[committed 2/5] libstdc++: Use nothrow new in std::stacktrace

[Jonathan Wakely via Gcc-patches]

Tested powerpc64-linux, pushed to trunk.

-- >8 --

We can avoid the overhead of handling a bad_alloc exception from
std::allocator<std::stacktrace_entry>::allocate by just calling the
nothrow operator new instead.

libstdc++-v3/ChangeLog:

        * include/std/stacktrace (basic_stacktrace::_Impl::_M_allocate):
        Use nothrow new instead of try block for std::allocator.
        (basic_stacktrace::_Impl::_M_deallocate): Use delete for
        std::allocator.
---
 libstdc++-v3/include/std/stacktrace | 42 ++++++++++++++++++++++++-----
 1 file changed, 35 insertions(+), 7 deletions(-)

diff --git a/libstdc++-v3/include/std/stacktrace 
b/libstdc++-v3/include/std/stacktrace
index 5f928f10dee..f36c5a9abef 100644
--- a/libstdc++-v3/include/std/stacktrace
+++ b/libstdc++-v3/include/std/stacktrace
@@ -30,6 +30,7 @@
 
 #if __cplusplus > 202002L && _GLIBCXX_HAVE_STACKTRACE
 #include <compare>
+#include <new>
 #include <string>
 #include <sstream>
 #include <bits/stl_algobase.h>
@@ -589,23 +590,43 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
          return std::min(__size_max, __alloc_max);
        }
 
+#if __has_builtin(__builtin_operator_new) >= 201802L
+# define _GLIBCXX_OPERATOR_NEW __builtin_operator_new
+# define _GLIBCXX_OPERATOR_DELETE __builtin_operator_delete
+#else
+# define _GLIBCXX_OPERATOR_NEW ::operator new
+# define _GLIBCXX_OPERATOR_DELETE ::operator delete
+#endif
+
        // Precondition: _M_frames == nullptr && __n != 0
        pointer
        _M_allocate(allocator_type& __alloc, size_type __n) noexcept
        {
          if (__n <= _S_max_size(__alloc)) [[likely]]
            {
-             __try
+             if constexpr (is_same_v<allocator_type, allocator<value_type>>)
                {
-                 _M_frames = __alloc.allocate(__n);
-                 _M_capacity = __n;
-                 return _M_frames;
+                 __n *= sizeof(value_type);
+                 void* const __p = _GLIBCXX_OPERATOR_NEW (__n, nothrow_t{});
+                 if (__p == nullptr) [[unlikely]]
+                   return nullptr;
+                 _M_frames = static_cast<pointer>(__p);
                }
-             __catch (...)
+             else
                {
+                 __try
+                   {
+                     _M_frames = __alloc.allocate(__n);
+                   }
+                 __catch (const std::bad_alloc&)
+                   {
+                     return nullptr;
+                   }
                }
+             _M_capacity = __n;
+             return _M_frames;
            }
-         return nullptr;;
+         return nullptr;
        }
 
        void
@@ -613,12 +634,19 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
        {
          if (_M_capacity)
            {
-             __alloc.deallocate(_M_frames, _M_capacity);
+             if constexpr (is_same_v<allocator_type, allocator<value_type>>)
+               _GLIBCXX_OPERATOR_DELETE (static_cast<void*>(_M_frames),
+                                         _M_capacity * sizeof(value_type));
+             else
+               __alloc.deallocate(_M_frames, _M_capacity);
              _M_frames = nullptr;
              _M_capacity = 0;
            }
        }
 
+#undef _GLIBCXX_OPERATOR_DELETE
+#undef _GLIBCXX_OPERATOR_NEW
+
        void
        _M_destroy() noexcept
        {
-- 
2.34.1