Index: include/clang/Driver/Options.td
===================================================================
--- include/clang/Driver/Options.td
+++ include/clang/Driver/Options.td
@@ -1655,6 +1655,7 @@
 def municode : Joined<["-"], "municode">, Group<m_Group>, Flags<[DriverOption]>;
 def mthreads : Joined<["-"], "mthreads">, Group<m_Group>, Flags<[DriverOption]>;
 def mcpu_EQ : Joined<["-"], "mcpu=">, Group<m_Group>;
+def mmcu_EQ : Joined<["-"], "mmcu=">, Group<m_Group>;
 def mdynamic_no_pic : Joined<["-"], "mdynamic-no-pic">, Group<m_Group>;
 def mfix_and_continue : Flag<["-"], "mfix-and-continue">, Group<clang_ignored_m_Group>;
 def mieee_fp : Flag<["-"], "mieee-fp">, Group<clang_ignored_m_Group>;
Index: lib/Driver/ToolChains/CommonArgs.cpp
===================================================================
--- lib/Driver/ToolChains/CommonArgs.cpp
+++ lib/Driver/ToolChains/CommonArgs.cpp
@@ -261,6 +261,12 @@
     arm::getARMArchCPUFromArgs(Args, MArch, MCPU, FromAs);
     return arm::getARMTargetCPU(MCPU, MArch, T);
   }
+
+  case llvm::Triple::avr:
+    if (const Arg *A = Args.getLastArg(options::OPT_mmcu_EQ))
+      return A->getValue();
+    return "";
+
   case llvm::Triple::mips:
   case llvm::Triple::mipsel:
   case llvm::Triple::mips64:
Index: test/Driver/avr-mmcu.c
===================================================================
--- /dev/null
+++ test/Driver/avr-mmcu.c
@@ -0,0 +1,5 @@
+// A test for the propagation of the -mmcu option to -cc1 and -cc1as
+
+// RUN: %clang -### -target avr -mmcu=atmega328p -save-temps %s 2>&1 | FileCheck %s
+// CHECK: clang{{.*}} "-cc1" {{.*}} "-target-cpu" "atmega328p"
+// CHECK: clang{{.*}} "-cc1as" {{.*}} "-target-cpu" "atmega328p"