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Re: [PATCH, IRA] Fix ALLOCNO_MODE in the case of paradoxical subreg.
- From: Wei Mi <wmi at google dot com>
- To: Vladimir Makarov <vmakarov at redhat dot com>
- Cc: GCC Patches <gcc-patches at gcc dot gnu dot org>, David Li <davidxl at google dot com>
- Date: Wed, 25 Sep 2013 11:00:54 -0700
- Subject: Re: [PATCH, IRA] Fix ALLOCNO_MODE in the case of paradoxical subreg.
- Authentication-results: sourceware.org; auth=none
- References: <CA+4CFy73kNt8naM0Ds_8q7cpCn77aTtVRgCHUBiSFacJMQ+L7g at mail dot gmail dot com> <524304C2 dot 1040304 at redhat dot com> <CA+4CFy7APRWjyjAecTQoo=S-+5f0G79Xa_My77eYQiJ1HBkr-g at mail dot gmail dot com> <52431B06 dot 4050405 at redhat dot com>
> To define for what occurrence of the pseudo we should do the
> transformation, we need to create allocnos and calculate reg classes to
> know what paradoxical subreg needs more hard regs (the transformations
> can not be done for all paradoxical subregs as my experience shows many
> RTL changes result in worse RA even if we have heuristics to remove the
> generated changes as in this case would be trying to assign the same
> hard reg for the original and the new pseudo).
> After doing the transformations, we need to recalculate reg classes
> and rebuild allocnos (both are expensive). To speed up the process it
> could be implemented as some kind of update of already existing data but
> it will complicate code much.
>
I see, thanks!
> So right now I think implementing this in LRA would be easier Still LRA
> has a pretty good register (re-)allocation (although it is worse than in
> IRA).
>
When you get an idea how to fix it in LRA, if you are still busy, I
would be happy to do the implementation if you could brief your idea.
Thanks,
Wei Mi.