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Re: New GCC releases comparison and comparison of GCC4.4 and LLVM2.5 on SPEC2000
- From: Steven Bosscher <stevenb dot gcc at gmail dot com>
- To: Chris Lattner <clattner at apple dot com>
- Cc: Vladimir Makarov <vmakarov at redhat dot com>, "gcc.gcc.gnu.org" <gcc at gcc dot gnu dot org>, Evan Cheng <evan dot cheng at apple dot com>
- Date: Wed, 13 May 2009 00:09:25 +0200
- Subject: Re: New GCC releases comparison and comparison of GCC4.4 and LLVM2.5 on SPEC2000
- References: <4A098018.email@example.com> <CFB21785-5057-4A8B-9DC7-1C0CBC4D0EDB@apple.com>
On Tue, May 12, 2009 at 7:45 PM, Chris Lattner <firstname.lastname@example.org> wrote:
> 2. You change two variables in your configurations: micro architecture and
> pointer size. ?Would you be willing to run x86-32 Core i7 numbers as well?
> ?LLVM in particular is completely untuned for the (really old and quirky)
> "netburst" architecture, but I'm interested to see how it runs for you on
> more modern Core i7 or Core2 processors in 32-bit mode.
FWIW, GCC is also completely untuned for NetBurst. There isn't even a
scheduler description for the P4, and there also isn't anything for
the funny branch predictor.
> 3. Your SPEC FP benchmarks tell me two things: GCC 4.4's fortran support is
> dramatically better than 4.2's (which llvm 2.5 uses), and your art/mgrid
> hacks apparently do great stuff :).
Something like the "art hack" is in ipa-struct-reorg, but it is not
enabled at any level. If gcc outperforms llvm on art by much, it's
more likely that some important opportunities for art are being
overlooked by llvm.
There also isn't anything special done for mgrid, except predictive
commoning (CSE around loops) which is not a hack, in the sense it is
helpful for a lot of numerical code and triggers several times in
things like generic Fortran blas/lapack routines.
Hope this helps,