Use only nonvarying rtxs as known values

From-SVN: r40505

gcc/ChangeLog

@@ -25,6 +25,10 @@ Thu Mar 15 11:24:29 EST 2001  John Wehle  (john@feith.com)
 	* cselib.c (hash_rtx): For REG and MEM, just use value of expression
 	without adding in rtx code and mode.
 
+	* alias.c (init_alias_analysis): Don't use any rtx whose value
+	varies as a known value.
+	Delete a superfluous test.
+
 	* config/ia64/ia64.c (maybe_rotate): New function, broken out of
 	ia64_sched_reorder.
 	(ia64_sched_reorder): Call maybe_rotate; also rotate after

gcc/alias.c

@@ -2276,6 +2276,7 @@ init_alias_analysis ()
 			   && REG_N_SETS (regno) == 1)
 			  || (note = find_reg_note (insn, REG_EQUIV, NULL_RTX)) != 0)
 		      && GET_CODE (XEXP (note, 0)) != EXPR_LIST
+		      && ! rtx_varies_p (XEXP (note, 0), 1)
 		      && ! reg_overlap_mentioned_p (SET_DEST (set), XEXP (note, 0)))
 		    {
 		      reg_known_value[regno] = XEXP (note, 0);
@@ -2289,8 +2290,7 @@ init_alias_analysis ()
 			   && GET_CODE (XEXP (src, 1)) == CONST_INT)
 		    {
 		      rtx op0 = XEXP (src, 0);
-		      if (reg_known_value[REGNO (op0)])
-			op0 = reg_known_value[REGNO (op0)];
+		      op0 = reg_known_value[REGNO (op0)];
 		      reg_known_value[regno]
 			= plus_constant_for_output (op0,
 						    INTVAL (XEXP (src, 1)));