diff --git a/include/clang/Driver/CC1Options.td b/include/clang/Driver/CC1Options.td
index 6f27c4a9bb1..f4a7f246ab5 100644
--- a/include/clang/Driver/CC1Options.td
+++ b/include/clang/Driver/CC1Options.td
@@ -385,6 +385,8 @@ def fno_dllexport_inlines : Flag<["-"], "fno-dllexport-inlines">;
 
 def sys_header_deps : Flag<["-"], "sys-header-deps">,
   HelpText<"Include system headers in dependency output">;
+def skip_unused_modulemap_file_deps : Flag<["-"], "skip-unused-modulemap-deps">,
+  HelpText<"Include module map files only for imported modules in dependency output">;
 def module_file_deps : Flag<["-"], "module-file-deps">,
   HelpText<"Include module files in dependency output">;
 def header_include_file : Separate<["-"], "header-include-file">,
diff --git a/include/clang/Frontend/DependencyOutputOptions.h b/include/clang/Frontend/DependencyOutputOptions.h
index f419d264364..e6d1df148d7 100644
--- a/include/clang/Frontend/DependencyOutputOptions.h
+++ b/include/clang/Frontend/DependencyOutputOptions.h
@@ -32,6 +32,7 @@ class DependencyOutputOptions {
                                      /// problems.
   unsigned AddMissingHeaderDeps : 1; ///< Add missing headers to dependency list
   unsigned IncludeModuleFiles : 1; ///< Include module file dependencies.
+  unsigned SkipUnusedModuleMaps : 1; ///< Skip unused module map dependencies.
 
   /// Destination of cl.exe style /showIncludes info.
   ShowIncludesDestination ShowIncludesDest = ShowIncludesDestination::None;
@@ -67,7 +68,7 @@ class DependencyOutputOptions {
 public:
   DependencyOutputOptions()
       : IncludeSystemHeaders(0), ShowHeaderIncludes(0), UsePhonyTargets(0),
-        AddMissingHeaderDeps(0), IncludeModuleFiles(0) {}
+        AddMissingHeaderDeps(0), IncludeModuleFiles(0), SkipUnusedModuleMaps(0) {}
 };
 
 }  // end namespace clang
diff --git a/include/clang/Lex/ModuleMap.h b/include/clang/Lex/ModuleMap.h
index 0f8abb3bacf..a8cf5c80a4a 100644
--- a/include/clang/Lex/ModuleMap.h
+++ b/include/clang/Lex/ModuleMap.h
@@ -59,6 +59,14 @@ class ModuleMapCallbacks {
   virtual void moduleMapFileRead(SourceLocation FileStart,
                                  const FileEntry &File, bool IsSystem) {}
 
+  /// Called when a module map file matches a module lookup
+  ///
+  /// \param File The file itself.
+  /// \param M The module found that matches this module map.
+  /// \param IsSystem Whether this is a module map from a system include path.
+  virtual void moduleMapFoundForModule(const FileEntry &File, const Module *M,
+                                       bool IsSystem) {}
+
   /// Called when a header is added during module map parsing.
   ///
   /// \param Filename The header file itself.
diff --git a/include/clang/Sema/Sema.h b/include/clang/Sema/Sema.h
index a5a55d642ac..aa8ccb5048a 100644
--- a/include/clang/Sema/Sema.h
+++ b/include/clang/Sema/Sema.h
@@ -536,13 +536,13 @@ class Sema {
   /// element type here is ExprWithCleanups::Object.
   SmallVector<BlockDecl*, 8> ExprCleanupObjects;
 
