fold-const.c (fold_truthop): Mask the lhs and rhs after merging adjacent bitfield references.

        * fold-const.c (fold_truthop): Mask the lhs and rhs after merging
        adjacent bitfield references.

From-SVN: r26004

gcc/ChangeLog

@@ -65,6 +65,9 @@ Fri Mar 26 10:43:47 1999  Nick Clifton  <nickc@cygnus.com>
 
 Fri Mar 26 01:59:15 1999  "Charles M. Hannum" <root@ihack.net>
 
+	* fold-const.c (fold_truthop): Mask the lhs and rhs after merging
+	adjacent bitfield references. 
+
 	* fold-const.c (fold_truthop): Verify that the lhs and rhs are
 	in the same bit position when optimizing bitfield references
 	which have the same mask.

gcc/fold-const.c

@@ -3956,20 +3956,32 @@ fold_truthop (code, truth_type, lhs, rhs)
 
       /* There is still another way we can do something:  If both pairs of
 	 fields being compared are adjacent, we may be able to make a wider
-	 field containing them both.  */
+	 field containing them both.
+
+	 Note that we still must mask the lhs/rhs expressions.  Furthermore,
+	 the mask must be shifted to account for the shift done by 
+	 make_bit_field_ref.  */
       if ((ll_bitsize + ll_bitpos == rl_bitpos
 	   && lr_bitsize + lr_bitpos == rr_bitpos)
 	  || (ll_bitpos == rl_bitpos + rl_bitsize
 	      && lr_bitpos == rr_bitpos + rr_bitsize))
-	return build (wanted_code, truth_type,
-		      make_bit_field_ref (ll_inner, type,
-					  ll_bitsize + rl_bitsize,
-					  MIN (ll_bitpos, rl_bitpos),
-					  ll_unsignedp),
-		      make_bit_field_ref (lr_inner, type,
-					  lr_bitsize + rr_bitsize,
-					  MIN (lr_bitpos, rr_bitpos),
-					  lr_unsignedp));
+	{
+	  lhs = make_bit_field_ref (ll_inner, type, ll_bitsize + rl_bitsize,
+				    MIN (ll_bitpos, rl_bitpos), ll_unsignedp);
+	  ll_mask = const_binop (RSHIFT_EXPR, ll_mask,
+				 size_int (MIN (xll_bitpos, xrl_bitpos)), 0);
+	  if (! all_ones_mask_p (ll_mask, ll_bitsize + rl_bitsize))
+	    lhs = build (BIT_AND_EXPR, type, lhs, ll_mask);
+
+	  rhs = make_bit_field_ref (lr_inner, type, lr_bitsize + rr_bitsize,
+				    MIN (lr_bitpos, rr_bitpos), lr_unsignedp);
+	  lr_mask = const_binop (RSHIFT_EXPR, lr_mask,
+				 size_int (MIN (xlr_bitpos, xrr_bitpos)), 0);
+	  if (! all_ones_mask_p (lr_mask, lr_bitsize + rr_bitsize))
+	    rhs = build (BIT_AND_EXPR, type, rhs, lr_mask);
+
+	  return build (wanted_code, truth_type, lhs, rhs);
+	}
 
       return 0;
     }