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

[Lang Hames]

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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