTy);
450 // Accesses from before the start or after the end of the object are not
452 Assert(Size == AliasAnalysis::UnknownSize ||
453 BaseSize == AliasAnalysis::UnknownSize ||
454 (Offset >= 0 && Offset + Size <= BaseSize),
455 "Undefined behavior: Buffer overflow", &I);
457 // Accesses that say that the memory is more aligned than it is are not
459 if (DL && Align == 0 && Ty && Ty->isSized())
460 Align = DL->getABITypeAlignment(Ty);
461 Assert(!BaseAlign || Align <= MinAlign(BaseAlign, Offset),
462 "Undefined behavior: Memory reference address is misaligned", &I);
466 void Lint::visitLoadInst(LoadInst &I) {
467 visitMemoryReference(I, I.getPointerOperand(),
468 AA->getTypeStoreSize(I.getType()), I.getAlignment(),
469 I.getType(), MemRef::Read);
472 void Lint::visitStoreInst(StoreInst &I) {
473 visitMemoryReference(I, I.getPointerOperand(),
474 AA->getTypeStoreSize(I.getOperand(0)->getType()),
476 I.getOperand(0)->getType(), MemRef::Write);
479 void Lint::visitXor(BinaryOperator &I) {
480 Assert(!isa<UndefValue>(I.getOperand(0)) || !isa<UndefValue>(I.getOperand(1)),
481 "Undefined result: xor(undef, undef)", &I);
484 void Lint::visitSub(BinaryOperator &I) {
485 Assert(!isa<UndefValue>(I.getOperand(0)) || !isa<UndefValue>(I.getOperand(1)),
486 "Undefined result: sub(undef, undef)", &I);
489 void Lint::visitLShr(BinaryOperator &I) {
490 if (ConstantInt *CI =
491 dyn_cast<ConstantInt>(findValue(I.getOperand(1), /*OffsetOk=*/false)))
492 Assert(CI->getValue().ult(cast<IntegerType>(I.getType())->getBitWidth()),
493 "Undefined result: Shift count out of range", &I);
496 void Lint::visitAShr(BinaryOperator &I) {
497 if (ConstantInt *CI =
498 dyn_cast<ConstantInt>(findValue(I.getOperand(1), /*OffsetOk=*/false)))
499 Assert(CI->getValue().ult(cast<IntegerType>(I.getType())->getBitWidth()),
500 "Undefined result: Shift count out of range", &I);
503 void Lint::visitShl(BinaryOperator &I) {
504 if (ConstantInt *CI =
505 dyn_cast<ConstantInt>(findValue(I.getOperand(1), /*OffsetOk=*/false)))
506 Assert(CI->getValue().ult(cast<IntegerType>(I.getType())->getBitWidth()),
507 "Undefined result: Shift count out of range", &I);
511 allPredsCameFromLandingPad(BasicBlock *BB,
512 SmallSet<BasicBlock *, 4> &VisitedBlocks) {
513 VisitedBlocks.insert(BB);
514 if (BB->isLandingPad())
516 // If we find a block with no predecessors, the search failed.
519 for (BasicBlock *Pred : predecessors(BB)) {
520 if (VisitedBlocks.count(Pred))
522 if (!allPredsCameFromLandingPad(Pred, VisitedBlocks))
529 allSuccessorsReachEndCatch(BasicBlock *BB, BasicBlock::iterator InstBegin,
530 IntrinsicInst **SecondBeginCatch,
531 SmallSet<BasicBlock *, 4> &VisitedBlocks) {
532 VisitedBlocks.insert(BB);
533 for (BasicBlock::iterator I = InstBegin, E = BB->end(); I != E; ++I) {
534 IntrinsicInst *IC = dyn_cast<IntrinsicInst>(I);
535 if (IC && IC->getIntrinsicID() == Intrinsic::eh_endcatch)
537 // If we find another begincatch while looking for an endcatch,
538 // that's also an error.
539 if (IC && IC->getIntrinsicID() == Intrinsic::eh_begincatch) {
540 *SecondBeginCatch = IC;
545 // If we reach a block with no successors while searching, the
546 // search has failed.
549 // Otherwise, search all of the successors.
550 for (BasicBlock *Succ : successors(BB)) {
551 if (VisitedBlocks.count(Succ))
553 if (!allSuccessorsReachEndCatch(Succ, Succ->begin(), SecondBeginCatch,
560 void Lint::visitEHBeginCatch(IntrinsicInst *II) {
561 // The checks in this function make a potentially dubious assumption about
562 // the CFG, namely that any block involved in a catch is only used for the
563 // catch. This will very likely be true of IR generated by a front end,
564 // but it may cease to be true, for example, if the IR is run through a
565 // pass which combines similar blocks.
