Re: Fix to mn10300 cmpsi pattern

[Matt Hiller <hiller at redhat dot com>]

On 27 Mar 2001, Alexandre Oliva wrote:

> > but %0 could be an address or extended register.  How about btst
> > 0,d0 instead?
> 
> Should be fine, with some comments explaining why it sets the flags
> correctly and why the actual register doesn't matter.  Using a data
> register will in fact generate smaller code than using the
> extended-register version of btst introduced in AM33.

	Okay. How's this?

Index: gcc/config/mn10300/mn10300.md
===================================================================
RCS file: /cvs/gcc/egcs/gcc/config/mn10300/mn10300.md,v
retrieving revision 1.38
diff -c -r1.38 mn10300.md
*** gcc/config/mn10300/mn10300.md	2000/12/06 03:56:43	1.38
--- gcc/config/mn10300/mn10300.md	2001/03/28 01:54:13
***************
*** 709,723 ****
    "* return output_tst (operands[0], insn);"
    [(set_attr "cc" "set_znv")])
  
  (define_insn "cmpsi"
    [(set (cc0)
  	(compare (match_operand:SI 0 "register_operand" "!*d*a*x,dax")
  		 (match_operand:SI 1 "nonmemory_operand" "!*0,daxi")))]
    ""
    "@
!   add 0,%0
    cmp %1,%0"
!   [(set_attr "cc" "invert,compare")])
  
  ;; ----------------------------------------------------------------------
  ;; ADD INSTRUCTIONS
--- 709,731 ----
    "* return output_tst (operands[0], insn);"
    [(set_attr "cc" "set_znv")])
  
+ ;; Ordinarily, the cmp instruction will set the Z bit of cc0 to 1 if
+ ;; its operands hold equal values, but the operands of a cmp
+ ;; instruction must be distinct registers.  In the case where we'd
+ ;; like to compare a register to itself, we can achieve this effect
+ ;; with a btst 0,d0 instead.  (This will not alter the contents of d0
+ ;; but will have the proper effect on cc0.  Using d0 is arbitrary; any
+ ;; data register would work.)
+ 
  (define_insn "cmpsi"
    [(set (cc0)
  	(compare (match_operand:SI 0 "register_operand" "!*d*a*x,dax")
  		 (match_operand:SI 1 "nonmemory_operand" "!*0,daxi")))]
    ""
    "@
!   btst 0,d0
    cmp %1,%0"
!   [(set_attr "cc" "compare,compare")])
  
  ;; ----------------------------------------------------------------------
  ;; ADD INSTRUCTIONS