diff --git a/llvm/test/CMakeLists.txt b/llvm/test/CMakeLists.txt
--- a/llvm/test/CMakeLists.txt
+++ b/llvm/test/CMakeLists.txt
@@ -51,6 +51,7 @@
           UnitTests
           bugpoint
           count
+          extract
           llc
           lli
           lli-child-target
diff --git a/llvm/test/lit.cfg.py b/llvm/test/lit.cfg.py
--- a/llvm/test/lit.cfg.py
+++ b/llvm/test/lit.cfg.py
@@ -145,7 +145,7 @@
 
 # FIXME: Why do we have both `lli` and `%lli` that do slightly different things?
 tools.extend([
-    'dsymutil', 'lli', 'lli-child-target', 'llvm-ar', 'llvm-as',
+    'dsymutil', 'extract', 'lli', 'lli-child-target', 'llvm-ar', 'llvm-as',
     'llvm-addr2line', 'llvm-bcanalyzer', 'llvm-config', 'llvm-cov',
     'llvm-cxxdump', 'llvm-cvtres', 'llvm-diff', 'llvm-dis', 'llvm-dwarfdump',
     'llvm-exegesis', 'llvm-extract', 'llvm-isel-fuzzer', 'llvm-ifs',
diff --git a/llvm/tools/extract/CMakeLists.txt b/llvm/tools/extract/CMakeLists.txt
new file mode 100644
--- /dev/null
+++ b/llvm/tools/extract/CMakeLists.txt
@@ -0,0 +1,7 @@
+set(LLVM_LINK_COMPONENTS
+  Support
+  )
+
+add_llvm_tool(extract
+  extract.cpp
+  )
diff --git a/llvm/tools/extract/extract.cpp b/llvm/tools/extract/extract.cpp
new file mode 100644
--- /dev/null
+++ b/llvm/tools/extract/extract.cpp
@@ -0,0 +1,106 @@
+//===- extract.cpp - Input splitting utility ------------------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+//
+// Split input into multipe parts separated by regex '^(.|//)--- ' and extract
+// the specified part.
+//
+//===----------------------------------------------------------------------===//
+
+#include "llvm/ADT/StringRef.h"
+#include "llvm/Support/CommandLine.h"
+#include "llvm/Support/FileOutputBuffer.h"
+#include "llvm/Support/LineIterator.h"
+#include "llvm/Support/MemoryBuffer.h"
+#include "llvm/Support/WithColor.h"
+#include <string>
+
+using namespace llvm;
+
+const char tool_name[] = "extract";
+
+static cl::OptionCategory cat("extract Options");
+
+static cl::opt<std::string> part(
+    cl::Positional,
+    cl::desc(
+        "Split input into multiple parts separated by regex '^(.|//)--- ' and "
+        "extract the specified part"),
+    cl::cat(cat));
+
+static cl::opt<std::string> input(cl::Positional, cl::desc("filename"),
+                                  cl::cat(cat));
+
+static cl::opt<std::string> output("o", cl::desc("Output filename"),
+                                   cl::value_desc("filename"), cl::init("-"),
+                                   cl::cat(cat));
+
+LLVM_ATTRIBUTE_NORETURN static void error(Twine message) {
+  WithColor::error(errs(), tool_name) << message << '\n';
+  exit(1);
+}
+
+LLVM_ATTRIBUTE_NORETURN static void error(StringRef filename, Twine message) {
+  WithColor::error(errs(), tool_name) << filename << ": " << message << '\n';
+  exit(1);
+}
+
+static void handle(MemoryBuffer &inputBuf, StringRef input) {
+  const char *docBegin = nullptr, *docEnd = nullptr;
+  int numEmptyLines = 0;
+  StringRef separator;
+  for (line_iterator i(inputBuf, /*SkipBlanks=*/false, '\0'); !i.is_at_eof();) {
+    StringRef line = *i++;
+    size_t markerLen = line.startswith("//") ? 6 : 5;
+    if (!(line.size() > markerLen &&
+          line.substr(markerLen - 4).startswith("--- ")))
+      continue;
+    separator = line.substr(0, markerLen);
+    StringRef cur = line.substr(markerLen);
+    if (cur == part) {
+      if (docBegin) {
+        error(input, "'" + separator + cur + "' occurs more than once");
+        exit(1);
+      }
+      numEmptyLines = i.line_number() - 1;
+      if (i.is_at_eof())
+        break;
+      docBegin = i->data();
+    } else if (docBegin && !docEnd) {
+      docEnd = line.data();
+    }
+  }
+  if (!docBegin)
+    error(input, "'" + separator + part + "' is not found");
+  if (!docEnd)
+    docEnd = inputBuf.getBufferEnd();
+
+  Expected<std::unique_ptr<FileOutputBuffer>> outputBuf =
+      FileOutputBuffer::create(output, numEmptyLines + (docEnd - docBegin));
+  if (!outputBuf)
+    error(input, toString(outputBuf.takeError()));
+  uint8_t *buf = (*outputBuf)->getBufferStart();
+  std::fill_n(buf, numEmptyLines, '\n');
+  std::copy(docBegin, docEnd, buf + numEmptyLines);
+  if (Error e = (*outputBuf)->commit())
+    error(input, toString(std::move(e)));
+}
+
+int main(int argc, const char **argv) {
+  cl::HideUnrelatedOptions({&cat});
+  cl::ParseCommandLineOptions(argc, argv, "extract\n", nullptr,
+                              /*EnvVar=*/nullptr,
+                              /*LongOptionsUseDoubleDash=*/true);
+
+  if (input.empty())
+    error("input filename is not specified");
+  ErrorOr<std::unique_ptr<MemoryBuffer>> buffer_or_err =
+      MemoryBuffer::getFileOrSTDIN(input);
+  if (std::error_code ec = buffer_or_err.getError())
+    error(input, ec.message());
+  handle(**buffer_or_err, input);
+}