[Bug gas/25550] Review .arch directives

[jbeulich at suse dot com]

https://sourceware.org/bugzilla/show_bug.cgi?id=25550

Jan Beulich <jbeulich at suse dot com> changed:

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                 CC|                            |jbeulich at suse dot com

--- Comment #1 from Jan Beulich <jbeulich at suse dot com> ---
However, as pointed out in the mail discussion already, consistent behavior
should result (which currently isn't the case):

1. Since .arch generally enables prereqs for the specified ISA extension (like
AVX for AVX512F), disabling an extension also should disable everything that it
is considered a prereq for.

2. Any ISA extension enabled should be enabled completely. The main anomaly
looks to be SSE/SSE2 insns accessing MMX registers, where strictly speaking the
MMX ISA extension isn't a prereq to the SSE* ones (it's only the registers that
are used), which gas also handles this way. A patch was already proposed to
address this:

https://sourceware.org/ml/binutils/2020-02/msg00250.html

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