Index: clang/include/clang/Serialization/ASTWriter.h
===================================================================
--- clang/include/clang/Serialization/ASTWriter.h
+++ clang/include/clang/Serialization/ASTWriter.h
@@ -475,7 +475,7 @@
   createSignature(StringRef AllBytes, StringRef ASTBlockBytes);
 
   void WriteInputFiles(SourceManager &SourceMgr, HeaderSearchOptions &HSOpts,
-                       bool Modules);
+                       std::set<std::string> &AffectingModuleMaps);
   void WriteSourceManagerBlock(SourceManager &SourceMgr,
                                const Preprocessor &PP);
   void WritePreprocessor(const Preprocessor &PP, bool IsModule);
Index: clang/lib/Serialization/ASTWriter.cpp
===================================================================
--- clang/lib/Serialization/ASTWriter.cpp
+++ clang/lib/Serialization/ASTWriter.cpp
@@ -149,6 +149,72 @@
 
 namespace {
 
+std::string ModuleMapFilePathForModule(const ModuleMap &Map,
+                                       Module *GivenModule) {
+  if (!GivenModule->PresumedModuleMapFile.empty()) {
+    return GivenModule->PresumedModuleMapFile;
+  }
+  auto *ModuleMapFile = Map.getModuleMapFileForUniquing(GivenModule);
+  if (!ModuleMapFile) {
+    return std::string();
+  }
+  return std::string(ModuleMapFile->getName());
+}
+
+std::set<std::string> GetAllModulemaps(const HeaderSearch &HS,
+                                       Module *RootModule) {
+  std::set<std::string> ModuleMaps{};
+  std::set<Module *> ProcessedModules;
+  std::set<Module *> ModulesToProcess{RootModule};
+
+  SmallVector<const FileEntry *, 16> FilesByUID;
+  HS.getFileMgr().GetUniqueIDMapping(FilesByUID);
+
+  if (FilesByUID.size() > HS.header_file_size())
+    FilesByUID.resize(HS.header_file_size());
+
+  for (unsigned UID = 0, LastUID = FilesByUID.size(); UID != LastUID; ++UID) {
+    const FileEntry *File = FilesByUID[UID];
+    if (!File)
+      continue;
+
+    const HeaderFileInfo *HFI =
+        HS.getExistingFileInfo(File, /*WantExternal*/false);
+    if (!HFI || (HFI->isModuleHeader && !HFI->isCompilingModuleHeader))
+      continue;
+
+    const auto KH = HS.findModuleForHeader(File, /*AllowTextual*/true);
+    if (!KH.getModule())
+      continue;
+
+    ModulesToProcess.insert(KH.getModule());
+  }
+
+  while (!ModulesToProcess.empty()) {
+    auto CurrentModule = ModulesToProcess.begin();
+    ProcessedModules.insert(*CurrentModule);
+
+    const std::string CurrentModuleMapFile =
+        ModuleMapFilePathForModule(HS.getModuleMap(), *CurrentModule);
+    if (CurrentModuleMapFile.empty()) {
+      ModulesToProcess.erase(CurrentModule);
+      continue;
+    }
+
+    ModuleMaps.insert(CurrentModuleMapFile);
+
+    for (auto *ImportedModule : (*CurrentModule)->Imports) {
+      if (!ImportedModule ||
+          ProcessedModules.find(ImportedModule) != ProcessedModules.end()) {
+        continue;
+      }
+      ModulesToProcess.insert(ImportedModule);
+    }
+    ModulesToProcess.erase(CurrentModule);
+  }
+  return ModuleMaps;
+}
+
 class ASTTypeWriter {
   ASTWriter &Writer;
   ASTWriter::RecordData Record;
@@ -1396,9 +1462,16 @@
     Stream.EmitRecordWithBlob(AbbrevCode, Record, origDir);
   }
 
+  std::set<std::string> AffectingModulemaps;
+  if (WritingModule) {
+    AffectingModulemaps = GetAllModulemaps(
+        PP.getHeaderSearchInfo(),
+        WritingModule);
+  }
+
   WriteInputFiles(Context.SourceMgr,
                   PP.getHeaderSearchInfo().getHeaderSearchOpts(),
-                  PP.getLangOpts().Modules);
+                  AffectingModulemaps);
   Stream.ExitBlock();
 }
 
@@ -1418,7 +1491,7 @@
 
 void ASTWriter::WriteInputFiles(SourceManager &SourceMgr,
                                 HeaderSearchOptions &HSOpts,
-                                bool Modules) {
+                                std::set<std::string> &AffectingModuleMaps) {
   using namespace llvm;
 
   Stream.EnterSubblock(INPUT_FILES_BLOCK_ID, 4);
@@ -1458,6 +1531,15 @@
     if (!Cache->OrigEntry)
       continue;
 
+    if (isModuleMap(File.getFileCharacteristic()) &&
+        !isSystem(File.getFileCharacteristic()) &&
+        !AffectingModuleMaps.empty() &&
+        AffectingModuleMaps.find(std::string(Cache->OrigEntry->getName())) ==
+            AffectingModuleMaps.end()) {
+      // Do not emit modulemaps that do not affect current module.
+      continue;
+    }
+
     InputFileEntry Entry;
     Entry.File = Cache->OrigEntry;
     Entry.IsSystemFile = isSystem(File.getFileCharacteristic());
@@ -1971,11 +2053,15 @@
     Record.push_back(SLoc->getOffset() - 2);
     if (SLoc->isFile()) {
       const SrcMgr::FileInfo &File = SLoc->getFile();
+      const SrcMgr::ContentCache *Content = &File.getContentCache();
+      if (Content->OrigEntry && InputFileIDs[Content->OrigEntry] == 0) {
+        // Do not emit files that were not listed as inputs.
+        continue;
+      }
       AddSourceLocation(File.getIncludeLoc(), Record);
       Record.push_back(File.getFileCharacteristic()); // FIXME: stable encoding
       Record.push_back(File.hasLineDirectives());
 
-      const SrcMgr::ContentCache *Content = &File.getContentCache();
       bool EmitBlob = false;
       if (Content->OrigEntry) {
         assert(Content->OrigEntry == Content->ContentsEntry &&