[patch] m68k: Fix PR target/19201.

[Kazu Hirata]

Hi,

Attached is a patch to fix PR target/19201.

Consider:

struct X { 
  char *a; 
  int b; 
}; 
 
void
f (struct X *x) 
{ 
  x->a[x->b] = 0; 
} 

m68k-elf-gcc -O2 -fomit-frame-pointer generates:

f:
        move.l 4(%sp),%a0
        move.l (%a0),%a1
        move.l 4(%a0),%a0
        clr.b (%a0,%a1.l)
        rts

With this patch,

f:
        move.l 4(%sp),%a0
        move.l (%a0),%a1
        add.l 4(%a0),%a1
        clr.b (%a1)
        rts

The patch performs this transformation with peephole2.

Tested on m68k.  OK to apply?

Kazu Hirata

2005-11-28  Kazu Hirata  <kazu@codesourcery.com>

	* config/m68k/m68k.md (a peephole2): New.
	* config/m68k/predicates.md (address_register_operand): Likewise.

Index: config/m68k/m68k.md
===================================================================
--- config/m68k/m68k.md	(revision 107541)
+++ config/m68k/m68k.md	(working copy)
@@ -7092,3 +7092,40 @@ (define_insn "conditional_trap"
   default: gcc_unreachable ();
   }
 })
+
+; Convert
+;
+; 	move.l 4(%a0),%a0
+; 	clr.b (%a0,%a1.l)
+;
+; into
+;
+; 	add.l 4(%a0),%a1
+; 	clr.b (%a1)
+;
+; The latter is shorter.  It is faster on all models except m68060.
+
+(define_peephole2
+  [(set (match_operand:SI 0 "register_operand" "")
+	(mem:SI (plus:SI (match_operand:SI 1 "register_operand" "")
+			 (match_operand:SI 2 "const_int_operand" ""))))
+   (set (mem:QI (plus:SI (match_operand:SI 3 "register_operand" "")
+			 (match_operand:SI 4 "register_operand" "")))
+	(const_int 0))]
+  "/* We'll always win in terms of size.  We don't win on mc68060 in
+      terms of performance.  */
+   (optimize_size || !TARGET_68060)
+   /* Make sure operands[5] will be an address register.  */
+   && ((operands[0] == operands[3]
+        && address_register_operand (operands[4], SImode))
+       || (operands[0] == operands[4]
+           && address_register_operand (operands[3], SImode)))
+   && peep2_reg_dead_p (2, operands[3])
+   && peep2_reg_dead_p (2, operands[4])"
+  [(set (match_dup 5)
+	(plus:SI (match_dup 5)
+		 (mem:SI (plus:SI (match_dup 1)
+				  (match_dup 2)))))
+   (set (mem:QI (match_dup 5))
+	(const_int 0))]
+  "operands[5] = (operands[0] == operands[3]) ? operands[4] : operands[3];")
Index: config/m68k/predicates.md
===================================================================
--- config/m68k/predicates.md	(revision 107541)
+++ config/m68k/predicates.md	(working copy)
@@ -170,3 +170,9 @@ (define_predicate "post_inc_operand"
 (define_predicate "pre_dec_operand"
   (and (match_code "mem")
        (match_test "GET_CODE (XEXP (op, 0)) == PRE_DEC")))
+
+;; Accept an address register operand.
+
+(define_predicate "address_register_operand"
+  (and (match_code "reg")
+       (match_test "ADDRESS_REG_P (op)")))