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Re: [PATCH,x86] Fix combine for condditional instructions.
- From: Uros Bizjak <ubizjak at gmail dot com>
- To: Yuri Rumyantsev <ysrumyan at gmail dot com>
- Cc: gcc-patches <gcc-patches at gcc dot gnu dot org>, Igor Zamyatin <izamyatin at gmail dot com>
- Date: Wed, 12 Dec 2012 12:38:02 +0100
- Subject: Re: [PATCH,x86] Fix combine for condditional instructions.
- References: <CAEoMCqSAQO8=moBn+X+V_EEQSkbQEa_HDmKk5GP_Nzm7m5Kbrw@mail.gmail.com>
On Wed, Dec 12, 2012 at 12:27 PM, Yuri Rumyantsev <ysrumyan@gmail.com> wrote:
> This fix is aimed to remove performance degradation introduced by new
> LRA phase that in fact is combining problem. Gcc combiner does
> propagation of memory load to if-then-else gimple that was splitted
> back by old reload phase. LRA does not perform such splitting. To
> avoid performance slowdown on important benchmark (this is true for
> all x86 targets) we decided to enhance 'ix86_legitimate_combined_insn'
> with a check on such propagation and consider such conditional
> instruction with memory operand as illegal one from performance point
> of view.
Is this true for all x86 targets? I have no objections to the
implementation, but these fine-tunings should be declared in
ix86_tune_features[] array, and used as conditions involving
TARGET_xxx in the code. Please see many examples in the i386 source
dir.
> Is it OK for 4.8 and mainline?
Hm, currently 4.8 _is_ mainline. Did you mean 4.7?
Thanks,
Uros.