Index: include/clang/Frontend/Utils.h
===================================================================
--- include/clang/Frontend/Utils.h
+++ include/clang/Frontend/Utils.h
@@ -77,7 +77,7 @@
 /// interface.
 class DependencyCollector {
 public:
-  void attachToPreprocessor(Preprocessor &PP);
+  virtual void attachToPreprocessor(Preprocessor &PP);
   virtual void attachToASTReader(ASTReader &R);
   llvm::ArrayRef<std::string> getDependencies() const { return Dependencies; }
 
@@ -136,6 +136,7 @@
     VFSWriter.addFileMapping(VPath, RPath);
   }
 
+  void attachToPreprocessor(Preprocessor &PP) override;
   void attachToASTReader(ASTReader &R) override;
 
   void writeFileMap();
Index: include/clang/Lex/ModuleMap.h
===================================================================
--- include/clang/Lex/ModuleMap.h
+++ include/clang/Lex/ModuleMap.h
@@ -50,6 +50,11 @@
   /// \param IsSystem Whether this is a module map from a system include path.
   virtual void moduleMapFileRead(SourceLocation FileStart,
                                  const FileEntry &File, bool IsSystem) {}
+
+  /// \brief Called when a header is added during module map parsing.
+  ///
+  /// \param File The header file itself.
+  virtual void moduleMapAddHeader(const FileEntry &File) {}
 };
   
 class ModuleMap {
Index: lib/Frontend/ModuleDependencyCollector.cpp
===================================================================
--- lib/Frontend/ModuleDependencyCollector.cpp
+++ lib/Frontend/ModuleDependencyCollector.cpp
@@ -12,6 +12,7 @@
 //===----------------------------------------------------------------------===//
 
 #include "clang/Frontend/Utils.h"
+#include "clang/Lex/Preprocessor.h"
 #include "clang/Serialization/ASTReader.h"
 #include "llvm/ADT/StringMap.h"
 #include "llvm/ADT/iterator_range.h"
@@ -22,7 +23,7 @@
 using namespace clang;
 
 namespace {
-/// Private implementation for ModuleDependencyCollector
+/// Private implementations for ModuleDependencyCollector
 class ModuleDependencyListener : public ASTReaderListener {
   ModuleDependencyCollector &Collector;
 public:
@@ -36,12 +37,30 @@
     return true;
   }
 };
+
+struct ModuleDependencyMMCallbacks : public ModuleMapCallbacks {
+  ModuleDependencyCollector &Collector;
+  ModuleDependencyMMCallbacks(ModuleDependencyCollector &Collector)
+      : Collector(Collector) {}
+
+  void moduleMapAddHeader(const FileEntry &File) override {
+    StringRef HeaderPath = File.getName();
+    if (llvm::sys::path::is_absolute(HeaderPath))
+      Collector.addFile(HeaderPath);
+  }
+};
+
 }
 
 void ModuleDependencyCollector::attachToASTReader(ASTReader &R) {
   R.addListener(llvm::make_unique<ModuleDependencyListener>(*this));
 }
 
+void ModuleDependencyCollector::attachToPreprocessor(Preprocessor &PP) {
+  PP.getHeaderSearchInfo().getModuleMap().addModuleMapCallbacks(
+      llvm::make_unique<ModuleDependencyMMCallbacks>(*this));
+}
+
 void ModuleDependencyCollector::writeFileMap() {
   if (Seen.empty())
     return;
Index: lib/Lex/ModuleMap.cpp
===================================================================
--- lib/Lex/ModuleMap.cpp
+++ lib/Lex/ModuleMap.cpp
@@ -812,6 +812,10 @@
     HeaderInfo.MarkFileModuleHeader(Header.Entry, Role,
                                     isCompilingModuleHeader);
   }
+
+  // Notify callbacks that we just added a new header.
+  for (const auto &Cb : Callbacks)
+    Cb->moduleMapAddHeader(*Header.Entry);
 }
 
