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Re: Partial PRE optimization causing slowdown

From: Jeff Law <law at redhat dot com>
To: Steve Ellcey <sellcey at mips dot com>, gcc at gcc dot gnu dot org
Date: Thu, 12 Dec 2013 12:22:57 -0700
Subject: Re: Partial PRE optimization causing slowdown
Authentication-results: sourceware.org; auth=none
References: <f8528a93-eca2-4727-a190-966cdd9ecc3f at BAMAIL02 dot ba dot imgtec dot org>

On 12/12/13 12:19, Steve Ellcey wrote:

I have a question about the partial pre (-ftree-partial-pre) optimization
that was added in GCC 4.8.  I have noticed that this optimization is slowing
down the bitmnp01 benchmark in the EEMBC1.1 suite on MIPS.  I see this with
the 4.8 GCC and with ToT GCC.  Comparing "-O3 -fno-tree-partial-pre" vs.
just "-O3" on the Tot GCC with MIPS, I see almost a 50% slowdown in the
benchmark due to the partial pre optimization.

I was wondering if anyone else has seen a slowdown like this on other
platforms or in other benchmarks.  I haven't submitted a bugzilla report
because I don't have a test case that I can include (EEMBC is licensed).

See BZ38785

jeff

References:
- Partial PRE optimization causing slowdown
  - From: Steve Ellcey

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