re PR rtl-optimization/34773 (miscompilation of vfprintf_r)

	PR rtl-optimization/34773
	* reg-notes.def (EQUAL): Mention significance of combination of
	REG_EQUAL and REG_RETVAL.
	* fwprop.c (try_fwprop_subst): Don't add REG_EQUAL to an
	insn that has a REG_RETVAL.

From-SVN: r132053

gcc/ChangeLog

+2008-02-01  Hans-Peter Nilsson  <hp@axis.com>
+
+	PR rtl-optimization/34773
+	* reg-notes.def (EQUAL): Mention significance of combination of
+	REG_EQUAL and REG_RETVAL.
+	* fwprop.c (try_fwprop_subst): Don't add REG_EQUAL to an
+	insn that has a REG_RETVAL.
+
 2008-02-01  Roger Sayle  <roger@eyesopen.com>
 
 	PR bootstrap/33781

gcc/fwprop.c

@@ -729,9 +729,12 @@ try_fwprop_subst (struct df_ref *use, rtx *loc, rtx new, rtx def_insn, bool set_
     {
       cancel_changes (0);
 
-      /* Can also record a simplified value in a REG_EQUAL note, making a
-	 new one if one does not already exist.  */
-      if (set_reg_equal)
+      /* Can also record a simplified value in a REG_EQUAL note,
+	 making a new one if one does not already exist.
+	 Don't do this if the insn has a REG_RETVAL note, because the
+	 combined presence means that the REG_EQUAL note refers to the
+	 (full) contents of the libcall value.  */
+      if (set_reg_equal && !find_reg_note (insn, REG_RETVAL, NULL_RTX))
 	{
 	  if (dump_file)
 	    fprintf (dump_file, " Setting REG_EQUAL note\n");

gcc/reg-notes.def

@@ -52,7 +52,9 @@ REG_NOTE (EQUIV)
 
 /* Like REG_EQUIV except that the destination is only momentarily
    equal to the specified rtx.  Therefore, it cannot be used for
-   substitution; but it can be used for cse.  */
+   substitution; but it can be used for cse.  Together with a
+   REG_RETVAL note, it means that the insn sets the full contents of
+   the libcall value.  */
 REG_NOTE (EQUAL)
 
 /* This insn copies the return-value of a library call out of the hard