[PATCH] D63225: AMDGPU: Fold readlane from copy of SGPR or imm

Fri Jun 14 18:05:14 PDT 2019

rampitec added a comment.

In D63225#1544642 <https://reviews.llvm.org/D63225#1544642>, @arsenm wrote:

> In D63225#1544639 <https://reviews.llvm.org/D63225#1544639>, @rampitec wrote:
>
> > This cannot work as written, at least readlane part. Maybe readfirstlane can, providing skip is always inserted around and def is in the same block. Otherwise it needs to be a virtual register and SSA.
>
>
> SIFoldOperands is SSA only, and physical registers are filtered out already

Why do we check for virtual registers all over the place place then, including the few lines above?

Also note, if virtual and SSA, then check for exec modification is not needed because that must be the only def anyway. Otherwise it reads undef that way or another.

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