Index: include/clang/Basic/DiagnosticDriverKinds.td
===================================================================
--- include/clang/Basic/DiagnosticDriverKinds.td
+++ include/clang/Basic/DiagnosticDriverKinds.td
@@ -150,6 +150,8 @@
   "The target '%0' is not a supported OpenMP host target.">;
 def err_drv_bitcode_unsupported_on_toolchain : Error<
   "-fembed-bitcode is not supported on versions of iOS prior to 6.0">;
+def err_drv_cxx_not_supported : Error<
+  "C++ is not supported for target '%0'">;
 
 def warn_O4_is_O3 : Warning<"-O4 is equivalent to -O3">, InGroup<Deprecated>;
 def warn_drv_lto_libpath : Warning<"libLTO.dylib relative to clang installed dir not found; using 'ld' default search path instead">,
Index: include/clang/Driver/ToolChain.h
===================================================================
--- include/clang/Driver/ToolChain.h
+++ include/clang/Driver/ToolChain.h
@@ -417,6 +417,10 @@
   virtual void AddCudaIncludeArgs(const llvm::opt::ArgList &DriverArgs,
                                   llvm::opt::ArgStringList &CC1Args) const;
 
+  /// \brief Add arguments to use MCU GCC toolchain includes.
+  virtual void AddIAMCUIncludeArgs(const llvm::opt::ArgList &DriverArgs,
+                                   llvm::opt::ArgStringList &CC1Args) const;
+
   /// \brief Return sanitizers which are available in this toolchain.
   virtual SanitizerMask getSupportedSanitizers() const;
 
Index: lib/Driver/Driver.cpp
===================================================================
--- lib/Driver/Driver.cpp
+++ lib/Driver/Driver.cpp
@@ -2438,6 +2438,7 @@
       TC = new toolchains::Minix(*this, Target, Args);
       break;
     case llvm::Triple::Linux:
+    case llvm::Triple::ELFIAMCU:
       if (Target.getArch() == llvm::Triple::hexagon)
         TC = new toolchains::HexagonToolChain(*this, Target, Args);
       else if ((Target.getVendor() == llvm::Triple::MipsTechnologies) &&
Index: lib/Driver/ToolChain.cpp
===================================================================
--- lib/Driver/ToolChain.cpp
+++ lib/Driver/ToolChain.cpp
@@ -696,3 +696,6 @@
 
 void ToolChain::AddCudaIncludeArgs(const ArgList &DriverArgs,
                                    ArgStringList &CC1Args) const {}
+
+void ToolChain::AddIAMCUIncludeArgs(const ArgList &DriverArgs,
+                                    ArgStringList &CC1Args) const {}
Index: lib/Driver/ToolChains.h
===================================================================
--- lib/Driver/ToolChains.h
+++ lib/Driver/ToolChains.h
@@ -806,6 +806,8 @@
       llvm::opt::ArgStringList &CC1Args) const override;
   void AddCudaIncludeArgs(const llvm::opt::ArgList &DriverArgs,
                           llvm::opt::ArgStringList &CC1Args) const override;
+  void AddIAMCUIncludeArgs(const llvm::opt::ArgList &DriverArgs,
+                           llvm::opt::ArgStringList &CC1Args) const override;
   bool isPIEDefault() const override;
   SanitizerMask getSupportedSanitizers() const override;
   void addProfileRTLibs(const llvm::opt::ArgList &Args,
Index: lib/Driver/ToolChains.cpp
===================================================================
--- lib/Driver/ToolChains.cpp
+++ lib/Driver/ToolChains.cpp
@@ -1570,9 +1570,13 @@
     break;
   case llvm::Triple::x86:
     LibDirs.append(begin(X86LibDirs), end(X86LibDirs));
-    TripleAliases.append(begin(X86Triples), end(X86Triples));
-    BiarchLibDirs.append(begin(X86_64LibDirs), end(X86_64LibDirs));
-    BiarchTripleAliases.append(begin(X86_64Triples), end(X86_64Triples));
+    // MCU toolchain is 32 bit only and its triple alias is TargetTriple
+    // itself, which will be appended below.
+    if (!TargetTriple.isOSIAMCU()) {
+      TripleAliases.append(begin(X86Triples), end(X86Triples));
+      BiarchLibDirs.append(begin(X86_64LibDirs), end(X86_64LibDirs));
+      BiarchTripleAliases.append(begin(X86_64Triples), end(X86_64Triples));
+    }
     break;
   case llvm::Triple::mips:
     LibDirs.append(begin(MIPSLibDirs), end(MIPSLibDirs));
@@ -1718,14 +1722,14 @@
 namespace {
 // Filter to remove Multilibs that don't exist as a suffix to Path
 class FilterNonExistent {
-  StringRef Base;
+  StringRef Base, File;
   vfs::FileSystem &VFS;
 
 public:
-  FilterNonExistent(StringRef Base, vfs::FileSystem &VFS)
-      : Base(Base), VFS(VFS) {}
+  FilterNonExistent(StringRef Base, StringRef File, vfs::FileSystem &VFS)
+      : Base(Base), File(File), VFS(VFS) {}
   bool operator()(const Multilib &M) {
-    return !VFS.exists(Base + M.gccSuffix() + "/crtbegin.o");
+    return !VFS.exists(Base + M.gccSuffix() + File);
   }
 };
 } // end anonymous namespace
@@ -1811,7 +1815,7 @@
   //     /usr
   //       /lib  <= crt*.o files compiled with '-mips32'
 
