llvm dev - Apr 2017 - Should ValueTracking::GetUnderlyingObject stop on Alloca instructions rather than calling SimplifyInstruction?

I notice that GetUnderlyingObject has a few checks, but alloca isn't one of
them. Then it fall backs to SimplifyInstruction which doesn't know about
alloca so falls back to just trying to constant fold it. This seems a
little silly since I assume alloca can't be constant folded. Should we just
detect this early in GetUnderlyingObject and stop?

~Craig
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Ping

~Craig

On Fri, Apr 7, 2017 at 1:25 PM, Craig Topper <craig.topper at gmail.com>
wrote:
> I notice that GetUnderlyingObject has a few checks, but alloca isn't
one
> of them. Then it fall backs to SimplifyInstruction which doesn't know
about
> alloca so falls back to just trying to constant fold it. This seems a
> little silly since I assume alloca can't be constant folded. Should we
just
> detect this early in GetUnderlyingObject and stop?
>
> ~Craig
>
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Yep. Makes sense to me. There's nothing to simplify or constant-fold 
about an alloca.

  -Hal

On 04/12/2017 04:23 PM, Craig Topper wrote:
> Ping
>
> ~Craig
>
> On Fri, Apr 7, 2017 at 1:25 PM, Craig Topper <craig.topper at gmail.com 
> <mailto:craig.topper at gmail.com>> wrote:
>
>     I notice that GetUnderlyingObject has a few checks, but alloca
>     isn't one of them. Then it fall backs to SimplifyInstruction which
>     doesn't know about alloca so falls back to just trying to constant
>     fold it. This seems a little silly since I assume alloca can't be
>     constant folded. Should we just detect this early in
>     GetUnderlyingObject and stop?
>
>     ~Craig
>
>
-- 
Hal Finkel
Lead, Compiler Technology and Programming Languages
Leadership Computing Facility
Argonne National Laboratory

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