[PATCH][ARM] PR 49526: Add support for smmul,smmla,smmls instructions

[Kyrill Tkachov]

Hi Yvan,

On 24/11/15 15:05, Yvan Roux wrote:
> Hi Kyrill,
>
> On 24 November 2015 at 14:31, Kyrill Tkachov <kyrylo.tkachov@arm.com> wrote:
>> Ping.
>>
>> Thanks,
>> Kyrill
>>
>>
>>
>> On 13/11/15 11:50, Kyrill Tkachov wrote:
>>> Ping.
>>> https://gcc.gnu.org/ml/gcc-patches/2015-11/msg00686.html
>>>
>>> Thanks,
>>> Kyrill
>>>
>>> On 06/11/15 17:05, Kyrill Tkachov wrote:
>>>> Hi all,
>>>>
>>>> This patch introduces support for the smmul, smmla and smmls instructions
>>>> that appear in armv6 architecture levels
>>>> and higher. To quote the SMMUL description from the ARMARM:
>>>> "Signed Most Significant Word Multiply multiplies two signed 32-bit
>>>> values, extracts the most significant 32 bits of
>>>> the result, and writes those bits to the destination register."
>>>>
>>>> The smmla and smmls are the multiply-accumulate and multiply-subtract
>>>> extensions of that multiply.
>>>> There also exists an smmulr variant that rounds the result rather than
>>>> truncating it.
>>>> However, when I tried adding patterns for those forms I got an LRA ICE
>>>> that I was not able to figure out.
>>>> I'll try to find a testcase for that, but in the meantime there's no
>>>> reason to not have patterns for the
>>>> non-rounding variants.
> I agree, but would be interested to give a look at the LRA issue when
> you have a testcase.

I've filed PR 68536 for the ICE I've been seeing. Any insight is, of course, welcome.

>>>> Bootstrapped and tested on arm-none-linux-gnueabihf.
>>>> I've seen this trigger in quite a few places in SPEC2006 where it always
>>>> made the code better.
>>>>
>>>> Ok for trunk?
> Patch looks good to me (but can't approved it), I just wonder if
> adding a subreg_highpart_p predicate in emit-rtl.c would be useful,
> looking at other usage of subreg_highpart_offset it doesn't seem to be
> the case, but maybe for consistency with the existing
> subreg_lowpart_p.

Perhaps, we can put it there if there's much scope for its reuse in other
parts of the compiler. I didn't put it there in the first place so as not to
extend the review scope of the patch to the midend...

Thanks for looking at this,
Kyrill

>
> Cheers,
> Yvan
>
>>>> Thanks,
>>>> Kyrill
>>>>
>>>> 2015-11-06  Kyrylo Tkachov  <kyrylo.tkachov@arm.com>
>>>>
>>>>      PR target/49526
>>>>      * config/arm/arm.md (*mulsidi3si_v6): New pattern.
>>>>      (*mulsidi3siaddsi_v6): Likewise.
>>>>      (*mulsidi3sisubsi_v6): Likewise.
>>>>      * config/arm/predicates.md (subreg_highpart_operator):
>>>>      New predicate.
>>>>
>>>> 2015-11-06  Kyrylo Tkachov  <kyrylo.tkachov@arm.com>
>>>>
>>>>      PR target/49526
>>>>      * gcc.target/arm/pr49526_1.c: New test.
>>>>      * gcc.target/arm/pr49526_2.c: Likewise.
>>>>      * gcc.target/arm/pr49526_3.c: Likewise.
>>>