Re: [PATCH v14 21/26] c++: Implement __rank built-in trait

[Patrick Palka <ppalka@redhat.com>]

On Tue, 30 Apr 2024, Jason Merrill wrote:

> On 2/28/24 11:26, Ken Matsui wrote:
> > This patch implements built-in trait for std::rank.
> 
> __rank seems too short, maybe __array_rank?
> 
> Actually, it occurs to me that perhaps we should have been adding __builtin to
> all of these rather than just __ and the library trait name.  I guess it's too
> late to do that for the GCC 14 traits, but we could do it for this group?

Clang already implements many of these built-in, without using
"__builtin" in their name.  Shouldn't we be consistent with Clang where
we can?

> 
> > gcc/cp/ChangeLog:
> > 
> > 	* cp-trait.def: Define __rank.
> > 	* constraint.cc (diagnose_trait_expr): Handle CPTK_RANK.
> > 	* semantics.cc (trait_expr_value): Likewise.
> > 	(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/constraint.cc                     |  3 +++
> >   gcc/cp/cp-trait.def                      |  1 +
> >   gcc/cp/semantics.cc                      | 23 ++++++++++++++++++++---
> >   gcc/testsuite/g++.dg/ext/has-builtin-1.C |  3 +++
> >   gcc/testsuite/g++.dg/ext/rank.C          | 24 ++++++++++++++++++++++++
> >   5 files changed, 51 insertions(+), 3 deletions(-)
> >   create mode 100644 gcc/testsuite/g++.dg/ext/rank.C
> > 
> > diff --git a/gcc/cp/constraint.cc b/gcc/cp/constraint.cc
> > index 000df847342..23ea66d9c12 100644
> > --- a/gcc/cp/constraint.cc
> > +++ b/gcc/cp/constraint.cc
> > @@ -3870,6 +3870,9 @@ diagnose_trait_expr (tree expr, tree args)
> >       case CPTK_IS_VOLATILE:
> >         inform (loc, "  %qT is not a volatile type", t1);
> >         break;
> > +    case CPTK_RANK:
> > +      inform (loc, "  %qT cannot yield a rank", t1);
> > +      break;
> >       case CPTK_REF_CONSTRUCTS_FROM_TEMPORARY:
> >         inform (loc, "  %qT is not a reference that binds to a temporary "
> >   	      "object of type %qT (direct-initialization)", t1, t2);
> > diff --git a/gcc/cp/cp-trait.def b/gcc/cp/cp-trait.def
> > index 2d1cb7c227c..85056c8140b 100644
> > --- a/gcc/cp/cp-trait.def
> > +++ b/gcc/cp/cp-trait.def
> > @@ -99,6 +99,7 @@ DEFTRAIT_EXPR (IS_TRIVIALLY_COPYABLE,
> > "__is_trivially_copyable", 1)
> >   DEFTRAIT_EXPR (IS_UNBOUNDED_ARRAY, "__is_unbounded_array", 1)
> >   DEFTRAIT_EXPR (IS_UNION, "__is_union", 1)
> >   DEFTRAIT_EXPR (IS_VOLATILE, "__is_volatile", 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 45dc509855a..7242db75248 100644
> > --- a/gcc/cp/semantics.cc
> > +++ b/gcc/cp/semantics.cc
> > @@ -12550,6 +12550,9 @@ 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:
> 
> This should have a gcc_unreachable.
> 
> > +
> >   #define DEFTRAIT_TYPE(CODE, NAME, ARITY) \
> >       case CPTK_##CODE:
> >   #include "cp-trait.def"
> > @@ -12622,7 +12625,10 @@ finish_trait_expr (location_t loc, cp_trait_kind
> > kind, tree type1, tree type2)
> >     if (processing_template_decl)
> >       {
> >         tree trait_expr = make_node (TRAIT_EXPR);
> > -      TREE_TYPE (trait_expr) = boolean_type_node;
> > +      if (kind == CPTK_RANK)
> > +	TREE_TYPE (trait_expr) = size_type_node;
> > +      else
> > +	TREE_TYPE (trait_expr) = boolean_type_node;
> >         TRAIT_EXPR_TYPE1 (trait_expr) = type1;
> >         TRAIT_EXPR_TYPE2 (trait_expr) = type2;
> >         TRAIT_EXPR_KIND (trait_expr) = kind;
> > @@ -12714,6 +12720,7 @@ finish_trait_expr (location_t loc, cp_trait_kind
> > kind, tree type1, tree type2)
> >       case CPTK_IS_UNBOUNDED_ARRAY:
> >       case CPTK_IS_UNION:
> >       case CPTK_IS_VOLATILE:
> > +    case CPTK_RANK:
> >         break;
> >         case CPTK_IS_LAYOUT_COMPATIBLE:
> > @@ -12745,8 +12752,18 @@ 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);
> > +    }
> > +  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 3aca273aad6..7f7b27f7aa7 100644
> > --- a/gcc/testsuite/g++.dg/ext/has-builtin-1.C
> > +++ b/gcc/testsuite/g++.dg/ext/has-builtin-1.C
> > @@ -179,6 +179,9 @@
> >   #if !__has_builtin (__is_volatile)
> >   # error "__has_builtin (__is_volatile) 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..28894184387
> > --- /dev/null
> > +++ b/gcc/testsuite/g++.dg/ext/rank.C
> > @@ -0,0 +1,24 @@
> > +// { dg-do compile { target c++11 } }
> > +
> > +#include <cstddef>
> > +
> > +#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);
> > +
> > +template<class T> void f(T) = delete;
> > +void f(size_t);
> > +
> > +template<class T>
> > +void g() { f(__rank(T)); }
> > +
> > +template void g<int>();
> 
>