Index: clang/docs/analyzer/user-docs/CrossTranslationUnit.rst
===================================================================
--- clang/docs/analyzer/user-docs/CrossTranslationUnit.rst
+++ clang/docs/analyzer/user-docs/CrossTranslationUnit.rst
@@ -81,12 +81,12 @@
   $
 
 The next step is to create a CTU index file which holds the `USR` name and location of external definitions in the
-source files:
+source files in format `USR-Length:USR File-Path`:
 
 .. code-block:: bash
 
   $ clang-extdef-mapping -p . foo.cpp
-  c:@F@foo# /path/to/your/project/foo.cpp
+  9:c:@F@foo# /path/to/your/project/foo.cpp
   $ clang-extdef-mapping -p . foo.cpp > externalDefMap.txt
 
 We have to modify `externalDefMap.txt` to contain the name of the `.ast` files instead of the source files:
@@ -283,7 +283,7 @@
 .. code-block:: bash
 
   $ clang-extdef-mapping -p . foo.cpp
-  c:@F@foo# /path/to/your/project/foo.cpp
+  9:c:@F@foo# /path/to/your/project/foo.cpp
   $ clang-extdef-mapping -p . foo.cpp > externalDefMap.txt
 
 Now everything is available for the CTU analysis.
Index: clang/include/clang/Basic/DiagnosticCrossTUKinds.td
===================================================================
--- clang/include/clang/Basic/DiagnosticCrossTUKinds.td
+++ clang/include/clang/Basic/DiagnosticCrossTUKinds.td
@@ -12,7 +12,7 @@
   "error opening '%0': required by the CrossTU functionality">;
 
 def err_extdefmap_parsing : Error<
-  "error parsing index file: '%0' line: %1 'UniqueID filename' format "
+  "error parsing index file: '%0' line: %1 'USR-Length:USR File-Path' format "
   "expected">;
 
 def err_multiple_def_index : Error<
Index: clang/lib/CrossTU/CrossTranslationUnit.cpp
===================================================================
--- clang/lib/CrossTU/CrossTranslationUnit.cpp
+++ clang/lib/CrossTU/CrossTranslationUnit.cpp
@@ -149,6 +149,36 @@
   return std::error_code(static_cast<int>(Code), *Category);
 }
 