567 // In general, if we encounter a block the isn't dominated by the catch
568 // block while we are searching the catch block's successors for a call
569 // to end catch intrinsic, then it is possible that it will be legal for
570 // a path through this block to never reach a call to llvm.eh.endcatch.
571 // An analogous statement could be made about our search for a landing
572 // pad among the catch block's predecessors.
574 // What is actually required is that no path is possible at runtime that
575 // reaches a call to llvm.eh.begincatch without having previously visited
576 // a landingpad instruction and that no path is possible at runtime that
577 // calls llvm.eh.begincatch and does not subsequently call llvm.eh.endcatch
578 // (mentally adjusting for the fact that in reality these calls will be
579 // removed before code generation).
581 // Because this is a lint check, we take a pessimistic approach and warn if
582 // the control flow is potentially incorrect.
584 SmallSet<BasicBlock *, 4> VisitedBlocks;
585 BasicBlock *CatchBB = II->getParent();
587 // The begin catch must occur in a landing pad block or all paths
588 // to it must have come from a landing pad.
589 Assert(allPredsCameFromLandingPad(CatchBB, VisitedBlocks),
590 "llvm.eh.begincatch may be reachable without passing a landingpad",
593 // Reset the visited block list.
594 VisitedBlocks.clear();
596 IntrinsicInst *SecondBeginCatch = nullptr;
598 // This has to be called before it is asserted. Otherwise, the first assert
599 // below can never be hit.
600 bool EndCatchFound = allSuccessorsReachEndCatch(
601 CatchBB, std::next(static_cast<BasicBlock::iterator>(II)),
602 &SecondBeginCatch, VisitedBlocks);
604 SecondBeginCatch == nullptr,
605 "llvm.eh.begincatch may be called a second time before llvm.eh.endcatch",
606 II, SecondBeginCatch);
607 Assert(EndCatchFound,
608 "Some paths from llvm.eh.begincatch may not reach llvm.eh.endcatch",
612 static bool allPredCameFromBeginCatch(
613 BasicBlock *BB, BasicBlock::reverse_iterator InstRbegin,
614 IntrinsicInst **SecondEndCatch, SmallSet<BasicBlock *, 4> &VisitedBlocks) {
615 VisitedBlocks.insert(BB);
616 // Look for a begincatch in this block.
617 for (BasicBlock::reverse_iterator RI = InstRbegin, RE = BB->rend(); RI != RE;
619 IntrinsicInst *IC = dyn_cast<IntrinsicInst>(&*RI);
620 if (IC && IC->getIntrinsicID() == Intrinsic::eh_begincatch)
622 // If we find another end catch before we find a begin catch, that's
624 if (IC && IC->getIntrinsicID() == Intrinsic::eh_endcatch) {
625 *SecondEndCatch = IC;
628 // If we encounter a landingpad instruction, the search failed.
629 if (isa<LandingPadInst>(*RI))
632 // If while searching we find a block with no predeccesors,
633 // the search failed.
636 // Search any predecessors we haven't seen before.
637 for (BasicBlock *Pred : predecessors(BB)) {
638 if (VisitedBlocks.count(Pred))
640 if (!allPredCameFromBeginCatch(Pred, Pred->rbegin(), SecondEndCatch,
647 void Lint::visitEHEndCatch(IntrinsicInst *II) {
648 // The check in this function makes a potentially dubious assumption about
649 // the CFG, namely that any block involved in a catch is only used for the
650 // catch. This will very likely be true of IR generated by a front end,
651 // but it may cease to be true, for example, if the IR is run through a
652 // pass which combines similar blocks.
654 // In general, if we encounter a block the isn't post-dominated by the
655 // end catch block while we are searching the end catch block's predecessors
656 // for a call to the begin catch intrinsic, then it is possible that it will
657 // be legal for a path to reach the end catch block without ever having
658 // called llvm.eh.begincatch.
660 // What is actually required is that no path is possible at runtime that
661 // reaches a call to llvm.eh.endcatch without having previously visited
662 // a call to llvm.eh.begincatch (mentally adjusting for the fact that in
663 // reality these calls will be removed before code generation).
665 // Because this is a lint check, we take a pessimistic approach and warn if
666 // the control flow is potentially incorrect.
668 BasicBlock *EndCatchBB = II->getParent();
670 // Alls paths to the end catch call must pass through a begin catch call.
672 // If llvm.eh.begincatch wasn't called in the current block, we'll use this
673 // lambda to recursively look for it in predecessors.
674 SmallSet<BasicBlock *, 4> VisitedBlocks;
675 IntrinsicInst *SecondEndCatch = nullptr;
677 // This has to be called before it is asserted. Otherwise, the first assert
678 // below can never be hit.
