On 04/05/12 19:48, Ian Lance Taylor wrote:
The i386 rep_movqi insn is an example:
(define_insn "*rep_movqi"
[(set (match_operand:P 2 "register_operand" "=c") (const_int 0))
(set (match_operand:P 0 "register_operand" "=D")
(plus:P (match_operand:P 3 "register_operand" "0")
(match_operand:P 5 "register_operand" "2")))
(set (match_operand:P 1 "register_operand" "=S")
(plus:P (match_operand:P 4 "register_operand" "1") (match_dup 5)))
(set (mem:BLK (match_dup 3))
(mem:BLK (match_dup 4)))
(use (match_dup 5))]
"!(fixed_regs[CX_REG] || fixed_regs[SI_REG] || fixed_regs[DI_REG])"
"%^rep{%;} movsb"
[(set_attr "type" "str")
(set_attr "prefix_rep" "1")
(set_attr "memory" "both")
(set_attr "mode" "QI")])
Thanks for the discussion on this which was enlightening.
The rep_movqi rule seems scarily like our block copy instruction.
By looking at it, the question that arises is, why the (use (match_dup
5))? I thought this was used to tell gcc that an operand was going to be
used in a way not specified by the rtl but operand 5 is specified
elsewhere in the rtl so gcc doesn't seem to need that (use ...) rule. Is
this redundant or not?
--
PMatos
