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Re: Question regarding "patch to remove temporary clobbers in LRA"


On 13-02-14 5:00 PM, Steven Bosscher wrote:
Hello Vlad,

Back in October, you added a patch to remove extra clobbers introduced by LRA:
http://gcc.gnu.org/ml/gcc-patches/2012-10/msg02531.html

This also disables some -frename-registers opportunities (a few 100 on
x86-64 for my collection of cc1-i files).

Do you think it's be possible (and worth the effort) to implement
something that keeps clobbers for registers that are live above the
clobber after removing the clobber?


I think # of missed opportunities you mentioned is enough reason to do this. Although I don't know what final improvement/ compilation speed will be at the end, In any case we can provide an option for this or make it by default for -O3 and above. I might be wrong but I guess it is mostly for 32-bit x86 with fp regs for now. It is hard for me to say is it worth to spend your time for this dying architecture. Although it can be useful for other architectures too. It is up to you. I believe we could add this code to GCC anyway.


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