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

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

On Thu, Mar 22, 2018 at 5:42 AM, Jan Beulich <JBeulich@suse.com> wrote:
>>>> On 22.03.18 at 13:18, <hjl.tools@gmail.com> wrote:
>> On Thu, Mar 22, 2018 at 5:06 AM, Jan Beulich <JBeulich@suse.com> wrote:
>>>>>> On 22.03.18 at 12:54, <hjl.tools@gmail.com> wrote:
>>>> On Thu, Mar 22, 2018 at 4:42 AM, Jan Beulich <JBeulich@suse.com> wrote:
>>>>>>>> On 22.03.18 at 12:23, <hjl.tools@gmail.com> wrote:
>>>>>> 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?
>>[...]
>> If we exclude integer instructions from this discussion, vector
>> instructions are quite consistent without suffix.   Yes, some vector
>> instructions do need suffixes, but only a few.
>
> Some _need_ suffixes, yes. Various other _allow_ for suffixes.
> Once again, would you mind actually reading what I've said in the
> patch description as well as answering the questions I've raised?
> _I did point out_ the inconsistencies I'm seeing, yet you continue
> to talk in general terms.

My point is that we shouldn't add suffix to vector instructions if
they can't be encoded uniquely.  That is OK If there are some
inconsistencies.

-- 
H.J.