[gcc r10-10304] libstdc++: Value-initialize objects held by EBO helpers [PR 100863]

[Jonathan Wakely <redi@gcc.gnu.org>]

https://gcc.gnu.org/g:cc56c03a7a7f034f98a835dcb7047ad3d2ace6bd

commit r10-10304-gcc56c03a7a7f034f98a835dcb7047ad3d2ace6bd
Author: Jonathan Wakely <jwakely@redhat.com>
Date:   Wed Jun 2 12:34:48 2021 +0100

    libstdc++: Value-initialize objects held by EBO helpers [PR 100863]
    
    The allocator, hash function and equality function should all be
    value-initialized by the default constructor of an unordered container.
    Do it in the EBO helper, so we don't have to get it right in multiple
    places.
    
    Signed-off-by: Jonathan Wakely <jwakely@redhat.com>
    
    libstdc++-v3/ChangeLog:
    
            PR libstdc++/100863
            PR libstdc++/65816
            * include/bits/hashtable_policy.h (_Hashtable_ebo_helper):
            Value-initialize subobject.
            * testsuite/23_containers/unordered_map/allocator/default_init.cc:
            Remove XFAIL.
            * testsuite/23_containers/unordered_set/allocator/default_init.cc:
            Remove XFAIL.
    
    (cherry picked from commit f8f0193b5b83f6e85d65015e79c803295baf5166)

Diff:
---
 libstdc++-v3/include/bits/hashtable_policy.h                         | 5 +++--
 .../testsuite/23_containers/unordered_map/allocator/default_init.cc  | 1 -
 .../testsuite/23_containers/unordered_set/allocator/default_init.cc  | 1 -
 3 files changed, 3 insertions(+), 4 deletions(-)

diff --git a/libstdc++-v3/include/bits/hashtable_policy.h b/libstdc++-v3/include/bits/hashtable_policy.h
index d34fc39a973..63958cc1d9c 100644
--- a/libstdc++-v3/include/bits/hashtable_policy.h
+++ b/libstdc++-v3/include/bits/hashtable_policy.h
@@ -1109,7 +1109,7 @@ namespace __detail
     struct _Hashtable_ebo_helper<_Nm, _Tp, true>
     : private _Tp
     {
-      _Hashtable_ebo_helper() = default;
+      _Hashtable_ebo_helper() noexcept(noexcept(_Tp())) : _Tp() { }
 
       template<typename _OtherTp>
 	_Hashtable_ebo_helper(_OtherTp&& __tp)
@@ -1135,7 +1135,7 @@ namespace __detail
       _Tp& _M_get() { return _M_tp; }
 
     private:
-      _Tp _M_tp;
+      _Tp _M_tp{};
     };
 
   /**
@@ -1789,6 +1789,7 @@ namespace __detail
 
   protected:
     _Hashtable_base() = default;
+
     _Hashtable_base(const _ExtractKey& __ex, const _H1& __h1, const _H2& __h2,
 		    const _Hash& __hash, const _Equal& __eq)
     : __hash_code_base(__ex, __h1, __h2, __hash), _EqualEBO(__eq)
diff --git a/libstdc++-v3/testsuite/23_containers/unordered_map/allocator/default_init.cc b/libstdc++-v3/testsuite/23_containers/unordered_map/allocator/default_init.cc
index 473a5f1ce47..3da42453152 100644
--- a/libstdc++-v3/testsuite/23_containers/unordered_map/allocator/default_init.cc
+++ b/libstdc++-v3/testsuite/23_containers/unordered_map/allocator/default_init.cc
@@ -17,7 +17,6 @@
 
 // { dg-do run { target c++11 } }
 // { dg-options "-O0" }
-// { dg-xfail-run-if "PR c++/65816" { *-*-* } }
 
 #include <unordered_map>
 #include <testsuite_hooks.h>
diff --git a/libstdc++-v3/testsuite/23_containers/unordered_set/allocator/default_init.cc b/libstdc++-v3/testsuite/23_containers/unordered_set/allocator/default_init.cc
index 37110dd6eb0..1f2f3516859 100644
--- a/libstdc++-v3/testsuite/23_containers/unordered_set/allocator/default_init.cc
+++ b/libstdc++-v3/testsuite/23_containers/unordered_set/allocator/default_init.cc
@@ -17,7 +17,6 @@
 
 // { dg-do run { target c++11 } }
 // { dg-options "-O0" }
-// { dg-xfail-run-if "PR c++/65816" { *-*-* } }
 
 #include <unordered_set>
 #include <testsuite_hooks.h>