Index: include/clang/Basic/DiagnosticDriverKinds.td
===================================================================
--- include/clang/Basic/DiagnosticDriverKinds.td
+++ include/clang/Basic/DiagnosticDriverKinds.td
@@ -405,4 +405,8 @@
 def warn_drv_moutline_unsupported_opt : Warning<
   "The '%0' architecture does not support -moutline; flag ignored">,
   InGroup<OptionIgnored>;
+
+def warn_drv_darwin_sdk_invalid_settings : Warning<
+  "SDK settings were ignored as 'SDKSettings.json' could not be parsed">,
+  InGroup<DiagGroup<"darwin-sdk-settings">>;
 }
Index: include/clang/Basic/TargetInfo.h
===================================================================
--- include/clang/Basic/TargetInfo.h
+++ include/clang/Basic/TargetInfo.h
@@ -1321,6 +1321,12 @@
     return None;
   }
 
+  /// \returns The version of the SDK which was used during the compilation if
+  /// one was specified, or an empty version otherwise.
+  const llvm::VersionTuple &getSDKVersion() const {
+    return getTargetOpts().SDKVersion;
+  }
+
   /// Check the target is valid after it is fully initialized.
   virtual bool validateTarget(DiagnosticsEngine &Diags) const {
     return true;
Index: include/clang/Basic/TargetOptions.h
===================================================================
--- include/clang/Basic/TargetOptions.h
+++ include/clang/Basic/TargetOptions.h
@@ -15,10 +15,11 @@
 #ifndef LLVM_CLANG_BASIC_TARGETOPTIONS_H
 #define LLVM_CLANG_BASIC_TARGETOPTIONS_H
 
-#include <string>
-#include <vector>
 #include "clang/Basic/OpenCLOptions.h"
+#include "llvm/Support/VersionTuple.h"
 #include "llvm/Target/TargetOptions.h"
+#include <string>
+#include <vector>
 
 namespace clang {
 
@@ -73,6 +74,9 @@
   // "default" for the case when the user has not explicitly specified a
   // code model.
   std::string CodeModel;
+
+  /// The version of the SDK which was used during the compilation.
+  VersionTuple SDKVersion;
 };
 
 }  // end namespace clang
Index: include/clang/Driver/CC1Options.td
===================================================================
--- include/clang/Driver/CC1Options.td
+++ include/clang/Driver/CC1Options.td
@@ -27,6 +27,8 @@
   HelpText<"Specify target triple (e.g. i686-apple-darwin9)">;
 def target_abi : Separate<["-"], "target-abi">,
   HelpText<"Target a particular ABI type">;
+def target_sdk_version_EQ : Joined<["-"], "target-sdk-version=">,
+  HelpText<"The version of target SDK used for compilation">;
 
 }
 
Index: include/clang/Driver/DarwinSDKInfo.h
===================================================================
--- /dev/null
+++ include/clang/Driver/DarwinSDKInfo.h
@@ -0,0 +1,42 @@
+//===--- DarwinSDKInfo.h - SDK Information parser for darwin ----*- C++ -*-===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef LLVM_CLANG_DRIVER_DARWIN_SDK_INFO_H
+#define LLVM_CLANG_DRIVER_DARWIN_SDK_INFO_H
+
+#include "clang/Basic/LLVM.h"
+#include "llvm/Support/Error.h"
+#include "llvm/Support/VersionTuple.h"
+#include "llvm/Support/VirtualFileSystem.h"
+
+namespace clang {
+namespace driver {
+
+/// The information about the darwin SDK that was used during this compilation.
+class DarwinSDKInfo {
+public:
+  DarwinSDKInfo(llvm::VersionTuple Version) : Version(Version) {}
+
+  const llvm::VersionTuple &getVersion() const { return Version; }
+
+private:
+  llvm::VersionTuple Version;
+};
+
+/// Parse the SDK information from the SDKSettings.json file.
+///
+/// \returns an error if the SDKSettings.json file is invalid, None if the
+/// SDK has no SDKSettings.json, or a valid \c DarwinSDKInfo otherwise.
+Expected<Optional<DarwinSDKInfo>> parseDarwinSDKInfo(llvm::vfs::FileSystem &VFS,
+                                                     StringRef SDKRootPath);
+
+} // end namespace driver
+} // end namespace clang
+
+#endif // LLVM_CLANG_DRIVER_DARWIN_SDK_INFO_H
Index: lib/CodeGen/ModuleBuilder.cpp
===================================================================
--- lib/CodeGen/ModuleBuilder.cpp
+++ lib/CodeGen/ModuleBuilder.cpp
@@ -132,6 +132,9 @@
 
