[PATCH] D106494: WIP: [AArch64][GlobalISel] Legalize ctpop s128

Sun Jul 25 14:10:56 PDT 2021

aemerson added a comment.

In D106494#2903324 <https://reviews.llvm.org/D106494#2903324>, @aemerson wrote:

> In D106494#2898851 <https://reviews.llvm.org/D106494#2898851>, @jroelofs wrote:
>
>> In D106494#2898756 <https://reviews.llvm.org/D106494#2898756>, @paquette wrote:
>>
>>> Do you have any idea of how to improve the zext behaviour?
>>
>> I was thinking about making `narrowScalar` do: `zext(add(trunc(ctpop(hi)), trunc(ctpop(lo)))` with the hope that some combine folds the inner `trunc(zext(ctpop(x))) => ctpop(x)`, but I haven't tried this yet.
>
> For the s32 -> s64 case, that should be folded to a G_ZEXT by D106768 <https://reviews.llvm.org/D106768>

Ah but these are going to be assigned to the FPR banks. We might be able to recognize the extend to s128 pattern and select the optimal code during selection.

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