FILECHECK(1)

📦
version 23.1.4 · 12 versions
, in arch rolling

🎀 NAME 🎀

okay so bestie, meet FileCheck(1) from LLVM — Flexible pattern matching file verifier. That's the official name, and honestly it's giving main-character energy for test files. 💖

✨ SYNOPSIS ✨

FileCheck match-filename [--check-prefixes=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. order matters, bestie ✨

The match-filename file specifies the file that contains the patterns to match. The file to verify is read from standard input unless the --input-file option is used.

🌸 OPTIONS 🌸

Options are parsed from the environment variable FILECHECK_OPTS and from the command line. ✨ both sources, no cap ✨

  • -help — Print a summary of command line options. short and sweet
  • --check-prefixes prefix1,prefix2,... — 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-prefixes argument allows you to specify (without the trailing ":") one or more prefixes to match. Multiple prefixes are useful for tests which might change for different run options, but most lines remain the same.
🚨 FileCheck does not permit duplicate prefixes, even if one is a check prefix and one is a comment prefix (see --comment-prefixes below).
  • --check-prefix prefix1,prefix2,... — An alias of --check-prefixes. same vibe, different spelling 💜
  • --comment-prefixes prefix1,prefix2,... — By default, FileCheck ignores any occurrence in match-filename of any check prefix if it is preceded on the same line by "COM:" or "RUN:". See the section The "COM:" directive for usage details.

These default comment prefixes can be overridden by --comment-prefixes if they are not appropriate for your testing environment. However, doing so is not recommended in LLVM's LIT-based test suites, which should be easier to maintain if they all follow a consistent comment style. In that case, consider proposing a change to the default comment prefixes instead. consistency is the moment 🌿

  • --allow-unused-prefixes — This option controls the behavior when using more than one prefix as specified by --check-prefixes, and some of these prefixes are missing in the test file. If true, this is allowed; if false, FileCheck will report an error, listing the missing prefixes. The default value is false. strict default, bestie ⚠️
  • --input-file filename — File to check (defaults to stdin). feed it a file if you don't wanna pipe 🫶
  • --match-full-lines — By default, FileCheck allows matches of anywhere on a line. This option will require all positive matches to cover an entire line. Leading and trailing whitespace is ignored, unless --strict-whitespace is also specified. (Note: negative matches from CHECK-NOT are not affected by this option!)

Passing this option is equivalent to inserting {{^ *}} or {{^}} before, and {{ *$}} or {{$}} after every positive check pattern. whole-line commitment 💍

  • --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. End-of-line sequences are canonicalized to UNIX-style \n in all modes. tabs vs spaces discourse, but make it FileCheck 😭
  • --ignore-case — By default, FileCheck uses case-sensitive matching. This option causes FileCheck to use case-insensitive matching. caps lock who?
  • --implicit-check-not check-pattern — Adds implicit negative checks for the specified patterns between positive checks. The option allows writing stricter tests without stuffing them with CHECK-NOTs.

For example, "--implicit-check-not warning:" can be useful when testing diagnostic messages from tools that don't have an option similar to clang -verify. With this option FileCheck will verify that input does not contain warnings not covered by any CHECK: patterns. quietly checking the NOISE 🔥

  • --dump-input <value> — Dump input to stderr, adding annotations representing currently enabled diagnostics. When there are multiple occurrences of this option, the value that appears earliest in the list below has precedence. The default is fail.
    • help — Explain input dump and quit
    • always — Always dump input
    • fail — Dump input on failure
    • never — Never dump input
  • --dump-input-context <N> — In the dump requested by --dump-input, print N input lines before and N input lines after any lines specified by --dump-input-filter. When there are multiple occurrences of this option, the largest specified N has precedence. The default is 5. context is kindness 🫶
  • --dump-input-filter <value> — In the dump requested by --dump-input, print only input lines of kind value plus any context specified by --dump-input-context. When there are multiple occurrences of this option, the value that appears earliest in the list below has precedence. The default is error when --dump-input=fail, and it's all when --dump-input=always.
    • all — All input lines
    • annotation-full — Input lines with annotations
    • annotation — Input lines with starting points of annotations
    • error — Input lines with starting points of error annotations
  • --enable-var-scope — Enables scope for regex variables.

