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Move to C++14
Summary: I just bumped the minimum compiler versions to support C++14 in D66188. Following [our process](http://llvm.org/docs/DeveloperPolicy.html#toolchain) and [our previous agreement](http://lists.llvm.org/pipermail/llvm-dev/2019-January/129452.html), I'm now officially bumping the C++ version to 14 and updating the documentation. Subscribers: mgorny, jkorous, dexonsmith, llvm-commits, chandlerc, thakis, EricWF, jyknight, lhames, JDevlieghere Tags: #llvm Differential Revision: https://reviews.llvm.org/D66195 git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@368887 91177308-0d34-0410-b5e6-96231b3b80d8
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JF Bastien
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@ -18,7 +18,7 @@ else()
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set(LINKER_IS_LLD_LINK FALSE)
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endif()
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set(LLVM_CXX_STD_default "c++11")
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set(LLVM_CXX_STD_default "c++14")
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# Preserve behaviour of legacy cache variables
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if (LLVM_ENABLE_CXX1Y)
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set(LLVM_CXX_STD_default "c++1y")
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@ -56,12 +56,12 @@ choice.
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C++ Standard Versions
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---------------------
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LLVM, Clang, and LLD are currently written using C++11 conforming code,
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LLVM, Clang, and LLD are currently written using C++14 conforming code,
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although we restrict ourselves to features which are available in the major
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toolchains supported as host compilers. The LLDB project is even more
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aggressive in the set of host compilers supported and thus uses still more
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features. Regardless of the supported features, code is expected to (when
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reasonable) be standard, portable, and modern C++11 code. We avoid unnecessary
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reasonable) be standard, portable, and modern C++14 code. We avoid unnecessary
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vendor-specific extensions, etc.
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C++ Standard Library
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@ -78,10 +78,10 @@ There are some exceptions such as the standard I/O streams library which are
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avoided. Also, there is much more detailed information on these subjects in the
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:doc:`ProgrammersManual`.
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Supported C++11 Language and Library Features
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Supported C++14 Language and Library Features
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---------------------------------------------
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While LLVM, Clang, and LLD use C++11, not all features are available in all of
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While LLVM, Clang, and LLD use C++14, not all features are available in all of
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the toolchains which we support. The set of features supported for use in LLVM
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is the intersection of those supported in the minimum requirements described
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in the :doc:`GettingStarted` page, section `Software`.
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@ -92,100 +92,9 @@ guidance below to help you know what to expect.
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Each toolchain provides a good reference for what it accepts:
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* Clang: https://clang.llvm.org/cxx_status.html
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* GCC: https://gcc.gnu.org/projects/cxx-status.html#cxx11
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* GCC: https://gcc.gnu.org/projects/cxx-status.html#cxx14
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* MSVC: https://msdn.microsoft.com/en-us/library/hh567368.aspx
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In most cases, the MSVC list will be the dominating factor. Here is a summary
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of the features that are expected to work. Features not on this list are
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unlikely to be supported by our host compilers.
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* Rvalue references: N2118_
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* But *not* Rvalue references for ``*this`` or member qualifiers (N2439_)
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* Static assert: N1720_
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* ``auto`` type deduction: N1984_, N1737_
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* Trailing return types: N2541_
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* Lambdas: N2927_
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* But *not* lambdas with default arguments.
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* ``decltype``: N2343_
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* Nested closing right angle brackets: N1757_
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* Extern templates: N1987_
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* ``nullptr``: N2431_
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* Strongly-typed and forward declarable enums: N2347_, N2764_
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* Local and unnamed types as template arguments: N2657_
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* Range-based for-loop: N2930_
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* But ``{}`` are required around inner ``do {} while()`` loops. As a result,
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``{}`` are required around function-like macros inside range-based for
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loops.
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* ``override`` and ``final``: N2928_, N3206_, N3272_
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* Atomic operations and the C++11 memory model: N2429_
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* Variadic templates: N2242_
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* Explicit conversion operators: N2437_
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* Defaulted and deleted functions: N2346_
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* Initializer lists: N2627_
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* Delegating constructors: N1986_
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* Default member initializers (non-static data member initializers): N2756_
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* Feel free to use these wherever they make sense and where the `=`
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syntax is allowed. Don't use braced initialization syntax.