 void ModuleMap::excludeHeader(Module *Mod, Module::Header Header) {
Index: test/Modules/Inputs/crash-recovery/usr/include/module.map
===================================================================
--- test/Modules/Inputs/crash-recovery/usr/include/module.map
+++ test/Modules/Inputs/crash-recovery/usr/include/module.map
@@ -3,4 +3,14 @@
   module stdio {
     header "stdio.h"
   }
+
+  module pthread {
+    header "pthread.h"
+    export *
+
+    module impl {
+      header "pthread_impl.h"
+      export *
+    }
+  }
 }
Index: test/Modules/Inputs/crash-recovery/usr/include/pthread.h
===================================================================
--- /dev/null
+++ test/Modules/Inputs/crash-recovery/usr/include/pthread.h
@@ -0,0 +1 @@
+#include "pthread/pthread_impl.h"
Index: test/Modules/Inputs/crash-recovery/usr/include/pthread/pthread_impl.h
===================================================================
--- /dev/null
+++ test/Modules/Inputs/crash-recovery/usr/include/pthread/pthread_impl.h
@@ -0,0 +1 @@
+#define _PTHREAD_MUTEX_SIG_init   0x32AAABA7
Index: test/Modules/Inputs/crash-recovery/usr/include/pthread_impl.h
===================================================================
--- /dev/null
+++ test/Modules/Inputs/crash-recovery/usr/include/pthread_impl.h
@@ -0,0 +1 @@
+#define _PTHREAD_MUTEX_SIG_init   0x32AAABA7
Index: test/Modules/crash-vfs-path-symlink-topheader.m
===================================================================
--- /dev/null
+++ test/Modules/crash-vfs-path-symlink-topheader.m
@@ -0,0 +1,50 @@
+// REQUIRES: crash-recovery, shell
+
+// FIXME: This XFAIL is cargo-culted from crash-report.c. Do we need it?
+// XFAIL: mingw32
+
+// Test clang can collect symbolic link headers used in modules.
+// crash reproducer if there's a symbolic link header file used in a module.
+
+// RUN: rm -rf %t
+// RUN: mkdir -p %t/i %t/m %t %t/sysroot
+// RUN: cp -a %S/Inputs/crash-recovery/usr %t/i/
+// RUN: rm -f %t/i/usr/include/pthread_impl.h
+// RUN: ln -s pthread/pthread_impl.h %t/i/usr/include/pthread_impl.h
+
+// RUN: not env FORCE_CLANG_DIAGNOSTICS_CRASH= TMPDIR=%t TEMP=%t TMP=%t \
+// RUN: %clang -fsyntax-only %s -I %/t/i -isysroot %/t/sysroot/ \
+// RUN:     -fmodules -fmodules-cache-path=%t/m/ 2>&1 | FileCheck %s
+
+// RUN: FileCheck --check-prefix=CHECKSRC %s -input-file %t/crash-vfs-*.m
+// RUN: FileCheck --check-prefix=CHECKSH %s -input-file %t/crash-vfs-*.sh
+// RUN: FileCheck --check-prefix=CHECKYAML %s -input-file \
+// RUN: %t/crash-vfs-*.cache/vfs/vfs.yaml
+// RUN: find %t/crash-vfs-*.cache/vfs | \
+// RUN:   grep "usr/include/pthread_impl.h" | count 1
+
+#include "usr/include/stdio.h"
+
+// CHECK: Preprocessed source(s) and associated run script(s) are located at:
+// CHECK-NEXT: note: diagnostic msg: {{.*}}.m
+// CHECK-NEXT: note: diagnostic msg: {{.*}}.cache
+
+// CHECKSRC: @import cstd.stdio;
+
+// CHECKSH: # Crash reproducer
+// CHECKSH-NEXT: # Driver args: "-fsyntax-only"
+// CHECKSH-NEXT: # Original command: {{.*$}}
+// CHECKSH-NEXT: "-cc1"
+// CHECKSH: "-isysroot" "{{[^"]*}}/sysroot/"
+// CHECKSH-NOT: "-fmodules-cache-path="
+// CHECKSH: "crash-vfs-{{[^ ]*}}.m"
+// CHECKSH: "-ivfsoverlay" "crash-vfs-{{[^ ]*}}.cache/vfs/vfs.yaml"
+
+// CHECKYAML: 'type': 'directory',
+// CHECKYAML: 'name': "",
+// CHECKYAML-NEXT: 'contents': [
+// CHECKYAML-NEXT:   {
+// CHECKYAML-NEXT:     'type': 'file',
+// CHECKYAML-NEXT:     'name': "pthread_impl.h",
+// CHECKYAML-NEXT:     'external-contents': "/{{.*}}/i/usr/include/pthread_impl.h"
+// CHECKYAML-NEXT:   },