Re: value computed is not used warnings

[Richard Henderson <rth at cygnus dot com>]

On Tue, Sep 19, 2000 at 02:02:37AM -0700, Mark Mitchell wrote:
> Actually, I think maybe the right fix is to have warn_if_unused_value
> ignore `void' expressions.  It already tries hard to avoid things that
> are explicitly cast to `void' and functions that return `void', but it
> doesn't deal with values that are magically `void' like a `void'
> STMT_EXPR.  Does that sound like a better fix?

Yes.


r~


        * stmt.c (expand_expr_stmt): Only call warn_if_unused_value
        if the tree has side effects.
        (warn_if_unused_value): Do not warn about void constructs.

Index: stmt.c
===================================================================
RCS file: /cvs/gcc/egcs/gcc/stmt.c,v
retrieving revision 1.168
diff -c -p -d -r1.168 stmt.c
*** stmt.c	2000/09/17 12:45:51	1.168
--- stmt.c	2000/09/19 13:36:50
*************** expand_expr_stmt (exp)
*** 1908,1919 ****
       except inside a ({...}) where they may be useful.  */
    if (expr_stmts_for_value == 0 && exp != error_mark_node)
      {
!       if (! TREE_SIDE_EFFECTS (exp)
! 	  && (extra_warnings || warn_unused_value)
! 	  && !(TREE_CODE (exp) == CONVERT_EXPR
! 	       && VOID_TYPE_P (TREE_TYPE (exp))))
! 	warning_with_file_and_line (emit_filename, emit_lineno,
! 				    "statement with no effect");
        else if (warn_unused_value)
  	warn_if_unused_value (exp);
      }
--- 1908,1921 ----
       except inside a ({...}) where they may be useful.  */
    if (expr_stmts_for_value == 0 && exp != error_mark_node)
      {
!       if (! TREE_SIDE_EFFECTS (exp))
! 	{
! 	  if ((extra_warnings || warn_unused_value)
! 	      && !(TREE_CODE (exp) == CONVERT_EXPR
! 		   && VOID_TYPE_P (TREE_TYPE (exp))))
! 	    warning_with_file_and_line (emit_filename, emit_lineno,
! 				        "statement with no effect");
! 	}
        else if (warn_unused_value)
  	warn_if_unused_value (exp);
      }
*************** warn_if_unused_value (exp)
*** 1978,1983 ****
--- 1980,1991 ----
    if (TREE_USED (exp))
      return 0;
  
+   /* Don't warn about void constructs.  This includes casting to void,
+      void function calls, and statement expressions with a final cast
+      to void.  */
+   if (VOID_TYPE_P (TREE_TYPE (exp)))
+     return 0;
+ 
    switch (TREE_CODE (exp))
      {
      case PREINCREMENT_EXPR:
*************** warn_if_unused_value (exp)
*** 2023,2031 ****
      case NOP_EXPR:
      case CONVERT_EXPR:
      case NON_LVALUE_EXPR:
-       /* Don't warn about values cast to void.  */
-       if (VOID_TYPE_P (TREE_TYPE (exp)))
- 	return 0;
        /* Don't warn about conversions not explicit in the user's program.  */
        if (TREE_NO_UNUSED_WARNING (exp))
  	return 0;
--- 2031,2036 ----