Index: lib/Driver/ToolChains/Darwin.h
===================================================================
--- lib/Driver/ToolChains/Darwin.h
+++ lib/Driver/ToolChains/Darwin.h
@@ -494,6 +494,10 @@
   void AddLinkRuntimeLibArgs(const llvm::opt::ArgList &Args,
                              llvm::opt::ArgStringList &CmdArgs) const override;
 
+  void AddClangCXXStdlibIncludeArgs(
+      const llvm::opt::ArgList &DriverArgs,
+      llvm::opt::ArgStringList &CC1Args) const override;
+
   void AddCXXStdlibLibArgs(const llvm::opt::ArgList &Args,
                            llvm::opt::ArgStringList &CmdArgs) const override;
 
Index: lib/Driver/ToolChains/Darwin.cpp
===================================================================
--- lib/Driver/ToolChains/Darwin.cpp
+++ lib/Driver/ToolChains/Darwin.cpp
@@ -1682,6 +1682,38 @@
   }
 }
 
+void DarwinClang::AddClangCXXStdlibIncludeArgs(
+    const llvm::opt::ArgList &DriverArgs,
+    llvm::opt::ArgStringList &CC1Args) const {
+  // The implementation from a base class will pass through the -stdlib to
+  // CC1Args.
+  // FIXME: this should not be necessary, remove usages in the frontend
+  //        (e.g. HeaderSearchOptions::UseLibcxx) and don't pipe -stdlib.
+  ToolChain::AddClangCXXStdlibIncludeArgs(DriverArgs, CC1Args);
+
+  if (DriverArgs.hasArg(options::OPT_nostdlibinc) ||
+      DriverArgs.hasArg(options::OPT_nostdincxx))
+    return;
+
+  switch (GetCXXStdlibType(DriverArgs)) {
+  case ToolChain::CST_Libcxx: {
+    llvm::StringRef InstallDir = getDriver().getInstalledDir();
+    if (InstallDir.empty())
+      break;
+    // On Darwin, libc++ may be installed alongside the compiler in
+    // include/c++/v1.
+    // Get from 'foo/bin' to 'foo'.
+    SmallString<128> P = llvm::sys::path::parent_path(InstallDir);
+    // Get to 'foo/include/c++/v1'.
+    llvm::sys::path::append(P, "include", "c++", "v1");
+    addSystemInclude(DriverArgs, CC1Args, P);
+    break;
+  }
+  case ToolChain::CST_Libstdcxx:
+    // FIXME: should we do something about it?
+    break;
+  }
+}
 void DarwinClang::AddCXXStdlibLibArgs(const ArgList &Args,
                                       ArgStringList &CmdArgs) const {
   CXXStdlibType Type = GetCXXStdlibType(Args);
Index: lib/Frontend/InitHeaderSearch.cpp
===================================================================
--- lib/Frontend/InitHeaderSearch.cpp
+++ lib/Frontend/InitHeaderSearch.cpp
@@ -476,22 +476,6 @@
   if (Lang.CPlusPlus && !Lang.AsmPreprocessor &&
       HSOpts.UseStandardCXXIncludes && HSOpts.UseStandardSystemIncludes) {
     if (HSOpts.UseLibcxx) {
-      if (triple.isOSDarwin()) {
-        // On Darwin, libc++ may be installed alongside the compiler in
-        // include/c++/v1.
-        if (!HSOpts.ResourceDir.empty()) {
-          // Remove version from foo/lib/clang/version
-          StringRef NoVer = llvm::sys::path::parent_path(HSOpts.ResourceDir);
-          // Remove clang from foo/lib/clang
-          StringRef Lib = llvm::sys::path::parent_path(NoVer);
-          // Remove lib from foo/lib
-          SmallString<128> P = llvm::sys::path::parent_path(Lib);
-
-          // Get foo/include/c++/v1
-          llvm::sys::path::append(P, "include", "c++", "v1");
-          AddUnmappedPath(P, CXXSystem, false);
-        }
-      }
       AddPath("/usr/include/c++/v1", CXXSystem, false);
     } else {
       AddDefaultCPlusPlusIncludePaths(Lang, triple, HSOpts);
Index: test/Driver/darwin-stdlib.cpp
===================================================================
--- test/Driver/darwin-stdlib.cpp
+++ test/Driver/darwin-stdlib.cpp
@@ -2,19 +2,20 @@
 // than the platform default. (see https://llvm.org/bugs/show_bug.cgi?id=30548)
 // XFAIL: default-cxx-stdlib-set
 
