LLVM Testing Infrastructure Guide


This document is the reference manual for the LLVM testing infrastructure. It documents the structure of the LLVM testing infrastructure, the tools needed to use it, and how to add and run tests.


In order to use the LLVM testing infrastructure, you will need all of the software required to build LLVM, as well as Python 2.5 or later.

LLVM testing infrastructure organization

The LLVM testing infrastructure contains two major categories of tests: regression tests and whole programs. The regression tests are contained inside the LLVM repository itself under llvm/test and are expected to always pass – they should be run before every commit.

The whole programs tests are referred to as the “LLVM test suite” (or “test-suite”) and are in the test-suite module in subversion. For historical reasons, these tests are also referred to as the “nightly tests” in places, which is less ambiguous than “test-suite” and remains in use although we run them much more often than nightly.

Regression tests

The regression tests are small pieces of code that test a specific feature of LLVM or trigger a specific bug in LLVM. The language they are written in depends on the part of LLVM being tested. These tests are driven by the Lit testing tool (which is part of LLVM), and are located in the llvm/test directory.

Typically when a bug is found in LLVM, a regression test containing just enough code to reproduce the problem should be written and placed somewhere underneath this directory. For example, it can be a small piece of LLVM IR distilled from an actual application or benchmark.


The test suite contains whole programs, which are pieces of code which can be compiled and linked into a stand-alone program that can be executed. These programs are generally written in high level languages such as C or C++.

These programs are compiled using a user specified compiler and set of flags, and then executed to capture the program output and timing information. The output of these programs is compared to a reference output to ensure that the program is being compiled correctly.

In addition to compiling and executing programs, whole program tests serve as a way of benchmarking LLVM performance, both in terms of the efficiency of the programs generated as well as the speed with which LLVM compiles, optimizes, and generates code.

The test-suite is located in the test-suite Subversion module.

Debugging Information tests

The test suite contains tests to check quality of debugging information. The test are written in C based languages or in LLVM assembly language.

These tests are compiled and run under a debugger. The debugger output is checked to validate of debugging information. See README.txt in the test suite for more information . This test suite is located in the debuginfo-tests Subversion module.

Quick start

The tests are located in two separate Subversion modules. The regressions tests are in the main “llvm” module under the directory llvm/test (so you get these tests for free with the main LLVM tree). Use make check-all to run the regression tests after building LLVM.

The more comprehensive test suite that includes whole programs in C and C++ is in the test-suite module. See test-suite Quickstart for more information on running these tests.

Regression tests

To run all of the LLVM regression tests, use the master Makefile in the llvm/test directory. LLVM Makefiles require GNU Make (read the LLVM Makefile Guide for more details):

% make -C llvm/test


% make check

If you have Clang checked out and built, you can run the LLVM and Clang tests simultaneously using:

% make check-all

To run the tests with Valgrind (Memcheck by default), use the LIT_ARGS make variable to pass the required options to lit. For example, you can use:

% make check LIT_ARGS="-v --vg --vg-leak"

to enable testing with valgrind and with leak checking enabled.

To run individual tests or subsets of tests, you can use the llvm-lit script which is built as part of LLVM. For example, to run the Integer/BitPacked.ll test by itself you can run:

% llvm-lit ~/llvm/test/Integer/BitPacked.ll

or to run all of the ARM CodeGen tests:

% llvm-lit ~/llvm/test/CodeGen/ARM

For more information on using the lit tool, see llvm-lit --help or the lit man page.

Debugging Information tests

To run debugging information tests simply checkout the tests inside clang/test directory.

% cd clang/test
% svn co http://llvm.org/svn/llvm-project/debuginfo-tests/trunk debuginfo-tests

These tests are already set up to run as part of clang regression tests.

Regression test structure

The LLVM regression tests are driven by lit and are located in the llvm/test directory.

This directory contains a large array of small tests that exercise various features of LLVM and to ensure that regressions do not occur. The directory is broken into several sub-directories, each focused on a particular area of LLVM.

Writing new regression tests

The regression test structure is very simple, but does require some information to be set. This information is gathered via configure and is written to a file, test/lit.site.cfg in the build directory. The llvm/test Makefile does this work for you.

In order for the regression tests to work, each directory of tests must have a lit.local.cfg file. lit looks for this file to determine how to run the tests. This file is just Python code and thus is very flexible, but we’ve standardized it for the LLVM regression tests. If you’re adding a directory of tests, just copy lit.local.cfg from another directory to get running. The standard lit.local.cfg simply specifies which files to look in for tests. Any directory that contains only directories does not need the lit.local.cfg file. Read the Lit documentation for more information.

Each test file must contain lines starting with “RUN:” that tell lit how to run it. If there are no RUN lines, lit will issue an error while running a test.

