[LLVMdev] InstCombine strips the inBounds attribute in GetElementPtr ConstantExpr

[Jingyue Wu]

I forgot to mention how to reproduce this issue:

Simply run "opt inbounds.ll -o inbounds.opt.ll -instcombine -S". The result
is attached.

Jingyue


On Tue, Apr 22, 2014 at 10:37 AM, Jingyue Wu <jingyue at google.com> wrote:

> Sure, Chandler. I was running late yesterday, and didn't get a chance to
> reduce it.
>
> Attached is a reduced test. One more thing I found is, to trigger this
> issue, the base of the GEP mustn't be a GlobalVariable; otherwise, LLVM
> will go to ConstantFold.cpp:2131 and generate an inbounds GEP ConstantExpr.
>
> 2127   // If all indices are known integers and normalized, we can do a
> simple
> 2128   // check for the "inbounds" property.
>
> 2129   if (!Unknown && !inBounds &&
>
> 2130       isa<GlobalVariable>(C) && isInBoundsIndices(Idxs))
>
> 2131     return ConstantExpr::getInBoundsGetElementPtr(C, Idxs);
>
>
> My attached test is reduced from a CUDA program that declares the global
> array as __shared__. Therefore, the base of the GEP is an addrspacecast
> from the global array.
>
> One possible fix is to pass IsInBounds to ConstantFoldInstOperands and
> CastGEPIndices, so that CastGEPIndices can inherit this attribute. Are
> there better ways?
>
> Let me know if you need more information.
>
> Jingyue
>
>
> On Mon, Apr 21, 2014 at 8:04 PM, Chandler Carruth <chandlerc at google.com>wrote:
>
>>
>> On Mon, Apr 21, 2014 at 7:59 PM, Jingyue Wu <jingyue at google.com> wrote:
>>
>>> I can't upload my program due to confidentiality, but the problem is
>>> obvious.
>>
>>
>> A reduced test case would still help, and should go into any fix to
>> ensure we don't regress here...
>>
>
>
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