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Re: [PATCH] x86: allow suffix-less sign-extending movsb, movsw, and movsl

>>> On 01.07.16 at 18:07, <> wrote:
> On Fri, Jul 1, 2016 at 8:32 AM, Jan Beulich <> wrote:
>>>>> On 01.07.16 at 17:23, <> wrote:
>>> On Fri, Jul 1, 2016 at 8:19 AM, Jan Beulich <> wrote:
>>>>>>> On 01.07.16 at 17:12, <> wrote:
>>>>> On Fri, Jul 1, 2016 at 7:55 AM, Jan Beulich <> wrote:
>>>>>>>>> On 01.07.16 at 16:24, <> wrote:
>>>>>>> So in the end, I guess the movzb/movzw change is fine, but this one is
>>>>>>> not. It's in inherent inconsistency related to the ability of leaving
>>>>>>> away the size suffixes in combination with the chosen mnemonics, it
>>>>>>> seems.
>>>>>> I do not understand what inconsistency you refer to here. The
>>>>>> only inconsistency I can see is that one can't omit the suffixes
>>>>>> from these three instructions, unlike any others with GPR
>>>>>> operands.
>>>>> This mnemonic inconsistency comes from ISA and AT&T syntax.
>>>>> But there are no issues now.
>>>> There is - as said, I fell into the trap seeing "movzb" in source code
>>>> and assuming I then could also use "movzw" or "movsb" (etc). I
>>>> can certainly open a bug if that helps you re-consider.
>>> It is unfortunate.  But it won't lead to wrong instructions being used.
>> So since I see that rational arguments won't lead anywhere here
>> - would you at least allow in the fix for the bug that this change
>> uncovered (the one hunk changing tc-i386.c), even if that also
>> doesn't seem to cause any issues right now?
> Please open a bug report with a testcase.

You're kidding? As said, the issue got uncovered only with the
other adjustments here; I'm not aware of a case where this
would cause a problem without the other changes, and I'm not
going to spend a whole lot of time trying to figure a broken case.


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