typeck.c (unary_complex_lvalue): Do not duplicate the argument to modify...

        * typeck.c (unary_complex_lvalue): Do not duplicate the
        argument to modify, pre-, or post-increment when used as an
        lvalue and when the argument has side-effects.

From-SVN: r43884

gcc/cp/ChangeLog

+2001-07-09  Erik Rozendaal  <dlr@acm.org>
+
+	* typeck.c (unary_complex_lvalue): Do not duplicate the
+	argument to modify, pre-, or post-increment when used as an
+	lvalue and when the argument has side-effects.
+
 2001-07-08  Joseph S. Myers  <jsm28@cam.ac.uk>
 
 	* decl.c (start_decl): Don't call SET_DEFAULT_DECL_ATTRIBUTES.

gcc/cp/typeck.c

@@ -4808,12 +4808,21 @@ unary_complex_lvalue (code, arg)
       || TREE_CODE (arg) == MIN_EXPR || TREE_CODE (arg) == MAX_EXPR)
     return rationalize_conditional_expr (code, arg);
 
+  /* Handle (a = b), (++a), and (--a) used as an "lvalue".  */
   if (TREE_CODE (arg) == MODIFY_EXPR
       || TREE_CODE (arg) == PREINCREMENT_EXPR
       || TREE_CODE (arg) == PREDECREMENT_EXPR)
+    {
+      tree lvalue = TREE_OPERAND (arg, 0);
+      if (TREE_SIDE_EFFECTS (lvalue))
+	{
+	  lvalue = stabilize_reference (lvalue);
+	  arg = build (TREE_CODE (arg), TREE_TYPE (arg),
+		       lvalue, TREE_OPERAND (arg, 1));
+	}
       return unary_complex_lvalue
-      (code, build (COMPOUND_EXPR, TREE_TYPE (TREE_OPERAND (arg, 0)),
-		    arg, TREE_OPERAND (arg, 0)));
+	(code, build (COMPOUND_EXPR, TREE_TYPE (lvalue), arg, lvalue));
+    }
 
   if (code != ADDR_EXPR)
     return 0;