[PATCH] D19426: [AArch64] Use the reciprocal estimation machinery

[Evandro Menezes via llvm-commits]

evandro added a comment.

James,

> Perhaps. The important thing is how we decide whether to perform this optimisation or not. A hook function, as we normally use, has the ability to be extended to add more logic. A subtarget feature does not. I wouldn’t like to see optimization decisions being switched on or off by subtarget features.


Whether it is to use the series or not in a loop bound by latency, as in the 1st example, and in a loop bound by throughput, as in the 2nd example, or in a sequence with many multiplications is still something that would still depend on the sub-target.  For, say, in a sub-target division or square root could take much longer than the series or there are plenty of units capable of multiplications.  Hopefully the context of this hook may allow querying the sub-target about such details.  I'll start working on this soon.

Still, methinks that this patch is good for some sub-targets as is and it shouldn't be the enemy of "perfection". ;-)

Thank you.


Repository:
  rL LLVM

http://reviews.llvm.org/D19426