Index: include/clang/Lex/HeaderSearch.h
===================================================================
--- include/clang/Lex/HeaderSearch.h
+++ include/clang/Lex/HeaderSearch.h
@@ -564,8 +564,7 @@
   ///
   /// \return \c true if the file can be used, \c false if we are not permitted to
   ///         find this file due to requirements from \p RequestingModule.
-  bool findUsableModuleForHeader(const FileEntry *File,
-                                 const DirectoryEntry *Root,
+  bool findUsableModuleForHeader(StringRef FileName, const DirectoryEntry *Root,
                                  Module *RequestingModule,
                                  ModuleMap::KnownHeader *SuggestedModule,
                                  bool IsSystemHeaderDir);
Index: lib/Basic/FileManager.cpp
===================================================================
--- lib/Basic/FileManager.cpp
+++ lib/Basic/FileManager.cpp
@@ -218,6 +218,9 @@
       *SeenFileEntries.insert(std::make_pair(Filename, nullptr)).first;
 
   // See if there is already an entry in the map.
+  // FIXME: Note that when first requested, the returned file name equals to the
+  // requested path. This is not true when returning a cached result. This is
+  // inconsistent and might lead to clients making the wrong assumptions.
   if (NamedFileEnt.second)
     return NamedFileEnt.second == NON_EXISTENT_FILE ? nullptr
                                                     : NamedFileEnt.second;
Index: lib/Lex/HeaderSearch.cpp
===================================================================
--- lib/Lex/HeaderSearch.cpp
+++ lib/Lex/HeaderSearch.cpp
@@ -258,7 +258,7 @@
     return nullptr;
 
   // If there is a module that corresponds to this header, suggest it.
-  if (!findUsableModuleForHeader(File, Dir ? Dir : File->getDir(),
+  if (!findUsableModuleForHeader(FileName, Dir ? Dir : File->getDir(),
                                  RequestingModule, SuggestedModule,
                                  IsSystemHeaderDir))
     return nullptr;
@@ -490,7 +490,7 @@
   // If we found the header and are allowed to suggest a module, do so now.
   if (FE && SuggestedModule) {
     // Find the framework in which this header occurs.
-    StringRef FrameworkPath = FE->getDir()->getName();
+    StringRef FrameworkPath = llvm::sys::path::parent_path(FrameworkName);
     bool FoundFramework = false;
     do {
       // Determine whether this directory exists.
@@ -517,8 +517,9 @@
               FE, FrameworkPath, RequestingModule, SuggestedModule, IsSystem))
         return nullptr;
     } else {
-      if (!HS.findUsableModuleForHeader(FE, getDir(), RequestingModule,
-                                        SuggestedModule, IsSystem))
+      if (!HS.findUsableModuleForHeader(FrameworkName, getDir(),
+                                        RequestingModule, SuggestedModule,
+                                        IsSystem))
         return nullptr;
     }
   }
@@ -1145,11 +1146,14 @@
 }
 
 bool HeaderSearch::findUsableModuleForHeader(
-    const FileEntry *File, const DirectoryEntry *Root, Module *RequestingModule,
+    StringRef FileName, const DirectoryEntry *Root, Module *RequestingModule,
     ModuleMap::KnownHeader *SuggestedModule, bool IsSystemHeaderDir) {
+  const FileEntry *File = getFileMgr().getFile(FileName, /*OpenFile=*/true);
   if (File && SuggestedModule) {
     // If there is a module that corresponds to this header, suggest it.
-    hasModuleMap(File->getName(), Root, IsSystemHeaderDir);
+    // FIXME: Look module through the filename to avoid FileManager leaking
+    // real paths when using the VFS...
+    hasModuleMap(FileName, Root, IsSystemHeaderDir);
     *SuggestedModule = findModuleForHeader(File);
   }
   return true;
Index: test/Modules/Inputs/crash-recovery/Users/bar/a.h
===================================================================
--- /dev/null
+++ test/Modules/Inputs/crash-recovery/Users/bar/a.h
@@ -0,0 +1,6 @@
+#ifndef _BAR_H
+#define _BAR_H
+
+#include "bar.h"
+
+#endif
Index: test/Modules/Inputs/crash-recovery/Users/bar/bar.h
===================================================================
--- /dev/null
+++ test/Modules/Inputs/crash-recovery/Users/bar/bar.h
@@ -0,0 +1,6 @@
+#ifndef __CLANG_MAX_ALIGN_T_DEFINED
+#define __CLANG_MAX_ALIGN_T_DEFINED
+
+typedef long double max_align_t;
+
+#endif
Index: test/Modules/Inputs/crash-recovery/Users/bar/module.modulemap
===================================================================
--- /dev/null
+++ test/Modules/Inputs/crash-recovery/Users/bar/module.modulemap
@@ -0,0 +1,3 @@
+module bar [system] [extern_c] {
+  header "bar.h"
+}
Index: test/Modules/Inputs/crash-recovery/Users/foo/foo.h
===================================================================
--- /dev/null
+++ test/Modules/Inputs/crash-recovery/Users/foo/foo.h
@@ -0,0 +1 @@
+#include <a.h>
Index: test/Modules/Inputs/crash-recovery/Users/foo/module.modulemap
===================================================================
--- /dev/null
+++ test/Modules/Inputs/crash-recovery/Users/foo/module.modulemap
@@ -0,0 +1,3 @@
+module foo [system] [extern_c] {
+  header "foo.h"
+}
Index: test/Modules/crash-vfs-module-redefinition.m
===================================================================
--- /dev/null
+++ test/Modules/crash-vfs-module-redefinition.m
@@ -0,0 +1,38 @@
+// REQUIRES: crash-recovery, system-darwin, shell
+
+// FIXME: This XFAIL is cargo-culted from crash-report.c. Do we need it?
+// XFAIL: mingw32
+
+// RUN: rm -rf %t
+// RUN: mkdir -p %t/i %t/m %t
+
+// RUN: not env FORCE_CLANG_DIAGNOSTICS_CRASH= TMPDIR=%t TEMP=%t TMP=%t \
+// RUN: %clang -fsyntax-only -nostdinc %s \
+// RUN:	    -I %S/Inputs/crash-recovery/Users/bar \
+// RUN:	    -I %S/Inputs/crash-recovery/Users -isysroot %/t/i/ \
+// 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
+
+#include <foo/foo.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 foo;
+
+// CHECKSH: # Crash reproducer
+// CHECKSH-NEXT: # Driver args: "-fsyntax-only"
+// CHECKSH-NEXT: # Original command: {{.*$}}
+// CHECKSH-NEXT: "-cc1"
+// CHECKSH: "-resource-dir"
+// CHECKSH: "-isysroot" "{{[^"]*}}/i/"
+// CHECKSH: "crash-vfs-{{[^ ]*}}.m"
+// CHECKSH: "-ivfsoverlay" "crash-vfs-{{[^ ]*}}.cache/vfs/vfs.yaml"
+// CHECKSH: "-fmodules-cache-path=crash-vfs-{{[^ ]*}}.cache/modules"
+
+// RUN: cd %t
+// RUN: chmod 755 crash-vfs-*.sh
+// RUN: ./crash-vfs-*.sh