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Re: [RFC PATCH, x86_64] Use -mno-sse[,2] to fall back to x87 FP argument passing convention
- From: "Richard Guenther" <richard dot guenther at gmail dot com>
- To: "Ian Lance Taylor" <iant at google dot com>
- Cc: "Uros Bizjak" <ubizjak at gmail dot com>, "GCC Patches" <gcc-patches at gcc dot gnu dot org>, "Jan Hubicka" <jh at suse dot cz>
- Date: Wed, 11 Oct 2006 10:48:11 +0200
- Subject: Re: [RFC PATCH, x86_64] Use -mno-sse[,2] to fall back to x87 FP argument passing convention
- References: <firstname.lastname@example.org> <email@example.com>
On 10 Oct 2006 22:35:03 -0700, Ian Lance Taylor <firstname.lastname@example.org> wrote:
Incidentally, I've thought that it might be interesting to experiment
with an x86_64 ABI which used ILP32, but which used the extra eight
registers, passed parameters in registers, and only preserved the low
32-bits of the caller-saved registers. For applications which could
live in a 32-bit address space, that would save the memory traffic
required to save and restore 64-bit registers on function entry and
exit. The result would be pretty similar to i386 code, but with 8
more registers. It should definitely run faster than i386 code, and I
think that due to improved memory traffic it would also run faster
than standard x86_64 code. But I haven't actually tried.
This idea pops up every once in a while. I think Honza even prototyped
it, but of course it adds yet another architecture (or set of multilibs). So
unless the improvement is very big (like getting rid of the
old 32bit ABI completely...) it isn't going to happen I guess.