Patch to warn about static initializers for zero length arrays

[Will Cohen <wcohen at redhat dot com>]

The following patch makes gcc print warnings for initializers of
zero length arrays as excess initializers.  This moves gcc toward
conforming with the C99 standard on flexible arrays (6.7.2.1).

	* extend.texi (Zero Length): State that static initializers for
	zero-length arrays are not allowed.

	* c-typeck.c (process_init_element): Flag initializers for zero
	length arrays.

	* tree.c (integer_all_onesp): Ignore TREE_INT_CST_HIGH if prec is
	exactly HOST_BITS_PERWIDE_INT.

I have also attached a file, zerolength.c, which demonstrates gcc
warning about the initializer.  Assuming that the patch is installed
the following messages should be generated:

bash$ native/gcc/xgcc -Bnative/gcc/ -c zerolength.c
zerolength.c:20: warning: excess elements in array initializer
zerolength.c:20: warning: (near initialization for `playbook.Play')


-Will Cohen
Index: tree.c
===================================================================
RCS file: /cvs/gcc/egcs/gcc/tree.c,v
retrieving revision 1.159
diff -c -2 -p -r1.159 tree.c
*** tree.c	2000/09/17 07:38:12	1.159
--- tree.c	2000/09/18 14:57:14
*************** integer_all_onesp (expr)
*** 1683,1686 ****
--- 1683,1692 ----
       actual bits, not the (arbitrary) range of the type.  */
    prec = GET_MODE_BITSIZE (TYPE_MODE (TREE_TYPE (expr)));
+ 
+   /* Shifting by the host word size is undefined according to the ANSI
+      standard, so we must handle this as a special case.  */
+   if (prec == HOST_BITS_PER_WIDE_INT)
+     return TREE_INT_CST_LOW (expr) == ~ (unsigned HOST_WIDE_INT) 0;
+   
    if (prec >= HOST_BITS_PER_WIDE_INT)
      {
Index: c-typeck.c
===================================================================
RCS file: /cvs/gcc/egcs/gcc/c-typeck.c,v
retrieving revision 1.90
diff -c -2 -p -r1.90 c-typeck.c
*** c-typeck.c	2000/09/18 05:02:11	1.90
--- c-typeck.c	2000/09/18 14:57:16
*************** process_init_element (value)
*** 6461,6465 ****
  
  	  if (constructor_max_index != 0
! 	      && tree_int_cst_lt (constructor_max_index, constructor_index))
  	    {
  	      pedwarn_init ("excess elements in array initializer");
--- 6461,6466 ----
  
  	  if (constructor_max_index != 0
! 	      && (tree_int_cst_lt (constructor_max_index, constructor_index)
! 		  || integer_all_onesp (constructor_max_index)))
  	    {
  	      pedwarn_init ("excess elements in array initializer");
Index: extend.texi
===================================================================
RCS file: /cvs/gcc/egcs/gcc/extend.texi,v
retrieving revision 1.63
diff -c -2 -p -r1.63 extend.texi
*** extend.texi	2000/09/06 21:24:56	1.63
--- extend.texi	2000/09/18 14:57:18
*************** In standard C, you would have to give @c
*** 890,893 ****
--- 890,897 ----
  means either you waste space or complicate the argument to @code{malloc}.
  
+ Static initialization of the zero-length array is not allowed.  A
+ warning will be generated for each initializer attempting to initialize
+ the zero-length array.
+ 
  @node Variable Length
  @section Arrays of Variable Length
/* zerolength.c */

struct PDATA
{
    unsigned int  Dummy:32;
    const char*   PName;
};

typedef struct PDATA    P_DATA;

struct PLAYBOOK {
        const char * BookName;
        P_DATA       Play[0];
};

struct PLAYBOOK playbook  =
{
  "BookName",
  {
    { 1, "PName0" },
  }
};