[PATCH] do not throw in std::make_exception_ptr

[Jonathan Wakely]

On 04/08/16 20:01 +0300, Gleb Natapov wrote:
>Instead of throwing an exception allocate its memory and initialize it
>explicitly. Makes std::make_exception_ptr more efficient since no stack
>unwinding is needed.
>
>In this version I hopefully addressed all Jonathan comments.
>
>* libsupc++/exception (std::exception): Move...
>* libsupc++/exception.h: ...here; New.
>* libsupc++/cxxabi.h (__cxa_allocate_exception): Move...
>* libsupc++/cxxabi_init_exception.h: ...here and add
>__cxa_init_primary_exception; New.
>* config/abi/pre/gnu-versioned-namespace.ver: add
>__cxa_init_primary_exception and std::exception_ptr(void*)
>* config/abi/pre/gnu.ver (CXXABI_1.3.11) : add
>__cxa_init_primary_exception and std::exception_ptr(void*)
>(CXXABI_1.3.11): New.
>* include/Makefile.am: add exception.h and cxxabi_init_exception.h
>* include/Makefile.in: Likewise.
>* libsupc++/Makefile.am: add exception.h and cxxabi_init_exception.h
>* libsupc++/Makefile.in: Likewise.
>* libsupc++/eh_throw.cc(__cxa_throw): add __cxa_init_primary_exception
>and use it
>* libsupc++/exception_ptr.h(std::make_exception_ptr): use
>__cxa_allocate_exception and __cxa_init_primary_exception to create
>exception pointer
>* libsupc++/typeinfo: include bits/exception.h instead of exception

This version is *much* easier to review :-)

>+namespace __cxxabiv1
>+{
>+  struct __cxa_refcounted_exception;
>+
>+  extern "C"
>+    {
>+      // Allocate memory for the primary exception plus the thrown object.
>+      void*
>+        __cxa_allocate_exception(size_t) _GLIBCXX_NOTHROW;

Please align __cxa_allocate_exception with the return type on the
previous line.

>+
>+      // Initialize exception

Please add "(this is a GNU extension)" to the comment.

>+      __cxa_refcounted_exception*
>+      __cxa_init_primary_exception(void *object, std::type_info *tinfo,
>+                void (_GLIBCXX_CDTOR_CALLABI *dest) (void *)) _GLIBCXX_NOTHROW;
>+
>+    }
>+} // namespace __cxxabiv1
>+
>+#endif
>+
>+#pragma GCC visibility pop
>+
>+#endif // _CXXABI_INIT_EXCEPTION_H
>index 63631f6..8be903b 100644
>--- a/libstdc++-v3/libsupc++/exception
>+++ b/libstdc++-v3/libsupc++/exception
>@@ -36,39 +36,12 @@
>
> #include <bits/c++config.h>
> #include <bits/atomic_lockfree_defines.h>
>+#include <bits/exception.h>
>
> extern "C++" {
>
> namespace std
> {
>-  /**
>-   * @defgroup exceptions Exceptions
>-   * @ingroup diagnostics
>-   *
>-   * Classes and functions for reporting errors via exception classes.
>-   * @{
>-   */

The Doxygen group that starts with @{ ends later in this file, but you
haven't moved the corresponding @} to the new file.

I can take care of fixing that up though (we want the contents of the
new file and this one to all be in the group).


>@@ -162,8 +169,12 @@ namespace std
>     swap(exception_ptr& __lhs, exception_ptr& __rhs)
>     { __lhs.swap(__rhs); }
>
>-  } // namespace __exception_ptr
>+    template<typename _Ex>
>+      static inline void
>+      __dest_thunk(void* x)
>+      { reinterpret_cast<_Ex*>(x)->~_Ex(); }

This is still 'static' so we get a separate instantiation in every
translation unit that uses make_exception_ptr. It should non 'inline'
but not 'static'.

Looking at it again now, is there any reason to use reinterpret_cast
rather than static_cast? I think they're identical in this context,
and I prefer not to only use reinterpret_cast as a last resort.

Other than that, I think this is good to commit.

I can't think of any way to test the changes beyond the existing tests
for exception_ptr, so we don't need new test files.