[PATCH] D74640: [LoopRotate] Add explicit flag to require MSSA.

Tue Sep 1 21:06:27 PDT 2020

asbirlea added a comment.

Thank you for the results! Looking at libclamav_unsp.c, I'm seeing 3.96% in instructions for ThinLTO, which I'm guessing matches the results you see.
The fluctuations may make sense, since with the additional MSSA updates in LoopRotate it can do more or less work, depending on the updates. For instructions per cycle I'm seeing it neutral results (0.5%), and for wall time (average over 20 run), also neutral.

Again, I'm not convinced this is worth pushing forward due to it only affecting the LPM, but since the change I'm undoing here was a previous large release regression in clang9, I'm glad to see the DomTree work payed off and this is now showing mixed results.
I'm fine with whichever decisions the reviewers lean towards.

Repository:
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https://reviews.llvm.org/D74640