[PATCH] D80175: [PowerPC][MachineCombiner] reassociate fma to expose more ILP

[Aaron H Liu via Phabricator via llvm-commits]

AaronLiu added a comment.

In D80175#2081521 <https://reviews.llvm.org/D80175#2081521>, @shchenz wrote:

> In D80175#2081483 <https://reviews.llvm.org/D80175#2081483>, @AaronLiu wrote:
>
> > Can you add a hidden option with init false?  You can turn it true later on.
> >  So that people can try with your option off and on? Thanks!
>
>
> Have you met some issues with this being turned on? This is specific for PowerPC, I have verified that on PowerPC there is no deg for the patch on the benchmarks I run. If you just want to see the impact of this patch, I would suggest you comment out the two newly added lines in function `PPCInstrInfo::getMachineCombinerPatterns`, it will turn off this opt.


>From a user perspective, for anyone who investigate a benchmark or debug a problem, it is very frequently to disable or enable many optimizations, and it is impossible for a user  to find someway to comment out some lines in some function for some optimizations and rebuild the compiler, and uncomment some lines and rebuild the compiler again and again.

I think this is a simple and reasonable suggestion. By the way, I do not have very strong opinion on this. -:)  What do you think? @jsji @nemanjai


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https://reviews.llvm.org/D80175