[PATCH] D32352: Go to eleven

[Sanjay Patel via Phabricator via llvm-commits]

spatel added a comment.

In https://reviews.llvm.org/D32352#735421, @avt77 wrote:

> In https://reviews.llvm.org/D32352#735393, @spatel wrote:
>
> > Is this or should this be limited when optimizing for size? I didn't count the instruction bytes...it might depend on the multiplier constant which version is smaller?
>
>
> It's already limited:
>
>   // An imul is usually smaller than the alternative sequence.
>   if (DAG.getMachineFunction().getFunction()->optForMinSize())


Ah, sorry I missed that. The fact that it is "MinSize" highlights that we're in a gray area for the DAG. That is, it's hard to know what the best sequence will be without looking at the instruction timing. Given that, we need to know if converting these muls is generally good. Do you have real or synthetic benchmark info for these cases? Is there a perf difference, for example, between Jaguar and Haswell (since those CPUs are specified in the tests)? Is the codegen ever different for those CPUs? If not, why are we adding different RUNs for them in this patch?


https://reviews.llvm.org/D32352