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

[Renato Golin via llvm-commits]

rengolin added a comment.

In https://reviews.llvm.org/D23583#518632, @evandro wrote:

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


Right, ignore me.

> 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.


I assumed the FMA fusion optimisation could just query the cost model in some way. Overriding the cost model for specific instructions in specific sub-architectures is the most logical solution to me.

> 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.


I understand the constraints, but I think we should design the back-end for all cores and not keep adding special cases to every different decision on every different core.

After all, moving from isCoreX() to hasCoreXFeatureY() seems pointless.


Repository:
  rL LLVM

https://reviews.llvm.org/D23583