internal error --insn does not satisfy its constraints

[pogde prashant <pogde at cse dot iitk dot ac dot in>]

Hii
	I tried to port gcc to 8085.
	but the resulting compiler is crashing giving the error message

	/*________________________________*/
	hello.c: In function `main':
	hello.c:4: internal error--insn does not satisfy its constraints:
	(insn 21 19 11 (set (mem:QI (reg:HI 1 B))
      	  	(reg:QI 0 A)) 2 {movqi+1} (nil)
    		(nil))
	xgcc: Internal compiler error: program cc1 got fatal signal 6
	/*________________________________*/
	
	I m not able to find out the error as i have a pattern
	in my md file which matches this intermediate code pointed
	by the above error message.
	i have a pattern
	(define_insn ""
 		 [(set (match_operand:QI 0 "indirect_operand" "=m")
        	(match_operand:QI 1 "register_operand"  "a"))]
  	""
  	"Stax %0"
	)
	defined in my md file.
	the constraint "a" specifies that the register should be
	"A"(accum).and i have checked the intermediate rtl dumps
	after gloabal register allocation and in insn 21 second operand is 
	allocated "A" register.
	also BC register pair is valid for indirect addressing.
	So I m not able to understand why is it giving error
	message
	"internal error--insn does not satisfy its constraints:"
		when both the constraints are satisfied by
	this pattern in md file.		

regards
prashant