regression on Adobe-C++/loop_unroll

[Chandler Carruth]

Evan, see the PR. Essentially, making LICM *better* causes a very strange
degradation in DSE. The thing that is found to be loop invariant *is* loop
invariant, and ostensibly should be moved into the exit block. I have not
yet uncovered the root cause of why this change would cause us to fail to
delete dead stores in some other function...


On Sun, Feb 9, 2014 at 10:19 AM, Evan Cheng <evan.cheng at apple.com> wrote:

> Do you have more detailed information on how this change is causing
> performance regression?
>
> Evan
>
> On Feb 6, 2014, at 11:19 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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