re PR debug/42728 ("-fcompare-debug failure (length)" at -O1)

	PR debug/42728
	* fwprop.c (all_uses_available_at): Return false if def_set dest
	is a REG that is used in def_insn.

	* gcc.dg/pr42728.c: New test.

From-SVN: r156037

gcc/ChangeLog

+2010-01-19  Jakub Jelinek  <jakub@redhat.com>
+
+	PR debug/42728
+	* fwprop.c (all_uses_available_at): Return false if def_set dest
+	is a REG that is used in def_insn.
+
 2010-01-19  Joern Rennecke  <amylaar@spamcop.net>
 
 	* doc/tm.texi (TARGET_FIXED_CONDITION_CODE_REGS): Add argument names.

gcc/fwprop.c

@@ -818,17 +818,23 @@ all_uses_available_at (rtx def_insn, rtx target_insn)
     }
   else
     {
+      rtx def_reg = REG_P (SET_DEST (def_set)) ? SET_DEST (def_set) : NULL_RTX;
+
       /* Look at all the uses of DEF_INSN, and see if they are not
 	 killed between DEF_INSN and TARGET_INSN.  */
       for (use_rec = DF_INSN_INFO_USES (insn_info); *use_rec; use_rec++)
 	{
 	  df_ref use = *use_rec;
+	  if (def_reg && rtx_equal_p (DF_REF_REG (use), def_reg))
+	    return false;
 	  if (use_killed_between (use, def_insn, target_insn))
 	    return false;
 	}
       for (use_rec = DF_INSN_INFO_EQ_USES (insn_info); *use_rec; use_rec++)
 	{
 	  df_ref use = *use_rec;
+	  if (def_reg && rtx_equal_p (DF_REF_REG (use), def_reg))
+	    return false;
 	  if (use_killed_between (use, def_insn, target_insn))
 	    return false;
 	}

gcc/testsuite/ChangeLog

+2010-01-19  Jakub Jelinek  <jakub@redhat.com>
+
+	PR debug/42728
+	* gcc.dg/pr42728.c: New test.
+
 2010-01-19  Anthony Green  <green@moxielogic.com>
 
 	* gcc.dg/tree-ssa/20040204-1.c: Expect this test to pass.

gcc/testsuite/gcc.dg/pr42728.c

+/* PR debug/42728 */
+/* { dg-do compile } */
+/* { dg-options "-O1 -fcompare-debug" } */
+
+void
+foo (char *a)
+{
+  char *b;
+  for (; *a; a++)
+    a = b++;
+}