[Bug lto/79062] -Walloca-larger-than and -Wformat-overflow warnings disabled by -flto

[bernd.edlinger at hotmail dot de]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=79062

Bernd Edlinger <bernd.edlinger at hotmail dot de> changed:

           What    |Removed                     |Added
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                 CC|                            |bernd.edlinger at hotmail dot de

--- Comment #5 from Bernd Edlinger <bernd.edlinger at hotmail dot de> ---
(In reply to Martin Sebor from comment #3)
> The following allows the format string to be recognized even with LTO.  The
> sprintf pass runs and seems to work correctly, but warnings from it for some
> reason do not appear on output.  It's as if they were disabled.  I'm not
> sure what's causing that.
> 
> diff --git a/gcc/gimple-ssa-sprintf.c b/gcc/gimple-ssa-sprintf.c
> index 85f97b2..687a87f 100644
> --- a/gcc/gimple-ssa-sprintf.c
> +++ b/gcc/gimple-ssa-sprintf.c
> @@ -373,7 +373,16 @@ get_format_string (tree format, location_t *ploc)
>    if (TREE_CODE (format) != STRING_CST)
>      return NULL;
>  
> -  if (TYPE_MAIN_VARIANT (TREE_TYPE (TREE_TYPE (format))) != char_type_node)
> +  tree type = TREE_TYPE (format);
> +  if (TREE_CODE (type) == ARRAY_TYPE)
> +    type = TREE_TYPE (type);
> +
> +  /* Can't just test that:
> +       TYPE_MAIN_VARIANT (TREE_TYPE (TREE_TYPE (format))) != char_type_node
> +     See bug 79062.  */
> +  if (TREE_CODE (type) != INTEGER_TYPE
> +      || TYPE_MODE (type) != TYPE_MODE (char_type_node)
> +      || TYPE_PRECISION (type) != TYPE_PRECISION (char_type_node))
>      {
>        /* Wide format string.  */
>        return NULL;

That looks wrong.

Does that mean that LTO creates a different char type,
i.e. other than char_type_node, signed_char_type_node
and unsigned_char_type_node ?

I think that would also break the TBAA machinery:

alias_set_type
gimple_get_alias_set (tree t)
{
  /* That's all the expressions we handle specially.  */
  if (!TYPE_P (t))
    return -1;

  /* For convenience, follow the C standard when dealing with
     character types.  Any object may be accessed via an lvalue that
     has character type.  */
  if (t == char_type_node
      || t == signed_char_type_node
      || t == unsigned_char_type_node)
    return 0;

which is used in LTO and relies on the same.