commit | a34f24689945e967e4ba4d79ed301d3a71870c7b | [log] [tgz] |
---|---|---|
author | Louis Dionne <ldionne.2@gmail.com> | Mon Nov 29 16:20:48 2021 -0500 |
committer | Louis Dionne <ldionne.2@gmail.com> | Tue Nov 30 06:01:45 2021 -0500 |
tree | 5c220fcd1a96286068c2f9ba58943001c1b61779 | |
parent | af059dfef5a766ceb0ac29318dfb7102131d933e [diff] |
[libc++][ABI BREAK] Do not use the C++03 emulation for std::nullptr_t by default We only support Clangs that implement nullptr as an extension in C++03 mode, and we don't support GCC in C++03 mode. Hence, this patch disables the use of the std::nullptr_t emulation in C++03 mode by default. Doing that is technically an ABI break since it changes the mangling for std::nullptr_t. However: (1) The only affected users are those compiling in C++03 mode that have std::nullptr_t as part of their ABI, which should be reasonably rare. (2) Those users already have a lingering problem in that their code will be incompatible in C++03 and C++11 modes because of that very ABI break. Hence, the only users that could really be inconvenienced about this change is those that planned on compiling in C++03 mode forever - for other users, we're just breaking them now instead of letting them break themselves later on when they try to upgrade to C++11. (3) The ABI break will cause a linker error since the mangling changed, and will not result in an obscure runtime error. Furthermore, if anyone is broken by this, they can define the _LIBCPP_ABI_USE_CXX03_NULLPTR_EMULATION macro to return to the previous behavior. We will then remove that macro after shipping this for one release if we haven't seen widespread issues. Concretely, the motivation for making this change is to make our own ABI consistent in C++03 and C++11 modes and to remove complexity around the definition of nullptr. Furthermore, we could investigate making nullptr a keyword in C++03 mode as a Clang extension -- I don't think that would break anyone, since libc++ already defines nullptr as a macro to something else. Only users that do not use libc++ and compile in C++03 mode could potentially be broken by that. Differential Revision: https://reviews.llvm.org/D109459
This directory and its sub-directories contain source code for LLVM, a toolkit for the construction of highly optimized compilers, optimizers, and run-time environments.
The README briefly describes how to get started with building LLVM. For more information on how to contribute to the LLVM project, please take a look at the Contributing to LLVM guide.
Taken from https://llvm.org/docs/GettingStarted.html.
Welcome to the LLVM project!
The LLVM project has multiple components. The core of the project is itself called “LLVM”. This contains all of the tools, libraries, and header files needed to process intermediate representations and convert them into object files. Tools include an assembler, disassembler, bitcode analyzer, and bitcode optimizer. It also contains basic regression tests.
C-like languages use the Clang front end. This component compiles C, C++, Objective-C, and Objective-C++ code into LLVM bitcode -- and from there into object files, using LLVM.
Other components include: the libc++ C++ standard library, the LLD linker, and more.
The LLVM Getting Started documentation may be out of date. The Clang Getting Started page might have more accurate information.
This is an example work-flow and configuration to get and build the LLVM source:
Checkout LLVM (including related sub-projects like Clang):
git clone https://github.com/llvm/llvm-project.git
Or, on windows, git clone --config core.autocrlf=false https://github.com/llvm/llvm-project.git
Configure and build LLVM and Clang:
cd llvm-project
cmake -S llvm -B build -G <generator> [options]
Some common build system generators are:
Ninja
--- for generating Ninja build files. Most llvm developers use Ninja.Unix Makefiles
--- for generating make-compatible parallel makefiles.Visual Studio
--- for generating Visual Studio projects and solutions.Xcode
--- for generating Xcode projects.Some common options:
-DLLVM_ENABLE_PROJECTS='...'
--- semicolon-separated list of the LLVM sub-projects you'd like to additionally build. Can include any of: clang, clang-tools-extra, compiler-rt,cross-project-tests, flang, libc, libclc, libcxx, libcxxabi, libunwind, lld, lldb, mlir, openmp, polly, or pstl.
For example, to build LLVM, Clang, libcxx, and libcxxabi, use -DLLVM_ENABLE_PROJECTS="clang;libcxx;libcxxabi"
.
-DCMAKE_INSTALL_PREFIX=directory
--- Specify for directory the full path name of where you want the LLVM tools and libraries to be installed (default /usr/local
).
-DCMAKE_BUILD_TYPE=type
--- Valid options for type are Debug, Release, RelWithDebInfo, and MinSizeRel. Default is Debug.
-DLLVM_ENABLE_ASSERTIONS=On
--- Compile with assertion checks enabled (default is Yes for Debug builds, No for all other build types).
cmake --build build [-- [options] <target>]
or your build system specified above directly.
The default target (i.e. ninja
or make
) will build all of LLVM.
The check-all
target (i.e. ninja check-all
) will run the regression tests to ensure everything is in working order.
CMake will generate targets for each tool and library, and most LLVM sub-projects generate their own check-<project>
target.
Running a serial build will be slow. To improve speed, try running a parallel build. That's done by default in Ninja; for make
, use the option -j NNN
, where NNN
is the number of parallel jobs, e.g. the number of CPUs you have.
For more information see CMake
Consult the Getting Started with LLVM page for detailed information on configuring and compiling LLVM. You can visit Directory Layout to learn about the layout of the source code tree.