[PATCH] D25291: [AArch64] Optionally use the reciprocal estimation machinery

[Evandro Menezes via llvm-commits]

evandro added a comment.

In https://reviews.llvm.org/D25291#564496, @jmolloy wrote:

> If you want to just enable reciprocal selection and test it, then a cl::opt flag seems most appropriate because that's how we enable experimental stuff broad-brush for testing. A CPU feature really isn't right as it ignores the important context that should go into deciding whether to use these instructions (on ARM/AArch64).


Adding an option is a good idea to provide a means for users to tap into this feature.

> Alternatively there may exist a target with such a slow SQRT unit that RSQRTE/RSQRTS is always better regardless of context, but I haven't seen any evidence for that either.

The M1 is it.  Indeed, not always, but most of the time.


Repository:
  rL LLVM

https://reviews.llvm.org/D25291