Test Producers

On the client-side, LNT comes with a number of built-in test data producers. This section focuses on the LLVM test-suite (aka nightly test) generator, since it is the primary test run using the LNT infrastructure, but note that LNT also includes tests for other interesting pieces of data, for example Clang compile-time performance.

LNT also makes it easy to add new test data producers and includes examples of custom data importers (e.g., to import buildbot build information into) and dynamic test data generators (e.g., abusing the infrastructure to plot graphs, for example).

Running a Local Server

It is useful to set up a local LNT server to view the results of tests, either for personal use or to preview results before submitting them to a public server. To set up a one-off server for testing:

# Create a new installation in /tmp/FOO.
$ lnt create /tmp/FOO
created LNT configuration in '/tmp/FOO'

# Run a local LNT server.
$ lnt runserver /tmp/FOO &> /tmp/FOO/runserver.log &
[2] 69694

# Watch the server log.
$ tail -f /tmp/FOO/runserver.log
* Running on http://localhost:8000/

Running Tests

The built-in tests are designed to be run via the lnt tool. The following tools for working with built-in tests are available:

lnt showtests
List the available tests. Tests are defined with an extensible architecture. FIXME: Point at docs on how to add a new test.
lnt runtest [<run options>] <test name> ... test arguments ...

Run the named test. The run tool itself accepts a number of options which are common to all tests. The most common option is --submit=<url> which specifies the server to submit the results to after testing is complete. See lnt runtest --help for more information on the available options.

The remainder of the options are passed to the test tool itself. The options are specific to the test, but well behaved tests should respond to lnt runtest <test name> --help. The following section provides specific documentation on the built-in tests.

Built-in Tests

LLVM CMake test-suite

The llvm test-suite can be run with the test-suite built-in test.

Running the test-suite via CMake and lit uses a different LNT test:

rm -rf /tmp/BAR
lnt runtest test-suite \
     --sandbox /tmp/BAR \
     --cc ~/llvm.obj.64/Release+Asserts/bin/clang \
     --cxx ~/llvm.obj.64/Release+Asserts/bin/clang++ \
     --use-cmake=/usr/local/bin/cmake \
     --use-lit=~/llvm/utils/lit/lit.py \
     --test-suite ~/llvm-test-suite \
     --cmake-cache Release

Since the CMake test-suite uses lit to run the tests and compare their output, LNT needs to know the path to your LLVM lit installation. The test-suite holds some common configurations in CMake caches. The --cmake-cache flag and the --cmake-define flag allow you to change how LNT configures cmake for the test-suite run.

LLVM Makefile test-suite (aka LLVM Nightly Test)


The Makefile test-suite is deprecated. Consider using the cmake based lnt runtest test-suite mode instead. It is actively maintained, collects additional metrics such as code size and has extra features such as producing and using PGO data.

The nt built-in test runs the LLVM test-suite execution and performance tests, in the “nightly test” configuration. This test allows running many different applications and benchmarks (e.g., SPEC), with various compile options, and in several different configurations (for example, using an LLVM compiler like clang or llvm-gcc, running under the LLVM JIT compiler using the LLVM lli bit-code interpreter, or testing new code generator passes).

The nt test requires that the LLVM test-suite repository, a working LLVM compiler, and a LLVM source and build tree are available. Currently, the LLVM build tree is expected to have been built-in the Release+Asserts configuration. Unlike the prior NewNightlyTest.pl, the nt tool does not checkout or build any thing, it is expected that users manage their own LLVM source and build trees. Ideally, each of the components should be based on the same LLVM revision (except perhaps the LLVM test-suite), but this is not required.

The test runs the LLVM test-suite builds and execution inside a user specificed sandbox directory. By default, each test run will be done in a timestamped directory inside the sandbox, and the results left around for post-mortem analysis. Currently, the user is responsible for cleaning up these directories to manage disk space.

The tests are always expected to be run using out-of-tree builds – this is a more robust model and allow sharing the same source trees across many test runs. One current limitation is that the LLVM test-suite repository will not function correctly if an in-tree build is done, followed by an out-of-tree build. It is very important that the LLVM test-suite repository be left pristine.