-  /// Store a list of either DeclRefExprs or MemberExprs
-  ///  that contain a reference to a variable (constant) that may or may not
-  ///  be odr-used in this Expr, and we won't know until all lvalue-to-rvalue
-  ///  and discarded value conversions have been applied to all subexpressions
-  ///  of the enclosing full expression.  This is cleared at the end of each
-  ///  full expression.
-  llvm::SmallPtrSet<Expr*, 2> MaybeODRUseExprs;
+  /// Store a set of either DeclRefExprs or MemberExprs that contain a reference
+  /// to a variable (constant) that may or may not be odr-used in this Expr, and
+  /// we won't know until all lvalue-to-rvalue and discarded value conversions
+  /// have been applied to all subexpressions of the enclosing full expression.
+  /// This is cleared at the end of each full expression.
+  using MaybeODRUseExprSet = llvm::SmallPtrSet<Expr *, 2>;
+  MaybeODRUseExprSet MaybeODRUseExprs;
 
   std::unique_ptr<sema::FunctionScopeInfo> PreallocatedFunctionScope;
 
@@ -982,7 +982,7 @@ class Sema {
     /// context (i.e. the number of TypoExprs created).
     unsigned NumTypos;
 
-    llvm::SmallPtrSet<Expr*, 2> SavedMaybeODRUseExprs;
+    MaybeODRUseExprSet SavedMaybeODRUseExprs;
 
     /// The lambdas that are present within this context, if it
     /// is indeed an unevaluated context.
diff --git a/lib/Analysis/ThreadSafetyCommon.cpp b/lib/Analysis/ThreadSafetyCommon.cpp
index 14d1d9c7a8f..24d450b62b5 100644
--- a/lib/Analysis/ThreadSafetyCommon.cpp
+++ b/lib/Analysis/ThreadSafetyCommon.cpp
@@ -277,18 +277,23 @@ til::SExpr *SExprBuilder::translateDeclRefExpr(const DeclRefExpr *DRE,
 
   // Function parameters require substitution and/or renaming.
   if (const auto *PV = dyn_cast_or_null<ParmVarDecl>(VD)) {
-    const auto *FD =
-        cast<FunctionDecl>(PV->getDeclContext())->getCanonicalDecl();
     unsigned I = PV->getFunctionScopeIndex();
-
-    if (Ctx && Ctx->FunArgs && FD == Ctx->AttrDecl->getCanonicalDecl()) {
-      // Substitute call arguments for references to function parameters
-      assert(I < Ctx->NumArgs);
-      return translate(Ctx->FunArgs[I], Ctx->Prev);
+    const DeclContext *D = PV->getDeclContext();
+    if (Ctx && Ctx->FunArgs) {
+      const Decl *Canonical = Ctx->AttrDecl->getCanonicalDecl();
+      if (isa<FunctionDecl>(D)
+              ? (cast<FunctionDecl>(D)->getCanonicalDecl() == Canonical)
+              : (cast<ObjCMethodDecl>(D)->getCanonicalDecl() == Canonical)) {
+        // Substitute call arguments for references to function parameters
+        assert(I < Ctx->NumArgs);
+        return translate(Ctx->FunArgs[I], Ctx->Prev);
+      }
     }
     // Map the param back to the param of the original function declaration
     // for consistent comparisons.
-    VD = FD->getParamDecl(I);
+    VD = isa<FunctionDecl>(D)
+             ? cast<FunctionDecl>(D)->getCanonicalDecl()->getParamDecl(I)
+             : cast<ObjCMethodDecl>(D)->getCanonicalDecl()->getParamDecl(I);
   }
 
   // For non-local variables, treat it as a reference to a named object.
diff --git a/lib/Driver/ToolChains/Clang.cpp b/lib/Driver/ToolChains/Clang.cpp
index b152793a67f..b1e63241bcd 100644
--- a/lib/Driver/ToolChains/Clang.cpp
+++ b/lib/Driver/ToolChains/Clang.cpp
@@ -1043,6 +1043,7 @@ void Clang::AddPreprocessingOptions(Compilation &C, const JobAction &JA,
     }
     CmdArgs.push_back("-dependency-file");
     CmdArgs.push_back(DepFile);
+    CmdArgs.push_back("-skip-unused-modulemap-deps");
 
