[PATCH][PR target/19201] Peephole to improve clearing items in structure for m68k

[PATCH][PR target/19201] Peephole to improve clearing items in structure for m68k
	* config/m68k/m68k.md (load feeding clear byte): New peephole2.

	* gcc.target/m68k/pr19201.c: New test.

From-SVN: r231597

gcc/ChangeLog

+2015-12-13  Kazu Kirata  <kazu@gcc.gnu.org>
+
+	* config/m68k/m68k.md (load feeding clear byte): New peephole2.
+
 2015-12-13  Tom de Vries  <tom@codesourcery.com>
 
 	* tree-ssa-structalias.c (find_func_clobbers): Handle sizes and kinds

gcc/config/m68k/m68k.md

@@ -7601,3 +7601,36 @@
 
 (include "cf.md")
 (include "sync.md")
+
+;; Convert
+;;
+;; 	move.l 4(%a0),%a0
+;; 	clr.b (%a0,%a1.l)
+;;
+;; into
+;;
+;; 	add.l 4(%a0),%a1
+;; 	clr.b (%a1)
+;;
+;; The latter is smaller.  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))]
+  "(optimize_size || !TUNE_68060)
+   && (operands[0] == operands[3] || operands[0] == operands[4])
+   && ADDRESS_REG_P (operands[1])
+   && ADDRESS_REG_P ((operands[0] == operands[3]) ? operands[4] : operands[3])
+   && 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];")

gcc/testsuite/ChangeLog

 2015-12-13  Jeff Law  <law@redhat.com>
 
+	* gcc.target/m68k/pr19201.c: New test.
+
 	* gcc.target/m68k/pr63347.c: Remove #include <stdlib> add -w to
 	command line options.
 	* gcc.target/m68k/20090709-1.c: Adjust expected output.

gcc/testsuite/gcc.target/m68k/pr19201.c

+/* { dg-options "-w -O2 -fomit-frame-pointer" } */
+/* { dg-final { scan-assembler-not "%a.,%\[ad\]..l" } } */
+
+struct X { 
+  char *a; 
+  /* other members */ 
+  int b; 
+}; 
+ 
+void f (struct X *x) 
+{ 
+  x->a[x->b] = 0; 
+}