Index: include/clang/Driver/Options.td
===================================================================
--- include/clang/Driver/Options.td
+++ include/clang/Driver/Options.td
@@ -1088,6 +1088,9 @@
   HelpText<"Force realign the stack at entry to every function">;
 def mstack_alignment : Joined<["-"], "mstack-alignment=">, Group<m_Group>, Flags<[CC1Option]>,
   HelpText<"Set the stack alignment">;
+def mthread_model : Separate<["-"], "mthread-model">, Group<m_Group>, Flags<[CC1Option]>,
+  HelpText<"The thread model to use, e.g. posix, single (posix by default)">;
+
 def mmmx : Flag<["-"], "mmmx">, Group<m_x86_Features_Group>;
 def mno_3dnowa : Flag<["-"], "mno-3dnowa">, Group<m_x86_Features_Group>;
 def mno_3dnow : Flag<["-"], "mno-3dnow">, Group<m_x86_Features_Group>;
Index: include/clang/Driver/ToolChain.h
===================================================================
--- include/clang/Driver/ToolChain.h
+++ include/clang/Driver/ToolChain.h
@@ -248,6 +248,9 @@
   /// UseSjLjExceptions - Does this tool chain use SjLj exceptions.
   virtual bool UseSjLjExceptions() const { return false; }
 
+  /// getThreadModel() - Which thread model does this target use?
+  virtual std::string getThreadModel() const { return "posix"; }
+
   /// ComputeLLVMTriple - Return the LLVM target triple to use, after taking
   /// command line arguments into account.
   virtual std::string
Index: include/clang/Frontend/CodeGenOptions.h
===================================================================
--- include/clang/Frontend/CodeGenOptions.h
+++ include/clang/Frontend/CodeGenOptions.h
@@ -134,6 +134,9 @@
   /// The name of the relocation model to use.
   std::string RelocationModel;
 
+  /// The thread model to use
+  std::string ThreadModel;
+
   /// Path to blacklist file for sanitizers.
   std::string SanitizerBlacklistFile;
 
Index: lib/CodeGen/BackendUtil.cpp
===================================================================
--- lib/CodeGen/BackendUtil.cpp
+++ lib/CodeGen/BackendUtil.cpp
@@ -425,6 +425,11 @@
 
   llvm::TargetOptions Options;
 
+  Options.ThreadModel =
+    llvm::StringSwitch<llvm::ThreadModel::Model>(CodeGenOpts.ThreadModel)
+      .Case("posix", llvm::ThreadModel::POSIX)
+      .Case("single", llvm::ThreadModel::Single);
+
   if (CodeGenOpts.DisableIntegratedAS)
     Options.DisableIntegratedAS = true;
 
Index: lib/Driver/Driver.cpp
===================================================================
--- lib/Driver/Driver.cpp
+++ lib/Driver/Driver.cpp
@@ -658,9 +658,12 @@
   OS << "Target: " << TC.getTripleString() << '\n';
 
   // Print the threading model.
-  //
-  // FIXME: Implement correctly.
-  OS << "Thread model: " << "posix" << '\n';
+  OS << "Thread model: ";
+  if (Arg *A = C.getArgs().getLastArg(options::OPT_mthread_model))
+    OS << A->getValue();
+  else
+    OS << TC.getThreadModel();
+  OS << '\n';
 }
 
 /// PrintDiagnosticCategories - Implement the --print-diagnostic-categories
Index: lib/Driver/Tools.cpp
===================================================================
--- lib/Driver/Tools.cpp
+++ lib/Driver/Tools.cpp
@@ -2773,6 +2773,12 @@
     }
   }
 
+  CmdArgs.push_back("-mthread-model");
+  if (Arg *A = Args.getLastArg(options::OPT_mthread_model))
+    CmdArgs.push_back(A->getValue());
+  else
+    CmdArgs.push_back(Args.MakeArgString(getToolChain().getThreadModel()));
+
   if (!Args.hasFlag(options::OPT_fmerge_all_constants,
                     options::OPT_fno_merge_all_constants))
     CmdArgs.push_back("-fno-merge-all-constants");
Index: lib/Frontend/CompilerInvocation.cpp
===================================================================
--- lib/Frontend/CompilerInvocation.cpp
+++ lib/Frontend/CompilerInvocation.cpp
@@ -440,6 +440,11 @@
                       Args.hasArg(OPT_cl_fast_relaxed_math);
   Opts.UnwindTables = Args.hasArg(OPT_munwind_tables);
   Opts.RelocationModel = Args.getLastArgValue(OPT_mrelocation_model, "pic");
+  Opts.ThreadModel = Args.getLastArgValue(OPT_mthread_model, "posix");
+  if (Opts.ThreadModel != "posix" && Opts.ThreadModel != "single")
+    Diags.Report(diag::err_drv_invalid_value)
+        << Args.getLastArg(OPT_mthread_model)->getAsString(Args)
+        << Opts.ThreadModel;
   Opts.TrapFuncName = Args.getLastArgValue(OPT_ftrap_function_EQ);
   Opts.UseInitArray = Args.hasArg(OPT_fuse_init_array);
 
Index: test/Driver/thread-model.c
===================================================================
--- test/Driver/thread-model.c
+++ test/Driver/thread-model.c
@@ -0,0 +1,13 @@
+// RUN: %clang -### -c %s -mthread-model posix -v 2>&1 | FileCheck -check-prefix CHECK-POSIX %s
+// RUN: %clang -### -c %s -mthread-model single -v 2>&1 | FileCheck -check-prefix CHECK-SINGLE %s
+// RUN: not %clang -c %s -mthread-model silly -v 2>&1 | FileCheck -check-prefix CHECK-INVALID %s
+// CHECK-POSIX: "-mthread-model" "posix"
+// CHECK-SINGLE: "-mthread-model" "single"
+// CHECK-INVALID: error: invalid value 'silly' in '-mthread-model silly'
+
+// RUN: %clang -### -target arm-unknown-linux-gnu -c %s -v 2>&1 | FileCheck -check-prefix CHECK-LINUX-POSIX %s
+// RUN: %clang -### -target arm-unknown-linux-gnu -c %s -v -mthread-model single 2>&1 | FileCheck -check-prefix CHECK-LINUX-SINGLE %s
+// CHECK-LINUX-POSIX: Thread model: posix
+// CHECK-LINUX-POSIX: "-mthread-model" "posix"
+// CHECK-LINUX-SINGLE: Thread model: single
+// CHECK-LINUX-SINGLE: "-mthread-model" "single"