This is the mail archive of the
binutils@sourceware.org
mailing list for the binutils project.
Re: [PATCH 2/5] x86: improve SIMD to‑scalar‑int conversion insn handling
>>> 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?
>
> 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.
Again - I think consistency is more important here. It would
anyway help if you answered the individual questions I've
raised above, not just the last one.
As to the effect on gcc: I'm quite certain that a bug they have
(and which I have a fix for, just that it's not the right time to
submit it, as the tree is basically frozen) is a more or less direct
result of the (enforced) lack of suffix on the 2usi conversions
here: They mis-compile usi2 conversions from 64-bit integers,
due to omitting the suffix from the generated assembly.
Just like for Intel syntax they always output the operand size,
for AT&T syntax they should always output a suffix if one can
sensibly be applied. This helps verifying that things are actually
consistent. But of course the assembler has to allow for it.
Jan