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

[Ken Matsui <kmatsui@cs.washington.edu>]

On Thu, Feb 15, 2024 at 6:14 PM Ken Matsui <kmatsui@cs.washington.edu> wrote:
>
> On Thu, Feb 15, 2024 at 1:48 PM Patrick Palka <ppalka@redhat.com> wrote:
> >
> > 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>();
> >
>
> Thank you!  I think this test should be the following, to fail with my
> patch as-is:
>
> -     void f(bool);
> +     void f(size_t);
>
> since we are expecting size_t from __rank.  The current patch passed
> this test and failed with a test with change, and my updated patch
> failed with this test and passed a test with this change.
>

Sorry, the wording was a bit confusing.  Just in case, here is what I meant.

v5
  passed yours (expect bool)
  failed with this change (expect size_t)

v6
  failed with yours (expect bool)
  passed this change (expect size_t)

Again, thank you for your review, Patrick!

> I will submit the updated patch soon.  Thank you for pointing this out!
>
> > > --
> > > 2.43.0
> > >
> > >
> >