[llvm-commits] [llvm] r162120 - in /llvm/trunk: include/llvm/Analysis/MemoryBuiltins.h lib/Analysis/MemoryBuiltins.cpp test/Transforms/InstCombine/objsize.ll
Eli Friedman
eli.friedman at gmail.com
Fri Aug 17 14:24:25 PDT 2012
On Fri, Aug 17, 2012 at 2:14 PM, Eli Friedman <eli.friedman at gmail.com> wrote:
> On Fri, Aug 17, 2012 at 12:47 PM, Benjamin Kramer <benny.kra at gmail.com> wrote:
>>
>> On 17.08.2012, at 21:39, Eli Friedman <eli.friedman at gmail.com> wrote:
>>
>>> On Fri, Aug 17, 2012 at 12:26 PM, Benjamin Kramer
>>> <benny.kra at googlemail.com> wrote:
>>>> Author: d0k
>>>> Date: Fri Aug 17 14:26:41 2012
>>>> New Revision: 162120
>>>>
>>>> URL: http://llvm.org/viewvc/llvm-project?rev=162120&view=rev
>>>> Log:
>>>> MemoryBuiltins: Properly guard ObjectSizeOffsetVisitor against cycles in the IR.
>>>>
>>>> The previous fix only checked for simple cycles, use a set to catch longer
>>>> cycles too.
>>>>
>>>> Drop the broken check from the ObjectSizeOffsetEvaluator. The BoundsChecking
>>>> pass doesn't have to deal with invalid IR like InstCombine does.
>>>>
>>>> Modified:
>>>> llvm/trunk/include/llvm/Analysis/MemoryBuiltins.h
>>>> llvm/trunk/lib/Analysis/MemoryBuiltins.cpp
>>>> llvm/trunk/test/Transforms/InstCombine/objsize.ll
>>>>
>>>> Modified: llvm/trunk/include/llvm/Analysis/MemoryBuiltins.h
>>>> URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/include/llvm/Analysis/MemoryBuiltins.h?rev=162120&r1=162119&r2=162120&view=diff
>>>> ==============================================================================
>>>> --- llvm/trunk/include/llvm/Analysis/MemoryBuiltins.h (original)
>>>> +++ llvm/trunk/include/llvm/Analysis/MemoryBuiltins.h Fri Aug 17 14:26:41 2012
>>>> @@ -146,6 +146,7 @@
>>>> bool RoundToAlign;
>>>> unsigned IntTyBits;
>>>> APInt Zero;
>>>> + SmallPtrSet<Instruction *, 8> SeenInsts;
>>>>
>>>> APInt align(APInt Size, uint64_t Align);
>>>>
>>>> @@ -203,7 +204,6 @@
>>>> const TargetData *TD;
>>>> LLVMContext &Context;
>>>> BuilderTy Builder;
>>>> - ObjectSizeOffsetVisitor Visitor;
>>>> IntegerType *IntTy;
>>>> Value *Zero;
>>>> CacheMapTy CacheMap;
>>>>
>>>> Modified: llvm/trunk/lib/Analysis/MemoryBuiltins.cpp
>>>> URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Analysis/MemoryBuiltins.cpp?rev=162120&r1=162119&r2=162120&view=diff
>>>> ==============================================================================
>>>> --- llvm/trunk/lib/Analysis/MemoryBuiltins.cpp (original)
>>>> +++ llvm/trunk/lib/Analysis/MemoryBuiltins.cpp Fri Aug 17 14:26:41 2012
>>>> @@ -358,11 +358,16 @@
>>>>
>>>> SizeOffsetType ObjectSizeOffsetVisitor::compute(Value *V) {
>>>> V = V->stripPointerCasts();
>>>> + if (Instruction *I = dyn_cast<Instruction>(V)) {
>>>> + // If we have already seen this instruction, bail out. Cycles can happen in
>>>> + // unreachable code after constant propagation.
>>>> + if (!SeenInsts.insert(I))
>>>> + return unknown();
>>>>
>>>> - if (GEPOperator *GEP = dyn_cast<GEPOperator>(V))
>>>> - return visitGEPOperator(*GEP);
>>>> - if (Instruction *I = dyn_cast<Instruction>(V))
>>>> + if (GEPOperator *GEP = dyn_cast<GEPOperator>(V))
>>>> + return visitGEPOperator(*GEP);
>>>> return visit(*I);
>>>> + }
>>>> if (Argument *A = dyn_cast<Argument>(V))
>>>> return visitArgument(*A);
>>>> if (ConstantPointerNull *P = dyn_cast<ConstantPointerNull>(V))
>>>> @@ -371,9 +376,12 @@
>>>> return visitGlobalVariable(*GV);
>>>> if (UndefValue *UV = dyn_cast<UndefValue>(V))
>>>> return visitUndefValue(*UV);
>>>> - if (ConstantExpr *CE = dyn_cast<ConstantExpr>(V))
>>>> + if (ConstantExpr *CE = dyn_cast<ConstantExpr>(V)) {
>>>> if (CE->getOpcode() == Instruction::IntToPtr)
>>>> return unknown(); // clueless
>>>> + if (CE->getOpcode() == Instruction::GetElementPtr)
>>>> + return visitGEPOperator(cast<GEPOperator>(*CE));
>>>> + }
>>>>
>>>> DEBUG(dbgs() << "ObjectSizeOffsetVisitor::compute() unhandled value: " << *V
>>>> << '\n');
>>>> @@ -473,10 +481,6 @@
>>>> }
>>>>
>>>> SizeOffsetType ObjectSizeOffsetVisitor::visitGEPOperator(GEPOperator &GEP) {
>>>> - // Ignore self-referencing GEPs, they can occur in unreachable code.