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.. _N2118: http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2006/n2118.html
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.. _N2439: http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2007/n2439.htm
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.. _N1720: http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2004/n1720.html
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.. _N1984: http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2006/n1984.pdf
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.. _N1737: http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2004/n1737.pdf
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.. _N2541: http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2008/n2541.htm
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.. _N2927: http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2009/n2927.pdf
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.. _N2343: http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2007/n2343.pdf
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.. _N1757: http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2005/n1757.html
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.. _N1987: http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2006/n1987.htm
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.. _N2431: http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2007/n2431.pdf
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.. _N2347: http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2007/n2347.pdf
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.. _N2764: http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2008/n2764.pdf
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.. _N2657: http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2008/n2657.htm
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.. _N2930: http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2009/n2930.html
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.. _N2928: http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2009/n2928.htm
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.. _N3206: http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2010/n3206.htm
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.. _N3272: http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2011/n3272.htm
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.. _N2429: http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2007/n2429.htm
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.. _N2242: http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2007/n2242.pdf
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.. _N2437: http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2007/n2437.pdf
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.. _N2346: http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2007/n2346.htm
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.. _N2627: http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2008/n2672.htm
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.. _N1986: http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2006/n1986.pdf
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.. _N2756: http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2008/n2756.htm
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The supported features in the C++11 standard libraries are less well tracked,
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but also much greater. Most of the standard libraries implement most of C++11's
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library. The most likely lowest common denominator is Linux support. For
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libc++, the support is just poorly tested and undocumented but expected to be
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largely complete. YMMV. For libstdc++, the support is documented in detail in
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`the libstdc++ manual`_. There are some very minor missing facilities that are
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unlikely to be common problems, and there are a few larger gaps that are worth
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being aware of:
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* Not all of the type traits are implemented
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* No regular expression library.
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* While most of the atomics library is well implemented, the fences are
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missing. Fortunately, they are rarely needed.
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* The locale support is incomplete.
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Other than these areas you should assume the standard library is available and
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working as expected until some build bot tells you otherwise. If you're in an
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uncertain area of one of the above points, but you cannot test on a Linux
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system, your best approach is to minimize your use of these features, and watch
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the Linux build bots to find out if your usage triggered a bug. For example, if
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you hit a type trait which doesn't work we can then add support to LLVM's
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traits header to emulate it.
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.. _the libstdc++ manual:
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https://gcc.gnu.org/onlinedocs/gcc-4.8.0/libstdc++/manual/manual/status.html#status.iso.2011
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Other Languages
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---------------
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@ -808,6 +717,9 @@ type is already obvious from the context. Another time when ``auto`` works well
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for these purposes is when the type would have been abstracted away anyways,
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often behind a container's typedef such as ``std::vector<T>::iterator``.
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Similarly, C++14 adds generic lambda expressions where parameter types can be
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``auto``. Use these where you would have used a template.
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Beware unnecessary copies with ``auto``
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^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
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@ -43,6 +43,12 @@
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# define __has_builtin(x) 0
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#endif
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#ifdef __cplusplus
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# if __cplusplus < 201402L
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# error Expected C++14 or later.
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# endif
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#endif
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/// \macro LLVM_GNUC_PREREQ
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/// Extend the default __GNUC_PREREQ even if glibc's features.h isn't
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/// available.
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@ -192,7 +192,7 @@ class is_trivially_copyable<T*> : public std::true_type {
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// If the compiler supports detecting whether a class is final, define
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// an LLVM_IS_FINAL macro. If it cannot be defined properly, this
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// macro will be left undefined.
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#if __cplusplus >= 201402L || defined(_MSC_VER)
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#if defined(__cplusplus) || defined(_MSC_VER)
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#define LLVM_IS_FINAL(Ty) std::is_final<Ty>()
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#elif __has_feature(is_final) || LLVM_GNUC_PREREQ(4, 7, 0)
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#define LLVM_IS_FINAL(Ty) __is_final(Ty)
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