[PATCH] D64353: [AMDGPU] Run '' after isel to simplify PHIs.

Mon Jul 8 11:11:59 PDT 2019

arsenm added a comment.

In D64353#1573974 <https://reviews.llvm.org/D64353#1573974>, @hliao wrote:

> In D64353#1573922 <https://reviews.llvm.org/D64353#1573922>, @arsenm wrote:
>
> > I think you should probably fix SILowerControlFlow
>
>
> the misplacement of def/use is not the fault of SILowerControlFlow but PHIEliminate. However, even PHIEliminate should not be blamed as cf.end is part of MBB prologue. cf.end should not take any input from PHI.
>
> In O2 <https://reviews.llvm.org/owners/package/2/> compilation, there won't be such issue as, in optimized RA, livevariable is used to eliminate PHI better. LiveVariables depends on unreachable-mbb-elimin, which remove the PHI to cf.end.

This isn't a property the pass should rely on. SILowerControlFlow should defend against unexpected iteration order and unreachable blocks

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https://reviews.llvm.org/D64353