-  FilterNonExistent NonExistent(Path, D.getVFS());
+  FilterNonExistent NonExistent(Path, "/crtbegin.o", D.getVFS());
 
   // Check for FSF toolchain multilibs
   MultilibSet FSFMipsMultilibs;
@@ -2144,7 +2148,9 @@
                         .flag("-m64")
                         .flag("+mx32");
 
-  FilterNonExistent NonExistent(Path, D.getVFS());
+  // GCC toolchain for IAMCU doesn't have crtbegin.o, so look for libgcc.a.
+  FilterNonExistent NonExistent(
+      Path, TargetTriple.isOSIAMCU() ? "/libgcc.a" : "/crtbegin.o", D.getVFS());
 
   // Determine default multilib from: 32, 64, x32
   // Also handle cases such as 64 on 32, 32 on 64, etc.
@@ -4125,6 +4131,16 @@
   }
 }
 
+void Linux::AddIAMCUIncludeArgs(const ArgList &DriverArgs,
+                                ArgStringList &CC1Args) const {
+  if (GCCInstallation.isValid()) {
+    CC1Args.push_back("-isystem");
+    CC1Args.push_back(DriverArgs.MakeArgString(
+        GCCInstallation.getParentLibPath() + "/../" +
+        GCCInstallation.getTriple().str() + "/include"));
+  }
+}
+
 bool Linux::isPIEDefault() const { return getSanitizerArgs().requiresPIE(); }
 
 SanitizerMask Linux::getSupportedSanitizers() const {
Index: lib/Driver/Tools.cpp
===================================================================
--- lib/Driver/Tools.cpp
+++ lib/Driver/Tools.cpp
@@ -296,6 +296,8 @@
                                     const ToolChain *AuxToolChain) const {
   Arg *A;
 
+  const bool IsIAMCU = getToolChain().getTriple().isOSIAMCU();
+
   CheckPreprocessingOptions(D, Args);
 
   Args.AddLastArg(CmdArgs, options::OPT_C);
@@ -562,10 +564,15 @@
       AuxToolChain->AddClangCXXStdlibIncludeArgs(Args, CmdArgs);
   }
 
-  // Add system include arguments.
-  getToolChain().AddClangSystemIncludeArgs(Args, CmdArgs);
-  if (AuxToolChain)
+  // Add system include arguments for all targets but IAMCU.
+  if (!IsIAMCU) {
+    getToolChain().AddClangSystemIncludeArgs(Args, CmdArgs);
+    if (AuxToolChain)
       AuxToolChain->AddClangCXXStdlibIncludeArgs(Args, CmdArgs);
+  }
+  // For IAMCU add special include arguments.
+  else
+    getToolChain().AddIAMCUIncludeArgs(Args, CmdArgs);
 
   // Add CUDA include arguments, if needed.
   if (types::isCuda(Inputs[0].getType()))
@@ -3602,6 +3609,7 @@
       getToolChain().getTriple().isWindowsCygwinEnvironment();
   bool IsWindowsMSVC = getToolChain().getTriple().isWindowsMSVCEnvironment();
   bool IsPS4CPU = getToolChain().getTriple().isPS4CPU();
+  bool IsIAMCU = getToolChain().getTriple().isOSIAMCU();
 
   // Check number of inputs for sanity. We need at least one input.
   assert(Inputs.size() >= 1 && "Must have at least one input.");
@@ -3612,6 +3620,10 @@
   bool IsCuda = types::isCuda(Input.getType());
   assert((IsCuda || Inputs.size() == 1) && "Unable to handle multiple inputs.");
 
+  // C++ is not supported for IAMCU.
+  if (IsIAMCU && types::isCXX(Input.getType()))
+    D.Diag(diag::err_drv_cxx_not_supported) << getToolChain().getTriple().str();
+
   // Invoke ourselves in -cc1 mode.
   //
   // FIXME: Implement custom jobs for internal actions.
Index: test/Driver/miamcu-opt.c
===================================================================
--- test/Driver/miamcu-opt.c
+++ test/Driver/miamcu-opt.c
@@ -17,5 +17,5 @@
 // CHECK: "-mfloat-abi" "soft"
 // CHECK: "-mstack-alignment=4"
 
-// CHECK: bin/gcc
+// CHECK: bin/ld
 // CHECK: "-static"
Index: test/Driver/miamcu-opt.cpp
===================================================================
--- /dev/null
+++ test/Driver/miamcu-opt.cpp
@@ -0,0 +1,3 @@
+// RUN: %clang -miamcu %s -### -o %t.o 2>&1 | FileCheck %s
+
+// CHECK: error: C++ is not supported for target 'i586-intel-elfiamcu'