+static bool parseCrossTUIndexItem(StringRef LineRef, StringRef &LookupName,
+                           StringRef &FilePath) {
+  // Find the length delimiter.
+  const size_t LengthDelimiter = LineRef.find(':');
+  if (StringRef::npos == LengthDelimiter)
+    return false;
+
+  // Parse the length of LookupName as USRLength.
+  size_t USRLength = 0;
+  if (LineRef.substr(0, LengthDelimiter).consumeInteger(10, USRLength))
+    return false;
+
+  // Check LookupName length out of bound and incorrect delimiter.
+  const size_t Delimiter = LengthDelimiter + USRLength + 1;
+  if (USRLength <= 0 || Delimiter >= LineRef.size() ||
+      ' ' != LineRef[Delimiter])
+    return false;
+
+  LookupName = LineRef.substr(0, Delimiter);
+  FilePath = LineRef.substr(Delimiter + 1);
+  return true;
+}
+
+#define IS_CTU_INDEX_KEY_VALID(FUNCTION_NAME)                                  \
+  ([](StringRef N) {                                                           \
+    std::string FN = N.str() + ' ';                                            \
+    StringRef LN, FP;                                                          \
+    return parseCrossTUIndexItem(FN, LN, FP) && N == LN && FP.empty();         \
+  }(FUNCTION_NAME))
+
 llvm::Expected<llvm::StringMap<std::string>>
 parseCrossTUIndex(StringRef IndexPath) {
   std::ifstream ExternalMapFile{std::string(IndexPath)};
@@ -160,24 +190,23 @@
   std::string Line;
   unsigned LineNo = 1;
   while (std::getline(ExternalMapFile, Line)) {
-    StringRef LineRef{Line};
-    const size_t Delimiter = LineRef.find(' ');
-    if (Delimiter > 0 && Delimiter != std::string::npos) {
-      StringRef LookupName = LineRef.substr(0, Delimiter);
-
-      // Store paths with posix-style directory separator.
-      SmallString<32> FilePath(LineRef.substr(Delimiter + 1));
-      llvm::sys::path::native(FilePath, llvm::sys::path::Style::posix);
-
-      bool InsertionOccured;
-      std::tie(std::ignore, InsertionOccured) =
-          Result.try_emplace(LookupName, FilePath.begin(), FilePath.end());
-      if (!InsertionOccured)
-        return llvm::make_error<IndexError>(
-            index_error_code::multiple_definitions, IndexPath.str(), LineNo);
-    } else
+    // Split lookup name and file path
+    StringRef LookupName, FilePathInIndex;
+    if (!parseCrossTUIndexItem(Line, LookupName, FilePathInIndex))
       return llvm::make_error<IndexError>(
           index_error_code::invalid_index_format, IndexPath.str(), LineNo);
+
+    // Store paths with posix-style directory separator.
+    SmallString<32> FilePath(FilePathInIndex);
+    llvm::sys::path::native(FilePath, llvm::sys::path::Style::posix);
+
+    bool InsertionOccured;
+    std::tie(std::ignore, InsertionOccured) =
+      Result.try_emplace(LookupName, FilePath.begin(), FilePath.end());
+    if (!InsertionOccured)
+      return llvm::make_error<IndexError>(
+          index_error_code::multiple_definitions, IndexPath.str(), LineNo);
+
     ++LineNo;
   }
   return Result;
@@ -223,7 +252,11 @@
   bool Ret = index::generateUSRForDecl(ND, DeclUSR);
   if (Ret)
     return {};
-  return std::string(DeclUSR.str());
+
+  SmallString<128> LNBuf;
+  llvm::raw_svector_ostream LNOS(LNBuf);
+  LNOS << DeclUSR.size() << ':' << DeclUSR;
+  return std::string(LNOS.str());
 }
 
 /// Recursively visits the decls of a DeclContext, and returns one with the
@@ -429,6 +462,8 @@
       return std::move(IndexLoadError);
 
     // Check if there is and entry in the index for the function.
+    assert(IS_CTU_INDEX_KEY_VALID(FunctionName) &&
+           "Invalid USR function name when accessing CTU index.");
     if (!NameFileMap.count(FunctionName)) {
       ++NumNotInOtherTU;
       return llvm::make_error<IndexError>(index_error_code::missing_definition);
@@ -457,6 +492,9 @@
     StringRef FunctionName, StringRef CrossTUDir, StringRef IndexName) {
   if (llvm::Error IndexLoadError = ensureCTUIndexLoaded(CrossTUDir, IndexName))
     return std::move(IndexLoadError);
+
+  assert(IS_CTU_INDEX_KEY_VALID(FunctionName) &&
+         "Invalid USR function name when accessing CTU index.");
   return NameFileMap[FunctionName];
 }
 
