microblaze unroll loops optimization

[Richard Henderson]

On 01/11/2013 07:20 PM, Michael Eager wrote:
> I still think it's a bit odd.  Other targets use the comparison
> operator (e.g., lt, ge, etc.).  Microblaze should as well.

Microblaze can't use the raw comparison operator because of how
the results of the cmp{,u} instructions are defined, especially
placing the result of < in the *high* bit.

You could, however, use two CCmodes for the result of the compares:

   (set (reg:CC r) (compare:CC (reg:SI x) (reg:SI y)))
   => cmp r, x, y

   (set (reg:CCU r) (compare:CCU (reg:SI x) (reg:SI y)))
   => cmpu r, x, y

and then the branch insns consume CC and CCU mode inputs:

   (set (pc)
        (if_then_else
          (match_operator 1 "mb_signed_cmp_op"	// eq, lt, le
            [(match_operand:CC 2 "register_operand" "r")
             (const_int 0)]0
          (label_ref (match_operand 0))
          (pc)))

and similar for "mb_unsigned_cmp_op" (eq, ltu, leu) with CCUmode.

I believe you'll find that MODE_CC modes default to word size
already, so if you arrange for mov{cc,ccu} patterns, reload will
spill/reload these values as required and everything will Just Work.


r~