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[Bug gas/25550] Review .arch directives
From: |
hjl.tools at gmail dot com |
Subject: |
[Bug gas/25550] Review .arch directives |
Date: |
Fri, 14 Feb 2020 13:22:07 +0000 |
https://sourceware.org/bugzilla/show_bug.cgi?id=25550
--- Comment #6 from H.J. Lu <hjl.tools at gmail dot com> ---
(In reply to Jan Beulich from comment #5)
> (In reply to H.J. Lu from comment #4)
> > (In reply to Jan Beulich from comment #3)
> > > (In reply to H.J. Lu from comment #2)
> > > > Is SSE2 a prerequisite for AVX?
> > >
> > > This can be viewed either way, I guess. The history of the ISA extensions
> > > suggests it is. But functionally nothing except the XMM registers have any
> > > overlap, I think.
> >
> > Why is AVX a prerequisite for AVX512?
>
> The correlation is largely the same as the one between SSE* and AVX.
I agree with you on both counts. I think treating MMX, SSE, AVX and AVX512
as separate ISA families gives assembler the most flexibility. Of course,
we need to document whatever behavior we decide.
> > > > For view point of assembly codes, enable MMX register without MMX ISA
> > > > makes no sense. For example, emms is needed for proper MMX usage.
> > >
> > > Not necessarily, one can certainly get away without (using 4 FFREEP in a
> > > row).
> >
> > What purpose does it serve?
>
> Well, I don't expect anyone would actively want to use it this way.
I think it is better to allow MMX register only if MMX ISA is enabled.
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