Index: clang/test/Analysis/Inputs/ctu-import.c.externalDefMap.ast-dump.txt
===================================================================
--- clang/test/Analysis/Inputs/ctu-import.c.externalDefMap.ast-dump.txt
+++ clang/test/Analysis/Inputs/ctu-import.c.externalDefMap.ast-dump.txt
@@ -1 +1 @@
-c:@F@testStaticImplicit ctu-import.c.ast
+23:c:@F@testStaticImplicit ctu-import.c.ast
Index: clang/test/Analysis/Inputs/ctu-lookup-name-with-space.cpp
===================================================================
--- /dev/null
+++ clang/test/Analysis/Inputs/ctu-lookup-name-with-space.cpp
@@ -0,0 +1,14 @@
+void f(int (*)(char));
+void f(bool (*)(char));
+
+struct G {
+  G() {
+    // CHECK-NOT: multiple definitions are found for the same key in index
+    f([](char) -> int { return 42; });
+    f([](char) -> bool { return true; });
+  }
+};
+
+int importee(int X) {
+  return 1 / X;
+}
Index: clang/test/Analysis/Inputs/ctu-other.c.externalDefMap.ast-dump.txt
===================================================================
--- clang/test/Analysis/Inputs/ctu-other.c.externalDefMap.ast-dump.txt
+++ clang/test/Analysis/Inputs/ctu-other.c.externalDefMap.ast-dump.txt
@@ -1,7 +1,7 @@
-c:@F@inlineAsm ctu-other.c.ast
-c:@F@g ctu-other.c.ast
-c:@F@f ctu-other.c.ast
-c:@F@enumCheck ctu-other.c.ast
-c:@F@identImplicit ctu-other.c.ast
-c:@F@structInProto ctu-other.c.ast
-c:@F@switchWithoutCases ctu-other.c.ast
+14:c:@F@inlineAsm ctu-other.c.ast
+6:c:@F@g ctu-other.c.ast
+6:c:@F@f ctu-other.c.ast
+14:c:@F@enumCheck ctu-other.c.ast
+18:c:@F@identImplicit ctu-other.c.ast
+18:c:@F@structInProto ctu-other.c.ast
+23:c:@F@switchWithoutCases ctu-other.c.ast
Index: clang/test/Analysis/Inputs/ctu-other.cpp.externalDefMap.ast-dump.txt
===================================================================
--- clang/test/Analysis/Inputs/ctu-other.cpp.externalDefMap.ast-dump.txt
+++ clang/test/Analysis/Inputs/ctu-other.cpp.externalDefMap.ast-dump.txt
@@ -1,30 +1,30 @@
-c:@N@chns@F@chf1#I# ctu-other.cpp.ast
-c:@N@myns@N@embed_ns@F@fens#I# ctu-other.cpp.ast
-c:@F@g#I# ctu-other.cpp.ast
-c:@S@mycls@F@fscl#I#S ctu-other.cpp.ast
-c:@S@mycls@F@fcl#I# ctu-other.cpp.ast
-c:@S@mycls@F@fvcl#I# ctu-other.cpp.ast
-c:@N@myns@S@embed_cls@F@fecl#I# ctu-other.cpp.ast
-c:@S@mycls@S@embed_cls2@F@fecl2#I# ctu-other.cpp.ast
-c:@S@derived@F@fvcl#I# ctu-other.cpp.ast
-c:@F@f#I# ctu-other.cpp.ast
-c:@N@myns@F@fns#I# ctu-other.cpp.ast
-c:@F@h#I# ctu-other.cpp.ast
-c:@F@h_chain#I# ctu-chain.cpp.ast
-c:@N@chns@S@chcls@F@chf4#I# ctu-chain.cpp.ast
-c:@N@chns@F@chf2#I# ctu-chain.cpp.ast
-c:@F@fun_using_anon_struct#I# ctu-other.cpp.ast
-c:@F@other_macro_diag#I# ctu-other.cpp.ast
-c:@extInt ctu-other.cpp.ast
-c:@N@intns@extInt ctu-other.cpp.ast
-c:@extS ctu-other.cpp.ast
-c:@S@A@a ctu-other.cpp.ast
-c:@extSC ctu-other.cpp.ast
-c:@S@ST@sc ctu-other.cpp.ast
-c:@extSCN ctu-other.cpp.ast
-c:@extSubSCN ctu-other.cpp.ast
-c:@extSCC ctu-other.cpp.ast
-c:@extU ctu-other.cpp.ast
-c:@S@TestAnonUnionUSR@Test ctu-other.cpp.ast
-c:@F@testImportOfIncompleteDefaultParmDuringImport#I# ctu-other.cpp.ast
-c:@F@testImportOfDelegateConstructor#I# ctu-other.cpp.ast
\ No newline at end of file
+19:c:@N@chns@F@chf1#I# ctu-other.cpp.ast
+30:c:@N@myns@N@embed_ns@F@fens#I# ctu-other.cpp.ast
+9:c:@F@g#I# ctu-other.cpp.ast
+21:c:@S@mycls@F@fscl#I#S ctu-other.cpp.ast
+19:c:@S@mycls@F@fcl#I# ctu-other.cpp.ast
+20:c:@S@mycls@F@fvcl#I# ctu-other.cpp.ast
+31:c:@N@myns@S@embed_cls@F@fecl#I# ctu-other.cpp.ast
+34:c:@S@mycls@S@embed_cls2@F@fecl2#I# ctu-other.cpp.ast
+22:c:@S@derived@F@fvcl#I# ctu-other.cpp.ast
+9:c:@F@f#I# ctu-other.cpp.ast
+18:c:@N@myns@F@fns#I# ctu-other.cpp.ast
