[Bug target/54272] [SH] Add support for addv / subv instructions

["olegendo at gcc dot gnu.org" <gcc-bugzilla at gcc dot gnu dot org>]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=54272

Oleg Endo <olegendo at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |ASSIGNED
   Last reconfirmed|                            |2012-08-16
     Ever Confirmed|0                           |1

--- Comment #5 from Oleg Endo <olegendo at gcc dot gnu.org> 2012-08-16 20:34:53 UTC ---
Regarding saturating arithmetic, I took the function FIXED_SSADD from
libgcc/fixed-bit.c and substituted FIXED_C_TYPE with int.

int test_01 (int a, int b)
{
  int c;
  int x, y, z;
  x = a;
  y = b;
  z = x + y;
  if ((((x ^ y) >> 31) & 1) == 0)
    {
      if (((z ^ x) >> 31) & 1)
        {
          z = 1;
          z = z << 31;
          if (x >= 0)
            z--;
        }
    }
  c = z;
  return c;
}

compiled with -O2 -m4 -ml:
        div0s   r4,r5
        mov     r4,r0
        bt/s    .L4
        add     r5,r0
        div0s   r0,r4
        bt/s    .L6
        cmp/pz  r4
.L4:
        rts
        nop
        .align 1
.L6:
        mov.l   .L7,r0
        movt    r1
        rts
        sub     r1,r0
.L8:
        .align 2
.L7:
        .long   -2147483648

In this case combine can successfully match the div0s sign comparison patterns
that I added in PR 52933.  However, after matching those, it does not try to
combine the patterns any further (probably because of the conditional
branches). I guess this would be a job for an optimization at the GIMPLE level.