[llvm-commits] [llvm] r162098 - in /llvm/trunk: lib/Analysis/MemoryBuiltins.cpp test/Transforms/InstCombine/objsize.ll

[Eli Friedman]

On Fri, Aug 17, 2012 at 11:07 AM, Benjamin Kramer <benny.kra at gmail.com> wrote:
>
> On 17.08.2012, at 19:47, Eli Friedman <eli.friedman at gmail.com> wrote:
>
>> On Fri, Aug 17, 2012 at 7:16 AM, Benjamin Kramer
>> <benny.kra at googlemail.com> wrote:
>>> Author: d0k
>>> Date: Fri Aug 17 09:16:37 2012
>>> New Revision: 162098
>>>
>>> URL: http://llvm.org/viewvc/llvm-project?rev=162098&view=rev
>>> Log:
>>> Guard MemoryBuiltins against self-looping GEPs, which can occur in unreachable code due to constant propagation.
>>>
>>> Fixes PR13621.
>>>
>>> Modified:
>>>    llvm/trunk/lib/Analysis/MemoryBuiltins.cpp
>>>    llvm/trunk/test/Transforms/InstCombine/objsize.ll
>>>
>>> Modified: llvm/trunk/lib/Analysis/MemoryBuiltins.cpp
>>> URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Analysis/MemoryBuiltins.cpp?rev=162098&r1=162097&r2=162098&view=diff
>>> ==============================================================================
>>> --- llvm/trunk/lib/Analysis/MemoryBuiltins.cpp (original)
>>> +++ llvm/trunk/lib/Analysis/MemoryBuiltins.cpp Fri Aug 17 09:16:37 2012
>>> @@ -473,6 +473,10 @@
>>> }
>>>
>>> SizeOffsetType ObjectSizeOffsetVisitor::visitGEPOperator(GEPOperator &GEP) {
>>> +  // Ignore self-referencing GEPs, they can occur in unreachable code.
>>> +  if (&GEP == GEP.getPointerOperand())
>>> +    return unknown();
>>
>> What happens when you have two GEPs referencing each other?
>
> I've wondered about this too, but can it really happen?

I don't see why not: dominance rules are completely ignored in unreachable code.

> I'm also not sure how to integrate a visited set into the instvisitor.

Just add a member, no?

-Eli