On 28/06/21 14:24 +0100, Jonathan Wakely wrote:
PR libstdc++/101236 shows that LLVM depends on being able to use
unique_ptr<T[]>::operator[] when T is incomplete. This is undefined, but
previously worked with libstdc++. When I added the conditional noexcept
to that operator we started to diagnose the incomplete type.
This change restores support for that case, by making the noexcept
condition check that the type is complete before checking whether
indexing on the pointer can throw. A workaround for PR c++/101239 is
needed to avoid a bogus error where G++ fails to do SFINAE on the
ill-formed p[n] expression and gets an ICE. Instead of checking that the
p[n] expression is valid in the trailing-return-type, we only check that
the element_type is complete.
libstdc++-v3/ChangeLog:
PR libstdc++/101236
* include/bits/unique_ptr.h (unique_ptr<T[], D>::operator[]):
Fail gracefully if element_type is incomplete.
* testsuite/20_util/unique_ptr/cons/incomplete.cc: Clarify that
the standard doesn't require this test to work for array types.
* testsuite/20_util/unique_ptr/lwg2762.cc: Check that incomplete
types can be used with array specialization.
* testsuite/20_util/unique_ptr/101236.cc: New test.
This (and the previous change that it tried to fix) needs to be
reverted, as attached.
Tested powerpc64le-linux. Committed to trunk.
commit bc8f0ed7042280282035168428f6afc839997cf0
Author: Jonathan Wakely <jwak...@redhat.com>
Date: Fri Jul 2 08:46:18 2021
libstdc++: Revert changes to std::unique_ptr<T[]>::operator[] [PR 101271]
This reverts the changes in r12-1778 which added a noexcept-specifier to
std::unique_ptr<T[]>::operator[], and the changes in r12-1844 which
tried to make it work with incomplete types (for PR 101236).
The noexcept-specifier is not required by the standard, and is causing
regressions, so just remove it.
Signed-off-by: Jonathan Wakely <jwak...@redhat.com>
libstdc++-v3/ChangeLog:
PR libstdc++/101271
* include/bits/unique_ptr.h (unique_ptr<T[],D>::operator[]):
Remove noexcept-specifier.
(unique_ptr<T[],D>::_S_nothrow_deref): Remove.
* testsuite/20_util/unique_ptr/lwg2762.cc: Remove checks for
operator[].
diff --git a/libstdc++-v3/include/bits/unique_ptr.h b/libstdc++-v3/include/bits/unique_ptr.h
index e478056c755..d483f13f2b0 100644
--- a/libstdc++-v3/include/bits/unique_ptr.h
+++ b/libstdc++-v3/include/bits/unique_ptr.h
@@ -491,20 +491,6 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
= __and_< is_base_of<_Tp, _Up>,
__not_<is_same<__remove_cv<_Tp>, __remove_cv<_Up>>> >;
- // This checks whether p[n] is noexcept, but fails gracefully when
- // element_type is incomplete. The standard requires a complete type
- // for unique_ptr<T[], D>, but we try to support it anyway (PR 101236).
- template<typename _Ptr, typename _Elt>
- static constexpr auto
- _S_nothrow_deref(size_t __n)
- -> decltype(sizeof(_Elt) != 0) // PR c++/101239
- { return noexcept(std::declval<_Ptr>()[__n]); }
-
- template<typename _Ptr, typename _Elt>
- static constexpr bool
- _S_nothrow_deref(...)
- { return false; }
-
public:
using pointer = typename __uniq_ptr_impl<_Tp, _Dp>::pointer;
using element_type = _Tp;
@@ -669,7 +655,6 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
/// Access an element of owned array.
typename std::add_lvalue_reference<element_type>::type
operator[](size_t __i) const
- noexcept(_S_nothrow_deref<pointer, element_type>(0))
{
__glibcxx_assert(get() != pointer());
return get()[__i];
diff --git a/libstdc++-v3/testsuite/20_util/unique_ptr/lwg2762.cc b/libstdc++-v3/testsuite/20_util/unique_ptr/lwg2762.cc
index c88237dd9ea..ea067eb3af3 100644
--- a/libstdc++-v3/testsuite/20_util/unique_ptr/lwg2762.cc
+++ b/libstdc++-v3/testsuite/20_util/unique_ptr/lwg2762.cc
@@ -12,11 +12,6 @@ struct deleter
int& operator*() && noexcept(B); // this is used by unique_ptr
int& operator*() const& = delete; // this should not be
- int& operator[](std::size_t) && noexcept(B); // this is used by unique_ptr
- int& operator[](std::size_t) const& = delete; // should not be used
- int& operator[](int) && = delete; // should not be used
- int& operator[](double) && = delete; // should not be used
-
int* operator->() noexcept(false); // noexcept here doesn't affect anything
// Needed for NullablePointer requirements
@@ -40,16 +35,3 @@ static_assert( noexcept(std::declval<std::unique_ptr<long>>().operator->()),
"operator-> is always noexcept" );
static_assert( noexcept(std::declval<UPtr<int, false>&>().operator->()),
"operator-> is always noexcept" );
-
-// This is not required by the standard, but we make it depend on the pointer.
-static_assert( noexcept(std::declval<std::unique_ptr<long[]>>()[0]), "QoI" );
-static_assert( noexcept(std::declval<UPtr<int[], true>&>()[0]), "QoI" );
-static_assert( ! noexcept(std::declval<UPtr<int[], false>&>()[0]), "QoI" );
-
-// This is forbidden by the standard ("T shall be a complete type")
-// but we try to support it anyway, see PR libstdc++/101236.
-struct Incomplete;
-static_assert( ! noexcept(std::declval<UPtr<Incomplete[], true>>()[0]),
- "this would be noexcept if the type was complete");
-static_assert( ! noexcept(std::declval<UPtr<Incomplete[], false>>()[0]),
- "this would still be noexcept(false) if the type was complete");
