re PR rtl-optimization/47763 (Useless initialization of register)

	PR rtl-optimization/47763
	* web.c (web_main): Ignore naked clobber when replacing register.

	testsuite/
	PR rtl-optimization/47763
	* gcc.dg/pr47763.c: New test.

From-SVN: r170422

gcc/ChangeLog

+2011-02-23  Jie Zhang  <jie@codesourcery.com>
+
+	PR rtl-optimization/47763
+	* web.c (web_main): Ignore naked clobber when replacing register.
+
 2011-02-22  Anatoly Sokolov  <aesok@post.ru>
 
 	* config/stormy16/stormy16.h (REG_OK_FOR_BASE_P, REG_OK_FOR_INDEX_P):

gcc/testsuite/ChangeLog

+2011-02-23  Jie Zhang  <jie@codesourcery.com>
+
+	PR rtl-optimization/47763
+	* gcc.dg/pr47763.c: New test.
+
 2011-02-22  Paul Thomas  <pault@gcc.gnu.org>
 
 	PR fortran/45743

gcc/testsuite/gcc.dg/pr47763.c

+/* { dg-do compile } */
+/* { dg-options "-O2 -funroll-loops -fdump-rtl-web" } */
+
+foo()
+{
+}
+
+/* { dg-final { scan-rtl-dump-not "Web oldreg" "web" } } */
+/* { dg-final { cleanup-rtl-dump "web" } } */

gcc/web.c

@@ -377,7 +377,17 @@ web_main (void)
     FOR_BB_INSNS (bb, insn)
     {
       unsigned int uid = INSN_UID (insn);
-      if (NONDEBUG_INSN_P (insn))
+
+      if (NONDEBUG_INSN_P (insn)
+	  /* Ignore naked clobber.  For example, reg 134 in the second insn
+	     of the following sequence will not be replaced.
+
+	       (insn (clobber (reg:SI 134)))
+
+	       (insn (set (reg:SI 0 r0) (reg:SI 134)))
+
+	     Thus the later passes can optimize them away.  */
+	  && GET_CODE (PATTERN (insn)) != CLOBBER)
 	{
 	  df_ref *use_rec;
 	  df_ref *def_rec;