Investigate cases where running llvm optimizer twice slows down code #1300
Labels
bugzilla
Issues migrated from bugzilla
code-quality
llvm-tools
All llvm tools that do not have corresponding tag
worksforme
Resolved as "works for me"
Extended Description
These two nightly tester tests:
http://llvm.org/nightlytest/test.php?machine=36&night=1063
http://llvm.org/nightlytest/test.php?machine=23&night=1064
Capture performance changes that were due to running llvm-gcc at -O0 instead of -O2. The basic
impact is that we're now runing 'gccas' once instead of twice on the input programs (far more realistic).
Some of these programs got slower, e.g. fldry. This turns out to be a phase-ordering issue. If these
can be tracked down and improved, that would be good.
More important, however, are the programs that sped up by disabling the run of the optimizer. This
implies that running the optimizer twice on the programs actually slowed them down, which is clearly
bad.
-Chris
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