[PATCH] D54710: [x86] don't try to convert add with undef operands to LEA

Wed Dec 5 09:33:12 PST 2018

aemerson added a comment.

In D54710#1319529 <https://reviews.llvm.org/D54710#1319529>, @spatel wrote:

> In D54710#1319436 <https://reviews.llvm.org/D54710#1319436>, @aemerson wrote:
>
> >   This seems to me to be a bug in ProcessImplicitDefs, for some reasoning killing the IMPLICIT_DEF even though there's a subreg use. GlobalISel MIR output looks fine to me.
>
>
> Regardless of whether there's a bug in ProcessImplicitDefs, we would have to correctly propagate the undef flag through this transform (from 'add' to 'lea') though? I'm proposing to avoid that for this case based on existing code that appears to do the same thing.

Ok, I'm not familiar with the x86 backend to be able to give an opinion on the specifics of this patch. @craig.topper?

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