c++: -Wdangling-reference tweak to unbreak aarch64

Bootstrapped/regtested on x86_64-pc-linux-gnu, ok for trunk?

aarch64-unknown-linux-gnu now bootstraps.

-- >8 --
My recent -Wdangling-reference change to not warn on std::span-like classes
unfortunately caused a new warning: extending reference_like_class_p also
opens the door to new warnings since we use reference_like_class_p for
checking the return type of the function: either it must be a reference
or a reference_like_class_p.

We can consider even non-templates as std::span-like to get rid of the
warning here.

gcc/cp/ChangeLog:

	* call.cc (reference_like_class_p): Consider even non-templates for
	std::span-like classes.

gcc/ChangeLog:

	* doc/invoke.texi: Update -Wdangling-reference documentation.

gcc/testsuite/ChangeLog:

	* g++.dg/warn/Wdangling-reference21.C: New test.
---
 gcc/cp/call.cc                                |  8 ++--
 gcc/doc/invoke.texi                           |  2 +-
 .../g++.dg/warn/Wdangling-reference21.C       | 44 +++++++++++++++++++
 3 files changed, 48 insertions(+), 6 deletions(-)
 create mode 100644 gcc/testsuite/g++.dg/warn/Wdangling-reference21.C


base-commit: 44764984cf24e27cf7756cffd197283b9c62db8b

On 2/1/24 16:23, Marek Polacek wrote:
> Bootstrapped/regtested on x86_64-pc-linux-gnu, ok for trunk?

OK.

> aarch64-unknown-linux-gnu now bootstraps.
> 
> -- >8 --
> My recent -Wdangling-reference change to not warn on std::span-like classes
> unfortunately caused a new warning: extending reference_like_class_p also
> opens the door to new warnings since we use reference_like_class_p for
> checking the return type of the function: either it must be a reference
> or a reference_like_class_p.
> 
> We can consider even non-templates as std::span-like to get rid of the
> warning here.
> 
> gcc/cp/ChangeLog:
> 
> 	* call.cc (reference_like_class_p): Consider even non-templates for
> 	std::span-like classes.
> 
> gcc/ChangeLog:
> 
> 	* doc/invoke.texi: Update -Wdangling-reference documentation.
> 
> gcc/testsuite/ChangeLog:
> 
> 	* g++.dg/warn/Wdangling-reference21.C: New test.
> ---
>   gcc/cp/call.cc                                |  8 ++--
>   gcc/doc/invoke.texi                           |  2 +-
>   .../g++.dg/warn/Wdangling-reference21.C       | 44 +++++++++++++++++++
>   3 files changed, 48 insertions(+), 6 deletions(-)
>   create mode 100644 gcc/testsuite/g++.dg/warn/Wdangling-reference21.C
> 
> diff --git a/gcc/cp/call.cc b/gcc/cp/call.cc
> index 42cbd0da036..1dac1470d3b 100644
> --- a/gcc/cp/call.cc
> +++ b/gcc/cp/call.cc
> @@ -14082,8 +14082,8 @@ reference_like_class_p (tree ctype)
>   	return true;
>       }
>   
> -  /* Avoid warning if CTYPE looks like std::span: it's a class template,
> -     has a T* member, and a trivial destructor.  For example,
> +  /* Avoid warning if CTYPE looks like std::span: it has a T* member and
> +     a trivial destructor.  For example,
>   
>         template<typename T>
>         struct Span {
> @@ -14092,9 +14092,7 @@ reference_like_class_p (tree ctype)
>         };
>   
>        is considered std::span-like.  */
> -  if (NON_UNION_CLASS_TYPE_P (ctype)
> -      && CLASSTYPE_TEMPLATE_INSTANTIATION (ctype)
> -      && TYPE_HAS_TRIVIAL_DESTRUCTOR (ctype))
> +  if (NON_UNION_CLASS_TYPE_P (ctype) && TYPE_HAS_TRIVIAL_DESTRUCTOR (ctype))
>       for (tree field = next_aggregate_field (TYPE_FIELDS (ctype));
>   	 field; field = next_aggregate_field (DECL_CHAIN (field)))
>         if (TYPE_PTR_P (TREE_TYPE (field)))
> diff --git a/gcc/doc/invoke.texi b/gcc/doc/invoke.texi
> index 14730c0c508..e9c691d63da 100644
> --- a/gcc/doc/invoke.texi
> +++ b/gcc/doc/invoke.texi
> @@ -3929,7 +3929,7 @@ struct Span @{
>   @};
>   @end smallexample
>   
> -as @code{std::span}-like; that is, the class is a non-union class template
> +as @code{std::span}-like; that is, the class is a non-union class
>   that has a pointer data member and a trivial destructor.
>   
>   This warning is enabled by @option{-Wall}.
> diff --git a/gcc/testsuite/g++.dg/warn/Wdangling-reference21.C b/gcc/testsuite/g++.dg/warn/Wdangling-reference21.C
> new file mode 100644
> index 00000000000..e1b6e3dd94c
> --- /dev/null
> +++ b/gcc/testsuite/g++.dg/warn/Wdangling-reference21.C
> @@ -0,0 +1,44 @@
> +// { dg-do compile { target c++11 } }
> +// { dg-options "-Wdangling-reference" }
> +// Reduced from config/aarch64/aarch64-early-ra.cc.
> +
> +template <typename T> struct array_slice {
> +  using iterator = T *;
> +  iterator begin();
> +  iterator end();
> +  iterator m_base;
> +};
> +
> +struct allocno_group_info { };
> +
> +char recog_data_2;
> +int record_constraints_op;
> +struct early_ra {
> +  using operand_mask = int;
> +  struct allocno_info {
> +    int is_earlyclobbered;
> +  };
> +  struct allocno_subgroup {
> +    array_slice<allocno_info> allocnos();
> +    allocno_group_info *group;
> +  };
> +  allocno_subgroup get_allocno_subgroup(int);
> +  void record_constraints();
> +};
> +void early_ra::record_constraints() {
> +  operand_mask earlyclobber_operands, matched_operands, unmatched_operands,
> +      matches_operands, op_mask = operand_mask();
> +  auto record_operand = [&](int, int) {
> +    operand_mask overlaps;
> +    matches_operands |= overlaps;
> +  };
> +  for (int opno = 0; recog_data_2; ++opno) {
> +    operand_mask op_mask = earlyclobber_operands |= op_mask;
> +    if (0)
> +      record_operand(1, 0);
> +  }
> +  if (op_mask || (matched_operands & unmatched_operands && 0))
> +    for (auto &allocno : get_allocno_subgroup(record_constraints_op).allocnos())
> +      allocno.is_earlyclobbered = true;
> +}
> +
> 
> base-commit: 44764984cf24e27cf7756cffd197283b9c62db8b