docs/CommandGuide/FileCheck.rst

FileCheck - Flexible pattern matching file verifier
===================================================

SYNOPSIS
--------

:program:`FileCheck` *match-filename* [*--check-prefix=XXX*] [*--strict-whitespace*]

DESCRIPTION
-----------

:program:`FileCheck` reads two files (one from standard input, and one
specified on the command line) and uses one to verify the other.  This
behavior is particularly useful for the testsuite, which wants to verify that
the output of some tool (e.g. :program:`llc`) contains the expected information
(for example, a movsd from esp or whatever is interesting).  This is similar to
using :program:`grep`, but it is optimized for matching multiple different
inputs in one file in a specific order.

The ``match-filename`` file specifies the file that contains the patterns to
match.  The file to verify is always read from standard input.

OPTIONS
-------

.. option:: -help

 Print a summary of command line options.

.. option:: --check-prefix prefix

 FileCheck searches the contents of ``match-filename`` for patterns to match.
 By default, these patterns are prefixed with "``CHECK:``".  If you'd like to
 use a different prefix (e.g. because the same input file is checking multiple
 different tool or options), the :option:`--check-prefix` argument allows you
 to specify a specific prefix to match.

.. option:: --input-file filename

  File to check (defaults to stdin).

.. option:: --strict-whitespace

 By default, FileCheck canonicalizes input horizontal whitespace (spaces and
 tabs) which causes it to ignore these differences (a space will match a tab).
 The :option:`--strict-whitespace` argument disables this behavior. End-of-line
 sequences are canonicalized to UNIX-style ``\n`` in all modes.

.. option:: -version

 Show the version number of this program.

EXIT STATUS
-----------

If :program:`FileCheck` verifies that the file matches the expected contents,
it exits with 0.  Otherwise, if not, or if an error occurs, it will exit with a
non-zero value.

TUTORIAL
--------

FileCheck is typically used from LLVM regression tests, being invoked on the RUN
line of the test.  A simple example of using FileCheck from a RUN line looks
like this:

.. code-block:: llvm

   ; RUN: llvm-as < %s | llc -march=x86-64 | FileCheck %s

This syntax says to pipe the current file ("``%s``") into ``llvm-as``, pipe
that into ``llc``, then pipe the output of ``llc`` into ``FileCheck``.  This
means that FileCheck will be verifying its standard input (the llc output)
against the filename argument specified (the original ``.ll`` file specified by
"``%s``").  To see how this works, let's look at the rest of the ``.ll`` file
(after the RUN line):

.. code-block:: llvm

   define void @sub1(i32* %p, i32 %v) {
   entry:
   ; CHECK: sub1:
   ; CHECK: subl
           %0 = tail call i32 @llvm.atomic.load.sub.i32.p0i32(i32* %p, i32 %v)
           ret void
   }

   define void @inc4(i64* %p) {
   entry:
   ; CHECK: inc4:
   ; CHECK: incq
           %0 = tail call i64 @llvm.atomic.load.add.i64.p0i64(i64* %p, i64 1)
           ret void
   }

Here you can see some "``CHECK:``" lines specified in comments.  Now you can
see how the file is piped into ``llvm-as``, then ``llc``, and the machine code
output is what we are verifying.  FileCheck checks the machine code output to
verify that it matches what the "``CHECK:``" lines specify.

The syntax of the "``CHECK:``" lines is very simple: they are fixed strings that
must occur in order.  FileCheck defaults to ignoring horizontal whitespace
differences (e.g. a space is allowed to match a tab) but otherwise, the contents
of the "``CHECK:``" line is required to match some thing in the test file exactly.

One nice thing about FileCheck (compared to grep) is that it allows merging
test cases together into logical groups.  For example, because the test above
is checking for the "``sub1:``" and "``inc4:``" labels, it will not match
unless there is a "``subl``" in between those labels.  If it existed somewhere
else in the file, that would not count: "``grep subl``" matches if "``subl``"
exists anywhere in the file.

