[Bug target/51708] New: SH Target: SHAD / SHLD constant not CSE-ed

[oleg.endo@t-online.de]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=51708

             Bug #: 51708
           Summary: SH Target: SHAD / SHLD constant not CSE-ed
    Classification: Unclassified
           Product: gcc
           Version: 4.7.0
            Status: UNCONFIRMED
          Severity: enhancement
          Priority: P3
         Component: target
        AssignedTo: unassigned@gcc.gnu.org
        ReportedBy: oleg.endo@t-online.de
            Target: sh*-*-*


If the shift amount is a constant for SHAD / SHLD insns it should be CSE-ed.
This could be done in a similar way as in the movnegt insn.
Example function:

int foo (int* a, int x, int n)
{
  int i;
  int count;

  for (i = 0; i < n; i ++)
    count += (*(a + i) << 12);

  return count;
}

compiled with -m4 -O3:
        cmp/pl  r6
        bf      .L11
        shll2   r6
        add     #-4,r6
        shlr2   r6
        add     #1,r6
.L9:
        mov.l   @r4+,r1
        mov     #12,r2    ! load constant in loop
        dt      r6
        shld    r2,r1     ! use constant in loop
        bf/s    .L9
        add     r1,r0
.L11:
        rts
        nop


better:
        cmp/pl  r6
        bf      .L11
        shll2   r6
        add     #-4,r6
        shlr2   r6
        add     #1,r6
        mov     #12,r2    ! load constant before loop
.L9:
        mov.l   @r4+,r1
        dt      r6
        shld    r2,r1     ! use constant in loop
        bf/s    .L9
        add     r1,r0
.L11:
        rts
        nop