Variables with names that start with $ are considered global and remain set throughout the file.

All other variables get undefined after each encountered CHECK-LABEL. scope it out, bestie 🦋

  • -D<VAR=VALUE> — Sets a filecheck pattern variable VAR with value VALUE that can be used in CHECK: lines.
  • -D#<FMT>,<NUMVAR>=<NUMERIC EXPRESSION> — Sets a filecheck numeric variable NUMVAR of matching format FMT to the result of evaluating <NUMERIC EXPRESSION> that can be used in CHECK: lines. See section FileCheck Numeric Variables and Expressions for details on supported numeric expressions. math but make it test-suite 🧮
  • -version — Show the version number of this program.
  • -v — Print good directive pattern matches. However, if -dump-input=fail or -dump-input=always, add those matches as input annotations instead. validated and visible ✨
  • -vv — Print information helpful in diagnosing internal FileCheck issues, such as discarded overlapping CHECK-DAG: matches, implicit EOF pattern matches, and CHECK-NOT: patterns that do not have matches. Implies -v. However, if -dump-input=fail or -dump-input=always, just add that information as input annotations instead. extra verbose, extra iconic 💅
  • --allow-deprecated-dag-overlap — Enable overlapping among matches in a group of consecutive CHECK-DAG: directives.
💀 Deprecated alert: this option is deprecated and is only provided for convenience as old tests are migrated to the new non-overlapping CHECK-DAG: implementation.
  • --allow-empty — Allow checking empty input. By default, empty input is rejected. empty input said "not today" 🙈
  • --color — Use colors in output (autodetected by default). pretty output supremacy 🌈

🦋 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. slay when it matches, bestie ✨

🌈 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:

; 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):

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. iconic behavior 💜

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 something 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. order is the whole plot 🍓

🧚 The FileCheck -check-prefixes option 🧚

The FileCheck -check-prefixes 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:

; RUN: llvm-as < %s | llc -mtriple=i686-apple-darwin9 -mattr=sse41 \
; RUN:              | FileCheck %s -check-prefixes=X32
; RUN: llvm-as < %s | llc -mtriple=x86_64-apple-darwin9 -mattr=sse41 \
; RUN:              | FileCheck %s -check-prefixes=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. both vibes validated 🌈

✨ The COM: directive ✨

Okay so sometimes you wanna disable a FileCheck directive but you don't wanna actually delete it (because bestie, what if you need it later?? 😭), or you wanna write a comment that mentions a directive by name. The COM: directive makes that trivially easy. Like, say you've got this:

; X32: pinsrd_1:
; X32:    pinsrd $1, 4(%esp), %xmm0

; COM: FIXME: X64 isn't working correctly yet for this part of codegen, but
; COM: X64 will have something similar to X32:
; COM:
; COM:   X64: pinsrd_1:
; COM:   X64:    pinsrd $1, %edi, %xmm0

Without COM:, you'd have to do some cursed combo of rewording and directive-syntax mangling to stop FileCheck from reading those commented-out X32: and X64: occurrences as actual directives. And on top of that, there've been proposals for FileCheck diagnostics that might side-eye those X64 occurrences (the ones with no trailing :) because they lowkey look like directive typos 🙈. Dodging all of that is tedious for a test author, and mangling the syntax makes your test code's whole purpose unclear. COM: says "not today" to all of it. 💅

A few important usage notes, bestie, don't skip these:

  • COM: inside another directive's pattern does not comment out the rest of the pattern. Example:
; X32: pinsrd $1, 4(%esp), %xmm0 COM: This is part of the X32 pattern!

If you need to temporarily comment out part of a directive's pattern, just move that part to another line. Why? Because FileCheck parses COM: exactly the same way it parses any other directive: only the first directive on the line is recognized as a directive. That's the whole tea. 🫖

  • For the sake of LIT, FileCheck treats RUN: just like COM:. If that's not it for your test environment, go look at --comment-prefixes.
  • FileCheck does not recognize COM, RUN, or any user-defined comment prefix as a comment directive if it's glued onto one of the usual check directive suffixes — things like -NEXT: or -NOT:, which we get into below. A combo like that gets treated as plain text instead. So if you need it to act as a comment directive in your test environment, define it as such with --comment-prefixes.

