Understanding IRA

[Jeff Law]

On 10/19/09 12:30, Ian Bolton wrote:
> Hi Jeff and Vladimir.
>
> Jeff: I'd be interested in trying the patch if you can send it my way.
>    
It's nothing special.

/* Return nonzero if REGNO is a particularly bad choice for reloading X.  */
static int
ira_bad_reload_regno_1 (int regno, rtx x)
{
   int x_regno;
   ira_allocno_t a;
   enum reg_class pref;

   /* We only deal with pseudo regs.  */
   if (! x || GET_CODE (x) != REG)
     return 0;

   x_regno = REGNO (x);
   if (x_regno < FIRST_PSEUDO_REGISTER)
     return 0;

   /* If the pseudo prefers REGNO explicitly, then do not consider
      REGNO a bad spill choice.  */
   pref = reg_preferred_class (x_regno);
   if (reg_class_size[pref] == 1
&& TEST_HARD_REG_BIT (reg_class_contents[pref], regno))
     return 0;

   /* If the pseudo conflicts with REGNO, then we consider REGNO a
      poor choice for a reload regno.  */
   a = ira_regno_allocno_map[x_regno];
   if (TEST_HARD_REG_BIT (ALLOCNO_TOTAL_CONFLICT_HARD_REGS (a), regno))
     return 1;

   return 0;
}

/* Return nonzero if REGNO is a particularly bad choice for reloading
    IN or OUT.  */
int
ira_bad_reload_regno (int regno, rtx in, rtx out)
{
   return (ira_bad_reload_regno_1 (regno, in)
           || ira_bad_reload_regno_1 (regno, out));
}

Then change the loop in allocate_reload_reg to iterate 3 times intead of 
2.  And add this fragment



  if (pass == 1
&& ira_bad_reload_regno (regnum, rld[r].in, rld[r].out))
                 continue;


To body of hte conditional starting with

if ((reload_reg_free_p ...


It's really just a hack.  I don't want to spend much time on that code 
as ultimately I want it all to go away.

Jeff