-// RUN: %clang -target x86_64-apple-darwin -arch arm64 -miphoneos-version-min=7.0 %s -### 2>&1 | FileCheck %s --check-prefix=CHECK-LIBCXX
-// RUN: %clang -target x86_64-apple-darwin -mmacosx-version-min=10.8 %s -### 2>&1 | FileCheck %s --check-prefix=CHECK-LIBSTDCXX
-// RUN: %clang -target x86_64-apple-darwin -mmacosx-version-min=10.9 %s -### 2>&1 | FileCheck %s --check-prefix=CHECK-LIBCXX
-// RUN: %clang -target x86_64-apple-darwin -arch armv7s -miphoneos-version-min=6.1 %s -### 2>&1 | FileCheck %s --check-prefix=CHECK-LIBSTDCXX
-// RUN: %clang -target x86_64-apple-darwin -arch armv7s -miphoneos-version-min=7.0 %s -### 2>&1 | FileCheck %s --check-prefix=CHECK-LIBCXX
-// RUN: %clang -target x86_64-apple-darwin -arch armv7k %s -### 2>&1 | FileCheck %s --check-prefix=CHECK-LIBCXX
+// RUN: %clang -target x86_64-apple-darwin -ccc-install-dir %S/Inputs/darwin_toolchain_tree/bin/ -arch arm64 -miphoneos-version-min=7.0 %s -### 2>&1 | FileCheck %s --check-prefix=CHECK-LIBCXX
+// RUN: %clang -target x86_64-apple-darwin -ccc-install-dir %S/Inputs/darwin_toolchain_tree/bin/ -mmacosx-version-min=10.8 %s -### 2>&1 | FileCheck %s --check-prefix=CHECK-LIBSTDCXX
+// RUN: %clang -target x86_64-apple-darwin -ccc-install-dir %S/Inputs/darwin_toolchain_tree/bin/ -mmacosx-version-min=10.9 %s -### 2>&1 | FileCheck %s --check-prefix=CHECK-LIBCXX
+// RUN: %clang -target x86_64-apple-darwin -ccc-install-dir %S/Inputs/darwin_toolchain_tree/bin/ -arch armv7s -miphoneos-version-min=6.1 %s -### 2>&1 | FileCheck %s --check-prefix=CHECK-LIBSTDCXX
+// RUN: %clang -target x86_64-apple-darwin -ccc-install-dir %S/Inputs/darwin_toolchain_tree/bin/ -arch armv7s -miphoneos-version-min=7.0 %s -### 2>&1 | FileCheck %s --check-prefix=CHECK-LIBCXX
+// RUN: %clang -target x86_64-apple-darwin -ccc-install-dir %S/Inputs/darwin_toolchain_tree/bin/ -arch armv7k %s -### 2>&1 | FileCheck %s --check-prefix=CHECK-LIBCXX
 
 // The purpose of this test is that the libc++ headers should be found
-// properly. At the moment this is done by passing -stdlib=libc++ down to the
-// cc1 invocation. If and when we change to finding them in the driver this test
-// should reflect that.
+// properly. We also pass -stdlib=libc++ to make sure the logic to add the
+// optional absolute include for libc++ from InitHeaderSearch.cpp also fires.
 
-// CHECK-LIBCXX: -stdlib=libc++
+// CHECK-LIBCXX: "-stdlib=libc++"
+// CHECK-LIBCXX: "-internal-isystem" "{{[^"]*}}{{[/\\]}}Inputs{{[/\\]}}darwin_toolchain_tree{{[/\\]}}bin{{[/\\]}}include{{[/\\]}}c++{{[/\\]}}v1"
 
 // CHECK-LIBSTDCXX-NOT: -stdlib=libc++
 // CHECK-LIBSTDCXX-NOT: -stdlib=libstdc++
+// CHECK-LIBSTDCXX-NOT: -internal-isystem
Index: test/Tooling/Inputs/mock-libcxx/include/c++/v1/mock_vector
===================================================================
--- test/Tooling/Inputs/mock-libcxx/include/c++/v1/mock_vector
+++ test/Tooling/Inputs/mock-libcxx/include/c++/v1/mock_vector
@@ -0,0 +1 @@
+class vector {};
Index: test/Tooling/clang-check-mac-libcxx-abspath.cpp
===================================================================
--- test/Tooling/clang-check-mac-libcxx-abspath.cpp
+++ test/Tooling/clang-check-mac-libcxx-abspath.cpp
@@ -0,0 +1,17 @@
+// Clang on MacOS can find libc++ living beside the installed compiler.
+// This test makes sure our libTooling-based tools emulate this properly.
+//
+// RUN: rm -rf %t
+// RUN: mkdir %t
+//
+// Install the mock libc++ (simulates the libc++ directory structure).
+// RUN: cp -r %S/Inputs/mock-libcxx %t/
+//
+// Pretend clang is installed beside the mock library that we provided.
+// RUN: echo '[{"directory":"%t","command":"%t/mock-libcxx/bin/clang++ -stdlib=libc++ -target x86_64-apple-darwin -c test.cpp","file":"test.cpp"}]' | sed -e 's/\\/\//g' > %t/compile_commands.json
+// RUN: cp "%s" "%t/test.cpp"
+// clang-check will produce an error code if the mock library is not found.
+// RUN: clang-check -p "%t" "%t/test.cpp"
+
+#include <mock_vector>
+vector v;
Index: test/Tooling/clang-check-mac-libcxx-relpath.cpp
===================================================================
--- test/Tooling/clang-check-mac-libcxx-relpath.cpp
+++ test/Tooling/clang-check-mac-libcxx-relpath.cpp
@@ -0,0 +1,17 @@
+// Clang on MacOS can find libc++ living beside the installed compiler.
+// This test makes sure our libTooling-based tools emulate this properly.
+//
+// RUN: rm -rf %t
+// RUN: mkdir %t
+//
+// Install the mock libc++ (simulates the libc++ directory structure).
+// RUN: cp -r %S/Inputs/mock-libcxx %t/
+//
+// Pretend clang is installed beside the mock library that we provided.
+// RUN: echo '[{"directory":"%t","command":"mock-libcxx/bin/clang++ -stdlib=libc++ -target x86_64-apple-darwin -c test.cpp","file":"test.cpp"}]' | sed -e 's/\\/\//g' > %t/compile_commands.json
+// RUN: cp "%s" "%t/test.cpp"
+// clang-check will produce an error code if the mock library is not found.
+// RUN: clang-check -p "%t" "%t/test.cpp"
+
+#include <mock_vector>
+vector v;