recog.c (split_insn): Consider attaching a REG_EQUAL note to the final insn of a split.

gcc/
	* recog.c (split_insn): Consider attaching a REG_EQUAL note to the
	final insn of a split.

From-SVN: r139802

gcc/ChangeLog

+2008-08-30  Richard Sandiford  <rdsandiford@googlemail.com>
+
+	* recog.c (split_insn): Consider attaching a REG_EQUAL note to the
+	final insn of a split.
+
 2008-08-30  Jan Hubicka  <jh@suse.cz>
 
 	* postreload-gcse.c (gate_handle_gcse2): Disable for functions

gcc/recog.c

@@ -2630,10 +2630,29 @@ split_insn (rtx insn)
   /* Split insns here to get max fine-grain parallelism.  */
   rtx first = PREV_INSN (insn);
   rtx last = try_split (PATTERN (insn), insn, 1);
+  rtx insn_set, last_set, note;
 
   if (last == insn)
     return NULL_RTX;
 
+  /* If the original instruction was a single set that was known to be
+     equivalent to a constant, see if we can say the same about the last
+     instruction in the split sequence.  The two instructions must set
+     the same destination.  */
+  insn_set = single_set (insn);
+  if (insn_set)
+    {
+      last_set = single_set (last);
+      if (last_set && rtx_equal_p (SET_DEST (last_set), SET_DEST (insn_set)))
+	{
+	  note = find_reg_equal_equiv_note (insn);
+	  if (note && CONSTANT_P (XEXP (note, 0)))
+	    set_unique_reg_note (last, REG_EQUAL, XEXP (note, 0));
+	  else if (CONSTANT_P (SET_SRC (insn_set)))
+	    set_unique_reg_note (last, REG_EQUAL, SET_SRC (insn_set));
+	}
+    }
+
   /* try_split returns the NOTE that INSN became.  */
   SET_INSN_DELETED (insn);
 
@@ -2651,6 +2670,7 @@ split_insn (rtx insn)
 	  first = NEXT_INSN (first);
 	}
     }
+
   return last;
 }