The following command shows an example of running the nt test suite on a local build:

$ rm -rf /tmp/BAR
$ lnt runtest nt \
     --sandbox /tmp/BAR \
     --cc ~/llvm.obj.64/Release+Asserts/bin/clang \
     --cxx ~/llvm.obj.64/Release+Asserts/bin/clang++ \
     --llvm-src ~/llvm \
     --llvm-obj ~/llvm.obj.64 \
     --test-suite ~/llvm-test-suite \
      -j 16
2010-04-17 23:46:40: using nickname: 'TESTER_NAME__clang_DEV__i386'
2010-04-17 23:46:40: creating sandbox: '/tmp/BAR'
2010-04-17 23:46:40: starting test in '/private/tmp/BAR/test-2010-04-17_23-46-40'
2010-04-17 23:46:40: configuring...
2010-04-17 23:46:50: testing...
2010-04-17 23:51:04: loading test data...
2010-04-17 23:51:05: generating report: '/private/tmp/BAR/test-2010-04-17_23-46-40/report.json'

The first seven arguments are all required – they specify the sandbox path, the compilers to test, and the paths to the required sources and builds. The TESTER_NAME argument is used to derive the name for this tester (in conjunction which some inferred information about the compiler under test). This name is used as a short identifier for the test machine; generally it should be the hostname of the machine or the name of the person who is responsible for the tester. The -j 16 argument is optional, in this case it specifies that tests should be run in parallel using up to 16 processes.

In this case, we can see from the output that the test created a new sandbox directory, then ran the test in a subdirectory in that sandbox. The test outputs a limited about of summary information as testing is in progress. The full information can be found in .log files within the test build directory (e.g., configure.log and test.log).

The final test step was to generate a test report inside the test directory. This report can now be submitted directly to an LNT server. For example, if we have a local server running as described earlier, we can run:

$ lnt submit http://localhost:8000/submitRun \

IMPORT: /tmp/FOO/lnt_tmp/data-2010-04-17_16-54-35ytpQm_.plist
  LOAD TIME: 0.34s
  IMPORT TIME: 5.23s
ADDED: 1 machines
ADDED: 1 runs
ADDED: 1990 tests

and view the results on our local server.

LNT-based NT test modules

In order to support more complicated tests, or tests which are not easily integrated into the more strict SingleSource or MultiSource layout of the LLVM test-suite module, the nt built-in test provides a mechanism for LLVM test-suite tests that just define an extension test module. These tests are passed the user configuration parameters for a test run and expected to return back the test results in the LNT native format.

Test modules are defined by providing a TestModule file in a subdirectory of the LNTBased root directory inside the LLVM test-suite repository. The TestModule file is expected to be a well-formed Python module that provides a test_class global variable which should be a subclass of the lnt.tests.nt.TestModule abstract base class.

The test class should override the execute_test method which is passed an options dictionary containg the NT user parameters which apply to test execution, and the test should return the test results as a list of lnt.testing.TestSamples objects.

The execute_test method is passed the following options describing information about the module itself:

  • MODULENAME - The name of the module (primarily intended for use in producing well structured test names).
  • SRCROOT - The path to the modules source directory.
  • OBJROOT - The path to a directory the module should use for temporary output (build products). The directory is guaranteed to exist but is not guaranteed to be clean.

The method is passed the following options which apply to how tests should be executed:

  • THREADS - The number of parallel processes to run during testing.
  • BUILD_THREADS - The number of parallel processes to use while building tests (if applicable).

The method is passed the following options which specify how and whether tests should be executed remotely. If any of these parameters are present then all are guaranteed to be present.

  • REMOTE_HOST - The host name of the remote machine to execute tests on.
  • REMOTE_USER - The user to log in to the remote machine as.
  • REMOTE_PORT - The port to connect to the remote machine on.
  • REMOTE_CLIENT - The rsh compatible client to use to connect to the remote machine with.

The method is passed the following options which specify how to build the tests:

  • CC - The C compiler command to use.
  • CXX - The C++ compiler command to use.
  • CFLAGS - The compiler flags to use for building C code.
  • CXXFLAGS - The compiler flags to use for building C++ code.

The method is passed the following optional parameters which specify the environment to use for various commands:

  • COMPILE_ENVIRONMENT_OVERRIDES [optional] - If given, a env style list of environment overrides to use when compiling.
  • LINK_ENVIRONMENT_OVERRIDES [optional] - If given, a env style list of environment overrides to use when linking.
  • EXECUTION_ENVIRONMENT_OVERRIDES [optional] - If given, a env style list of environment overrides to use when executing tests.

For more information, see the example tests in the LLVM test-suite repository under the LNT/Examples directory.

Capturing Linux perf profile info

When using the CMake driver in the test-suite, LNT can also capture profile information using linux perf. This can then be explored through the LNT webUI as demonstrated at http://blog.llvm.org/2016/06/using-lnt-to-track-performance.html .

To capture these profiles, use command line option --use-perf=all. A typical command line using this for evaluating the performance of generated code looks something like the following:

lnt runtest test-suite \
     --sandbox SANDBOX \
     --cc ~/bin/clang \
     --use-cmake=/usr/local/bin/cmake \
     --use-lit=~/llvm/utils/lit/lit.py \
     --test-suite ~/llvm-test-suite \
     --benchmarking-only \
     --build-threads 8 \
     --threads 1 \
     --use-perf=all \
     --exec-multisample=5 \
     --run-under 'taskset -c 1'

Bisecting: --single-result and --single-result-predicate

The LNT driver for the CMake-based test suite comes with helpers for bisecting conformance and performance changes with llvmlab bisect.

llvmlab bisect is part of the zorg repository and allows easy bisection of some predicate through a build cache. The key to using llvmlab effectively is to design a good predicate command - one which exits with zero on ‘pass’ and nonzero on ‘fail’.

