path: root/docs/CommandGuide/FileCheck.rst

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

SYNOPSIS
--------

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

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

**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. llc) contains the expected information (for example, a movsd from esp or
whatever is interesting).  This is similar to using 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
-------

**-help**

 Print a summary of command line options.

**--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 **--check-prefix** argument allows you to specify
 a specific prefix to match.

**--input-file** *filename*

  File to check (defaults to stdin).

**--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 **--strict-whitespace** argument disables this behavior.


**-version**

 Show the version number of this program.

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

If **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 ``-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 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
   }


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, 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``".  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.

FileCheck variables can be defined multiple times, and uses always get the
latest value.  Note that variables are all read at the start of a "``CHECK``"
line and are all defined at the end.  This means that if you have something
like "``CHECK: [[XYZ:.*]]x[[XYZ]]``", the check line will read the previous
value of the ``XYZ`` variable and define a new one after the match is
performed.  If you need to do something like this you can probably take
advantage of the fact that FileCheck is not actually line-oriented when it
matches, this allows you to define two separate "``CHECK``" lines that match on
the same line.


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