🌸 The CHECK-NEXT: directive 🌸

Sometimes you wanna match lines and verify the matches happen on exactly consecutive lines with nothing in between. That's CHECK: + CHECK-NEXT:'s whole job. Custom check prefix? Just use <PREFIX>-NEXT:. Like, this works exactly how you'd expect:

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's exactly one newline between it and the previous directive. And ngl, a CHECK-NEXT: cannot be the first directive in a file. 💀

🦋 The CHECK-SAME: directive 🦋

Sometimes you wanna match lines and verify the matches land on the same line as the previous match. CHECK: + CHECK-SAME: has you covered. Custom prefix? <PREFIX>-SAME:.

CHECK-SAME: is genuinely so powerful when you pair it with CHECK-NOT: (described below). Iconic duo fr.

For example, this does what you'd expect:

!0 = !DILocation(line: 5, scope: !1, inlinedAt: !2)

; CHECK:       !DILocation(line: 5,
; CHECK-NOT:               column:
; CHECK-SAME:              scope: ![[SCOPE:[0-9]+]]

CHECK-SAME: directives reject the input if there are any newlines between it and the previous directive. Zero newlines or bust.

CHECK-SAME: is also a lifesaver when you don't wanna write matchers for fields that don't matter. Say you're testing a tool that spits out stuff like:

Name: foo
Field1: ...
Field2: ...
Field3: ...
Value: 1

Name: bar
Field1: ...
Field2: ...
Field3: ...
Value: 2

Name: baz
Field1: ...
Field2: ...
Field3: ...
Value: 1

To verify foo has the value 1, you might first write:

CHECK: Name: foo
CHECK: Value: 1{{$}}

But bestie... that's a bad test 😭. If foo's value changes, the test still passes, because that CHECK: Value: 1 line would just match the value from baz. Sneaky. To fix it you could add CHECK-NEXT matchers for every FieldN: line, but that's verbose and you'd have to update it the second someone adds Field4. A way more succinct fix using CHECK-SAME::

CHECK:      Name: foo
CHECK:      Value:
CHECK-SAME:        {{ 1$}}

That verifies the next time Value: shows up in the output, it's got the value 1. Slay. ✨

Note: a CHECK-SAME: cannot be the first directive in a file.

🎀 The CHECK-EMPTY: directive 🎀

Need to check that the next line has nothing on it — not even whitespace? Use CHECK-EMPTY:. Literally empty. Void. Nothing.

declare void @foo()

declare void @bar()
; CHECK: foo
; CHECK-EMPTY:
; CHECK-NEXT: bar

Just like CHECK-NEXT:, the directive fails if there's 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 💜

CHECK-NOT: verifies that a string doesn't occur between two matches (or before the first match, or after the last match). It's the vibe check for stuff that shouldn't be there. 🚫

For example, to verify a load got removed by a transformation:

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-COUNT: directive ⭐

Need to match multiple lines with the same pattern over and over? You can just repeat a plain CHECK: as many times as you need. But if that looks too boring (fair), use a counted check: CHECK-COUNT-<num>:, where <num> is a positive decimal number. It'll match the pattern exactly <num> times — no more, no less. Custom prefix? <PREFIX>-COUNT-<num>: gives you the same effect.

Simple example, look how cute:

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 🌈

When you gotta match strings that don't come in a strictly sequential order, CHECK-DAG: is your girl. It verifies them between two matches (or before the first match, or after the last match). For example, clang emits vtable globals in reverse order — but with CHECK-DAG: we can keep the checks in the natural order:

// 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 =

You can mix CHECK-NOT: directives with CHECK-DAG: directives to exclude strings sitting between the surrounding CHECK-DAG: directives. But heads up: because of that, the surrounding CHECK-DAG: directives cannot be reordered. So like, all occurrences matching CHECK-DAG: before CHECK-NOT: must not fall behind occurrences matching CHECK-DAG: after CHECK-NOT:. Example:

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

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

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

; 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, either order of those two add instructions is allowed. Flexible. 🧚

If you're defining and using variables inside the same CHECK-DAG: block, be aware that the definition rule can match after its use.

