[PATCH] D23583: [AArch64] Add feature has-fast-fma

[Evandro Menezes via llvm-commits]

evandro added a comment.

In https://reviews.llvm.org/D23583#518591, @rengolin wrote:

> > For instance, whether it should fold into FMA twice, back to back.
>
>
> This may be remnants of an ARMv7 issue around OOO cores having a hazard for FMA+FMA...


I doubt it, since the folding is done in the middle end.

> > As a matter of fact, it seems to me that most "big" targets would benefit from folding into FMA more aggressively.

> 

> 

> I tend to agree, but I don't have evidence. The best evidence would be some benchmark results or scheduling descriptions.

> 

> I'm not against this change in itself, but I really think this is a matter for the scheduler, not a target feature.


I disagree.  `isFMAFasterThanFMulAndFAdd()` is static and there's no good reason why `enableAggressiveFMAFusion()` cannot be static either.   In this sense, this feature is no different than the many of the existing features in AArch64.

Furthermore, I'm afraid that generalizing it to query the scheduling model would expand the scope of this feature beyond the hardware that I have available to test it on.


Repository:
  rL LLVM

https://reviews.llvm.org/D23583