[PATCH] D19821: [EarlyCSE] Use MemorySSA if available.

[Philip Reames via llvm-commits]

reames added a comment.

Sorry for not responding to this for so long.

My objection is primarily from a compile time concern.  Right now, EarlyCSE is a *very* cheap pass to run.  If you can keep it fast (even when we have to reconstruct MemorySSA) I don't object to having EarlyCSE MemorySSA based.  I think that is a very hard bar to pass in practice.  In particular, the bar is not total O3 time.  It's EarlyCSE time.  I fully expect that the more precise analysis may speed up other passes, but we can't assume that happens for all inputs.  (As I write this, I'm recognizing that this might be too high a bar to set.  If you think I'm being unreasonable, argue why and what a better line should be.)

Given I'm not going to have time to be active involved in this thread, I'm going to defer to other reviewers.  If they think this is a good idea, I will not actively block the thread.


https://reviews.llvm.org/D19821