diff --git a/llvm/test/tools/llvm-mc/doc-id-disassemble.s b/llvm/test/tools/llvm-mc/doc-id-disassemble.s
new file mode 100644
--- /dev/null
+++ b/llvm/test/tools/llvm-mc/doc-id-disassemble.s
@@ -0,0 +1,15 @@
+# REQUIRES: x86-registered-target
+# RUN: llvm-mc -triple=x86_64 --disassemble --doc-id=aa %s | \
+# RUN:   FileCheck %s --check-prefix=AA --implicit-check-not=retq
+
+# AA: nop
+
+# RUN: llvm-mc -triple=x86_64 --disassemble --doc-id=bb %s | \
+# RUN:   FileCheck %s --check-prefix=BB --implicit-check-not=nop
+
+# BB: retq
+
+#-- aa
+0x90
+#-- bb
+0xc3
diff --git a/llvm/test/tools/llvm-mc/doc-id.s b/llvm/test/tools/llvm-mc/doc-id.s
new file mode 100644
--- /dev/null
+++ b/llvm/test/tools/llvm-mc/doc-id.s
@@ -0,0 +1,26 @@
+# RUN: llvm-mc --doc-id=aa --preserve-comments %s 2>&1 | FileCheck %s --check-prefix=AA --implicit-check-not=warning:
+
+# AA: {{.*}}.s:1:1: warning: aa
+# AA: # Comments are preserved.
+
+# RUN: llvm-mc --doc-id=bb %s 2>&1 | FileCheck %s --check-prefix=BB --implicit-check-not=warning:
+
+# BB: {{.*}}.s:2:1: warning: bb
+
+# RUN: not llvm-mc --doc-id=dup %s 2>&1 | FileCheck %s --check-prefix=DUP
+
+# DUP: error: {{.*}}.s: '#-- dup' occurred more than once
+
+# RUN: not llvm-mc --doc-id=not_exist %s 2>&1 | FileCheck %s --check-prefix=NOT_EXIST
+
+# NOT_EXIST: error: {{.*}}.s: '#-- not_exist' not found
+
+#-- aa
+.warning "aa"
+# Comments are preserved.
+#-- bb
+
+.warning "bb"
+#-- dup
+.warning "dup"
+#-- dup
diff --git a/llvm/tools/llvm-mc/llvm-mc.cpp b/llvm/tools/llvm-mc/llvm-mc.cpp
--- a/llvm/tools/llvm-mc/llvm-mc.cpp
+++ b/llvm/tools/llvm-mc/llvm-mc.cpp
@@ -32,7 +32,9 @@
 #include "llvm/Support/FormattedStream.h"
 #include "llvm/Support/Host.h"
 #include "llvm/Support/InitLLVM.h"
+#include "llvm/Support/LineIterator.h"
 #include "llvm/Support/MemoryBuffer.h"
+#include "llvm/Support/SmallVectorMemoryBuffer.h"
 #include "llvm/Support/SourceMgr.h"
 #include "llvm/Support/TargetRegistry.h"
 #include "llvm/Support/TargetSelect.h"
@@ -46,6 +48,12 @@
 static cl::opt<std::string>
 InputFilename(cl::Positional, cl::desc("<input file>"), cl::init("-"));
 
+static cl::opt<std::string> DocId(
+    "doc-id",
+    cl::desc("Treat input as separated by \"--- \", feed the part specified "
+             "by \"--- <id>\" to assembler/disassembler"),
+    cl::value_desc("id"));
+
 static cl::opt<std::string> OutputFilename("o", cl::desc("Output filename"),
                                            cl::value_desc("filename"),
                                            cl::init("-"));
@@ -306,6 +314,37 @@
   return Res;
 }
 
+static void handleDocId(std::unique_ptr<MemoryBuffer> &Buf, StringRef ProgName,
+                        StringRef FileName) {
+  const char *DocBegin = nullptr, *DocEnd = nullptr;
+  for (line_iterator I(*Buf, /*SkipBlanks=*/false, '\0'); !I.is_at_eof();) {
+    StringRef Line = *I++;
+    if (!Line.consume_front("#-- "))
+      continue;
+    if (Line == DocId.getValue()) {
+      if (DocBegin) {
+        WithColor::error(errs(), ProgName)
+            << FileName << ": '#-- " << Line << "' occurred more than once\n";
+        exit(1);
+      }
+      if (I.is_at_eof())
+        break;
+      DocBegin = I->data();
+    } else if (DocBegin && !DocEnd) {
+      DocEnd = Line.data();
+    }
+  }
+  if (!DocBegin) {
+    WithColor::error(errs(), ProgName)
+        << FileName << ": '#-- " << DocId << "' not found\n";
+    exit(1);
+  }
+  if (!DocEnd)
+    DocEnd = Buf->getBufferEnd();
+  Buf.reset(new SmallVectorMemoryBuffer(SmallVector<char, 0>(DocBegin, DocEnd),
+                                        Buf->getBufferIdentifier()));
+}
+
 int main(int argc, char **argv) {
   InitLLVM X(argc, argv);
 
@@ -339,6 +378,8 @@
         << InputFilename << ": " << EC.message() << '\n';
     return 1;
   }
+  if (!DocId.empty())
+    handleDocId(*BufferPtr, ProgName, InputFilename);
   MemoryBuffer *Buffer = BufferPtr->get();
 
   SourceMgr SrcMgr;