fold-const.c (fold, [...]): When folding VAR++ == CONST or VAR-- == CONST…

fold-const.c (fold, [...]): When folding VAR++ == CONST or VAR-- == CONST construct a proper mask if...

        * fold-const.c (fold, case EQ_EXPR): When folding VAR++ == CONST
        or VAR-- == CONST construct a proper mask if VAR is a bitfield.
        Cope with CONST being out of range for the bitfield.

From-SVN: r20198

gcc/ChangeLog

+Tue Jun  2 22:50:10 1998  Andreas Schwab  <schwab@issan.informatik.uni-dortmund.de>
+
+	* fold-const.c (fold, case EQ_EXPR): When folding VAR++ == CONST
+	or VAR-- == CONST construct a proper mask if VAR is a bitfield.
+	Cope with CONST being out of range for the bitfield.
+
 Tue Jun  2 22:28:31 1998  Bernd Schmidt <crux@ohara.Informatik.RWTH-Aachen.DE>
 
 	* expr.c (emit_move_insn_1): When moving complex values in several

gcc/fold-const.c

@@ -5222,11 +5222,35 @@ fold (expr)
 		      = TREE_INT_CST_LOW (DECL_SIZE
 					  (TREE_OPERAND
 					   (TREE_OPERAND (varop, 0), 1)));
-
+		    tree mask, unsigned_type;
+		    int precision;
+		    tree folded_compare;
+
+		    /* First check whether the comparison would come out
+		       always the same.  If we don't do that we would
+		       change the meaning with the masking.  */
+		    if (constopnum == 0)
+		      folded_compare = fold (build (code, type, constop,
+						    TREE_OPERAND (varop, 0)));
+		    else
+		      folded_compare = fold (build (code, type,
+						    TREE_OPERAND (varop, 0),
+						    constop));
+		    if (integer_zerop (folded_compare)
+			|| integer_onep (folded_compare))
+		      return omit_one_operand (type, folded_compare, varop);
+
+		    unsigned_type = type_for_size (size, 1);
+		    precision = TYPE_PRECISION (unsigned_type);
+		    mask = build_int_2 (~0, ~0);
+		    TREE_TYPE (mask) = unsigned_type;
+		    force_fit_type (mask, 0);
+		    mask = const_binop (RSHIFT_EXPR, mask,
+					size_int (precision - size), 0);
 		    newconst = fold (build (BIT_AND_EXPR,
 					    TREE_TYPE (varop), newconst,
 					    convert (TREE_TYPE (varop),
-						     build_int_2 (size, 0))));
+						     mask)));
 		  }
 							 
 
@@ -5255,11 +5279,32 @@ fold (expr)
 		      = TREE_INT_CST_LOW (DECL_SIZE
 					  (TREE_OPERAND
 					   (TREE_OPERAND (varop, 0), 1)));
-
+		    tree mask, unsigned_type;
+		    int precision;
+		    tree folded_compare;
+
+		    if (constopnum == 0)
+		      folded_compare = fold (build (code, type, constop,
+						    TREE_OPERAND (varop, 0)));
+		    else
+		      folded_compare = fold (build (code, type,
+						    TREE_OPERAND (varop, 0),
+						    constop));
+		    if (integer_zerop (folded_compare)
+			|| integer_onep (folded_compare))
+		      return omit_one_operand (type, folded_compare, varop);
+
+		    unsigned_type = type_for_size (size, 1);
+		    precision = TYPE_PRECISION (unsigned_type);
+		    mask = build_int_2 (~0, ~0);
+		    TREE_TYPE (mask) = TREE_TYPE (varop);
+		    force_fit_type (mask, 0);
+		    mask = const_binop (RSHIFT_EXPR, mask,
+					size_int (precision - size), 0);
 		    newconst = fold (build (BIT_AND_EXPR,
 					    TREE_TYPE (varop), newconst,
 					    convert (TREE_TYPE (varop),
-						     build_int_2 (size, 0))));
+						     mask)));
 		  }