[PATCH] D65360: [AArch64][GlobalISel] Eliminate redundant G_ZEXT when the source is implicitly zext-loaded

Sun Jul 28 15:27:12 PDT 2019

aemerson added a comment.

In D65360#1603790 <https://reviews.llvm.org/D65360#1603790>, @arsenm wrote:

> In D65360#1603526 <https://reviews.llvm.org/D65360#1603526>, @aemerson wrote:
>
> > In D65360#1603454 <https://reviews.llvm.org/D65360#1603454>, @arsenm wrote:
> >
> > > Shouldn’t the combiner have already gotten his?
> >
> >
> > It does catch these cases, but sometimes these patterns arise later after the combiner due to some other optimization or DCE. By then the combiner has already run so we don’t merge these into G_ZEXTLOAD.
>
>
> I kind of think this is an issue of not running another combiner round, and the selector should do minimal work

Sure, for O2 <https://reviews.llvm.org/owners/package/2/> or Os we will have another combiner run, but at O0 we’re compile time sensitive, so I think the selector should deal with simple cases where it can. Reducing code size still has benefits at -O0.

Repository:
  rG LLVM Github Monorepo

CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D65360/new/

https://reviews.llvm.org/D65360