RUN lines are specified in the comments of the test program using the keyword RUN followed by a colon, and lastly the command (pipeline) to execute. Together, these lines form the “script” that lit executes to run the test case. The syntax of the RUN lines is similar to a shell’s syntax for pipelines including I/O redirection and variable substitution. However, even though these lines may look like a shell script, they are not. RUN lines are interpreted by lit. Consequently, the syntax differs from shell in a few ways. You can specify as many RUN lines as needed.

lit performs substitution on each RUN line to replace LLVM tool names with the full paths to the executable built for each tool (in $(LLVM_OBJ_ROOT)/$(BuildMode)/bin). This ensures that lit does not invoke any stray LLVM tools in the user’s path during testing.

Each RUN line is executed on its own, distinct from other lines unless its last character is \. This continuation character causes the RUN line to be concatenated with the next one. In this way you can build up long pipelines of commands without making huge line lengths. The lines ending in \ are concatenated until a RUN line that doesn’t end in \ is found. This concatenated set of RUN lines then constitutes one execution. lit will substitute variables and arrange for the pipeline to be executed. If any process in the pipeline fails, the entire line (and test case) fails too.

Below is an example of legal RUN lines in a .ll file:

; RUN: llvm-as < %s | llvm-dis > %t1
; RUN: llvm-dis < %s.bc-13 > %t2
; RUN: diff %t1 %t2

As with a Unix shell, the RUN lines permit pipelines and I/O redirection to be used.

There are some quoting rules that you must pay attention to when writing your RUN lines. In general nothing needs to be quoted. lit won’t strip off any quote characters so they will get passed to the invoked program. To avoid this use curly braces to tell lit that it should treat everything enclosed as one value.

In general, you should strive to keep your RUN lines as simple as possible, using them only to run tools that generate textual output you can then examine. The recommended way to examine output to figure out if the test passes is using the FileCheck tool. [The usage of grep in RUN lines is deprecated - please do not send or commit patches that use it.]

Fragile tests

It is easy to write a fragile test that would fail spuriously if the tool being tested outputs a full path to the input file. For example, opt by default outputs a ModuleID:

$ cat example.ll
define i32 @main() nounwind {
    ret i32 0

$ opt -S /path/to/example.ll
; ModuleID = '/path/to/example.ll'

define i32 @main() nounwind {
    ret i32 0

ModuleID can unexpetedly match against CHECK lines. For example:

; RUN: opt -S %s | FileCheck

define i32 @main() nounwind {
    ; CHECK-NOT: load
    ret i32 0

This test will fail if placed into a download directory.

To make your tests robust, always use opt ... < %s in the RUN line. opt does not output a ModuleID when input comes from stdin.

Platform-Specific Tests

Whenever adding tests that require the knowledge of a specific platform, either related to code generated, specific output or back-end features, you must make sure to isolate the features, so that buildbots that run on different architectures (and don’t even compile all back-ends), don’t fail.

The first problem is to check for target-specific output, for example sizes of structures, paths and architecture names, for example:

  • Tests containing Windows paths will fail on Linux and vice-versa.
  • Tests that check for x86_64 somewhere in the text will fail anywhere else.
  • Tests where the debug information calculates the size of types and structures.

Also, if the test rely on any behaviour that is coded in any back-end, it must go in its own directory. So, for instance, code generator tests for ARM go into test/CodeGen/ARM and so on. Those directories contain a special lit configuration file that ensure all tests in that directory will only run if a specific back-end is compiled and available.

For instance, on test/CodeGen/ARM, the lit.local.cfg is:

config.suffixes = ['.ll', '.c', '.cpp', '.test']
if not 'ARM' in config.root.targets:
  config.unsupported = True

Other platform-specific tests are those that depend on a specific feature of a specific sub-architecture, for example only to Intel chips that support AVX2.

For instance, test/CodeGen/X86/psubus.ll tests three sub-architecture variants:

; RUN: llc -mcpu=core2 < %s | FileCheck %s -check-prefix=SSE2
; RUN: llc -mcpu=corei7-avx < %s | FileCheck %s -check-prefix=AVX1
; RUN: llc -mcpu=core-avx2 < %s | FileCheck %s -check-prefix=AVX2

And the checks are different:

; SSE2: @test1
; SSE2: psubusw LCPI0_0(%rip), %xmm0
; AVX1: @test1
; AVX1: vpsubusw LCPI0_0(%rip), %xmm0, %xmm0
; AVX2: @test1
; AVX2: vpsubusw LCPI0_0(%rip), %xmm0, %xmm0

So, if you’re testing for a behaviour that you know is platform-specific or depends on special features of sub-architectures, you must add the specific triple, test with the specific FileCheck and put it into the specific directory that will filter out all other architectures.


Besides replacing LLVM tool names the following substitutions are performed in RUN lines:

Replaced by a single %. This allows escaping other substitutions.

File path to the test case’s source. This is suitable for passing on the command line as the input to an LLVM tool.