+9:c:@F@h#I# ctu-other.cpp.ast
+15:c:@F@h_chain#I# ctu-chain.cpp.ast
+27:c:@N@chns@S@chcls@F@chf4#I# ctu-chain.cpp.ast
+19:c:@N@chns@F@chf2#I# ctu-chain.cpp.ast
+29:c:@F@fun_using_anon_struct#I# ctu-other.cpp.ast
+24:c:@F@other_macro_diag#I# ctu-other.cpp.ast
+9:c:@extInt ctu-other.cpp.ast
+17:c:@N@intns@extInt ctu-other.cpp.ast
+7:c:@extS ctu-other.cpp.ast
+8:c:@S@A@a ctu-other.cpp.ast
+8:c:@extSC ctu-other.cpp.ast
+10:c:@S@ST@sc ctu-other.cpp.ast
+9:c:@extSCN ctu-other.cpp.ast
+12:c:@extSubSCN ctu-other.cpp.ast
+9:c:@extSCC ctu-other.cpp.ast
+7:c:@extU ctu-other.cpp.ast
+26:c:@S@TestAnonUnionUSR@Test ctu-other.cpp.ast
+53:c:@F@testImportOfIncompleteDefaultParmDuringImport#I# ctu-other.cpp.ast
+39:c:@F@testImportOfDelegateConstructor#I# ctu-other.cpp.ast
Index: clang/test/Analysis/Inputs/plist-macros-with-expansion-ctu.c.externalDefMap.txt
===================================================================
--- clang/test/Analysis/Inputs/plist-macros-with-expansion-ctu.c.externalDefMap.txt
+++ clang/test/Analysis/Inputs/plist-macros-with-expansion-ctu.c.externalDefMap.txt
@@ -1,4 +1,4 @@
-c:@F@F1 plist-macros-ctu.c.ast
-c:@F@F2 plist-macros-ctu.c.ast
-c:@F@F3 plist-macros-ctu.c.ast
-c:@F@F_H plist-macros-ctu.c.ast
+7:c:@F@F1 plist-macros-ctu.c.ast
+7:c:@F@F2 plist-macros-ctu.c.ast
+7:c:@F@F3 plist-macros-ctu.c.ast
+8:c:@F@F_H plist-macros-ctu.c.ast
Index: clang/test/Analysis/ctu-inherited-default-ctor.cpp
===================================================================
--- clang/test/Analysis/ctu-inherited-default-ctor.cpp
+++ clang/test/Analysis/ctu-inherited-default-ctor.cpp
@@ -4,7 +4,7 @@
 // RUN: %clang_cc1 -std=c++14 -triple x86_64-pc-linux-gnu \
 // RUN:   -emit-pch -o %t/ctudir/ctu-inherited-default-ctor-other.cpp.ast \
 // RUN:    %S/Inputs/ctu-inherited-default-ctor-other.cpp
-// RUN: echo "c:@N@clang@S@DeclContextLookupResult@SingleElementDummyList ctu-inherited-default-ctor-other.cpp.ast" \
+// RUN: echo "59:c:@N@clang@S@DeclContextLookupResult@SingleElementDummyList ctu-inherited-default-ctor-other.cpp.ast" \
 // RUN:   > %t/ctudir/externalDefMap.txt
 //
 // RUN: %clang_analyze_cc1 -std=c++14 -triple x86_64-pc-linux-gnu \
Index: clang/test/Analysis/ctu-lookup-name-with-space.cpp
===================================================================
--- /dev/null
+++ clang/test/Analysis/ctu-lookup-name-with-space.cpp
@@ -0,0 +1,22 @@
+// RUN: rm -rf %t
+// RUN: mkdir %t
+
+// RUN: cp %s %t/trigger.cpp
+// RUN: cp %S/Inputs/ctu-lookup-name-with-space.cpp %t/importee.cpp
+// RUN: echo '"%t/importee.cpp" : ["g++", "-c", "%t/importee.cpp"]' > %t/invocations.yaml
+// RUN: echo '[{"directory": "%t", "command": "g++ -c %t/importee.cpp", "file": "%t/importee.cpp"}, {"directory": "%t", "command": "g++ -c %t/trigger.cpp", "file": "%t/trigger.cpp"}]' > %t/compile_commands.json
+
+// RUN: %clang_extdef_map -p %t %t/importee.cpp > %t/externalDefMap.txt
+
+// RUN: cd %t && %clang_cc1 -fsyntax-only -analyze \
+// RUN:   -analyzer-checker=core \
+// RUN:   -analyzer-config experimental-enable-naive-ctu-analysis=true \
+// RUN:   -analyzer-config ctu-dir=. \
+// RUN:   -analyzer-config ctu-invocation-list=invocations.yaml \
+// RUN:   -verify trigger.cpp 2>&1 | FileCheck --allow-empty importee.cpp
+
+int importee(int);
+
+void trigger() {
+  importee(0); // expected-warning@importee.cpp:13 {{Division by zero}}
+}
Index: clang/test/Analysis/func-mapping-test.cpp
===================================================================
--- clang/test/Analysis/func-mapping-test.cpp
+++ clang/test/Analysis/func-mapping-test.cpp
@@ -3,10 +3,10 @@
 int f(int) {
   return 0;
 }
-// CHECK-DAG: c:@F@f#I#
+// CHECK-DAG: 9:c:@F@f#I#
 
