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Re: [patch][rfc] Hookize SMALL_REGISTER_CLASSES, make SSE register classes not small
- From: "Steven Bosscher" <stevenb dot gcc at gmail dot com>
- To: "Michael Meissner" <meissner at linux dot vnet dot ibm dot com>, "Steven Bosscher" <stevenb dot gcc at gmail dot com>, gcc-patches <gcc-patches at gcc dot gnu dot org>, "Jan Hubicha" <jh at suse dot cz>, "Richard Guenther" <rguenther at suse dot de>, "Ian Lance Taylor" <ian at airs dot com>
- Date: Wed, 10 Dec 2008 15:53:20 +0100
- Subject: Re: [patch][rfc] Hookize SMALL_REGISTER_CLASSES, make SSE register classes not small
- References: <571f6b510812091430i2fe373cct1788ead26e988d81@mail.gmail.com> <20081210013854.GB438@hungry-tiger.westford.ibm.com>
On Wed, Dec 10, 2008 at 2:38 AM, Michael Meissner
<meissner@linux.vnet.ibm.com> wrote:
> Back when I was at AMD, I often times thought about making
> SMALL_REGISTER_CLASSES false for x86_64 bit (where you have more registers),
> but I never got around to doing it.
We tried it at SuSE a couple of years ago. It does not work. There
are too many instructions that require special registers. But the SSE
instructions don't have special requirements.
That's exactly why I decided to try to make SMALL_REGISTER_CLASSES
depend no machine mode. It's a safe bet that the compiler doesn't
have to walk on eggs for a register in an SSE mode (and
AFAIU-the-x86_64-instruction-set, also not for 64-bit integer
instructions?).
Gr.
Steven