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

[Kyrill Tkachov]

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.

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?

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.
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