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FileCheck - Flexible pattern matching file verifier


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


: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 read from standard input unless the :option:`--input-file` option is used.


Options are parsed from the environment variable FILECHECK_OPTS and from the command line.


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.




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):

; CHECK: sub1:
; CHECK: subl
        ret void

define void @inc4(i64* %p) {
; CHECK: inc4:
; CHECK: incq
        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 :program:`llc`. Here's a simple example:


        ret <4 x i32> %tmp1
; X32: pinsrd_1:

; 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:

     %tmp9 = shufflevector <2 x double> %tmp3,
                            <2 x double> %tmp7,
                            <2 x i32> < i32 0, i32 2 >
     ret void

; CHECK:          t2:
; CHECK:             movl    8(%esp), %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-SAME:" directive

Sometimes you want to match lines and would like to verify that matches happen on the same line as the previous match. In this case, you can use "CHECK:" and "CHECK-SAME:" directives to specify this. If you specified a custom check prefix, just use "<PREFIX>-SAME:".

"CHECK-SAME:" is particularly powerful in conjunction with "CHECK-NOT:" (described below).

For example, the following works like you'd expect:


; CHECK:       !DILocation(line: 5,
; CHECK-NOT:               column:

"CHECK-SAME:" directives reject the input if there are any newlines between it and the previous directive. A "CHECK-SAME:" cannot be the first directive in a file.

The "CHECK-EMPTY:" directive

If you need to check that the next line has nothing on it, not even whitespace, you can use the "CHECK-EMPTY:" directive.

declare void @foo()

declare void @bar()
; CHECK: foo

Just like "CHECK-NEXT:" the directive will fail if there is more than one newline before it finds the next blank line, and it 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:

  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-COUNT:" directive

If you need to match multiple lines with the same pattern over and over again you can repeat a plain CHECK: as many times as needed. If that looks too boring you can instead use a counted check "CHECK-COUNT-<num>:", where <num> is a positive decimal number. It will match the pattern exactly <num> times, no more and no less. If you specified a custom check prefix, just use "<PREFIX>-COUNT-<num>:" for the same effect. Here is a simple example:

Loop at depth 1
Loop at depth 1
Loop at depth 1
Loop at depth 1
  Loop at depth 2
    Loop at depth 3

; CHECK-COUNT-6: Loop at depth {{[0-9]+}}
; CHECK-NOT:     Loop at depth {{[0-9]+}}

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:


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

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



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

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,




So, for instance, the code below will pass:

vmov.32 d0[1]
vmov.32 d0[0]

While this other code, will not:

vmov.32 d1[1]
vmov.32 d0[0]

While this can be very useful, it's also dangerous, because in the case of register sequence, you must have a strong order (read before write, copy before use, etc). If the definition your test is looking for doesn't match (because of a bug in the compiler), it may match further away from the use, and mask real bugs away.


A CHECK-DAG: directive skips matches that overlap the matches of any preceding CHECK-DAG: directives in the same CHECK-DAG: block. Not only is this non-overlapping behavior consistent with other directives, but it's also necessary to handle sets of non-unique strings or patterns. For example, the following directives look for unordered log entries for two tasks in a parallel program, such as the OpenMP runtime:

// CHECK-DAG: [[THREAD_ID:[0-9]+]]: task_begin
// CHECK-DAG: [[THREAD_ID]]: task_end

The second pair of directives is guaranteed not to match the same log entries as the first pair even though the patterns are identical and even if the text of the log entries is identical because the thread ID manages to be reused.

The "CHECK-LABEL:" directive



For example,

; CHECK-LABEL: C_ctor_base:
; CHECK: bl A_ctor_base
; CHECK: mov r0, [[SAVETHIS]]
  ret %struct.C* %this

; CHECK-LABEL: D_ctor_base:



CHECK-LABEL: directives cannot contain variable definitions or uses.

FileCheck Regex Matching Syntax

All FileCheck directives 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}}. FileCheck implements a POSIX regular expression matcher; it supports Extended POSIX regular expressions (ERE). 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:



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 String Substitution Blocks

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` supports string substitution blocks that allow string variables to be defined and substituted into patterns. Here is a simple example:

; CHECK: test5:

The first check line matches a regex %[a-z]+ and captures it into the string variable REGISTER. The second line verifies that whatever is in REGISTER occurs later in the file after an "andw". :program:`FileCheck` string substitution blocks are always contained in [[ ]] pairs, and string variable 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 substitution.

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


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 Numeric Substitution Blocks

:program:`FileCheck` also supports numeric substitution blocks that allow defining numeric variables and checking for numeric values that satisfy a numeric expression constraint based on those variables via a numeric substitution. This allows CHECK: directives to verify a numeric relation between two numbers, such as the need for consecutive registers to be used.

The syntax to define a numeric variable is [[#<NUMVAR>:]] where <NUMVAR> is the name of the numeric variable to define to the matching value.

For example:

; CHECK: mov r[[#REG:]], 42

would match mov r5, 42 and set REG to the value 5.

The syntax of a numeric substitution is [[#<expr>]] where <expr> is an expression. An expression is recursively defined as:

  • a numeric operand, or
  • an expression followed by an operator and a numeric operand.

A numeric operand is a previously defined numeric variable, or an integer literal. The supported operators are + and -. Spaces are accepted before, after and between any of these elements.

For example:

; CHECK: load r[[#REG:]], [r0]
; CHECK: load r[[#REG+1]], [r1]

The above example would match the text:

load r5, [r0]
load r6, [r1]

but would not match the text:

load r5, [r0]
load r7, [r1]

due to 7 being unequal to 5 + 1.

The --enable-var-scope option has the same effect on numeric variables as on string variables.

Important note: In its current implementation, an expression cannot use a numeric variable defined on the same line.

FileCheck Pseudo Numeric Variables

Sometimes there's a need to verify output that contains 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 expressions understand the @LINE pseudo numeric variable which evaluates to the line number of the CHECK pattern where it is found.


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

To support legacy uses of @LINE as a special string variable, :program:`FileCheck` also accepts the following uses of @LINE with string substitution block syntax: [[@LINE]], [[@LINE+<offset>]] and [[@LINE-<offset>]] without any spaces inside the brackets and where offset is an integer.

Matching Newline Characters



matches output of the form (from llvm-dwarfdump):

DW_AT_location [DW_FORM_sec_offset]   (0x00000233)

letting us set the :program:`FileCheck` variable DLOC to the desired value 0x00000233, extracted from the line immediately preceding "intd".