Porting GCC: Compare-and-Branch-Instructions

[Prashant Pogde]

Hi,

	U can write something like ::

first in "config/i8051.h"
	extern struct rtx_def *i8051_compare_op0;    /* operand 0 for comparisons */
	extern struct rtx_def *i8051_compare_op1;    /* operand 1 for comparisons */

	then in md file :
	NOTE here i m replacing define_insn with define_expand.


(define_expand "cmpqi"
  [(set (cc0) (compare (match_operand:QI 0 "register_operand" "%a,a")
                       (match_operand:QI 1 "nonmemory_operand" "r,i")))]

  ""
  "*
  {
	i8051_compare_op0 = operands[0];
	i8051_compare_op1 = operands[1];
	DONE;
  }")

(define_insn "beq"
  [(set (pc)
   (if_then_else (lt (cc0)
                     (const_int 0))
                 (label_ref (match_operand 0 "" ""))
                 (pc)))]
  ""
  "*
  {
	;; here u can emit instruction CJNE with operands 
	;; i8051_compare_op0, i8051_compare_op1 & operands[0] according
	;;	to ur assembly syntax for it.
	
  }")


>Or do you know another GCC Target Machine that works this way so that I
>can read its machine description ?
	I don't know exactly where u can find similar instructions, 
	but i got this idea from i386.md.

	well I too am new to gcc backend,and i m not sure if it will work :)
	but u can try it.

regards
prashant


     -----==-                                Prashant Pogde
      ----==-- _                             Graduate Student
      ---==---(_)__  __ ____  __             Deptt. of Computer Sc. & Engg. 
      --==---/ / _ \/ // /\ \/ /             IIT Kanpur -208016 
      -=====/_/_//_/_,_/ /_/_\      	     e-mail: pogde@cse.iitk.ac.in 
    The choice of a GNU generation           phone : (0512) 597653