loop-iv.c (suitable_set_for_replacement): Renamed from simplify_using_assignment...

	* loop-iv.c (suitable_set_for_replacement): Renamed from
	simplify_using_assignment; changed to return bool and to accept new
	args DEST and SRC.  Return true iff we find a source/destination pair
	that can be used to make a replacement, and fill SRC and DEST if so.
	Remove arg ALTERED.  Don't deal with altered regs here.  All callers
	changed.
	(simplify_using_initial_values): Deal with altered regs here and track
	more precisely the effect they have on the validity of our expression.

From-SVN: r145351

gcc/ChangeLog

+2009-03-31  Bernd Schmidt  <bernd.schmidt@analog.com>
+
+	* loop-iv.c (suitable_set_for_replacement): Renamed from
+	simplify_using_assignment; changed to return bool and to accept new
+	args DEST and SRC.  Return true iff we find a source/destination pair
+	that can be used to make a replacement, and fill SRC and DEST if so.
+	Remove arg ALTERED.  Don't deal with altered regs here.  All callers
+	changed.
+	(simplify_using_initial_values): Deal with altered regs here and track
+	more precisely the effect they have on the validity of our expression.
+
 2009-03-31  Ramana Radhakrishnan  <ramana.radhakrishnan@arm.com>
 
         PR target/27237

gcc/loop-iv.c

@@ -1364,39 +1364,23 @@ simple_rhs_p (rtx rhs)
     }
 }
 
-/* Simplifies *EXPR using assignment in INSN.  ALTERED is the set of registers
-   altered so far.  */
+/* A subroutine of simplify_using_initial_values, this function examines INSN
+   to see if it contains a suitable set that we can use to make a replacement.
+   If it is suitable, return true and set DEST and SRC to the lhs and rhs of
+   the set; return false otherwise.  */
 
-static void
-simplify_using_assignment (rtx insn, rtx *expr, regset altered)
+static bool
+suitable_set_for_replacement (rtx insn, rtx *dest, rtx *src)
 {
   rtx set = single_set (insn);
   rtx lhs = NULL_RTX, rhs;
-  bool ret = false;
 
-  if (set)
-    {
-      lhs = SET_DEST (set);
-      if (!REG_P (lhs)
-	  || altered_reg_used (&lhs, altered))
-	ret = true;
-    }
-  else
-    ret = true;
-
-  note_stores (PATTERN (insn), mark_altered, altered);
-  if (CALL_P (insn))
-    {
-      int i;
-
-      /* Kill all call clobbered registers.  */
-      for (i = 0; i < FIRST_PSEUDO_REGISTER; i++)
-	if (TEST_HARD_REG_BIT (regs_invalidated_by_call, i))
-	  SET_REGNO_REG_SET (altered, i);
-    }
+  if (!set)
+    return false;
 
-  if (ret)
-    return;
+  lhs = SET_DEST (set);
+  if (!REG_P (lhs))
+    return false;
 
   rhs = find_reg_equal_equiv_note (insn);
   if (rhs)
@@ -1405,12 +1389,11 @@ simplify_using_assignment (rtx insn, rtx *expr, regset altered)
     rhs = SET_SRC (set);
 
   if (!simple_rhs_p (rhs))
-    return;
-
-  if (for_each_rtx (&rhs, altered_reg_used, altered))
-    return;
+    return false;
 
-  *expr = simplify_replace_rtx (*expr, lhs, rhs);
+  *dest = lhs;
+  *src = rhs;
+  return true;
 }
 
 /* Checks whether A implies B.  */
@@ -1762,9 +1745,10 @@ eliminate_implied_conditions (enum rtx_code op, rtx *head, rtx tail)
 static void
 simplify_using_initial_values (struct loop *loop, enum rtx_code op, rtx *expr)
 {
-  rtx head, tail, insn;
+  bool expression_valid;
+  rtx head, tail, insn, last_valid_expr;
   rtx neutral, aggr;
-  regset altered;
+  regset altered, this_altered;
   edge e;
 
   if (!*expr)
@@ -1829,7 +1813,10 @@ simplify_using_initial_values (struct loop *loop, enum rtx_code op, rtx *expr)
     return;
 
   altered = ALLOC_REG_SET (&reg_obstack);
+  this_altered = ALLOC_REG_SET (&reg_obstack);
 
+  expression_valid = true;
+  last_valid_expr = *expr;
   while (1)
     {
       insn = BB_END (e->src);
@@ -1843,29 +1830,52 @@ simplify_using_initial_values (struct loop *loop, enum rtx_code op, rtx *expr)
 	    {
 	      simplify_using_condition (cond, expr, altered);
 	      if (CONSTANT_P (*expr))
-		{
-		  FREE_REG_SET (altered);
-		  return;
-		}
+		goto out;
 	    }
 	}
 
       FOR_BB_INSNS_REVERSE (e->src, insn)
 	{
+	  rtx src, dest;
+
 	  if (!INSN_P (insn))
 	    continue;
-	    
-	  simplify_using_assignment (insn, expr, altered);
-	  if (CONSTANT_P (*expr))
+
+	  CLEAR_REG_SET (this_altered);
+	  note_stores (PATTERN (insn), mark_altered, this_altered);
+	  if (CALL_P (insn))
 	    {
-	      FREE_REG_SET (altered);
-	      return;
+	      int i;
+		  
+	      /* Kill all call clobbered registers.  */
+	      for (i = 0; i < FIRST_PSEUDO_REGISTER; i++)
+		if (TEST_HARD_REG_BIT (regs_invalidated_by_call, i))
+		  SET_REGNO_REG_SET (this_altered, i);
 	    }
-	  if (for_each_rtx (expr, altered_reg_used, altered))
+
+	  if (suitable_set_for_replacement (insn, &dest, &src))
 	    {
-	      FREE_REG_SET (altered);
-	      return;
+	      *expr = simplify_replace_rtx (*expr, dest, src);
+	      if (CONSTANT_P (*expr))
+		goto out;
 	    }
+	  else
+	    /* If we did not use this insn to make a replacement, any overlap
+	       between stores in this insn and our expression will cause the
+	       expression to become invalid.  */
+	    if (for_each_rtx (expr, altered_reg_used, this_altered))
+	      goto out;
+
+	  IOR_REG_SET (altered, this_altered);
+
+	  /* If the expression now contains regs that have been altered, we
+	     can't return it to the caller.  However, it is still valid for
+	     further simplification, so keep searching to see if we can
+	     eventually turn it into a constant.  */
+	  if (for_each_rtx (expr, altered_reg_used, altered))
+	    expression_valid = false;
+	  if (expression_valid)
+	    last_valid_expr = *expr;
 	}
 
       if (!single_pred_p (e->src)
@@ -1874,7 +1884,11 @@ simplify_using_initial_values (struct loop *loop, enum rtx_code op, rtx *expr)
       e = single_pred_edge (e->src);
     }
 
+ out:
+  if (!CONSTANT_P (*expr))
+    *expr = last_valid_expr;
   FREE_REG_SET (altered);
+  FREE_REG_SET (this_altered);
 }
 
 /* Transforms invariant IV into MODE.  Adds assumptions based on the fact