[PATCH] D40556: SIFixSGPRCopies should not change non-divergent PHI

[Alexander Timofeev via llvm-commits]

Hi Samuel,

sure I will look at this. I'll let you know when I get an idea of what
going wrong there.

Alexander

On Thu, Mar 15, 2018 at 6:46 PM, Samuel Pitoiset via Phabricator <
reviews at reviews.llvm.org> wrote:

> hakzsam added a comment.
> Herald added a subscriber: llvm-commits.
>
> Hi guys,
>
> This change appears to introduce a regression. It hangs nier:automata with
> the RADV Vulkan driver, reverting the commit fixes the issue.
>
> Here's the full LLVM IR of that shader https://hastebin.com/minayakiri
>
> I have also tried to reduce the testcase, but I'm not 100% sure it's
> correct, in case you want to have a look too https://hastebin.com/
> olatenegej
>
> After comparing with/without that change, it appears that some VGPR PHIs
> are SGPR PHIs now.
>
> I know this is why this change has been submitted initially (ie. to not
> use VGPR PHIs when the control flow is uniform), but I wonder if the new
> postdominance frontier is correct is *all* situations.
>
> The concept of VGPR/SGPR PHIs seems tricky and I'm not sure to fully
> understand it.
>
> Can you check (and/or explain) if the SGPR PHIs in that shader are
> expected?
>
> Thanks in advance,
> Samuel.
>
>
> Repository:
>   rL LLVM
>
> https://reviews.llvm.org/D40556
>
>
>
>
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