     // Add a default target if one wasn't specified.
     if (!Args.hasArg(options::OPT_MT) && !Args.hasArg(options::OPT_MQ)) {
diff --git a/lib/Frontend/CompilerInvocation.cpp b/lib/Frontend/CompilerInvocation.cpp
index 534b8b3f545..790a53e439d 100644
--- a/lib/Frontend/CompilerInvocation.cpp
+++ b/lib/Frontend/CompilerInvocation.cpp
@@ -1337,6 +1337,7 @@ static void ParseDependencyOutputArgs(DependencyOutputOptions &Opts,
   Opts.Targets = Args.getAllArgValues(OPT_MT);
   Opts.IncludeSystemHeaders = Args.hasArg(OPT_sys_header_deps);
   Opts.IncludeModuleFiles = Args.hasArg(OPT_module_file_deps);
+  Opts.SkipUnusedModuleMaps = Args.hasArg(OPT_skip_unused_modulemap_file_deps);
   Opts.UsePhonyTargets = Args.hasArg(OPT_MP);
   Opts.ShowHeaderIncludes = Args.hasArg(OPT_H);
   Opts.HeaderIncludeOutputFile = Args.getLastArgValue(OPT_header_include_file);
diff --git a/lib/Frontend/DependencyFile.cpp b/lib/Frontend/DependencyFile.cpp
index a03d4b79c8b..5b433c6788f 100644
--- a/lib/Frontend/DependencyFile.cpp
+++ b/lib/Frontend/DependencyFile.cpp
@@ -161,6 +161,7 @@ class DFGImpl : public PPCallbacks {
   bool AddMissingHeaderDeps;
   bool SeenMissingHeader;
   bool IncludeModuleFiles;
+  bool SkipUnusedModuleMaps;
   DependencyOutputFormat OutputFormat;
   unsigned InputFileIndex;
 
@@ -177,6 +178,7 @@ class DFGImpl : public PPCallbacks {
       AddMissingHeaderDeps(Opts.AddMissingHeaderDeps),
       SeenMissingHeader(false),
       IncludeModuleFiles(Opts.IncludeModuleFiles),
+      SkipUnusedModuleMaps(Opts.SkipUnusedModuleMaps),
       OutputFormat(Opts.OutputFormat),
       InputFileIndex(0) {
     for (const auto &ExtraDep : Opts.ExtraDeps) {
@@ -210,6 +212,7 @@ class DFGImpl : public PPCallbacks {
   bool AddFilename(StringRef Filename);
   bool includeSystemHeaders() const { return IncludeSystemHeaders; }
   bool includeModuleFiles() const { return IncludeModuleFiles; }
+  bool skipUnusedModuleMaps() const { return SkipUnusedModuleMaps; }
 };
 
 class DFGMMCallback : public ModuleMapCallbacks {
@@ -218,9 +221,17 @@ class DFGMMCallback : public ModuleMapCallbacks {
   DFGMMCallback(DFGImpl &Parent) : Parent(Parent) {}
   void moduleMapFileRead(SourceLocation Loc, const FileEntry &Entry,
                          bool IsSystem) override {
+    if (Parent.skipUnusedModuleMaps())
+      return;
     if (!IsSystem || Parent.includeSystemHeaders())
       Parent.AddFilename(Entry.getName());
   }
+  void moduleMapFoundForModule(const FileEntry &Entry, const Module *M,
+                               bool IsSystem) override {
+    if (Parent.skipUnusedModuleMaps() &&
+        (!IsSystem || Parent.includeSystemHeaders()))
+      Parent.AddFilename(Entry.getName());
+  }
 };
 
 class DFGASTReaderListener : public ASTReaderListener {
diff --git a/lib/Lex/ModuleMap.cpp b/lib/Lex/ModuleMap.cpp
index 6baf0548eb2..582dae1f58e 100644
--- a/lib/Lex/ModuleMap.cpp
+++ b/lib/Lex/ModuleMap.cpp
@@ -764,8 +764,17 @@ ModuleMap::isHeaderUnavailableInModule(const FileEntry *Header,
 