So for instance, this code will pass:

; CHECK-DAG: vmov.32 [[REG2:d[0-9]+]][0]
; CHECK-DAG: vmov.32 [[REG2]][1]
vmov.32 d0[1]
vmov.32 d0[0]

While this other code will not:

; CHECK-DAG: vmov.32 [[REG2:d[0-9]+]][0]
; CHECK-DAG: vmov.32 [[REG2]][1]
vmov.32 d1[1]
vmov.32 d0[0]

And like... that's super useful but it's also dangerous, okay? 😭 Because with a register sequence you need a strong order (read before write, copy before use, etc). If the definition your test is hunting for doesn't match (say, because of a compiler bug), it might match way further away from the use — and then it masks real bugs away. Not the vibe.

In those cases, to enforce the order, put a non-DAG directive between the DAG-blocks. Periodt.

One more thing: a CHECK-DAG: directive skips matches that overlap the matches of any preceding CHECK-DAG: directives in the same CHECK-DAG: block. This non-overlapping behavior isn't just consistent with other directives — it's also necessary to handle sets of non-unique strings or patterns. For example, these directives look for unordered log entries for two tasks in a parallel program, like the OpenMP runtime:

// CHECK-DAG: [[THREAD_ID:[0-9]+]]: task_begin
// CHECK-DAG: [[THREAD_ID]]: task_end
//
// 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 get reused. Wild, right? 💀

The CHECK-LABEL: directive 💅

okay so here's the vibe: sometimes you've got a file with a bunch of tests split into logical blocks, and one or more CHECK: directives can accidentally pass by matching lines way down in a later block 🫠. Like yeah an error will usually get generated eventually, but the check that gets flagged as causing the error might have literally nothing to do with the actual source of the problem. messy.

so to get better error messages in these cases, you've got the "CHECK-LABEL:" directive ✨. It's treated identically to a normal CHECK directive, EXCEPT FileCheck makes one extra assumption: a line matched by the directive cannot also be matched by any other check present in match-filename. It's meant for lines containing labels or other unique identifiers 🎀.

conceptually, CHECK-LABEL divides the input stream into separate blocks, and each one gets processed independently — which prevents a CHECK: directive in one block from matching a line in another block 👑. And if --enable-var-scope is in effect, all local variables get cleared at the beginning of the block 🧹.

for example:

define %struct.C* @C_ctor_base(%struct.C* %this, i32 %x) {
entry:
; CHECK-LABEL: C_ctor_base:
; CHECK: mov [[SAVETHIS:r[0-9]+]], r0
; CHECK: bl A_ctor_base
; CHECK: mov r0, [[SAVETHIS]]
  %0 = bitcast %struct.C* %this to %struct.A*
  %call = tail call %struct.A* @A_ctor_base(%struct.A* %0)
  %1 = bitcast %struct.C* %this to %struct.B*
  %call2 = tail call %struct.B* @B_ctor_base(%struct.B* %1, i32 %x)
  ret %struct.C* %this
}

define %struct.D* @D_ctor_base(%struct.D* %this, i32 %x) {
entry:
; CHECK-LABEL: D_ctor_base:

using CHECK-LABEL: directives here is what guarantees those three CHECK: directives only accept lines from the body of the @C_ctor_base function — even if the patterns also match lines found later in the file 🔥. AND, bonus: if one of those three CHECK: directives fails, FileCheck will recover by continuing to the next block, so you can detect multiple test failures in a single invocation. efficiency slay.

there's no requirement that CHECK-LABEL: directives contain strings that correspond to actual syntactic labels in a source or output language — they just have to uniquely match a single line in the file being verified 💖.

⚠️ ok important: CHECK-LABEL: directives cannot contain variable definitions or uses. that's the rule, no cap.

Directive modifiers 🎀

a directive modifier can be appended to a directive by following the directive with {<modifier>} — and the only supported value for <modifier> is LITERAL 🌸.

the LITERAL directive modifier does a literal match. Like, the modifier makes the directive not recognize any syntax for regex matching, variable capture, or any substitutions 🚫. super useful when the text you're matching would otherwise need excessive escaping. for example, this performs literal matches instead of treating these as regular expressions:

Input: [[[10, 20]], [[30, 40]]]
Output %r10: [[10, 20]]
Output %r10: [[30, 40]]

; CHECK{LITERAL}: [[[10, 20]], [[30, 40]]]
; CHECK-DAG{LITERAL}: [[30, 40]]
; CHECK-DAG{LITERAL}: [[10, 20]]

