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Re: [PATCH,RFC] Disallow reordering of x87 insns while scheduling
- From: Richard Henderson <rth at redhat dot com>
- To: Roger Sayle <roger at eyesopen dot com>
- Cc: gcc-patches at gcc dot gnu dot org
- Date: Sat, 16 Apr 2005 23:44:38 -0700
- Subject: Re: [PATCH,RFC] Disallow reordering of x87 insns while scheduling
- References: <Pine.LNX.4.44.0504162021460.19102-100000@www.eyesopen.com>
On Sat, Apr 16, 2005 at 08:58:46PM -0600, Roger Sayle wrote:
> This is clearly a problem for code size, so perhaps the patch below
> should be restricted to -Os. However, on many members of the IA-32
> family, there's also performance consequences for these fxch insns.
Are there? AFAIK, from Pentium 1 on they are pretty much free.
> Thoughts?
I think you're severely penalizing Pentium 1, which is *not*
out-of-order, and which *does* rely on the compiler to interleave
fp operations via fxch in order to keep the pipelines full.
r~