 extern const int x = 5;
-// CHECK-DAG: c:@x
+// CHECK-DAG: 4:c:@x
 
 // Non-const variables should not be collected.
 int y = 5;
@@ -18,29 +18,29 @@
   int a;
 };
 extern S const s = {.a = 2};
-// CHECK-DAG: c:@s
+// CHECK-DAG: 4:c:@s
 
 struct SF {
   const int a;
 };
 SF sf = {.a = 2};
-// CHECK-DAG: c:@sf
+// CHECK-DAG: 5:c:@sf
 
 struct SStatic {
   static const int a = 4;
 };
 const int SStatic::a;
-// CHECK-DAG: c:@S@SStatic@a
+// CHECK-DAG: 14:c:@S@SStatic@a
 
 extern int const arr[5] = { 0, 1 };
-// CHECK-DAG: c:@arr
+// CHECK-DAG: 6:c:@arr
 
 union U {
   const int a;
   const unsigned int b;
 };
 U u = {.a = 6};
-// CHECK-DAG: c:@u
+// CHECK-DAG: 4:c:@u
 
 // No USR can be generated for this.
 // Check for no crash in this case.
Index: clang/unittests/CrossTU/CrossTranslationUnitTest.cpp
===================================================================
--- clang/unittests/CrossTU/CrossTranslationUnitTest.cpp
+++ clang/unittests/CrossTU/CrossTranslationUnitTest.cpp
@@ -61,7 +61,7 @@
     ASSERT_FALSE(llvm::sys::fs::createTemporaryFile("index", "txt", IndexFD,
                                                     IndexFileName));
     llvm::ToolOutputFile IndexFile(IndexFileName, IndexFD);
-    IndexFile.os() << "c:@F@f#I# " << ASTFileName << "\n";
+    IndexFile.os() << "9:c:@F@f#I# " << ASTFileName << "\n";
     IndexFile.os().flush();
     EXPECT_TRUE(llvm::sys::fs::exists(IndexFileName));
 
@@ -154,9 +154,9 @@
 
 TEST(CrossTranslationUnit, IndexFormatCanBeParsed) {
   llvm::StringMap<std::string> Index;
-  Index["a"] = "/b/f1";
-  Index["c"] = "/d/f2";
-  Index["e"] = "/f/f3";
+  Index["1:a"] = "/b/f1";
+  Index["1:c"] = "/d/f2";
+  Index["1:e"] = "/f/f3";
   std::string IndexText = createCrossTUIndexString(Index);
 
   int IndexFD;