Re: [PATCH 2/5] x86: improve SIMD to‑scalar‑int conversion insn handling

[H.J. Lu]

On Thu, Mar 22, 2018 at 12:42 AM, Jan Beulich <JBeulich@suse.com> wrote:
>>>> On 21.03.18 at 20:17, <hjl.tools@gmail.com> wrote:
>> On Wed, Mar 21, 2018 at 7:20 AM, Jan Beulich <JBeulich@suse.com> wrote:
>>> In the course of folding their patterns (possible now that the pointless
>>> and partly even bogus VecESize are no longer in the way) I've noticed
>>> that vcvt*2usi, other than their vcvt*2si counterparts, didn't allow for
>>> any suffixes. As with all insns touching GPRs, these should be permitted
>>> even if they're not required for determining operand sizes. In turn I've
>>> noticed that only a very limited set of cases had a suffix added in
>>> disassembly with -Msuffix, while all suffixes should be output in that
>>> mode.
>>>
>>> gas/
>>> 2018-03-21  Jan Beulich  <jbeulich@suse.com>
>>>
>>>         * testsuite/gas/i386/cvt-2si.d, testsuite/gas/i386/cvt-2si.s:
>>>         New.
>>>         * testsuite/gas/i386/i386.exp: Run new test.
>>>         * testsuite/gas/i386/ilp32/x86-64-simd-suffix.d,
>>>         testsuite/gas/i386/simd-suffix.d,
>>>         testsuite/gas/i386/x86-64-simd-suffix.d: Adjust expectations.
>>>
>>> opcodes/
>>> 2018-03-21  Jan Beulich  <jbeulich@suse.com>
>>>
>>>         * i386-dis.c (prefix_table): Replace Y by S for cvt*2si.
>>>         (vex_len_table): Replace Y by S for vcvt*2si.
>>>         (putop): Replace plain 'Y' handling by abort().
>>>         * i386-dis-evex.h (evex_table): Replace Y by S for vcvt*2si.
>>>         * i386-opc.tbl (vcvt*d2si): Fold AVX512 forms. Add ToDword.
>>>         (vcvt*s2si): Fold AVX512 forms. Add ToQword.
>>>         * i386-tlb.h: Re-generate.
>>
>> I prefer not to add suffixes to vector instructions with GPRs unless it
>> is required.
>
> I'm afraid I don't follow - suffixes (in particular in suffix-always
> mode) aren't an optional thing. I actually consider it a mistake
> for the compiler to omit them, and the compiler _has to_ omit
> them right now because we don't accept them. Furthermore -
> did you look at the state things are currently in? If you didn't
> want suffixes when not needed, why is there the Y format in
> the first place? And why said inconsistency between 2usi and
> 2si conversions in the assembler? And more fundamentally -
> why are vector insns different from others touching GPRs?

I'd to keep AT&T mnemonic as close to SDM as possible.
There are not much we can do about integer instructions.
But we should do our best for vector instructions.   There
are some exceptions as you have noticed.   A suffix is needed
for some vector instructions to tell size.

-- 
H.J.