[Bug target/51797] New: Arm backend missed the mls related optimization

["carrot at google dot com" <gcc-bugzilla at gcc dot gnu dot org>]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=51797

             Bug #: 51797
           Summary: Arm backend missed the mls related optimization
    Classification: Unclassified
           Product: gcc
           Version: 4.7.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: target
        AssignedTo: unassigned@gcc.gnu.org
        ReportedBy: carrot@google.com
            Target: arm-linux-androideabi


compile the following code with options -march=armv7-a -mthumb -Os


int t0i(int a, int b)
{
  return a - 368 * b;
}

GCC 4.7 generates:

t0i:
    ldr    r3, .L2
    mla    r0, r3, r1, r0
    bx    lr
.L3:
    .align    2
.L2:
    .word    -368


When compiled with -O3, gcc generates:

t0i:
    movw    r3, #65168
    movt    r3, 65535
    mla    r0, r3, r1, r0
    bx    lr


But an optimized result should be:

t0i:
     movw r3, 368
     mls  r0, r3, r1, r0
     bx   lr

It is faster and smaller than either of Os/O3 result.