[PATCH] [x86] add a reassociation optimization to increase ILP via the MachineCombiner pass

[Gerolf Hoflehner]

Hi Sanjay

Any HPC benchmark is a good candidate. But I was just curious if you had spotted some noticeable gains.

Cheers
Gerolf
> On Jun 8, 2015, at 5:53 PM, Sanjay Patel <spatel at rotateright.com> wrote:
> 
> In http://reviews.llvm.org/D10321#185353, @Gerolf wrote:
> 
>> I'm also curious about performance numbers.
> 
> 
> Hi Gerolf -
> 
> Thanks for the review! I'll work on the inline comments soon.
> 
> For perf numbers, I see no difference running the benchmarking subset of test-suite on x86 with AVX and -ffast-math; this is as expected because this pass isn't firing more than a handful of times on any test.
> 
> Do you have suggestions for other benchmarks? My motivating examples for this patch are:
> https://llvm.org/bugs/show_bug.cgi?id=17305
> https://llvm.org/bugs/show_bug.cgi?id=21768
> https://llvm.org/bugs/show_bug.cgi?id=23116
> http://reviews.llvm.org/D8941
> 
> I can create a toy test case and measure that the perf matches the IACA output in:
> https://llvm.org/bugs/show_bug.cgi?id=17305#c0
> 
> 
> http://reviews.llvm.org/D10321
> 
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