Re: [PATCH] c++: init_priority and SUPPORTS_INIT_PRIORITY [PR107638]

[Andrew Pinski <pinskia@gmail.com>]

On Fri, Nov 11, 2022 at 10:48 AM Patrick Palka via Gcc-patches
<gcc-patches@gcc.gnu.org> wrote:
>
> The commit r13-3706-gd0a492faa6478c for correcting the result of
> __has_attribute(init_priority) causes a bootstrap failure on hppa64-hpux
> because it assumes SUPPORTS_INIT_PRIORITY expands to a simple constant,
> but on this target SUPPORTS_INIT_PRIORITY is defined as
>
>   #define SUPPORTS_INIT_PRIORITY (TARGET_GNU_LD ? 1 : 0)
>
> (where TARGET_GNU_LD expands to something in terms of global_options)
> which means we can't use this macro to statically exclude the entry
> for init_priority when defining the cxx_attribute_table.
>
> So instead of trying to exclude init_priority from the attribute table
> for sake of __has_attribute, this patch just makes __has_attribute
> handle init_priority specially.
>
> Bootstrapped and regtested on x86_64-pc-linux-gnu, does this look OK for
> trunk?  Also sanity checked by artificially defining SUPPORTS_INIT_PRIORITY
> to 0.
>
>         PR c++/107638
>
> gcc/c-family/ChangeLog:
>
>         * c-lex.cc (c_common_has_attribute): Return 1 for init_priority
>         iff SUPPORTS_INIT_PRIORITY.
>
> gcc/cp/ChangeLog:
>
>         * tree.cc (cxx_attribute_table): Don't conditionally exclude
>         the init_priority entry.
>         (handle_init_priority_attribute): Remove ATTRIBUTE_UNUSED.
>         Return error_mark_node if !SUPPORTS_INIT_PRIORITY.
> ---
>  gcc/c-family/c-lex.cc |  9 +++++++++
>  gcc/cp/tree.cc        | 11 +++++++----
>  2 files changed, 16 insertions(+), 4 deletions(-)
>
> diff --git a/gcc/c-family/c-lex.cc b/gcc/c-family/c-lex.cc
> index 89c65aca28a..2fe562c7ccf 100644
> --- a/gcc/c-family/c-lex.cc
> +++ b/gcc/c-family/c-lex.cc
> @@ -380,6 +380,15 @@ c_common_has_attribute (cpp_reader *pfile, bool std_syntax)
>                 result = 201907;
>               else if (is_attribute_p ("assume", attr_name))
>                 result = 202207;
> +             else if (is_attribute_p ("init_priority", attr_name))
> +               {
> +                 /* The (non-standard) init_priority attribute is always
> +                    included in the attribute table, but we don't want to
> +                    advertise the attribute unless the target actually
> +                    supports init priorities.  */
> +                 result = SUPPORTS_INIT_PRIORITY ? 1 : 0;
> +                 attr_name = NULL_TREE;
> +               }
>             }
>           else
>             {
> diff --git a/gcc/cp/tree.cc b/gcc/cp/tree.cc
> index c30bbeb0839..2324c2269fc 100644
> --- a/gcc/cp/tree.cc
> +++ b/gcc/cp/tree.cc
> @@ -5010,10 +5010,8 @@ const struct attribute_spec cxx_attribute_table[] =
>  {
>    /* { name, min_len, max_len, decl_req, type_req, fn_type_req,
>         affects_type_identity, handler, exclude } */
> -#if SUPPORTS_INIT_PRIORITY
>    { "init_priority",  1, 1, true,  false, false, false,
>      handle_init_priority_attribute, NULL },
> -#endif

Hmm, seems like this could be better handled if attribute_spec has
another field which takes a function which returns if it is supported
or not.
And maybe remove some of the special cases inside c_common_has_attribute.
I suspect there are some target ones which need special casing in more
fancy way.
An example of this is arm_handle_cmse_nonsecure_entry in config/arm/arm.cc .
Where this attribute is not supported unless you use -mcmse option.
Seems would be use if you want to use __has_attribute on
cmse_nonsecure_entry to get the right value there too.

Note I am not blocking this patch for this but just thinking out loud
of how to improve this so special casing is not needed.

Thanks,
Andrew Pinski


>    { "abi_tag", 1, -1, false, false, false, true,
>      handle_abi_tag_attribute, NULL },
>    { NULL, 0, 0, false, false, false, false, NULL, NULL }
> @@ -5041,13 +5039,19 @@ const struct attribute_spec std_attribute_table[] =
>
>  /* Handle an "init_priority" attribute; arguments as in
>     struct attribute_spec.handler.  */
> -ATTRIBUTE_UNUSED static tree
> +static tree
>  handle_init_priority_attribute (tree* node,
>                                 tree name,
>                                 tree args,
>                                 int /*flags*/,
>                                 bool* no_add_attrs)
>  {
> +  if (!SUPPORTS_INIT_PRIORITY)
> +    /* Treat init_priority as an unrecognized attribute (mirroring the
> +       result of __has_attribute) if the target doesn't support init
> +       priorities.  */
> +    return error_mark_node;
> +
>    tree initp_expr = TREE_VALUE (args);
>    tree decl = *node;
>    tree type = TREE_TYPE (decl);
> @@ -5105,7 +5109,6 @@ handle_init_priority_attribute (tree* node,
>          pri);
>      }
>
> -  gcc_assert (SUPPORTS_INIT_PRIORITY);
>    SET_DECL_INIT_PRIORITY (decl, pri);
>    DECL_HAS_INIT_PRIORITY_P (decl) = 1;
>    return NULL_TREE;
> --
> 2.38.1.420.g319605f8f0
>