Re: [PATCH v5 13/14] c++: Implement __rank built-in trait

[Patrick Palka <ppalka@redhat.com>]

On Thu, 15 Feb 2024, Ken Matsui wrote:

> This patch implements built-in trait for std::rank.
> 
> gcc/cp/ChangeLog:
> 
> 	* cp-trait.def: Define __rank.
> 	* semantics.cc (trait_expr_value): Handle CPTK_RANK.
> 	(finish_trait_expr): Likewise.
> 
> gcc/testsuite/ChangeLog:
> 
> 	* g++.dg/ext/has-builtin-1.C: Test existence of __rank.
> 	* g++.dg/ext/rank.C: New test.
> 
> Signed-off-by: Ken Matsui <kmatsui@gcc.gnu.org>
> ---
>  gcc/cp/cp-trait.def                      |  1 +
>  gcc/cp/semantics.cc                      | 18 ++++++++++++++++--
>  gcc/testsuite/g++.dg/ext/has-builtin-1.C |  3 +++
>  gcc/testsuite/g++.dg/ext/rank.C          | 14 ++++++++++++++
>  4 files changed, 34 insertions(+), 2 deletions(-)
>  create mode 100644 gcc/testsuite/g++.dg/ext/rank.C
> 
> diff --git a/gcc/cp/cp-trait.def b/gcc/cp/cp-trait.def
> index 11270f3ae6b..3d5a7970563 100644
> --- a/gcc/cp/cp-trait.def
> +++ b/gcc/cp/cp-trait.def
> @@ -95,6 +95,7 @@ DEFTRAIT_EXPR (IS_TRIVIALLY_ASSIGNABLE, "__is_trivially_assignable", 2)
>  DEFTRAIT_EXPR (IS_TRIVIALLY_CONSTRUCTIBLE, "__is_trivially_constructible", -1)
>  DEFTRAIT_EXPR (IS_TRIVIALLY_COPYABLE, "__is_trivially_copyable", 1)
>  DEFTRAIT_EXPR (IS_UNION, "__is_union", 1)
> +DEFTRAIT_EXPR (RANK, "__rank", 1)
>  DEFTRAIT_EXPR (REF_CONSTRUCTS_FROM_TEMPORARY, "__reference_constructs_from_temporary", 2)
>  DEFTRAIT_EXPR (REF_CONVERTS_FROM_TEMPORARY, "__reference_converts_from_temporary", 2)
>  DEFTRAIT_TYPE (REMOVE_ALL_EXTENTS, "__remove_all_extents", 1)
> diff --git a/gcc/cp/semantics.cc b/gcc/cp/semantics.cc
> index 256e7ef8166..4f285909b83 100644
> --- a/gcc/cp/semantics.cc
> +++ b/gcc/cp/semantics.cc
> @@ -12538,6 +12538,9 @@ trait_expr_value (cp_trait_kind kind, tree type1, tree type2)
>      case CPTK_IS_DEDUCIBLE:
>        return type_targs_deducible_from (type1, type2);
>  
> +    /* __rank is handled in finish_trait_expr. */
> +    case CPTK_RANK:
> +
>  #define DEFTRAIT_TYPE(CODE, NAME, ARITY) \
>      case CPTK_##CODE:
>  #include "cp-trait.def"
> @@ -12698,6 +12701,7 @@ finish_trait_expr (location_t loc, cp_trait_kind kind, tree type1, tree type2)
>      case CPTK_IS_SAME:
>      case CPTK_IS_SCOPED_ENUM:
>      case CPTK_IS_UNION:
> +    case CPTK_RANK:
>        break;
>  
>      case CPTK_IS_LAYOUT_COMPATIBLE:
> @@ -12729,8 +12733,18 @@ finish_trait_expr (location_t loc, cp_trait_kind kind, tree type1, tree type2)
>        gcc_unreachable ();
>      }
>  
> -  tree val = (trait_expr_value (kind, type1, type2)
> -	      ? boolean_true_node : boolean_false_node);
> +  tree val;
> +  if (kind == CPTK_RANK)
> +    {
> +      size_t rank = 0;
> +      for (; TREE_CODE (type1) == ARRAY_TYPE; type1 = TREE_TYPE (type1))
> +	++rank;
> +      val = build_int_cst (size_type_node, rank);

So this will be the first expression-yielding trait that's not a bool.
That's no problem conceptually, but I think we hardcode their bool-ness
near the top of finish_trait_expr when returning a templated version of
the trait.  We should instead give templated __rank the type size_type_node.

> +    }
> +  else
> +    val = (trait_expr_value (kind, type1, type2)
> +	   ? boolean_true_node : boolean_false_node);
> +
>    return maybe_wrap_with_location (val, loc);
>  }
>  
> diff --git a/gcc/testsuite/g++.dg/ext/has-builtin-1.C b/gcc/testsuite/g++.dg/ext/has-builtin-1.C
> index 5b590db1cf6..a00193c1a81 100644
> --- a/gcc/testsuite/g++.dg/ext/has-builtin-1.C
> +++ b/gcc/testsuite/g++.dg/ext/has-builtin-1.C
> @@ -167,6 +167,9 @@
>  #if !__has_builtin (__is_union)
>  # error "__has_builtin (__is_union) failed"
>  #endif
> +#if !__has_builtin (__rank)
> +# error "__has_builtin (__rank) failed"
> +#endif
>  #if !__has_builtin (__reference_constructs_from_temporary)
>  # error "__has_builtin (__reference_constructs_from_temporary) failed"
>  #endif
> diff --git a/gcc/testsuite/g++.dg/ext/rank.C b/gcc/testsuite/g++.dg/ext/rank.C
> new file mode 100644
> index 00000000000..bab062d776e
> --- /dev/null
> +++ b/gcc/testsuite/g++.dg/ext/rank.C
> @@ -0,0 +1,14 @@
> +// { dg-do compile { target c++11 } }
> +
> +#define SA(X) static_assert((X),#X)
> +
> +class ClassType { };
> +
> +SA(__rank(int) == 0);
> +SA(__rank(int[2]) == 1);
> +SA(__rank(int[][4]) == 2);
> +SA(__rank(int[2][2][4][4][6][6]) == 6);
> +SA(__rank(ClassType) == 0);
> +SA(__rank(ClassType[2]) == 1);
> +SA(__rank(ClassType[][4]) == 2);
> +SA(__rank(ClassType[2][2][4][4][6][6]) == 6);

We should have a test that the __rank inside a template has the correct
type, something like (this should currently fail with your patch as-is
due to the hardcoded bool type):

    template<class T> void f(T) = delete;
    void f(bool);

    template<class T>
    void g() { f(__rank(T)); }

    template void g<int>();

> -- 
> 2.43.0
> 
>