[llvm] r204076 - Use range metadata instead of introducing selects.

[Lang Hames]

For Andy, or anyone else at Apple looking in to this, this
was <rdar://problem/16368461>.

Cheers,
Lang.


On Wed, Apr 9, 2014 at 11:51 AM, Lang Hames <lhames at gmail.com> wrote:

> Hi Guys,
>
> I picked on fourinarow because it was the largest regression due to this
> patch, but it wasn't the only one. There were about 30 test-suite
> regressions according to our testers, including:
>
> "12% slower on MultiSource/Benchmarks/FreeBench/analyzer/analyze"
> "9% slower MultiSource/Benchmarks/sim/sim"
> "4.5% slower on External/SPEC/CINT2000/164_gzip/164_gzip"
> "7% slower on External/SPEC/CINT2006/462_libquantum/462_libquantum"
>
> We should do the right thing at IR time, but before this patch goes back
> in we need to identify and fix whatever is going wrong in CodeGen, or
> verify that it's no longer a problem. If this goes back in and the
> regressions re-appear we'll just need to revert it again.
>
> - Lang.
>
>
>
> On Wed, Apr 9, 2014 at 2:59 AM, Rafael Espíndola <
> rafael.espindola at gmail.com> wrote:
>
>> > Ok. If we know that the number instructions before coalescing is
>> > less-or-equal and the spill count is greater in each of the regressions,
>> > that enough of a clue to pin it on coalescing/scheduling/regalloc.
>> >
>> > I don't like to prevent the right thing at IR level just because
>> downstream
>> > codegen happens to make bad decisions.
>>
>> +1
>>
>> Dan, can you commit it again and open a bug about the codegen issue?
>>
>> Thanks,
>> Rafael
>>
>
>
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