 Module *ModuleMap::findModule(StringRef Name) const {
   llvm::StringMap<Module *>::const_iterator Known = Modules.find(Name);
-  if (Known != Modules.end())
-    return Known->getValue();
+  if (Known != Modules.end()) {
+    Module *M = Known->getValue();
+    // Notify callbacks that we found a module map for the module.
+    if (!M->DefinitionLoc.isInvalid())
+      for (const auto &Cb : Callbacks)
+        Cb->moduleMapFoundForModule(
+            *getContainingModuleMapFile(M), M,
+            SourceMgr.getFileCharacteristic(M->DefinitionLoc) ==
+                SrcMgr::C_System_ModuleMap);
+    return M;
+  }
 
   return nullptr;
 }
diff --git a/lib/Sema/SemaExpr.cpp b/lib/Sema/SemaExpr.cpp
index c123c552f32..9d64507e546 100644
--- a/lib/Sema/SemaExpr.cpp
+++ b/lib/Sema/SemaExpr.cpp
@@ -15604,7 +15604,12 @@ ExprResult Sema::ActOnConstantExpression(ExprResult Res) {
 }
 
 void Sema::CleanupVarDeclMarking() {
-  for (Expr *E : MaybeODRUseExprs) {
+  // Iterate through a local copy in case MarkVarDeclODRUsed makes a recursive
+  // call.
+  MaybeODRUseExprSet LocalMaybeODRUseExprs;
+  std::swap(LocalMaybeODRUseExprs, MaybeODRUseExprs);
+
+  for (Expr *E : LocalMaybeODRUseExprs) {
     VarDecl *Var;
     SourceLocation Loc;
     if (DeclRefExpr *DRE = dyn_cast<DeclRefExpr>(E)) {
@@ -15621,10 +15626,10 @@ void Sema::CleanupVarDeclMarking() {
                        /*MaxFunctionScopeIndex Pointer*/ nullptr);
   }
 
-  MaybeODRUseExprs.clear();
+  assert(MaybeODRUseExprs.empty() &&
+         "MarkVarDeclODRUsed failed to cleanup MaybeODRUseExprs?");
 }
 
