Many profitable optimizations cannot be performed at -Oz, due to
unrotated loops. While this is worse for size (minimally), many of the
optimizations significantly reduce code size, such as memcpy
optimizations and other patterns found by loop idiom recognition.
Related discussion can be found in issue #50308.
This patch adds an experimental, backend-only flag to allow loop header
duplication, regardless of the optimization level. Downstream consumers
can experiment with this flag, and if it is profitable, we can adjust
the compiler's defaults accordingly, and expose any useful frontend
flags to opt into the new behavior.
It was already disabled under -Oz in
buildFunctionSimplificationPipeline(), but not in
buildModuleOptimizationPipeline()/addPGOInstrPasses().
Reviewed By: fhahn
Differential Revision: https://reviews.llvm.org/D89927
As it's causing some bot failures (and per request from kbarton).
This reverts commit r358543/ab70da07286e618016e78247e4a24fcb84077fda.
llvm-svn: 358546
After changes in rL231820 loop re-rotation is performed even in -Oz mode. Since loop rotation is disabled for -Oz, it seems loop re-rotation should be disabled too.
Differential Revision: http://reviews.llvm.org/D10961
llvm-svn: 241897
