Documentation: add a section to prevent spurious test failures like the one

[oota-llvm.git] / docs / TestingGuide.rst

=================================
LLVM Testing Infrastructure Guide
=================================

Written by John T. Criswell, Daniel Dunbar, Reid Spencer, and Tanya
Lattner

.. contents::
   :local:

.. toctree::
   :hidden:

   TestSuiteMakefileGuide

Overview
========

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.

Requirements
============

In order to use the LLVM testing infrastructure, you will need all of
the software required to build LLVM, as well as
`Python <http://python.org>`_ 2.4 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 :doc:`Lit <CommandGuide/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.

``test-suite``
--------------

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 :ref:`test-suite Quickstart
<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 :doc:`LLVM
Makefile Guide <MakefileGuide>` for more details):

.. code-block:: bash

    % make -C llvm/test

or:

.. code-block:: bash

    % make check

If you have `Clang <http://clang.llvm.org/>`_ checked out and built, you
can run the LLVM and Clang tests simultaneously using:

.. code-block:: bash

    % make check-all

To run the tests with Valgrind (Memcheck by default), just append
``VG=1`` to the commands above, e.g.:

.. code-block:: bash

    % make check VG=1

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:

.. code-block:: bash

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

or to run all of the ARM CodeGen tests:

.. code-block:: bash

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

For more information on using the :program:`lit` tool, see ``llvm-lit --help``
or the :doc:`lit man page <CommandGuide/lit>`.

Debugging Information tests
---------------------------

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

.. code-block:: bash

    % 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 :program:`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. :program:`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 :doc:`Lit
documentation <CommandGuide/lit>` for more information.

Each test file must contain lines starting with "RUN:" that tell :program:`lit`
how to run it. If there are no RUN lines, :program:`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 :program:`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 :program:`lit`.
Consequently, the syntax differs from shell in a few ways. You can specify
as many RUN lines as needed.

:program:`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 :program:`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. :program:`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:

.. code-block:: llvm

    ; 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. However, the usage is slightly different than
for Bash. In general, it's useful to read the code of other tests to figure out
what you can use in yours. The major differences are:

-  You can't do ``2>&1``. That will cause :program:`lit` to write to a file
   named ``&1``. Usually this is done to get stderr to go through a pipe. You
   can do that with ``|&`` so replace this idiom:
   ``... 2>&1 | grep`` with ``... |& grep``
-  You can only redirect to a file, not to another descriptor and not
   from a here document.

There are some quoting rules that you must pay attention to when writing
your RUN lines. In general nothing needs to be quoted. :program:`lit` won't
strip off any quote characters so they will get passed to the invoked program.
For example:

.. code-block:: bash

    ... | grep 'find this string'

This will fail because the ``'`` characters are passed to ``grep``. This would
make ``grep`` to look for ``'find`` in the files ``this`` and
``string'``. To avoid this use curly braces to tell :program:`lit` that it
should treat everything enclosed as one value. So our example would become:

.. code-block:: bash

    ... | grep {find this string}

In general, you should strive to keep your RUN lines as simple as possible,
using them only to run tools that generate the output you can then examine. The
recommended way to examine output to figure out if the test passes it using the
:doc:`FileCheck tool <CommandGuide/FileCheck>`. The usage of ``grep`` in RUN
lines is discouraged.

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, :program:`opt` by
default outputs a ``ModuleID``:

.. code-block:: console

  $ 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:

.. code-block:: llvm

  ; 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.
:program:`opt` does not output a ``ModuleID`` when input comes from stdin.

The FileCheck utility
---------------------

A powerful feature of the RUN lines is that it allows any arbitrary
commands to be executed as part of the test harness. While standard
(portable) unix tools like ``grep`` work fine on run lines, as you see
above, there are a lot of caveats due to interaction with shell syntax,
and we want to make sure the run lines are portable to a wide range of
systems. Another major problem is that ``grep`` is not very good at checking
to verify that the output of a tools contains a series of different
output in a specific order. The :program:`FileCheck` tool was designed to
help with these problems.

:program:`FileCheck` is designed to read a file to check from standard input,
and the set of things to verify from a file specified as a command line
argument. :program:`FileCheck` is described in :doc:`the FileCheck man page
<CommandGuide/FileCheck>`.

Variables and substitutions
---------------------------

With a RUN line there are a number of substitutions that are permitted.
To make a substitution just write the variable's name preceded by a ``$``.
Additionally, for compatibility reasons with previous versions of the
test library, certain names can be accessed with an alternate syntax: a
% prefix. These alternates are deprecated and may go away in a future
version.

Here are the available variable names. The alternate syntax is listed in
parentheses.

``$test`` (``%s``)
   The full path to the test case's source. This is suitable for passing on
   the command line as the input to an LLVM tool.

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

``$srcdir``
   The source directory from where the ``make check`` was run.

``objdir``
   The object directory that corresponds to the ``$srcdir``.

``subdir``
   A partial path from the ``test`` directory that contains the
   sub-directory that contains the test source being executed.

``srcroot``
   The root directory of the LLVM src tree.

``objroot``
   The root directory of the LLVM object tree. This could be the same as
   the srcroot.

``path``
   The path to the directory that contains the test case source. This is
   for locating any supporting files that are not generated by the test,
   but used by the test.

``tmp``
   The 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.

``target_triplet`` (``%target_triplet``)
   The target triplet that corresponds to the current host machine (the one
   running the test cases). This should probably be called "host".

``link`` (``%link``)
   This full link command used to link LLVM executables. This has all the
   configured ``-I``, ``-L`` and ``-l`` options.

``shlibext`` (``%shlibext``)
   The suffix for the host platforms shared library (DLL) files. This
   includes the period as the first character.

To add more variables, look at ``test/lit.cfg``.

Other Features
--------------

To make RUN line writing easier, there are several helper scripts and programs
in the ``llvm/test/Scripts`` directory. This directory is in the PATH
when running tests, so you can just call these scripts using their name.
For example:

``ignore``
   This script runs its arguments and then always returns 0. This is useful
   in cases where the test needs to cause a tool to generate an error (e.g.
   to check the error output). However, any program in a pipeline that
   returns a non-zero result will cause the test to fail.  This script
   overcomes that issue and nicely documents that the test case is
   purposefully ignoring the result code of the tool
``not``
   This script 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:

.. code-block:: llvm

    ; XFAIL: darwin,sun

To make the output more useful, :program:`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:

(a) it prevents special interpretation of lines that are part of the test
    program, not the instructions to the test case, and

(b) 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:

``test-suite`` Quickstart
-------------------------

The modern way of running the ``test-suite`` is focused on testing and
benchmarking complete compilers using the
`LNT <http://llvm.org/docs/lnt>`_ testing infrastructure.

For more information on using LNT to execute the ``test-suite``, please
see the `LNT Quickstart <http://llvm.org/docs/lnt/quickstart.html>`_
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 :doc:`Test Suite Makefile Guide <TestSuiteMakefileGuide>`.