       M->setTargetTriple(Ctx->getTargetInfo().getTriple().getTriple());
       M->setDataLayout(Ctx->getTargetInfo().getDataLayout());
+      const auto &SDKVersion = Ctx->getTargetInfo().getSDKVersion();
+      if (!SDKVersion.empty())
+        M->setSDKVersion(SDKVersion);
       Builder.reset(new CodeGen::CodeGenModule(Context, HeaderSearchOpts,
                                                PreprocessorOpts, CodeGenOpts,
                                                *M, Diags, CoverageInfo));
Index: lib/Driver/CMakeLists.txt
===================================================================
--- lib/Driver/CMakeLists.txt
+++ lib/Driver/CMakeLists.txt
@@ -12,6 +12,7 @@
 add_clang_library(clangDriver
   Action.cpp
   Compilation.cpp
+  DarwinSDKInfo.cpp
   Distro.cpp
   Driver.cpp
   DriverOptions.cpp
Index: lib/Driver/DarwinSDKInfo.cpp
===================================================================
--- /dev/null
+++ lib/Driver/DarwinSDKInfo.cpp
@@ -0,0 +1,44 @@
+//===--- DarwinSDKInfo.cpp - SDK Information parser for darwin - ----------===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+
+#include "clang/Driver/DarwinSDKInfo.h"
+#include "llvm/Support/ErrorOr.h"
+#include "llvm/Support/JSON.h"
+#include "llvm/Support/MemoryBuffer.h"
+#include "llvm/Support/Path.h"
+
+using namespace clang::driver;
+using namespace clang;
+
+Expected<Optional<DarwinSDKInfo>>
+driver::parseDarwinSDKInfo(llvm::vfs::FileSystem &VFS, StringRef SDKRootPath) {
+  llvm::SmallString<256> Filepath = SDKRootPath;
+  llvm::sys::path::append(Filepath, "SDKSettings.json");
+  llvm::ErrorOr<std::unique_ptr<llvm::MemoryBuffer>> File =
+      VFS.getBufferForFile(Filepath);
+  if (!File) {
+    // If the file couldn't be read, assume it just doesn't exist.
+    return None;
+  }
+  Expected<llvm::json::Value> Result =
+      llvm::json::parse(File.get()->getBuffer());
+  if (!Result)
+    return Result.takeError();
+
+  if (const auto *Obj = Result->getAsObject()) {
+    auto VersionString = Obj->getString("Version");
+    if (VersionString) {
+      VersionTuple Version;
+      if (!Version.tryParse(*VersionString))
+        return DarwinSDKInfo(Version);
+    }
+  }
+  return llvm::make_error<llvm::StringError>("invalid SDKSettings.json",
+                                             llvm::inconvertibleErrorCode());
+}
Index: lib/Driver/ToolChains/Darwin.cpp
===================================================================
--- lib/Driver/ToolChains/Darwin.cpp
+++ lib/Driver/ToolChains/Darwin.cpp
@@ -13,6 +13,7 @@
 #include "clang/Basic/AlignedAllocation.h"
 #include "clang/Basic/ObjCRuntime.h"
 #include "clang/Driver/Compilation.h"
+#include "clang/Driver/DarwinSDKInfo.h"
 #include "clang/Driver/Driver.h"
 #include "clang/Driver/DriverDiagnostic.h"
 #include "clang/Driver/Options.h"
@@ -2037,6 +2038,22 @@
   return TargetVersion < alignedAllocMinVersion(OS);
 }
 
+static Optional<DarwinSDKInfo> parseSDKSettings(llvm::vfs::FileSystem &VFS,
+                                                const ArgList &Args,
+                                                const Driver &TheDriver) {
+  const Arg *A = Args.getLastArg(options::OPT_isysroot);
+  if (!A)
+    return None;
+  StringRef isysroot = A->getValue();
+  auto SDKInfoOrErr = driver::parseDarwinSDKInfo(VFS, isysroot);
+  if (!SDKInfoOrErr) {
+    llvm::consumeError(SDKInfoOrErr.takeError());
+    TheDriver.Diag(diag::warn_drv_darwin_sdk_invalid_settings);
+    return None;
+  }
+  return *SDKInfoOrErr;
+}
+
 void Darwin::addClangTargetOptions(const llvm::opt::ArgList &DriverArgs,
                                    llvm::opt::ArgStringList &CC1Args,
                                    Action::OffloadKind DeviceOffloadKind) const {
@@ -2046,6 +2063,15 @@
                                 options::OPT_fno_aligned_allocation) &&
       isAlignedAllocationUnavailable())
     CC1Args.push_back("-faligned-alloc-unavailable");
+
+  // Read the SDKSettings.json file for more information, like the SDK version
+  // that we can pass down to the compiler.
+  if (auto SDKInfo = parseSDKSettings(getVFS(), DriverArgs, getDriver())) {
+    std::string Arg;
+    llvm::raw_string_ostream OS(Arg);
+    OS << "-target-sdk-version=" << SDKInfo->getVersion();
+    CC1Args.push_back(DriverArgs.MakeArgString(OS.str()));
+  }
 }
 
