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

[Yvan Roux]

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.

>>> 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.

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.
>>
>>
>