mirror of git://gcc.gnu.org/git/gcc.git
d942bc80e4
When the contained value is not trivially copy (or move) constructible the union's copy (or move) constructor will be deleted, and so the _Optional_payload delegating constructors are invalid. G++ fails to diagnose this because it incorrectly performs copy elision in the delegating constructors. Clang does diagnose it (llvm.org/PR40245). The solution is to avoid performing any copy (or move) when the contained value's copy (or move) constructor isn't trivial. Instead the contained value can be constructed by calling _M_construct. This is OK, because the relevant constructor doesn't need to be constexpr when the contained value isn't trivially copy (or move) constructible. Additionally, this patch removes a lot of code duplication in the _Optional_payload partial specializations and the _Optional_base partial specialization, by hoisting it into common base classes. The Python pretty printer for std::optional needs to be adjusted to support the new layout. Retain support for the old layout, and add a test to verify that the support still works. PR libstdc++/87855 * include/std/optional (_Optional_payload_base): New class template for common code hoisted from _Optional_payload specializations. Use a template for the union, to allow a partial specialization for types with non-trivial destructors. Add constructors for in-place initialization to the union. (_Optional_payload(bool, const _Optional_payload&)): Use _M_construct to perform non-trivial copy construction, instead of relying on non-standard copy elision in a delegating constructor. (_Optional_payload(bool, _Optional_payload&&)): Likewise for non-trivial move construction. (_Optional_payload): Derive from _Optional_payload_base and use it for everything except the non-trivial assignment operators, which are defined as needed. (_Optional_payload<false, C, M>): Derive from the specialization _Optional_payload<true, false, false> and add a destructor. (_Optional_base_impl::_M_destruct, _Optional_base_impl::_M_reset): Forward to corresponding members of _Optional_payload. (_Optional_base_impl::_M_is_engaged, _Optional_base_impl::_M_get): Hoist common members from _Optional_base. (_Optional_base): Make all members and base class public. (_Optional_base::_M_get, _Optional_base::_M_is_engaged): Move to _Optional_base_impl. * python/libstdcxx/v6/printers.py (StdExpOptionalPrinter): Add support for new std::optional layout. * testsuite/libstdc++-prettyprinters/compat.cc: New test. From-SVN: r267742 |
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| libgfortran | ||
| libgo | ||
| libgomp | ||
| libhsail-rt | ||
| libiberty | ||
| libitm | ||
| libobjc | ||
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README
This directory contains the GNU Compiler Collection (GCC). The GNU Compiler Collection is free software. See the files whose names start with COPYING for copying permission. The manuals, and some of the runtime libraries, are under different terms; see the individual source files for details. The directory INSTALL contains copies of the installation information as HTML and plain text. The source of this information is gcc/doc/install.texi. The installation information includes details of what is included in the GCC sources and what files GCC installs. See the file gcc/doc/gcc.texi (together with other files that it includes) for usage and porting information. An online readable version of the manual is in the files gcc/doc/gcc.info*. See http://gcc.gnu.org/bugs/ for how to report bugs usefully. Copyright years on GCC source files may be listed using range notation, e.g., 1987-2012, indicating that every year in the range, inclusive, is a copyrightable year that could otherwise be listed individually.