 DerivedArgList *
Index: lib/Frontend/CompilerInvocation.cpp
===================================================================
--- lib/Frontend/CompilerInvocation.cpp
+++ lib/Frontend/CompilerInvocation.cpp
@@ -3188,6 +3188,14 @@
   Opts.ForceEnableInt128 = Args.hasArg(OPT_fforce_enable_int128);
   Opts.NVPTXUseShortPointers = Args.hasFlag(
       options::OPT_fcuda_short_ptr, options::OPT_fno_cuda_short_ptr, false);
+  if (Arg *A = Args.getLastArg(options::OPT_target_sdk_version_EQ)) {
+    llvm::VersionTuple Version;
+    if (Version.tryParse(A->getValue()))
+      Diags.Report(diag::err_drv_invalid_value)
+          << A->getAsString(Args) << A->getValue();
+    else
+      Opts.SDKVersion = Version;
+  }
 }
 
 bool CompilerInvocation::CreateFromArgs(CompilerInvocation &Res,
Index: test/CodeGen/darwin-sdk-version.c
===================================================================
--- /dev/null
+++ test/CodeGen/darwin-sdk-version.c
@@ -0,0 +1,4 @@
+// RUN: %clang_cc1 -triple x86_64-apple-macosx10.14 -target-sdk-version=10.14.1 -emit-llvm -o - %s | FileCheck %s
+
+// CHECK: !llvm.module.flags = !{!0
+// CHECK: !0 = !{i32 2, !"SDK Version", [3 x i32] [i32 10, i32 14, i32 1]}
Index: test/Driver/Inputs/MacOSX10.14.sdk/SDKSettings.json
===================================================================
--- /dev/null
+++ test/Driver/Inputs/MacOSX10.14.sdk/SDKSettings.json
@@ -0,0 +1 @@
+{"Version":"10.14"}
Index: test/Driver/darwin-sdk-version.c
===================================================================
--- /dev/null
+++ test/Driver/darwin-sdk-version.c
@@ -0,0 +1,25 @@
+// RUN: %clang -target x86_64-apple-macosx10.13 -isysroot %S/Inputs/MacOSX10.14.sdk -c -### %s 2>&1 \
+// RUN:   | FileCheck %s
+// RUN: env SDKROOT=%S/Inputs/MacOSX10.14.sdk %clang -target x86_64-apple-macosx10.13 -c -### %s 2>&1 \
+// RUN:   | FileCheck %s
+//
+// RUN: rm -rf %t/SDKs/MacOSX10.14.sdk
+// RUN: mkdir -p %t/SDKs/MacOSX10.14.sdk
+// RUN: %clang -target x86_64-apple-macosx10.13 -isysroot %t/SDKs/MacOSX10.14.sdk -c -### %s 2>&1 \
+// RUN:   | FileCheck --check-prefix=NO_VERSION %s
+//
+// RUN: rm -rf %t/SDKs/MacOSX10.14.sdk
+// RUN: mkdir -p %t/SDKs/MacOSX10.14.sdk
+// RUN: echo '{broken json' > %t/SDKs/MacOSX10.14.sdk/SDKSettings.json
+// RUN: %clang -target x86_64-apple-macosx10.13 -isysroot %t/SDKs/MacOSX10.14.sdk -c -### %s 2>&1 \
+// RUN:   | FileCheck --check-prefixes=NO_VERSION,ERROR %s
+//
+// RUN: rm -rf %t/SDKs/MacOSX10.14.sdk
+// RUN: mkdir -p %t/SDKs/MacOSX10.14.sdk
+// RUN: echo '{"Version":1}' > %t/SDKs/MacOSX10.14.sdk/SDKSettings.json
+// RUN: %clang -target x86_64-apple-macosx10.13 -isysroot %t/SDKs/MacOSX10.14.sdk -c -### %s 2>&1 \
+// RUN:   | FileCheck --check-prefixes=NO_VERSION,ERROR %s
+
+// CHECK: -target-sdk-version=10.14
+// NO_VERSION-NOT: target-sdk-version
+// ERROR: warning: SDK settings were ignored as 'SDKSettings.json' could not be parsed