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  3. modules/


This is the benchmark runner for llvm test-suite. It is only available when the test-suite was built with cmake. It runs benchmarks, checks the results and collects various metrics such as runtime, compile time or code size.

The runner is implemented as a custom test format for the llvm-lit tool.

.test Files

.test files specify how to run a benchmark and check the results.

Each line in a .test file may specify a PREPARE:, RUN: or VERIFY: command as a shell command. Each kind can be specified multiple times. A benchmark run will first execute all PREPARE: commands, then all RUN: commands and finally all VERIFY: commands. Metrics like runtime or profile data are collected for the RUN: commands.

Commands are specified as shell commands. However only a subset of posix shell functionality is supported: Assigning environment variables, redirecting input and outputs, changing the directory and executing commands. (see for details).


RUN: ./mybenchmark --size 500 --verbose > run0.txt
VERIFY: diff reference_results0.txt run0.txt
RUN: ./mybenchmark --size 300 --seed 5555 --verbose > run1.txt
VERIFY: diff reference_results1.txt run1.txt

TODO: Document METRIC: lines.


Running cmake on the test-suite creates a and .test files for each bechmark. llvm-lit can then be used as usual. You may alternatively install lit from the python package index. Examples:

# Run all benchmark in the current directory an subdirecories one at a time.
$ llvm-lit -j1 .

# Run a single benchmark and show executed commands and collected metrics.
$ llvm-lit -a SingleSource/Benchmarks/Misc/pi.test

# Run benchmarks with reduced lit output but save collected metrics to json
# file. This format is used by LNT or viewable by test-suite/utils/
$ llvm-lit . -o result.json -s

Testing Modules

The benchmark runner behaviour is defined and enhanced by testing modules. Testing modules can modify the command lines to run the benchmark and register callbacks to collect metrics.

The list of modules is defined in the file (config.test_modules) which in turn is generated by cmake. The module list is influenced by a number of cmake flags. For a complete list consult the cmake code; typical examples are:

  • cmake -DTEST_SUITE_RUN_BENCHMARKS=Off removes the run module, so no benchmarks are actually run; this is useful as code size data, compiletime, or compilation statistics can be collected anyway.
  • cmake -DTEST_SUITE_RUN_UNDER=qemu enable the run_under module and will prefix all benchmark invocations with the specified command (here: qemu).
  • cmake -DTEST_SUITE_REMOTE_HOST=xxx enabled the remote module that uses ssh to run benchmarks on a remote device (assuming shared file systems).
  • cmake -DTEST_SUITE_PROFILE_GENERATE compiles benchmark with -fprofile-instr-generate and enables the profilegen module that runs llvm-profdata after running the benchmarks. To use LLVM IR PGO instead of the clang frontend's PGO feature, set -DTEST_SUITE_USE_IR_PGO=On.

Available modules are found in the litsupport/modules directory.

Developing New Modules

Testing modules consist of a python module with a mutatePlan(context, plan) function. Modules can:

  • Modify the scripts used to execute the benchmark (plan.preparescript, plan.runscript, plan.verifyscript). A script is a list of strings with shell commands. Modifying the list is best done via the testplan.mutateScript function which sets context.tmpBase to a unique for the command to be modified. The shellcommand module helps analyzing and modifying posix shell command lines.

  • Append a function to the plan.metric_collectors list. The metric collector functions are executed after the benchmark scripts ran. Metrics must be returned as a dictionary with int, float or string values (anything supported by lit.Test.toMetricValue()).

  • The context object is passed to all testing modules and metric collectors and may be used to communicate information between them. context.executable contains the path to the benchmark executable; context.config contains the lit configuration coming from a combination of, lit.cfg and lit.local.cfg files for the benchmark.