Re: RFA: Fix calculation of size of builtin setjmp buffer

[Eric Botcazou <ebotcazou@adacore.com>]

> Ah - you are worried about the case where STACK_SAVEAREA_MODE() is
> smaller than Pmode, yes ?

No, simply that the modified formula is plain wrong.  The code does:

  tmp = size_int (5 * BITS_PER_WORD / POINTER_SIZE - 1);
  tmp = build_index_type (tmp);
  tmp = build_array_type (ptr_type_node, tmp);

so, in the end, the size of the buffer is:

  [(5 * BITS_PER_WORD / POINTER_SIZE - 1) + 1] * POINTER_SIZE

which boilds down to:

  5 * BITS_PER_WORD

provided that POINTER_SIZE <= BITS_PER_WORD.


So we have a problem if POINTER_SIZE > BITS_PER_WORD, in which case it's 
sufficient to use 5 * POINTER_SIZE instead.

> OK then, how about this revised version of the patch where the size
> computation is now:
> 
>       tmp = size_int (MAX (GET_MODE_SIZE (STACK_SAVEAREA_MODE
> (SAVE_NONLOCAL))
> 			   / GET_MODE_SIZE (Pmode), 1)
> 		      + 2 /* Stack pointer and frame pointer.  */
> 		      + 1 /* Slop for mips.  */
> 		      - 1);
> 
> OK to apply ?

No, that's too complicated and risky, just do the following:

      /* builtin_setjmp takes a pointer to 5 words or pointers.  */
      if (POINTER_SIZE > BITS_PER_WORD)
	tmp = size_int (4);
      else
	tmp = size_int (5 * BITS_PER_WORD / POINTER_SIZE - 1);

which is simple and safe.

-- 
Eric Botcazou