[PATCH] D113778: [AMDGPU] Use shift for b64 mov

Fri Nov 12 09:02:41 PST 2021

sebastian-ne added a comment.

In D113778#3127676 <https://reviews.llvm.org/D113778#3127676>, @arsenm wrote:

> In D113778#3127670 <https://reviews.llvm.org/D113778#3127670>, @foad wrote:
>
>> In D113778#3127658 <https://reviews.llvm.org/D113778#3127658>, @arsenm wrote:
>>
>>> 64-bit shifts were quarter rate instructions last I checked, so this is slower
>>
>> The Write64Bit definitions in SISchedule.td suggest they are half rate on most subtargets and full rate on gfx90a.
>
> I think that's probably wrong. Comments in performShlCombine for example say it's quarter rate

It seems to be quarter rate (or something slow) on gfx9, full rate on gfx90a and half rate on gfx10?
Then it would be worth using on gfx90a and gfx10+.

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