679 bool BeginCatchFound =
680 allPredCameFromBeginCatch(EndCatchBB, BasicBlock::reverse_iterator(II),
681 &SecondEndCatch, VisitedBlocks);
683 SecondEndCatch == nullptr,
684 "llvm.eh.endcatch may be called a second time after llvm.eh.begincatch",
686 Assert(BeginCatchFound,
687 "llvm.eh.endcatch may be reachable without passing llvm.eh.begincatch",
691 static bool isZero(Value *V, const DataLayout *DL, DominatorTree *DT,
692 AssumptionCache *AC) {
693 // Assume undef could be zero.
694 if (isa<UndefValue>(V))
697 VectorType *VecTy = dyn_cast<VectorType>(V->getType());
699 unsigned BitWidth = V->getType()->getIntegerBitWidth();
700 APInt KnownZero(BitWidth, 0), KnownOne(BitWidth, 0);
701 computeKnownBits(V, KnownZero, KnownOne, DL, 0, AC,
702 dyn_cast<Instruction>(V), DT);
703 return KnownZero.isAllOnesValue();
706 // Per-component check doesn't work with zeroinitializer
707 Constant *C = dyn_cast<Constant>(V);
711 if (C->isZeroValue())
714 // For a vector, KnownZero will only be true if all values are zero, so check
715 // this per component
716 unsigned BitWidth = VecTy->getElementType()->getIntegerBitWidth();
717 for (unsigned I = 0, N = VecTy->getNumElements(); I != N; ++I) {
718 Constant *Elem = C->getAggregateElement(I);
719 if (isa<UndefValue>(Elem))
722 APInt KnownZero(BitWidth, 0), KnownOne(BitWidth, 0);
723 computeKnownBits(Elem, KnownZero, KnownOne, DL);
724 if (KnownZero.isAllOnesValue())
731 void Lint::visitSDiv(BinaryOperator &I) {
732 Assert(!isZero(I.getOperand(1), DL, DT, AC),
733 "Undefined behavior: Division by zero", &I);
736 void Lint::visitUDiv(BinaryOperator &I) {
737 Assert(!isZero(I.getOperand(1), DL, DT, AC),
738 "Undefined behavior: Division by zero", &I);
741 void Lint::visitSRem(BinaryOperator &I) {
742 Assert(!isZero(I.getOperand(1), DL, DT, AC),
743 "Undefined behavior: Division by zero", &I);
746 void Lint::visitURem(BinaryOperator &I) {
747 Assert(!isZero(I.getOperand(1), DL, DT, AC),
748 "Undefined behavior: Division by zero", &I);
751 void Lint::visitAllocaInst(AllocaInst &I) {
752 if (isa<ConstantInt>(I.getArraySize()))
753 // This isn't undefined behavior, it's just an obvious pessimization.
754 Assert(&I.getParent()->getParent()->getEntryBlock() == I.getParent(),
755 "Pessimization: Static alloca outside of entry block", &I);
757 // TODO: Check for an unusual size (MSB set?)
760 void Lint::visitVAArgInst(VAArgInst &I) {
761 visitMemoryReference(I, I.getOperand(0), AliasAnalysis::UnknownSize, 0,
762 nullptr, MemRef::Read | MemRef::Write);
765 void Lint::visitIndirectBrInst(IndirectBrInst &I) {
766 visitMemoryReference(I, I.getAddress(), AliasAnalysis::UnknownSize, 0,
767 nullptr, MemRef::Branchee);
769 Assert(I.getNumDestinations() != 0,
770 "Undefined behavior: indirectbr with no destinations", &I);
773 void Lint::visitExtractElementInst(ExtractElementInst &I) {
774 if (ConstantInt *CI =
775 dyn_cast<ConstantInt>(findValue(I.getIndexOperand(),
776 /*OffsetOk=*/false)))
777 Assert(CI->getValue().ult(I.getVectorOperandType()->getNumElements()),
778 "Undefined result: extractelement index out of range", &I);
781 void Lint::visitInsertElementInst(InsertElementInst &I) {
782 if (ConstantInt *CI =
783 dyn_cast<ConstantInt>(findValue(I.getOperand(2),
784 /*OffsetOk=*/false)))
785 Assert(CI->getValue().ult(I.getType()->getNumElements()),
786 "Undefined result: insertelement index out of range", &I);
789 void Lint::visitUnreachableInst(UnreachableInst &I) {
790 // This isn't undefined behavior, it's merely suspicious.