-
 static void DoMarkVarDeclReferenced(Sema &SemaRef, SourceLocation Loc,
                                     VarDecl *Var, Expr *E) {
   assert((!E || isa<DeclRefExpr>(E) || isa<MemberExpr>(E)) &&
diff --git a/test/Modules/Inputs/dependency-skip-unused/module.modulemap b/test/Modules/Inputs/dependency-skip-unused/module.modulemap
new file mode 100644
index 00000000000..e50630d3a18
--- /dev/null
+++ b/test/Modules/Inputs/dependency-skip-unused/module.modulemap
@@ -0,0 +1 @@
+module A {}
diff --git a/test/Modules/Inputs/dependency-skip-unused/x/module.modulemap b/test/Modules/Inputs/dependency-skip-unused/x/module.modulemap
new file mode 100644
index 00000000000..a8ecb09390a
--- /dev/null
+++ b/test/Modules/Inputs/dependency-skip-unused/x/module.modulemap
@@ -0,0 +1 @@
+module X {}
diff --git a/test/Modules/Inputs/dependency-skip-unused/y/module.modulemap b/test/Modules/Inputs/dependency-skip-unused/y/module.modulemap
new file mode 100644
index 00000000000..e6830bc2b4f
--- /dev/null
+++ b/test/Modules/Inputs/dependency-skip-unused/y/module.modulemap
@@ -0,0 +1 @@
+module Y {}
diff --git a/test/Modules/dependency-skip-unused-modulemaps.m b/test/Modules/dependency-skip-unused-modulemaps.m
new file mode 100644
index 00000000000..fb9a049f9c8
--- /dev/null
+++ b/test/Modules/dependency-skip-unused-modulemaps.m
@@ -0,0 +1,10 @@
+// RUN: rm -rf %t.cache %t.d %t.cmd
+// RUN: %clang_cc1 -fsyntax-only -fmodules -fimplicit-module-maps -fmodules-cache-path=%t.cache -dependency-file %t.d -MT dependencies -I%S/Inputs/dependency-skip-unused/x -I%S/Inputs/dependency-skip-unused/y -I%S/Inputs/dependency-skip-unused -skip-unused-modulemap-deps %s
+// RUN: FileCheck %s < %t.d
+// CHECK-NOT: dependency-skip-unused{{.}}x{{.}}module.modulemap
+// CHECK-NOT: dependency-skip-unused{{.}}y{{.}}module.modulemap
+
+// RUN: %clang -fsyntax-only -fmodules -fimplicit-module-maps -fmodules-cache-path=%t.cache -MMD -MT dependencies -MF %t.d -I%S/Inputs/dependency-skip-unused/x -I%S/Inputs/dependency-skip-unused/y -I%S/Inputs/dependency-skip-unused %s -### 2>&1 | FileCheck -check-prefix=CC1_INV %s
+// CC1_INV: -skip-unused-modulemap-deps
+
+@import A;
diff --git a/test/SemaCXX/blocks.cpp b/test/SemaCXX/blocks.cpp
index 0521802172f..aacf63cfab4 100644
--- a/test/SemaCXX/blocks.cpp
+++ b/test/SemaCXX/blocks.cpp
@@ -145,3 +145,11 @@ namespace test6c {
             A::foo(); });
   }
 }
+
+namespace test7 {
+struct S {};
+void f() {
+  constexpr S s;
+  auto some_block = ^{ (void)s; };
+}
+}
diff --git a/test/SemaObjCXX/no-crash-thread-safety-analysis.mm b/test/SemaObjCXX/no-crash-thread-safety-analysis.mm
new file mode 100644
index 00000000000..6abd391dc2e
--- /dev/null
+++ b/test/SemaObjCXX/no-crash-thread-safety-analysis.mm
@@ -0,0 +1,15 @@
+// RUN: %clang_cc1 -fsyntax-only -Wthread-safety -Wno-objc-root-class %s
+
+// Thread safety analysis used to crash when used with ObjC methods.
+
+#include "thread-safety-analysis.h"
+
+@interface MyInterface
+- (void)doIt:(class Lock *)myLock;
+@end
+
+@implementation MyInterface
+- (void)doIt:(class Lock *)myLock {
+  AutoLock lock(*myLock);
+}
+@end
diff --git a/test/SemaObjCXX/thread-safety-analysis.h b/test/SemaObjCXX/thread-safety-analysis.h
new file mode 100644
index 00000000000..f657b7e50a9
--- /dev/null
+++ b/test/SemaObjCXX/thread-safety-analysis.h
@@ -0,0 +1,17 @@
+class __attribute__((lockable)) Lock {
+public:
+  void Acquire() __attribute__((exclusive_lock_function())) {}
+  void Release() __attribute__((unlock_function())) {}
+};
+
+class __attribute__((scoped_lockable)) AutoLock {
+public:
+  AutoLock(Lock &lock) __attribute__((exclusive_lock_function(lock)))
+  : lock_(lock) {
+    lock.Acquire();
+  }
+  ~AutoLock() __attribute__((unlock_function())) { lock_.Release(); }
+
+private:
+  Lock &lock_;
+};
diff --git a/test/SemaObjCXX/warn-thread-safety-analysis.mm b/test/SemaObjCXX/warn-thread-safety-analysis.mm
index 262ab7d108a..a50c6f2ee13 100644
--- a/test/SemaObjCXX/warn-thread-safety-analysis.mm
+++ b/test/SemaObjCXX/warn-thread-safety-analysis.mm
@@ -1,22 +1,6 @@
 // RUN: %clang_cc1 -fsyntax-only -verify -Wthread-safety -Wthread-safety-beta -Wno-objc-root-class %s
 
-class __attribute__((lockable)) Lock {
-public:
-  void Acquire() __attribute__((exclusive_lock_function())) {}
-  void Release() __attribute__((unlock_function())) {}
-};
-
-class __attribute__((scoped_lockable)) AutoLock {
-public:
-  AutoLock(Lock &lock) __attribute__((exclusive_lock_function(lock)))
-  : lock_(lock) {
-    lock.Acquire();
-  }
-  ~AutoLock() __attribute__((unlock_function())) { lock_.Release(); }
-
-private:
-  Lock &lock_;
-};
+#include "thread-safety-analysis.h"
 
 @interface MyInterface {
 @private