FileCheck Regex Matching Syntax 🦋

every FileCheck directive takes a pattern to match. for most uses of FileCheck, fixed string matching is perfectly sufficient 😌. but for some things you want a more flexible form of matching. so FileCheck lets you 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) 💅. and because we want fixed string matching for the majority of what we do, FileCheck was designed to support mixing and matching fixed string matching with regular expressions. which means you can write stuff like this:

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

in this case any offset from the ESP register is allowed, and any xmm register is allowed 🔥.

since regular expressions are enclosed with double braces, they're visually distinct — and you don't need escape characters within the double braces like you would in C 🎉. in the rare case you wanna match double braces explicitly from the input, you can use something ugly like {{[}][}]}} as your pattern 🙈. or, if you're using the repetition count syntax — for example [[:xdigit:]]{8} to match exactly 8 hex digits — you'd need to add parentheses like this {{([[:xdigit:]]{8})}} to avoid confusion with FileCheck's closing double-brace 🧚.

FileCheck String Substitution Blocks 💜

it's often useful to match a pattern and then verify it occurs again later in the file. for codegen tests this is great for allowing any register, but verifying that that register is used consistently later 👑. to do this, FileCheck supports string substitution blocks that let string variables be defined and substituted into patterns. simple example:

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

the first check line matches a regex %[a-z]+ and captures it into the string variable REGISTER 🎀. the second line verifies that whatever's in REGISTER occurs later in the file after an "andw".

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's a definition of the variable; otherwise it's a substitution ✨.

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. like:

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

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

if --enable-var-scope is in effect, variables with names that start with $ are considered to be global. all other variables are local 🫶. all local variables get undefined at the beginning of each CHECK-LABEL block. global variables are not affected by CHECK-LABEL. this makes it easier to ensure individual tests aren't affected by variables set in preceding tests 💖.

FileCheck Numeric Substitution Blocks 🔢

FileCheck also supports numeric substitution blocks, which let you define numeric variables and check for numeric values that satisfy a numeric expression constraint based on those variables — via a numeric substitution ✨. this lets CHECK: directives verify a numeric relation between two numbers, like the need for consecutive registers to be used 👑

the syntax to capture a numeric value is [[#%<fmtspec>,<NUMVAR>:]] where:

  • %<fmtspec>, is an optional format specifier to indicate what number format to match and the minimum number of digits to expect 🎀.
  • <NUMVAR>: is an optional definition of variable <NUMVAR> from the captured value.

the syntax of <fmtspec> is: #.<precision><conversion specifier> where:

  • # is an optional flag available for hex values (see <conversion specifier> below) which requires the value matched to be prefixed by 0x 💅.
  • .<precision> is an optional printf-style precision specifier in which <precision> indicates the minimum number of digits that the value matched must have, expecting leading zeros if needed 🌸.
  • <conversion specifier> is an optional scanf-style conversion specifier to indicate what number format to match (e.g. hex number). currently accepted format specifiers are %u, %d, %x and %X. if absent, the format specifier defaults to %u ⭐.

for example:

; CHECK: mov r[[#REG:]], 0x[[#%.8X,ADDR:]]

would match mov r5, 0x0000FEFE and set REG to the value 5 and ADDR to the value 0xFEFE 🔥. note that, due to the precision, it would fail to match mov r5, 0xFEFE 💀.

and since the numeric variable definition is optional, you can also just check that a numeric value is present in a given format 👀. that's handy when the value itself isn't useful, for instance:

; CHECK-NOT: mov r0, r[[#]]

to check that a value is synthesized rather than moved around 🧚.

the syntax of a numeric substitution is [[#%<fmtspec>, <constraint> <expr>]] where:

  • <fmtspec> is the same format specifier as for defining a variable, but here it indicates how a numeric expression value should be matched against 💖. if absent, both components of the format specifier are inferred from the matching format of the numeric variable(s) used by the expression constraint if any — and it defaults to %u if no numeric variable is used, denoting that the value should be unsigned with no leading zeros 🌈. in case of conflict between format specifiers of several numeric variables, the conversion specifier becomes mandatory but the precision specifier remains optional.
  • <constraint> is the constraint describing how the value to match must relate to the value of the numeric expression. the only currently accepted constraint is == for an exact match, and it's the default if <constraint> isn't provided 👑. no matching constraint must be specified when the <expr> is empty.
  • <expr> is an expression. an expression is in turn 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, an integer literal, or a function 🎀. spaces are accepted before, after and between any of these elements. numeric operands have 64-bit precision. overflow and underflow are rejected 🚫. there's no support for operator precedence, but parentheses can be used to change the evaluation order ✨.