791 Assert(&I == I.getParent()->begin() ||
792 std::prev(BasicBlock::iterator(&I))->mayHaveSideEffects(),
793 "Unusual: unreachable immediately preceded by instruction without "
798 /// findValue - Look through bitcasts and simple memory reference patterns
799 /// to identify an equivalent, but more informative, value. If OffsetOk
800 /// is true, look through getelementptrs with non-zero offsets too.
802 /// Most analysis passes don't require this logic, because instcombine
803 /// will simplify most of these kinds of things away. But it's a goal of
804 /// this Lint pass to be useful even on non-optimized IR.
805 Value *Lint::findValue(Value *V, bool OffsetOk) const {
806 SmallPtrSet<Value *, 4> Visited;
807 return findValueImpl(V, OffsetOk, Visited);
810 /// findValueImpl - Implementation helper for findValue.
811 Value *Lint::findValueImpl(Value *V, bool OffsetOk,
812 SmallPtrSetImpl<Value *> &Visited) const {
813 // Detect self-referential values.
814 if (!Visited.insert(V).second)
815 return UndefValue::get(V->getType());
817 // TODO: Look through sext or zext cast, when the result is known to
818 // be interpreted as signed or unsigned, respectively.
819 // TODO: Look through eliminable cast pairs.
820 // TODO: Look through calls with unique return values.
821 // TODO: Look through vector insert/extract/shuffle.
822 V = OffsetOk ? GetUnderlyingObject(V, DL) : V->stripPointerCasts();
823 if (LoadInst *L = dyn_cast<LoadInst>(V)) {
824 BasicBlock::iterator BBI = L;
825 BasicBlock *BB = L->getParent();
826 SmallPtrSet<BasicBlock *, 4> VisitedBlocks;
828 if (!VisitedBlocks.insert(BB).second)
830 if (Value *U = FindAvailableLoadedValue(L->getPointerOperand(),
832 return findValueImpl(U, OffsetOk, Visited);
833 if (BBI != BB->begin()) break;
834 BB = BB->getUniquePredecessor();
838 } else if (PHINode *PN = dyn_cast<PHINode>(V)) {
839 if (Value *W = PN->hasConstantValue())
841 return findValueImpl(W, OffsetOk, Visited);
842 } else if (CastInst *CI = dyn_cast<CastInst>(V)) {
843 if (CI->isNoopCast(DL))
844 return findValueImpl(CI->getOperand(0), OffsetOk, Visited);
845 } else if (ExtractValueInst *Ex = dyn_cast<ExtractValueInst>(V)) {
846 if (Value *W = FindInsertedValue(Ex->getAggregateOperand(),
849 return findValueImpl(W, OffsetOk, Visited);
850 } else if (ConstantExpr *CE = dyn_cast<ConstantExpr>(V)) {
851 // Same as above, but for ConstantExpr instead of Instruction.
852 if (Instruction::isCast(CE->getOpcode())) {
853 if (CastInst::isNoopCast(Instruction::CastOps(CE->getOpcode()),
854 CE->getOperand(0)->getType(),
856 DL ? DL->getIntPtrType(V->getType()) :
857 Type::getInt64Ty(V->getContext())))
858 return findValueImpl(CE->getOperand(0), OffsetOk, Visited);
859 } else if (CE->getOpcode() == Instruction::ExtractValue) {
860 ArrayRef<unsigned> Indices = CE->getIndices();
861 if (Value *W = FindInsertedValue(CE->getOperand(0), Indices))
863 return findValueImpl(W, OffsetOk, Visited);
867 // As a last resort, try SimplifyInstruction or constant folding.
868 if (Instruction *Inst = dyn_cast<Instruction>(V)) {
869 if (Value *W = SimplifyInstruction(Inst, DL, TLI, DT, AC))
870 return findValueImpl(W, OffsetOk, Visited);
871 } else if (ConstantExpr *CE = dyn_cast<ConstantExpr>(V)) {
872 if (Value *W = ConstantFoldConstantExpression(CE, DL, TLI))
874 return findValueImpl(W, OffsetOk, Visited);
880 //===----------------------------------------------------------------------===//
881 // Implement the public interfaces to this file...
882 //===----------------------------------------------------------------------===//
884 FunctionPass *llvm::createLintPass() {
888 /// lintFunction - Check a function for errors, printing messages on stderr.
890 void llvm::lintFunction(const Function &f) {
891 Function &F = const_cast<Function&>(f);
892 assert(!F.isDeclaration() && "Cannot lint external functions");
894 legacy::FunctionPassManager FPM(F.getParent());
895 Lint *V = new Lint();
900 /// lintModule - Check a module for errors, printing messages on stderr.
902 void llvm::lintModule(const Module &M) {
903 legacy::PassManager PM;
904 Lint *V = new Lint();
906 PM.run(const_cast<Module&>(M));