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RE: Question about "instruction merge" pass when optimizing for size
- From: Matthew Fortune <Matthew dot Fortune at imgtec dot com>
- To: DJ Delorie <dj at redhat dot com>, "sarah at hederstierna dot com" <fredrik at hederstierna dot com>
- Cc: "gcc at gcc dot gnu dot org" <gcc at gcc dot gnu dot org>, Robert Suchanek <Robert dot Suchanek at imgtec dot com>
- Date: Wed, 19 Aug 2015 20:51:51 +0000
- Subject: RE: Question about "instruction merge" pass when optimizing for size
- Authentication-results: sourceware.org; auth=none
- References: <CE36BD26828FA5408B9F87E4DD2ACB0B0135774D9F16 at MBXVS01 dot HMC dot local> <4ad27b0cf3dd4b12a4a2a4530ce2f15a at DAG03 dot HMC dot local> <201508192038 dot t7JKcVV7000807 at greed dot delorie dot com>
DJ Delorie <email@example.com> writes:
> I've seen this on other targets too, sometimes so bad I write a quick
> target-specific "stupid move optimizer" pass to clean it up.
> A generic pass would be much harder, but very useful.
Robert (on cc) is currently attempting some improvements to the regrename
pass to try and propagate registers back from the destination of a move
in order that the move becomes a no-op. This is for a few cases we have
seen for MIPS. If successful that may clean up a small number of such
problems for all targets.