[PATCH] D40177: performance improvements for ThunderX2 T99

[Stefan Teleman via Phabricator via llvm-commits]

steleman added a comment.

> Please avoid getProcFamily() checks outside of AArch64SubtargetInfo. Use target features and transfer the logic into SubtargetInfo!

Can you please explain the rationale behind this restriction?

It's certainly not supported by the class interface design, as the Subtarget pointer is accessible and Subtarget->getProcFamily() is accessible as well.

It also does not appear to be a real restriction at all, considering that Subtarget->getProcFamily() is already being used in AArch64ISelLowering.cpp.

What you are asking here is the implementation of a new target feature. This seems (a) unnecessary and (b) introduces unnecessary code complexity.

For starters, aggressive FMA is a compiler-dependent subjective decision. It's not a target-dependent objective attribute, such as LSE or Neon. What's //aggressive FMA// to LLVM is not aggressive at all to GCC for example.

The design implication is that, for every single existing public interface we are going to implement an additional, functionally duplicative, target feature. Which really isn't a target feature to being with.

The implementation implication is that, a one-line code change becomes a 10-line code change that accomplishes the same exact thing as the one-line change.

Thank you in advance for your explanation.


Repository:
  rL LLVM

https://reviews.llvm.org/D40177