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Testing libc++
.. contents::
Getting Started
libc++ uses LIT to configure and run its tests.
The primary way to run the libc++ tests is by using `make check-libcxx`.
However since libc++ can be used in any number of possible
configurations it is important to customize the way LIT builds and runs
the tests. This guide provides information on how to use LIT directly to
test libc++.
Please see the `Lit Command Guide`_ for more information about LIT.
.. _LIT Command Guide:
Setting up the Environment
After building libc++ you must setup your environment to test libc++ using
#. Create a shortcut to the actual lit executable so that you can invoke it
easily from the command line.
.. code-block:: bash
$ alias lit='python path/to/llvm/utils/lit/'
#. Tell LIT where to find your build configuration.
.. code-block:: bash
$ export LIBCXX_SITE_CONFIG=path/to/build-libcxx/test/
Example Usage
Once you have your environment set up and you have built libc++ you can run
parts of the libc++ test suite by simply running `lit` on a specified test or
directory. For example:
.. code-block:: bash
$ cd path/to/src/libcxx
$ lit -sv test/std/re # Run all of the std::regex tests
$ lit -sv test/std/depr/depr.c.headers/stdlib_h.pass.cpp # Run a single test
$ lit -sv test/std/atomics test/std/threads # Test std::thread and std::atomic
Sometimes you'll want to change the way LIT is running the tests. Custom options
can be specified using the `--param=<name>=<val>` flag. The most common option
you'll want to change is the standard dialect (ie -std=c++XX). By default the
test suite will select the newest C++ dialect supported by the compiler and use
that. However if you want to manually specify the option like so:
.. code-block:: bash
$ lit -sv test/std/containers # Run the tests with the newest -std
$ lit -sv --param=std=c++03 test/std/containers # Run the tests in C++03
Occasionally you'll want to add extra compile or link flags when testing.
You can do this as follows:
.. code-block:: bash
$ lit -sv --param=compile_flags='-Wcustom-warning'
$ lit -sv --param=link_flags='-L/custom/library/path'
Some other common examples include:
.. code-block:: bash
# Specify a custom compiler.
$ lit -sv --param=cxx_under_test=/opt/bin/g++ test/std
# Enable warnings in the test suite
$ lit -sv --param=enable_warnings=true test/std
# Use UBSAN when running the tests.
$ lit -sv --param=use_sanitizer=Undefined
LIT Options
:program:`lit` [*options*...] [*filenames*...]
Command Line Options
To use these options you pass them on the LIT command line as --param NAME or
--param NAME=VALUE. Some options have default values specified during CMake's
configuration. Passing the option on the command line will override the default.
.. program:: lit
.. option:: cxx_under_test=<path/to/compiler>
Specify the compiler used to build the tests.
.. option:: cxx_stdlib_under_test=<stdlib name>
**Values**: libc++, libstdc++
Specify the C++ standard library being tested. Unless otherwise specified
libc++ is used. This option is intended to allow running the libc++ test
suite against other standard library implementations.
.. option:: std=<standard version>
**Values**: c++98, c++03, c++11, c++14, c++17, c++2a
Change the standard version used when building the tests.
.. option:: libcxx_site_config=<path/to/>
Specify the site configuration to use when running the tests. This option
overrides the environment variable LIBCXX_SITE_CONFIG.
.. option:: cxx_headers=<path/to/headers>
Specify the c++ standard library headers that are tested. By default the
headers in the source tree are used.
.. option:: cxx_library_root=<path/to/lib/>
Specify the directory of the libc++ library to be tested. By default the
library folder of the build directory is used. This option cannot be used
when use_system_cxx_lib is provided.
.. option:: cxx_runtime_root=<path/to/lib/>
Specify the directory of the libc++ library to use at runtime. This directory
is not added to the linkers search path. This can be used to compile tests
against one version of libc++ and run them using another. The default value
for this option is `cxx_library_root`.
.. option:: use_system_cxx_lib=<bool>
**Default**: False
Enable or disable testing against the installed version of libc++ library.
Note: This does not use the installed headers.
.. option:: use_lit_shell=<bool>
Enable or disable the use of LIT's internal shell in ShTests. If the
environment variable LIT_USE_INTERNAL_SHELL is present then that is used as
the default value. Otherwise the default value is True on Windows and False
on every other platform.
.. option:: compile_flags="<list-of-args>"
Specify additional compile flags as a space delimited string.
Note: This options should not be used to change the standard version used.
.. option:: link_flags="<list-of-args>"
Specify additional link flags as a space delimited string.
.. option:: debug_level=<level>
**Values**: 0, 1
Enable the use of debug mode. Level 0 enables assertions and level 1 enables
assertions and debugging of iterator misuse.
.. option:: use_sanitizer=<sanitizer name>
**Values**: Memory, MemoryWithOrigins, Address, Undefined
Run the tests using the given sanitizer. If LLVM_USE_SANITIZER was given when
building libc++ then that sanitizer will be used by default.
.. option:: color_diagnostics
Enable the use of colorized compile diagnostics. If the color_diagnostics
option is specified or the environment variable LIBCXX_COLOR_DIAGNOSTICS is
present then color diagnostics will be enabled.
.. option:: llvm_unwinder
Enable the use of LLVM unwinder instead of libgcc.
.. option:: builtins_library
Path to the builtins library to use instead of libgcc.
Environment Variables
.. envvar:: LIBCXX_SITE_CONFIG=<path/to/>
Specify the site configuration to use when running the tests.
Also see `libcxx_site_config`.
If ``LIBCXX_COLOR_DIAGNOSTICS`` is defined then the test suite will attempt
to use color diagnostic outputs from the compiler.
Also see `color_diagnostics`.
Libc++ contains benchmark tests separately from the test of the test suite.
The benchmarks are written using the `Google Benchmark`_ library, a copy of which
is stored in the libc++ repository.
For more information about using the Google Benchmark library see the
`official documentation <>`_.
.. _`Google Benchmark`:
Building Benchmarks
The benchmark tests are not built by default. The benchmarks can be built using
the ``cxx-benchmarks`` target.
An example build would look like:
.. code-block:: bash
$ cd build
$ cmake [options] <path to libcxx sources>
$ make cxx-benchmarks
This will build all of the benchmarks under ``<libcxx-src>/benchmarks`` to be
built against the just-built libc++. The compiled tests are output into
The benchmarks can also be built against the platforms native standard library
is useful for comparing the performance of libc++ to other standard libraries.
The compiled benchmarks are named ``<test>.libcxx.out`` if they test libc++ and
``<test>.native.out`` otherwise.
Also See:
* :ref:`Building Libc++ <build instructions>`
* :ref:`CMake Options`
Running Benchmarks
The benchmarks must be run manually by the user. Currently there is no way
to run them as part of the build.
For example:
.. code-block:: bash
$ cd build/benchmarks
$ make cxx-benchmarks
$ ./algorithms.libcxx.out # Runs all the benchmarks
$ ./algorithms.libcxx.out --benchmark_filter=BM_Sort.* # Only runs the sort benchmarks
For more information about running benchmarks see `Google Benchmark`_.