[PATCH] D78582: [InstCombine] substitute equivalent constant to reduce logic-of-icmps

Thu Apr 23 11:21:34 PDT 2020

spatel added a comment.

In D78582#1999502 <https://reviews.llvm.org/D78582#1999502>, @nikic wrote:

> It looks like this caused a +0.40% text size increase <http://llvm-compile-time-tracker.com/compare.php?from=7003a1da37b2aae5b17460922efde9efde2c229d&to=c79227cabb3059b4f01c07b6f8bfc7986a71d156&stat=size-text> on kimwitu++. There's a corresponding > 10% compile-time increase <http://llvm-compile-time-tracker.com/compare.php?from=7003a1da37b2aae5b17460922efde9efde2c229d&to=c79227cabb3059b4f01c07b6f8bfc7986a71d156&stat=instructions&details=on> on the main.cc file, so that's likely the relevant one.
>
> If you have time, it would be good to double check what's going on there, as text size increase usually means we're losing optimizations.

I'm going to expose my lack of git knowledge here, but how do we know this commit is to blame for the difference?
How do I determine the build flags that are needed to repro?
I tried reverting this patch locally and compiling /testsuite/trunk/MultiSource/Applications/kimwitu++/main.cc, and the IR is identical to pre-revert compiled at -O2 or -O3.

Repository:
  rG LLVM Github Monorepo

CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D78582/new/

https://reviews.llvm.org/D78582