Re: splitting add instructions

["Paulo J. Matos" <pocmatos@gmail.com>]

On 18/07/11 17:53, Richard Henderson wrote:
>
> Otherwise, have a look at the mn10300 and rx ports.

What's the idea behind the rx port *_flags alternative define_insn?
For example:
(define_insn "abssi2"
   [(set (match_operand:SI         0 "register_operand" "=r,r")
         (abs:SI (match_operand:SI 1 "register_operand"  "0,r")))
    (clobber (reg:CC CC_REG))]
   ""
   "@
   abs\t%0
   abs\t%1, %0"
   [(set_attr "length" "2,3")]
)

(define_insn "*abssi2_flags"
   [(set (match_operand:SI         0 "register_operand" "=r,r")
         (abs:SI (match_operand:SI 1 "register_operand"  "0,r")))
    (set (reg CC_REG)
         (compare (abs:SI (match_dup 1))
                  (const_int 0)))]
   ;; Note - although the ABS instruction does set the O bit in the 
processor
   ;; status word, it does not do so in a way that is comparable with 
the CMP
   ;; instruction.  Hence we use CC_ZSmode rather than CC_ZSOmode.
   "reload_completed && rx_match_ccmode (insn, CC_ZSmode)"
   "@
   abs\t%0
   abs\t%1, %0"
   [(set_attr "length" "2,3")]
)

What's the point of the second define insn? The first insn seems to take 
us from expansion to asm generation so I can't see where the second one 
will come into play except in an expansion after reload but that doesn't 
happen, right?

-- 

PMatos