llvm dev - Jul 2011 - [LLVMdev] Confusion with a Use of a getelementptr instruction being a Use of a select instruction instead

Hello,

I'm doing some Def/Use analysis, and I'm hung up on one tricky spot. 
The BB
in question is attached.  Ignore the red.

The issue is that '%13 = load...' instruction does not show up as a Use
for
the '%scevgep25' definition, and I feel like it should.  Instead, it
shows
up as a Use for '%iftmp.55.0 = select...', though Operand(0) for this
'%13 load' instruction [listed as a Use for '%iftmp.55.0 =
select...'] is
reported as the %scevgep25 instruction, which is correct.

Sorry if that was a bit convoluted.  Essentially, it seems that
'getelementptr' instructions with their Use's instructions being
(direct or
indirect)operands to 'select' instructions have their Uses show up as
Uses
for the select only and not for the getelementptr instruction.

Does anyone have any idea why this might be happening?  All the other
def/use information I get seems correct.

Thanks,
Griffin
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On 7/6/11 2:06 PM, Griffin Wright wrote:
> Hello,
>
> I'm doing some Def/Use analysis, and I'm hung up on one tricky
spot.
> The BB in question is attached.  Ignore the red.
>
> The issue is that '%13 = load...' instruction does not show up as a
> Use for the '%scevgep25' definition, and I feel like it should.  
> Instead, it shows up as a Use for '%iftmp.55.0 = select...', though
> Operand(0) for this '%13 = load' instruction [listed as a Use for 
> '%iftmp.55.0 = select...'] is reported as the %scevgep25
instruction,
> which is correct.
I'm not understanding all of the details of the behavior you're 
describing, but I agree that the %13 load should be a use of %scevgep25 
and that the select is a use of %14 and %15.

How are you iterating over the uses of %scevgep25?  Are you removing or 
inserting instructions while iterating over the uses, thereby 
potentially invalidating the use_iterator?  Invalidating the 
use_iterator would be my first guess.

-- John T.
>
> Sorry if that was a bit convoluted.  Essentially, it seems that 
> 'getelementptr' instructions with their Use's instructions
being
> (direct or indirect)operands to 'select' instructions have their
Uses
> show up as Uses for the select only and not for the getelementptr 
> instruction.
>
> Does anyone have any idea why this might be happening?  All the other 
> def/use information I get seems correct.
>
> Thanks,
> Griffin
>
>
>
> _______________________________________________
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> LLVMdev at cs.uiuc.edu         http://llvm.cs.uiuc.edu
> http://lists.cs.uiuc.edu/mailman/listinfo/llvmdev
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