the supported operators are:

  • + — returns the sum of its two operands.
  • - — returns the difference of its two operands.

the syntax of a function call is <name>(<arguments>) where:

  • name is a predefined string literal. accepted values are:
    • add — returns the sum of its two operands.
    • div — returns the quotient of its two operands.
    • max — returns the largest of its two operands.
    • min — returns the smallest of its two operands.
    • mul — returns the product of its two operands.
    • sub — returns the difference of its two operands.
  • <arguments> is a comma separated list of expressions 🦋.

for example:

; CHECK: load r[[#REG:]], [r0]
; CHECK: load r[[#REG+1]], [r1]
; CHECK: Loading from 0x[[#%x,ADDR:]]
; CHECK-SAME: to 0x[[#ADDR + 7]]

the above example would match the text:

load r5, [r0]
load r6, [r1]
Loading from 0xa0463440 to 0xa0463447

but it would not match the text:

the way 7 is literally not 5 + 1, and a0463443 is not a0463440 + 7 😭 so bestie… that check just isn't checking. it failed, periodt.

okay so a numeric variable can also be defined to the result of a numeric expression 💅 in that case the numeric expression constraint gets checked first, and if it's verified the variable is assigned the value. the unified syntax for both checkin' a numeric expression and capturing its value into a numeric variable is:

[[#%<fmtspec>,<NUMVAR>: <constraint> <expr>]]

with each element working exactly like we described earlier 🫶 and yes you can use this to make your testcase way more self-describing by using variables instead of raw values, like:

   ; CHECK: mov r[[#REG_OFFSET:]], 0x[[#%X,FIELD_OFFSET:12]]
   ; CHECK-NEXT: load r[[#]], [r[[#REG_BASE:]], r[[#REG_OFFSET]]]

which would match:

   mov r4, 0xC
   load r6, [r5, r4]

slay. and the --enable-var-scope option has the exact same effect on numeric variables as it does on string variables 👑

Important note: in its current implementation, an expression cannot use a numeric variable defined earlier in the same CHECK directive. no cap, that's just how it is rn 💀

✨ FileCheck Pseudo Numeric Variables ✨

sometimes you gotta verify output that contains line numbers of the match file — like when you're testing compiler diagnostics, iykyk 🙈 this introduces a certain fragility in the match file structure, because "CHECK:" lines contain absolute line numbers in that same file, and those have to be updated every single time line numbers shift because of text being added or deleted. the way that's so annoying 😭

to support this case, FileCheck expressions understand the @LINE pseudo numeric variable, which evaluates to the line number of the CHECK pattern where it's found ⭐

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

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

to support legacy uses of @LINE as a special string variable, FileCheck also accepts the following uses of @LINE with the string substitution block syntax: [[@LINE]], [[@LINE+<offset>]] and [[@LINE-<offset>]] — with no spaces inside the brackets, and where offset is an integer 🧚

🌸 Matching Newline Characters 🌸

to match newline characters in regular expressions, you can use the character class [[:space:]] 💖 for example, the following pattern:

   // CHECK: DW_AT_location [DW_FORM_sec_offset] ([[DLOC:0x[0-9a-f]+]]){{[[:space:]].*}}"intd"

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

   DW_AT_location [DW_FORM_sec_offset]   (0x00000233)
   DW_AT_name [DW_FORM_strp]  ( .debug_str[0x000000c9] = "intd")

which lets us set the FileCheck variable DLOC to the desired value 0x00000233, extracted from the line immediately preceding "intd" 👑 iconic behavior honestly.

💜 Author 💜

maintained by the LLVM Team (https://llvm.org/). 🫶

2003-2026, LLVM Project 🌈

and that's the whole page bestie, we ate that fr fr 🔥 this was FILECHECK(1), section 23, dated 2026-10-20 — go forth and check some files, mwah 💋✨

📦 where this page comes from