A couple of va_gc_atomic tweaks

The only current user of va_gc_atomic is Ada's:

    vec<Entity_Id, va_gc_atomic>

It uses the generic gt_pch_nx routines (with gt_pch_nx being the
“note pointers” hooks), such as:

    template<typename T, typename A>
    void
    gt_pch_nx (vec<T, A, vl_embed> *v)
    {
      extern void gt_pch_nx (T &);
      for (unsigned i = 0; i < v->length (); i++)
	gt_pch_nx ((*v)[i]);
    }

It then defines gt_pch_nx routines for Entity_Id &.

The problem is that if we wanted to take the same approach for
an array of unsigned ints, we'd need to define:

    inline void gt_pch_nx (unsigned int &) { }

which would then be ambiguous with:

    inline void gt_pch_nx (unsigned int) { }

The point of va_gc_atomic is that the elements don't need to be GCed,
and so we have:

    template<typename T>
    void
    gt_ggc_mx (vec<T, va_gc_atomic, vl_embed> *v ATTRIBUTE_UNUSED)
    {
      /* Nothing to do.  Vectors of atomic types wrt GC do not need to
	 be traversed.  */
    }

I think it's therefore reasonable to assume that no pointers will
need to be processed for PCH either.

The patch also relaxes the array_slice constructor for vec<T, va_gc> *
so that it handles all embedded vectors.

Bootstrapped & regression-tested on aarch64-linux-gnu (all languages).
OK to install?

Richard


gcc/
	* vec.h (gt_pch_nx): Add overloads for va_gc_atomic.
	(array_slice): Relax va_gc constructor to handle all vectors
	with a vl_embed layout.

gcc/ada/
	* gcc-interface/decl.cc (gt_pch_nx): Remove overloads for Entity_Id.
---
 gcc/ada/gcc-interface/decl.cc | 11 -----------
 gcc/vec.h                     | 22 ++++++++++++++++++----
 2 files changed, 18 insertions(+), 15 deletions(-)

On Wed, Jun 28, 2023 at 11:37 PM Richard Sandiford via Gcc-patches
<gcc-patches@gcc.gnu.org> wrote:
>
> The only current user of va_gc_atomic is Ada's:
>
>     vec<Entity_Id, va_gc_atomic>
>
> It uses the generic gt_pch_nx routines (with gt_pch_nx being the
> “note pointers” hooks), such as:
>
>     template<typename T, typename A>
>     void
>     gt_pch_nx (vec<T, A, vl_embed> *v)
>     {
>       extern void gt_pch_nx (T &);
>       for (unsigned i = 0; i < v->length (); i++)
>         gt_pch_nx ((*v)[i]);
>     }
>
> It then defines gt_pch_nx routines for Entity_Id &.
>
> The problem is that if we wanted to take the same approach for
> an array of unsigned ints, we'd need to define:
>
>     inline void gt_pch_nx (unsigned int &) { }
>
> which would then be ambiguous with:
>
>     inline void gt_pch_nx (unsigned int) { }
>
> The point of va_gc_atomic is that the elements don't need to be GCed,
> and so we have:
>
>     template<typename T>
>     void
>     gt_ggc_mx (vec<T, va_gc_atomic, vl_embed> *v ATTRIBUTE_UNUSED)
>     {
>       /* Nothing to do.  Vectors of atomic types wrt GC do not need to
>          be traversed.  */
>     }
>
> I think it's therefore reasonable to assume that no pointers will
> need to be processed for PCH either.
>
> The patch also relaxes the array_slice constructor for vec<T, va_gc> *
> so that it handles all embedded vectors.
>
> Bootstrapped & regression-tested on aarch64-linux-gnu (all languages).
> OK to install?

OK.

Thanks,
Richard.

> Richard
>
>
> gcc/
>         * vec.h (gt_pch_nx): Add overloads for va_gc_atomic.
>         (array_slice): Relax va_gc constructor to handle all vectors
>         with a vl_embed layout.
>
> gcc/ada/
>         * gcc-interface/decl.cc (gt_pch_nx): Remove overloads for Entity_Id.
> ---
>  gcc/ada/gcc-interface/decl.cc | 11 -----------
>  gcc/vec.h                     | 22 ++++++++++++++++++----
>  2 files changed, 18 insertions(+), 15 deletions(-)
>
> diff --git a/gcc/ada/gcc-interface/decl.cc b/gcc/ada/gcc-interface/decl.cc
> index 494b24e2111..ee913a017d2 100644
> --- a/gcc/ada/gcc-interface/decl.cc
> +++ b/gcc/ada/gcc-interface/decl.cc
> @@ -163,17 +163,6 @@ struct GTY((for_user)) tree_entity_vec_map
>    vec<Entity_Id, va_gc_atomic> *to;
>  };
>
> -void
> -gt_pch_nx (Entity_Id &)
> -{
> -}
> -
> -void
> -gt_pch_nx (Entity_Id *x, gt_pointer_operator op, void *cookie)
> -{
> -  op (x, NULL, cookie);
> -}
> -
>  struct dummy_type_hasher : ggc_cache_ptr_hash<tree_entity_vec_map>
>  {
>    static inline hashval_t
> diff --git a/gcc/vec.h b/gcc/vec.h
> index 36918915701..6f7b0487eb6 100644
> --- a/gcc/vec.h
> +++ b/gcc/vec.h
> @@ -1390,6 +1390,13 @@ gt_pch_nx (vec<T, A, vl_embed> *v)
>      gt_pch_nx ((*v)[i]);
>  }
>
> +template<typename T>
> +void
> +gt_pch_nx (vec<T, va_gc_atomic, vl_embed> *)
> +{
> +  /* No pointers to note.  */
> +}
> +
>  template<typename T, typename A>
>  void
>  gt_pch_nx (vec<T *, A, vl_embed> *v, gt_pointer_operator op, void *cookie)
> @@ -1407,6 +1414,13 @@ gt_pch_nx (vec<T, A, vl_embed> *v, gt_pointer_operator op, void *cookie)
>      gt_pch_nx (&((*v)[i]), op, cookie);
>  }
>
> +template<typename T>
> +void
> +gt_pch_nx (vec<T, va_gc_atomic, vl_embed> *, gt_pointer_operator, void *)
> +{
> +  /* No pointers to note.  */
> +}
> +
>
>  /* Space efficient vector.  These vectors can grow dynamically and are
>     allocated together with their control data.  They are suited to be
> @@ -2286,12 +2300,12 @@ public:
>    array_slice (vec<OtherT> &v)
>      : m_base (v.address ()), m_size (v.length ()) {}
>
> -  template<typename OtherT>
> -  array_slice (const vec<OtherT, va_gc> *v)
> +  template<typename OtherT, typename A>
> +  array_slice (const vec<OtherT, A, vl_embed> *v)
>      : m_base (v ? v->address () : nullptr), m_size (v ? v->length () : 0) {}
>
> -  template<typename OtherT>
> -  array_slice (vec<OtherT, va_gc> *v)
> +  template<typename OtherT, typename A>
> +  array_slice (vec<OtherT, A, vl_embed> *v)
>      : m_base (v ? v->address () : nullptr), m_size (v ? v->length () : 0) {}
>
>    iterator begin () { return m_base; }
> --
> 2.25.1
>