[gcc r15-4979] libstdc++: More user-friendly failed assertions from shared_ptr dereference

[Jonathan Wakely via Gcc-cvs]

https://gcc.gnu.org/g:1b169ee7e25129fede3aadbeb72037017d1d5a47

commit r15-4979-g1b169ee7e25129fede3aadbeb72037017d1d5a47
Author: Jonathan Wakely <jwak...@redhat.com>
Date:   Wed Oct 30 11:41:47 2024 +0000

    libstdc++: More user-friendly failed assertions from shared_ptr dereference
    
    Currently dereferencing an empty shared_ptr prints a complicated
    internal type in the assertion message:
    
    include/bits/shared_ptr_base.h:1377: std::__shared_ptr_access<_Tp, _Lp, 
<anonymous>, <anonymous> >::element_type& std::__shared_ptr_access<_Tp, _Lp, 
<anonymous>, <anonymous> >::operator*() const [with _Tp = 
std::filesystem::__cxx11::recursive_directory_iterator::_Dir_stack; 
__gnu_cxx::_Lock_policy _Lp = __gnu_cxx::_S_atomic; bool <anonymous> = false; 
bool <anonymous> = false; element_type = 
std::filesystem::__cxx11::recursive_directory_iterator::_Dir_stack]: Assertion 
'_M_get() != nullptr' failed.
    
    Users don't care about any of the _Lp and <anonymous> template
    parameters, so this is unnecessarily verbose.
    
    We can simplify it to something that only mentions "shared_ptr_deref"
    and the element type:
    
    include/bits/shared_ptr_base.h:1371: _Tp* std::__shared_ptr_deref(_Tp*) 
[with _Tp = filesystem::__cxx11::recursive_directory_iterator::_Dir_stack]: 
Assertion '__p != nullptr' failed.
    
    libstdc++-v3/ChangeLog:
    
            * include/bits/shared_ptr_base.h (__shared_ptr_deref): New
            function template.
            (__shared_ptr_access, __shared_ptr_access<>): Use it.

Diff:
---
 libstdc++-v3/include/bits/shared_ptr_base.h | 28 +++++++++++++++++-----------
 1 file changed, 17 insertions(+), 11 deletions(-)

diff --git a/libstdc++-v3/include/bits/shared_ptr_base.h 
b/libstdc++-v3/include/bits/shared_ptr_base.h
index 9a7617e7014f..ee01594ce0c5 100644
--- a/libstdc++-v3/include/bits/shared_ptr_base.h
+++ b/libstdc++-v3/include/bits/shared_ptr_base.h
@@ -1337,6 +1337,15 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
     { };
 
 
+  template<typename _Tp>
+    [[__gnu__::__always_inline__]]
+    inline _Tp*
+    __shared_ptr_deref(_Tp* __p)
+    {
+      __glibcxx_assert(__p != nullptr);
+      return __p;
+    }
+
   // Define operator* and operator-> for shared_ptr<T>.
   template<typename _Tp, _Lock_policy _Lp,
           bool = is_array<_Tp>::value, bool = is_void<_Tp>::value>
@@ -1347,10 +1356,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
 
       element_type&
       operator*() const noexcept
-      {
-       __glibcxx_assert(_M_get() != nullptr);
-       return *_M_get();
-      }
+      { return *std::__shared_ptr_deref(_M_get()); }
 
       element_type*
       operator->() const noexcept
@@ -1392,10 +1398,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
       [[__deprecated__("shared_ptr<T[]>::operator* is absent from C++17")]]
       element_type&
       operator*() const noexcept
-      {
-       __glibcxx_assert(_M_get() != nullptr);
-       return *_M_get();
-      }
+      { return *std::__shared_ptr_deref(_M_get()); }
 
       [[__deprecated__("shared_ptr<T[]>::operator-> is absent from C++17")]]
       element_type*
@@ -1406,13 +1409,16 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
       }
 #endif
 
+#pragma GCC diagnostic push
+#pragma GCC diagnostic ignored "-Wc++17-extensions"
       element_type&
       operator[](ptrdiff_t __i) const noexcept
       {
-       __glibcxx_assert(_M_get() != nullptr);
-       __glibcxx_assert(!extent<_Tp>::value || __i < extent<_Tp>::value);
-       return _M_get()[__i];
+       if constexpr (extent<_Tp>::value)
+         __glibcxx_assert(__i < extent<_Tp>::value);
+       return std::__shared_ptr_deref(_M_get())[__i];
       }
+#pragma GCC diagnostic pop
 
     private:
       element_type*