LNT normally runs one or more tests then produces a test report. It always exits with status zero unless an internal error occurred. The --single-result argument changes LNT’s behaviour - it will only run one specific test and will apply a predicate to the result of that test to determine LNT’s exit status.

The --single-result-predicate argument defines the predicate to use. This is a Python expression that is executed in a context containing several pre-set variables:

  • status - Boolean passed or failed (True for passed, False for failed).
  • exec_time - Execution time (note that exec is a reserved keyword in Python!)
  • compile (or compile_time) - Compilation time

Any metrics returned from the test, such as “score” or “hash” are also added to the context.

The default predicate is simply status - so this can be used to debug correctness regressions out of the box. More complex predicates are possible; for example exec_time < 3.0 would bisect assuming that a ‘good’ result takes less than 3 seconds.

Full example using llvmlab to debug a performance improvement:

llvmlab bisect --min-rev=261265 --max-rev=261369 \
  lnt runtest test-suite \
    --cc '%(path)s/bin/clang' \
    --sandbox SANDBOX \
    --test-suite /work/llvm-test-suite \
    --use-lit lit \
    --run-under 'taskset -c 5' \
    --cflags '-O3 -mthumb -mcpu=cortex-a57' \
    --single-result MultiSource/Benchmarks/TSVC/Expansion-flt/Expansion-flt \
    --single-result-predicate 'exec_time > 8.0'

Producing Diagnositic Reports

The test-suite module can produce a diagnostic report which might be useful for figuring out what is going on with a benchmark:

lnt runtest test-suite \
       --sandbox /tmp/BAR \
       --cc ~/llvm.obj.64/Release+Asserts/bin/clang \
       --cxx ~/llvm.obj.64/Release+Asserts/bin/clang++ \
       --use-cmake=/usr/local/bin/cmake \
       --use-lit=~/llvm/utils/lit/lit.py \
       --test-suite ~/llvm-test-suite \
       --cmake-cache Release \
       --diagnose --only-test SingleSource/Benchmarks/Stanford/Bubblesort

This will run the test-suite many times over, collecting useful information in a report directory. The report collects many things like execution profiles, compiler time reports, intermediate files, binary files, and build information.


The best way to run the test-suite in a cross-compiling setup with the cmake driver is to use cmake’s built-in support for cross-compiling as much as possible. In practice, the recommended way to cross-compile is to use a cmake toolchain file (see https://cmake.org/cmake/help/v3.0/manual/cmake-toolchains.7.html#cross-compiling)

An example command line for cross-compiling on an X86 machine, targeting AArch64 linux, is:

lnt runtest test-suite \
       --sandbox SANDBOX \
       --test-suite /work/llvm-test-suite \
       --use-lit lit \
       --cppflags="-O3" \
       --run-under=$HOME/dev/aarch64-emu/aarch64-qemu.sh \

The key part here is the CMAKE_TOOLCHAIN_FILE define. As you’re cross-compiling, you may need a –run-under command as the produced binaries probably won’t run natively on your development machine, but something extra needs to be done (e.g. running under a qemu simulator, or transferring the binaries to a development board). This isn’t explained further here.

In your toolchain file, it’s important to specify that the cmake variables defining the toolchain must be cached in CMakeCache.txt, as that’s where lnt reads them from to figure out which compiler was used when needing to construct metadata for the json report. An example is below. The important keywords to make the variables appear in the CMakeCache.txt are “CACHE STRING “” FORCE”:

$ cat clang_aarch64_linux.cmake
set(triple aarch64-linux-gnu )
set(CMAKE_C_COMPILER /home/user/build/bin/clang CACHE STRING "" FORCE)
set(CMAKE_CXX_COMPILER /home/user/build/bin/clang++ CACHE STRING "" FORCE)
set(CMAKE_SYSROOT /home/user/aarch64-emu/sysroot-glibc-linaro-2.23-2016.11-aarch64-linux-gnu )
set(CMAKE_C_COMPILER_EXTERNAL_TOOLCHAIN /home/user/aarch64-emu/gcc-linaro-6.2.1-2016.11-x86_64_aarch64-linux-gnu )
set(CMAKE_CXX_COMPILER_EXTERNAL_TOOLCHAIN /home/user/aarch64-emu/gcc-linaro-6.2.1-2016.11-x86_64_aarch64-linux-gnu )