Re: [PATCH] c++: ICE with __has_unique_object_representations [PR115476]

[Jason Merrill <jason@redhat.com>]

On 6/25/24 07:15, Jonathan Wakely wrote:
> On Tue, 25 Jun 2024 at 03:12, Jason Merrill <jason@redhat.com> wrote:
>>
>> On 6/18/24 10:31, Marek Polacek wrote:
>>> Bootstrapped/regtested on x86_64-pc-linux-gnu, ok for trunk/14/13?
>>
>> Makes sense to me, though probably the [meta.unary.prop] table should be
>> adjusted in the same way.  Jonathan, what do you think?
> 
> Just to make sure I understand correctly, the suggestion is to change
> the precondition for the trait to something like:
> 
> "remove_all_extents_t<T> shall be a complete type or cv void."
> 
> i.e. if T is incomplete then T[] cannot be used with the trait, right?

Yes.

Jason

>>
>>> -- >8 --
>>> Here we started to ICE with r13-25: in check_trait_type, for "X[]" we
>>> return true here:
>>>
>>>     if (kind == 1 && TREE_CODE (type) == ARRAY_TYPE && !TYPE_DOMAIN (type))
>>>       return true; // Array of unknown bound. Don't care about completeness.
>>>
>>> and then end up crashing in record_has_unique_obj_representations:
>>>
>>> 4836    if (cur != wi::to_offset (sz))
>>>
>>> because sz is null.
>>>
>>> https://eel.is/c++draft/type.traits#tab:meta.unary.prop-row-47-column-3-sentence-1
>>> says that the preconditions for __has_unique_object_representations are:
>>> "T shall be a complete type, cv void, or an array of unknown bound" and
>>> that "For an array type T, the same result as
>>> has_unique_object_representations_v<remove_all_extents_t<T>>" so T[]
>>> should be treated as T.  So we should use kind==2 for the trait.
>>>
>>>        PR c++/115476
>>>
>>> gcc/cp/ChangeLog:
>>>
>>>        * semantics.cc (finish_trait_expr)
>>>        <case CPTK_HAS_UNIQUE_OBJ_REPRESENTATIONS>: Move below to call
>>>        check_trait_type with kind==2.
>>>
>>> gcc/testsuite/ChangeLog:
>>>
>>>        * g++.dg/cpp1z/has-unique-obj-representations4.C: New test.
>>> ---
>>>    gcc/cp/semantics.cc                              |  2 +-
>>>    .../cpp1z/has-unique-obj-representations4.C      | 16 ++++++++++++++++
>>>    2 files changed, 17 insertions(+), 1 deletion(-)
>>>    create mode 100644 gcc/testsuite/g++.dg/cpp1z/has-unique-obj-representations4.C
>>>
>>> diff --git a/gcc/cp/semantics.cc b/gcc/cp/semantics.cc
>>> index 08f5f245e7d..42251b6764b 100644
>>> --- a/gcc/cp/semantics.cc
>>> +++ b/gcc/cp/semantics.cc
>>> @@ -12966,7 +12966,6 @@ finish_trait_expr (location_t loc, cp_trait_kind kind, tree type1, tree type2)
>>>        case CPTK_HAS_NOTHROW_COPY:
>>>        case CPTK_HAS_TRIVIAL_COPY:
>>>        case CPTK_HAS_TRIVIAL_DESTRUCTOR:
>>> -    case CPTK_HAS_UNIQUE_OBJ_REPRESENTATIONS:
>>>          if (!check_trait_type (type1))
>>>        return error_mark_node;
>>>          break;
>>> @@ -12976,6 +12975,7 @@ finish_trait_expr (location_t loc, cp_trait_kind kind, tree type1, tree type2)
>>>        case CPTK_IS_STD_LAYOUT:
>>>        case CPTK_IS_TRIVIAL:
>>>        case CPTK_IS_TRIVIALLY_COPYABLE:
>>> +    case CPTK_HAS_UNIQUE_OBJ_REPRESENTATIONS:
>>>          if (!check_trait_type (type1, /* kind = */ 2))
>>>        return error_mark_node;
>>>          break;
>>> diff --git a/gcc/testsuite/g++.dg/cpp1z/has-unique-obj-representations4.C b/gcc/testsuite/g++.dg/cpp1z/has-unique-obj-representations4.C
>>> new file mode 100644
>>> index 00000000000..d6949dc7005
>>> --- /dev/null
>>> +++ b/gcc/testsuite/g++.dg/cpp1z/has-unique-obj-representations4.C
>>> @@ -0,0 +1,16 @@
>>> +// PR c++/115476
>>> +// { dg-do compile { target c++11 } }
>>> +
>>> +struct X;
>>> +static_assert(__has_unique_object_representations(X), "");     // { dg-error "invalid use of incomplete type" }
>>> +static_assert(__has_unique_object_representations(X[]), "");  // { dg-error "invalid use of incomplete type" }
>>> +static_assert(__has_unique_object_representations(X[1]), "");  // { dg-error "invalid use of incomplete type" }
>>> +static_assert(__has_unique_object_representations(X[][1]), "");  // { dg-error "invalid use of incomplete type" }
>>> +
>>> +struct X {
>>> +  int x;
>>> +};
>>> +static_assert(__has_unique_object_representations(X), "");
>>> +static_assert(__has_unique_object_representations(X[]), "");
>>> +static_assert(__has_unique_object_representations(X[1]), "");
>>> +static_assert(__has_unique_object_representations(X[][1]), "");
>>>
>>> base-commit: 7f9be55a4630134a237219af9cc8143e02080380
>>
>