The FileCheck -check-prefix option
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

The FileCheck :option:`-check-prefix` option allows multiple test
configurations to be driven from one `.ll` file.  This is useful in many
circumstances, for example, testing different architectural variants with
:program:`llc`.  Here's a simple example:

.. code-block:: llvm

   ; RUN: llvm-as < %s | llc -mtriple=i686-apple-darwin9 -mattr=sse41 \
   ; RUN:              | FileCheck %s -check-prefix=X32
   ; RUN: llvm-as < %s | llc -mtriple=x86_64-apple-darwin9 -mattr=sse41 \
   ; RUN:              | FileCheck %s -check-prefix=X64

   define <4 x i32> @pinsrd_1(i32 %s, <4 x i32> %tmp) nounwind {
           %tmp1 = insertelement <4 x i32>; %tmp, i32 %s, i32 1
           ret <4 x i32> %tmp1
   ; X32: pinsrd_1:
   ; X32:    pinsrd $1, 4(%esp), %xmm0

   ; X64: pinsrd_1:
   ; X64:    pinsrd $1, %edi, %xmm0
   }

In this case, we're testing that we get the expected code generation with
both 32-bit and 64-bit code generation.

The "CHECK-NEXT:" directive
~~~~~~~~~~~~~~~~~~~~~~~~~~~

Sometimes you want to match lines and would like to verify that matches
happen on exactly consecutive lines with no other lines in between them.  In
this case, you can use "``CHECK:``" and "``CHECK-NEXT:``" directives to specify
this.  If you specified a custom check prefix, just use "``<PREFIX>-NEXT:``".
For example, something like this works as you'd expect:

.. code-block:: llvm

   define void @t2(<2 x double>* %r, <2 x double>* %A, double %B) {
 	%tmp3 = load <2 x double>* %A, align 16
 	%tmp7 = insertelement <2 x double> undef, double %B, i32 0
 	%tmp9 = shufflevector <2 x double> %tmp3,
                               <2 x double> %tmp7,
                               <2 x i32> < i32 0, i32 2 >
 	store <2 x double> %tmp9, <2 x double>* %r, align 16
 	ret void

   ; CHECK:          t2:
   ; CHECK: 	        movl	8(%esp), %eax
   ; CHECK-NEXT: 	movapd	(%eax), %xmm0
   ; CHECK-NEXT: 	movhpd	12(%esp), %xmm0
   ; CHECK-NEXT: 	movl	4(%esp), %eax
   ; CHECK-NEXT: 	movapd	%xmm0, (%eax)
   ; CHECK-NEXT: 	ret
   }

"``CHECK-NEXT:``" directives reject the input unless there is exactly one
newline between it and the previous directive.  A "``CHECK-NEXT:``" cannot be
the first directive in a file.

The "CHECK-NOT:" directive
~~~~~~~~~~~~~~~~~~~~~~~~~~

The "``CHECK-NOT:``" directive is used to verify that a string doesn't occur
between two matches (or before the first match, or after the last match).  For
example, to verify that a load is removed by a transformation, a test like this
can be used:

.. code-block:: llvm

   define i8 @coerce_offset0(i32 %V, i32* %P) {
     store i32 %V, i32* %P

     %P2 = bitcast i32* %P to i8*
     %P3 = getelementptr i8* %P2, i32 2

     %A = load i8* %P3
     ret i8 %A
   ; CHECK: @coerce_offset0
   ; CHECK-NOT: load
   ; CHECK: ret i8
   }

