regression on Adobe-C++/loop_unroll

[Chandler Carruth]

So this doesn't reproduce for me at all when I just compile and
loop_unroll.cpp from the test suite for x86 (sandybridge). Not really sure
what all is required to observe this slowdown.

I've also checked and we have no interesting benchmark regressions on our
internal benchmarks with that revision... Really weird.

Can you provide before/after bitcode? File a bug as well to track it if its
this severe?

On Fri Feb 07 2014 at 12:32:34 AM, Chandler Carruth <chandlerc at gmail.com>
wrote:

> It's really weird because the public performance bots don't show this
> regression:
>
> http://llvm.org/perf/db_default/v4/nts/21277
>
> It would be really nice to get the stuff that people have hard
> requirements on posted to the LNT dashboard...
>
> It's also particularly weird because this shouldn't really have changed
> the way LICM works. Looking into it though...
>
> On Thu Feb 06 2014 at 11:19:21 AM, Gerolf Hoflehner <ghoflehner at apple.com>
> wrote:
>
> Hi Chandler
>
> your commit seems to cause a major regression (>20%)  on loop_unroll and
> other benchmarks as well. This is ( at least)  on x86 under -O3 -flto and
> seems to be due to the loss of LICM. Please take a look.
>
> Cheers
> Gerolf
>
> ------------------------------------------------------------------------
> r200067 | chandlerc | 2014-01-24 20:07:24 -0800 (Fri, 24 Jan 2014) | 44
> lines
>
> [LPM] Make LCSSA a utility with a FunctionPass that applies it to all
> the loops in a function, and teach LICM to work in the presance of
> LCSSA.
>
>
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