[PATCH] D40855: [PowerPC] LSR tunings for PowerPC

[Stefan Pintilie via Phabricator via llvm-commits]

stefanp added a comment.

@hfinkel 
Hi Hal, 
Yes that is correct. We are increasing the size of the class of equal elements.
The idea is that LSR will only replace one formula with another if it finds something with a lower cost. By returning false more often LSR will do fewer replacements and that is what we mean by more conservative. Maybe that's not really clear in the comment and I can update the comment to make it more clear.

I think you are looking for a theoretical reason as to why we picked this formula over others. However, the reason we settled on this formula as opposed to what is on x86 for example was based on the performance testing that we did. We tried a number of options and this one came out the best. We used this formula as an opportunity to tune LSR.


https://reviews.llvm.org/D40855