[llvm] r192567 - Allow pinsrw/pinsrb/pextrb/pextrw/movmskps/movmskpd/pmovmskb/extractps instructions to parse either GR32 or GR64 without resorting to duplicating instructions.

[Ahmed Bougacha]

On Tue, Jun 23, 2015 at 8:19 PM, Craig Topper <craig.topper at gmail.com> wrote:
> I don't believe current versions of gas add a rex.w prefix for   extractps
> $7, %xmm0, %rcx   so I think current behavior is consistent. I don't have
> access to any other assemblers to test.

True, it doesn't.  I also tried inline-asm given to icc, it doesn't
either. However, the OS X as(1) (-v says based on "GNU assembler
version 1.38") does.

-Ahmed

> On Tue, Jun 23, 2015 at 2:20 PM, Ahmed Bougacha <ahmed.bougacha at gmail.com>
> wrote:
>>
>> How about something like the attached patch?
>> I'd personally prefer having separate instructions: it's simpler with
>> less special cases, and it makes the operand types a little easier to
>> work with (admittedly not a concern for in-tree code, only stuff like
>> "smart" disassemblers would use that).
>>
>> -Ahmed
>>
>> On Tue, Jun 23, 2015 at 11:45 AM, Ahmed Bougacha
>> <ahmed.bougacha at gmail.com> wrote:
>> > On Mon, Jun 22, 2015 at 11:29 PM, Craig Topper <craig.topper at gmail.com>
>> > wrote:
>> >> I think I agree, but I'd like to find a way to do this without
>> >> duplicating
>> >> the instructions again. Maybe we can keep the register encodings
>> >> unmodified
>> >> instead of calling getGR32FromGR64, then detect whether we need REX.W
>> >> in the
>> >> encoder? May need a new TSFlag to enable this behavior.
>> >
>> > Yes, that might work; I'll have a look.
>> >
>> > Thanks!
>> > -Ahmed
>> >
>> >> On Mon, Jun 22, 2015 at 5:40 PM, Ahmed Bougacha
>> >> <ahmed.bougacha at gmail.com>
>> >> wrote:
>> >>>
>> >>> Hi Craig,
>> >>>
>> >>> Forgive the necromancy, but I'm wondering if this is the right thing:
>> >>> we remove users' freedom to pick encodings (used by some, for padding
>> >>> and such), for no good reason: with this commit, generated code uses
>> >>> GR32 encodings, even if the assembly explicitly specified a GR64
>> >>> register.
>> >>>
>> >>> Of course, that's starting from assembly;  if the compiler generates
>> >>> the larger equivalent encoding that should be fixed, but I don't think
>> >>> that's ever the case, as AFAICT GR32 is preferred by the various
>> >>> patterns.
>> >>>
>> >>> What do you think about restoring the previous behavior?
>> >>> -Ahmed
>
>
>
>
> --
> ~Craig