Re: [PATCH 10/10] x86: correct VFPCLASSP{S,D} operand size handling

[Jan Beulich <jbeulich at suse dot com>]

On 06.08.2019 23:11,  H.J. Lu  wrote:
> On Tue, Aug 6, 2019 at 7:29 AM Jan Beulich <jbeulich@suse.com> wrote:
> > With AVX512VL disabled (e.g. when writing code for the Knights family
> > of processors) these insns aren't ambiguous when used with a memory
> > source, and hence should be accepted without suffix or operand size
> > specifier. When AVX512VL is enabled, to be consistent with this as
> > well as other ambiguous operand size handling it seems better to just
> > wanrn about the ambiguity in AT&T mode, and still default to 512-bit
> > operands (on the assumption that the code may have been written without
> > AVX512VL in mind yet).
> >
> > gas/
> > 2019-08-XX  Jan Beulich  <jbeulich@suse.com>
> >
> >          * config/tc-i386.c (avx512): New (at file scope), moved from
> >          (check_VecOperands): ... here.
> >          (process_suffix): Add [XYZ]MMword operand size handling.
> >          * testsuite/gas/i386/noavx512-2.s, testsuite/gas/i386/noreg16.s,
> >          testsuite/gas/i386/noreg32.s, testsuite/gas/i386/noreg64.s: Add
> >          VFPCLASS tests.
> >          * testsuite/gas/i386/noavx512-2.l, testsuite/gas/i386/noreg16.d,
> >          testsuite/gas/i386/noreg16.l, testsuite/gas/i386/noreg32.d,
> >          testsuite/gas/i386/noreg32.l, testsuite/gas/i386/noreg64.d,
> >          testsuite/gas/i386/noreg64.l: Adjust expectations.
> >
> > opcodes/
> > 2019-08-XX  Jan Beulich  <jbeulich@suse.com>
> >
> >          * i386-opc.tbl (vfpclasspd, vfpclassps): Add Unspecified.
> >          * i386-tbl.h: Re-generate.
>
> We should keep the suffix even if AVX512VL isn't enabled so that
> we don't need to check if AVX512VL isn't enabled to interpret the
> instruction.

But that's wrong (and fixing this is the whole point of this patch).
As you've said elsewhere, unambiguous (SIMD in particular) insns
should not require any use of suffixes.

Jan