The "CHECK-DAG:" directive
~~~~~~~~~~~~~~~~~~~~~~~~~~

If it's necessary to match strings that don't occur in a strictly sequential
order, "``CHECK-DAG:``" could be used to verify them between two matches (or
before the first match, or after the last match). For example, clang emits
vtable globals in reverse order. Using ``CHECK-DAG:``, we can keep the checks
in the natural order:

.. code-block:: c++

    // RUN: %clang_cc1 %s -emit-llvm -o - | FileCheck %s

    struct Foo { virtual void method(); };
    Foo f;  // emit vtable
    // CHECK-DAG: @_ZTV3Foo =

    struct Bar { virtual void method(); };
    Bar b;
    // CHECK-DAG: @_ZTV3Bar =


With captured variables, ``CHECK-DAG:`` is able to match valid topological
orderings of a DAG with edges from the definition of a variable to its use.
It's useful, e.g., when your test cases need to match different output
sequences from the instruction scheduler. For example,

.. code-block:: llvm

   ; CHECK-DAG: add [[REG1:r[0-9]+]], r1, r2
   ; CHECK-DAG: add [[REG2:r[0-9]+]], r3, r4
   ; CHECK:     mul r5, [[REG1]], [[REG2]]

In this case, any order of that two ``add`` instructions will be allowed.

``CHECK-NOT:`` directives could be mixed with ``CHECK-DAG:`` directives to
exclude strings between the surrounding ``CHECK-DAG:`` directives. As a result,
the surrounding ``CHECK-DAG:`` directives cannot be reordered, i.e. all
occurrences matching ``CHECK-DAG:`` before ``CHECK-NOT:`` must not fall behind
occurrences matching ``CHECK-DAG:`` after ``CHECK-NOT:``. For example,

.. code-block:: llvm

   ; CHECK-DAG: BEFORE
   ; CHECK-NOT: NOT
   ; CHECK-DAG: AFTER

This case will reject input strings where ``BEFORE`` occurs after ``AFTER``.

FileCheck Pattern Matching Syntax
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

The "``CHECK:``" and "``CHECK-NOT:``" directives both take a pattern to match.
For most uses of FileCheck, fixed string matching is perfectly sufficient.  For
some things, a more flexible form of matching is desired.  To support this,
FileCheck allows you to specify regular expressions in matching strings,
surrounded by double braces: ``{{yourregex}}``.  Because we want to use fixed
string matching for a majority of what we do, FileCheck has been designed to
support mixing and matching fixed string matching with regular expressions.
This allows you to write things like this:

.. code-block:: llvm

   ; CHECK: movhpd	{{[0-9]+}}(%esp), {{%xmm[0-7]}}

In this case, any offset from the ESP register will be allowed, and any xmm
register will be allowed.

Because regular expressions are enclosed with double braces, they are
visually distinct, and you don't need to use escape characters within the double
braces like you would in C.  In the rare case that you want to match double
braces explicitly from the input, you can use something ugly like
``{{[{][{]}}`` as your pattern.

FileCheck Variables
~~~~~~~~~~~~~~~~~~~

It is often useful to match a pattern and then verify that it occurs again
later in the file.  For codegen tests, this can be useful to allow any register,
but verify that that register is used consistently later.  To do this,
:program:`FileCheck` allows named variables to be defined and substituted into
patterns.  Here is a simple example:

.. code-block:: llvm

   ; CHECK: test5:
   ; CHECK:    notw	[[REGISTER:%[a-z]+]]
   ; CHECK:    andw	{{.*}}[[REGISTER]]

The first check line matches a regex ``%[a-z]+`` and captures it into the
variable ``REGISTER``.  The second line verifies that whatever is in
``REGISTER`` occurs later in the file after an "``andw``".  :program:`FileCheck`
variable references are always contained in ``[[ ]]`` pairs, and their names can
be formed with the regex ``[a-zA-Z][a-zA-Z0-9]*``.  If a colon follows the name,
then it is a definition of the variable; otherwise, it is a use.

:program:`FileCheck` variables can be defined multiple times, and uses always
get the latest value.  Variables can also be used later on the same line they
were defined on. For example:

.. code-block:: llvm

    ; CHECK: op [[REG:r[0-9]+]], [[REG]]

Can be useful if you want the operands of ``op`` to be the same register,
and don't care exactly which register it is.

FileCheck Expressions
~~~~~~~~~~~~~~~~~~~~~

Sometimes there's a need to verify output which refers line numbers of the
match file, e.g. when testing compiler diagnostics.  This introduces a certain
fragility of the match file structure, as "``CHECK:``" lines contain absolute
line numbers in the same file, which have to be updated whenever line numbers
change due to text addition or deletion.

To support this case, FileCheck allows using ``[[@LINE]]``,
``[[@LINE+<offset>]]``, ``[[@LINE-<offset>]]`` expressions in patterns. These
expressions expand to a number of the line where a pattern is located (with an
optional integer offset).

This way match patterns can be put near the relevant test lines and include
relative line number references, for example:

.. code-block:: c++

   // CHECK: test.cpp:[[@LINE+4]]:6: error: expected ';' after top level declarator
   // CHECK-NEXT: {{^int a}}
   // CHECK-NEXT: {{^     \^}}
   // CHECK-NEXT: {{^     ;}}
   int a