Re: [PATCH] x86: fix AVX* dependencies of ".arch .nosse*"

["H.J. Lu" <hjl dot tools at gmail dot com>]

On Thu, Feb 13, 2020 at 1:23 AM Jan Beulich <jbeulich@suse.com> wrote:
>
> Since ".arch .avx*" enables SSE*, disabling SSE* should also disable
> AVX*. Together with 7deea9aad866 ('x86: fix SSE4a dependencies of
> ".arch .nosse*"') I think this makes clear that the whole .arch logic
> needs an overhaul, such that the mechanism to enable features implies
> the reverse operation when disabling any, without having to modify two
> places. Arm64's approach may be worthwhile to consider cloning.
>
> Note that while commit 1848e567343e ("Update x86 CPU_XXX_FLAGS
> handling") introducing the testcase which needs fixing here explicitly
> says "Don't disable AVX nor AVX512 when disabling SSE", I don't see why
> this would be. Furthermore it also says "Don't disable AVX512 when
> disabling AVX", which too has been undone meanwhile (commit 89199bb5a027
> ["ix86: Disable AVX512F when disabling AVX2"], PR gas/24359). The only
> sensible (consistent) alternative therefore would be to avoid enabling
> SSE* with ".arch .avx*", like is done for SSE* wrt MMX (in turn leading
> to inconsistencies with SSE insns accessing MMX registers).
>

The intended usages are to build an object:

1. Without MMX, but with SSE, AVX and AVX512.
2. Without SEE nor MMX, but with AVX and AVX512.
3. Without SSE, MMX, AVX, but with AVX512.

enforced by assembler.  Your patch doesn't help it.

-- 
H.J.