>>>> - if (&GEP == GEP.getPointerOperand())
>>>> - return unknown();
>>>> -
>>>> SizeOffsetType PtrData = compute(GEP.getPointerOperand());
>>>> if (!bothKnown(PtrData) || !GEP.hasAllConstantIndices())
>>>> return unknown();
>>>> @@ -510,10 +514,6 @@
>>>> }
>>>>
>>>> SizeOffsetType ObjectSizeOffsetVisitor::visitSelectInst(SelectInst &I) {
>>>> - // ignore malformed self-looping selects
>>>> - if (I.getTrueValue() == &I || I.getFalseValue() == &I)
>>>> - return unknown();
>>>> -
>>>> SizeOffsetType TrueSide = compute(I.getTrueValue());
>>>> SizeOffsetType FalseSide = compute(I.getFalseValue());
>>>> if (bothKnown(TrueSide) && bothKnown(FalseSide) && TrueSide == FalseSide)
>>>> @@ -533,8 +533,7 @@
>>>>
>>>> ObjectSizeOffsetEvaluator::ObjectSizeOffsetEvaluator(const TargetData *TD,
>>>> LLVMContext &Context)
>>>> -: TD(TD), Context(Context), Builder(Context, TargetFolder(TD)),
>>>> -Visitor(TD, Context) {
>>>> +: TD(TD), Context(Context), Builder(Context, TargetFolder(TD)) {
>>>> IntTy = TD->getIntPtrType(Context);
>>>> Zero = ConstantInt::get(IntTy, 0);
>>>> }
>>>> @@ -559,6 +558,7 @@
>>>> }
>>>>
>>>> SizeOffsetEvalType ObjectSizeOffsetEvaluator::compute_(Value *V) {
>>>> + ObjectSizeOffsetVisitor Visitor(TD, Context);
>>>> SizeOffsetType Const = Visitor.compute(V);
>>>> if (Visitor.bothKnown(Const))
>>>> return std::make_pair(ConstantInt::get(Context, Const.first),
>>>> @@ -719,10 +719,6 @@
>>>> }
>>>>
>>>> SizeOffsetEvalType ObjectSizeOffsetEvaluator::visitSelectInst(SelectInst &I) {
>>>> - // ignore malformed self-looping selects
>>>> - if (I.getTrueValue() == &I || I.getFalseValue() == &I)
>>>> - return unknown();
>>>> -
>>>> SizeOffsetEvalType TrueSide = compute_(I.getTrueValue());
>>>> SizeOffsetEvalType FalseSide = compute_(I.getFalseValue());
>>>>
>>>>
>>>> Modified: llvm/trunk/test/Transforms/InstCombine/objsize.ll
>>>> URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Transforms/InstCombine/objsize.ll?rev=162120&r1=162119&r2=162120&view=diff
>>>> ==============================================================================
>>>> --- llvm/trunk/test/Transforms/InstCombine/objsize.ll (original)
>>>> +++ llvm/trunk/test/Transforms/InstCombine/objsize.ll Fri Aug 17 14:26:41 2012
>>>> @@ -247,7 +247,8 @@
>>>>
>>>> ; technically reachable, but this malformed IR may appear as a result of constant propagation
>>>> xpto:
>>>> - %gep = getelementptr i8* %gep, i32 1
>>>> + %gep2 = getelementptr i8* %gep, i32 1
>>>> + %gep = getelementptr i8* %gep2, i32 1
>>>> %o = call i32 @llvm.objectsize.i32(i8* %gep, i1 true)
>>>> ; CHECK: ret i32 undef
>>>> ret i32 %o
>>>
>>> Err, wait a sec: this testcase isn't valid! The verifier should catch it.
>>
>> The verifier only runs after the specified pass, instcombine removes dead code so it doesn't fire. It's really hard to find a test case for this without writing invalid IR, and if you have a reduced one it tends to be fragile :(
>
> Ah.
>
> Random idea: would it be possible to avoid this whole mess by making
> sure instcombine never visits unreachable instructions?
Err, wait, instcombine already erases all dead instructions. Given
that, how can you possibly end up visiting an instruction which
references itself?
-Eli
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