Example: /home/user/llvm/test/MC/ELF/foo_test.s


Directory path to the test case’s source.

Example: /home/user/llvm/test/MC/ELF


File path to a temporary file name that could be used for this test case. The file name won’t conflict with other test cases. You can append to it if you need multiple temporaries. This is useful as the destination of some redirected output.

Example: /home/user/llvm.build/test/MC/ELF/Output/foo_test.s.tmp


Directory of %t.

Example: /home/user/llvm.build/test/MC/ELF/Output


Expands to the path separator, i.e. : (or ; on Windows).

LLVM-specific substitutions:


The suffix for the host platforms shared library files. This includes the period as the first character.

Example: .so (Linux), .dylib (OS X), .dll (Windows)


The suffix for the host platforms executable files. This includes the period as the first character.

Example: .exe (Windows), empty on Linux.

%(line), %(line+<number>), %(line-<number>)
The number of the line where this substitution is used, with an optional integer offset. This can be used in tests with multiple RUN lines, which reference test file’s line numbers.

Clang-specific substitutions:

Invokes the Clang driver.
Invokes the Clang driver for C++.
Invokes the CL-compatible Clang driver.
Invokes the G++-compatible Clang driver.
Invokes the Clang frontend.
%itanium_abi_triple, %ms_abi_triple
These substitutions can be used to get the current target triple adjusted to the desired ABI. For example, if the test suite is running with the i686-pc-win32 target, %itanium_abi_triple will expand to i686-pc-mingw32. This allows a test to run with a specific ABI without constraining it to a specific triple.

To add more substituations, look at test/lit.cfg or lit.local.cfg.

Other Features

To make RUN line writing easier, there are several helper programs. These helpers are in the PATH when running tests, so you can just call them using their name. For example:

This program runs its arguments and then inverts the result code from it. Zero result codes become 1. Non-zero result codes become 0.

Sometimes it is necessary to mark a test case as “expected fail” or XFAIL. You can easily mark a test as XFAIL just by including XFAIL: on a line near the top of the file. This signals that the test case should succeed if the test fails. Such test cases are counted separately by the testing tool. To specify an expected fail, use the XFAIL keyword in the comments of the test program followed by a colon and one or more failure patterns. Each failure pattern can be either * (to specify fail everywhere), or a part of a target triple (indicating the test should fail on that platform), or the name of a configurable feature (for example, loadable_module). If there is a match, the test is expected to fail. If not, the test is expected to succeed. To XFAIL everywhere just specify XFAIL: *. Here is an example of an XFAIL line:

; XFAIL: darwin,sun

To make the output more useful, lit will scan the lines of the test case for ones that contain a pattern that matches PR[0-9]+. This is the syntax for specifying a PR (Problem Report) number that is related to the test case. The number after “PR” specifies the LLVM bugzilla number. When a PR number is specified, it will be used in the pass/fail reporting. This is useful to quickly get some context when a test fails.

Finally, any line that contains “END.” will cause the special interpretation of lines to terminate. This is generally done right after the last RUN: line. This has two side effects:

  1. it prevents special interpretation of lines that are part of the test program, not the instructions to the test case, and
  2. it speeds things up for really big test cases by avoiding interpretation of the remainder of the file.

test-suite Overview

The test-suite module contains a number of programs that can be compiled and executed. The test-suite includes reference outputs for all of the programs, so that the output of the executed program can be checked for correctness.

test-suite tests are divided into three types of tests: MultiSource, SingleSource, and External.

  • test-suite/SingleSource

    The SingleSource directory contains test programs that are only a single source file in size. These are usually small benchmark programs or small programs that calculate a particular value. Several such programs are grouped together in each directory.

  • test-suite/MultiSource

    The MultiSource directory contains subdirectories which contain entire programs with multiple source files. Large benchmarks and whole applications go here.

  • test-suite/External

    The External directory contains Makefiles for building code that is external to (i.e., not distributed with) LLVM. The most prominent members of this directory are the SPEC 95 and SPEC 2000 benchmark suites. The External directory does not contain these actual tests, but only the Makefiles that know how to properly compile these programs from somewhere else. When using LNT, use the --test-externals option to include these tests in the results.

test-suite Quickstart

The modern way of running the test-suite is focused on testing and benchmarking complete compilers using the LNT testing infrastructure.

For more information on using LNT to execute the test-suite, please see the LNT Quickstart documentation.

test-suite Makefiles

Historically, the test-suite was executed using a complicated setup of Makefiles. The LNT based approach above is recommended for most users, but there are some testing scenarios which are not supported by the LNT approach. In addition, LNT currently uses the Makefile setup under the covers and so developers who are interested in how LNT works under the hood may want to understand the Makefile based setup.

For more information on the test-suite Makefile setup, please see the Test Suite Makefile Guide.