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Re: [Patch, i386] Avoid LCP stalls (issue5975045)
- From: "H.J. Lu" <hjl dot tools at gmail dot com>
- To: Teresa Johnson <tejohnson at google dot com>
- Cc: reply at codereview dot appspotmail dot com, gcc-patches at gcc dot gnu dot org
- Date: Wed, 4 Apr 2012 17:39:37 -0700
- Subject: Re: [Patch, i386] Avoid LCP stalls (issue5975045)
- References: <20120405000700.5020E61583@tjsboxrox.mtv.corp.google.com>
On Wed, Apr 4, 2012 at 5:07 PM, Teresa Johnson <email@example.com> wrote:
> New patch to avoid LCP stalls based on feedback from earlier patch. I modified
> H.J.'s old patch to perform the peephole2 to split immediate moves to HImode
> memory. This is now enabled for Core2, Corei7 and Generic.
> I verified that this enables the splitting to occur in the case that originally
> motivated the optimization. If we subsequently find situations where LCP stalls
> are hurting performance but an extra register is required to perform the
> splitting, then we can revisit whether this should be performed earlier.
> I also measured SPEC 2000/2006 performance using Generic64 on an AMD Opteron
> and the results were neutral.
What are the performance impacts on Core i7? I didn't notice any significant
changes when I worked on it for Core 2.