diff --git a/clang/lib/Driver/ToolChains/CommonArgs.cpp b/clang/lib/Driver/ToolChains/CommonArgs.cpp
--- a/clang/lib/Driver/ToolChains/CommonArgs.cpp
+++ b/clang/lib/Driver/ToolChains/CommonArgs.cpp
@@ -382,6 +382,10 @@
   }
 
   case llvm::Triple::avr:
+    // We encourage users to use '-mcpu' as their first choice,
+    // rather than the old '-mmcu' (inherited from avr-gcc).
+    if (const Arg *A = Args.getLastArg(options::OPT_mcpu_EQ))
+      return A->getValue();
     if (const Arg *A = Args.getLastArg(options::OPT_mmcu_EQ))
       return A->getValue();
     return "";
diff --git a/clang/test/Driver/avr-mmcu.c b/clang/test/Driver/avr-mmcu.c
--- a/clang/test/Driver/avr-mmcu.c
+++ b/clang/test/Driver/avr-mmcu.c
@@ -1,13 +1,16 @@
 // A test for the propagation of the -mmcu option to -cc1 and -cc1as
 
+// RUN: %clang -### --target=avr -mcpu=attiny11 -save-temps %s 2>&1 | FileCheck -check-prefix=CHECK0 %s
 // RUN: %clang -### --target=avr -mmcu=attiny11 -save-temps %s 2>&1 | FileCheck -check-prefix=CHECK0 %s
 // CHECK0: "-cc1" {{.*}} "-target-cpu" "attiny11"
 // CHECK0: "-cc1as" {{.*}} "-target-cpu" "attiny11"
 
+// RUN: %clang -### --target=avr -mcpu=at90s2313 -save-temps %s 2>&1 | FileCheck -check-prefix=CHECK1 %s
 // RUN: %clang -### --target=avr -mmcu=at90s2313 -save-temps %s 2>&1 | FileCheck -check-prefix=CHECK1 %s
 // CHECK1: "-cc1" {{.*}} "-target-cpu" "at90s2313"
 // CHECK1: "-cc1as" {{.*}} "-target-cpu" "at90s2313"
 
+// RUN: %clang -### --target=avr -mcpu=at90s8515 -save-temps %s 2>&1 | FileCheck -check-prefix=CHECK2 %s
 // RUN: %clang -### --target=avr -mmcu=at90s8515 -save-temps %s 2>&1 | FileCheck -check-prefix=CHECK2 %s
 // CHECK2: "-cc1" {{.*}} "-target-cpu" "at90s8515"
 // CHECK2: "-cc1as" {{.*}} "-target-cpu" "at90s8515"
@@ -20,34 +23,18 @@
 // CHECK4: "-cc1" {{.*}} "-target-cpu" "attiny88"
 // CHECK4: "-cc1as" {{.*}} "-target-cpu" "attiny88"
 
-// RUN: %clang -### --target=avr -mmcu=attiny88 -save-temps %s 2>&1 | FileCheck -check-prefix=CHECK5 %s
-// CHECK5: "-cc1" {{.*}} "-target-cpu" "attiny88"
-// CHECK5: "-cc1as" {{.*}} "-target-cpu" "attiny88"
-
 // RUN: %clang -### --target=avr -mmcu=atmega8u2 -save-temps %s 2>&1 | FileCheck -check-prefix=CHECK6 %s
 // CHECK6: "-cc1" {{.*}} "-target-cpu" "atmega8u2"
 // CHECK6: "-cc1as" {{.*}} "-target-cpu" "atmega8u2"
 
-// RUN: %clang -### --target=avr -mmcu=atmega8u2 -save-temps %s 2>&1 | FileCheck -check-prefix=CHECK7 %s
-// CHECK7: "-cc1" {{.*}} "-target-cpu" "atmega8u2"
-// CHECK7: "-cc1as" {{.*}} "-target-cpu" "atmega8u2"
-
 // RUN: %clang -### --target=avr -mmcu=atmega8a -save-temps %s 2>&1 | FileCheck -check-prefix=CHECK8 %s
 // CHECK8: "-cc1" {{.*}} "-target-cpu" "atmega8a"
 // CHECK8: "-cc1as" {{.*}} "-target-cpu" "atmega8a"
 
-// RUN: %clang -### --target=avr -mmcu=atmega8a -save-temps %s 2>&1 | FileCheck -check-prefix=CHECK9 %s
-// CHECK9: "-cc1" {{.*}} "-target-cpu" "atmega8a"
-// CHECK9: "-cc1as" {{.*}} "-target-cpu" "atmega8a"
-
 // RUN: %clang -### --target=avr -mmcu=atmega16a -save-temps %s 2>&1 | FileCheck -check-prefix=CHECKa %s
 // CHECKa: "-cc1" {{.*}} "-target-cpu" "atmega16a"
 // CHECKa: "-cc1as" {{.*}} "-target-cpu" "atmega16a"
 
-// RUN: %clang -### --target=avr -mmcu=atmega16a -save-temps %s 2>&1 | FileCheck -check-prefix=CHECKb %s
-// CHECKb: "-cc1" {{.*}} "-target-cpu" "atmega16a"
-// CHECKb: "-cc1as" {{.*}} "-target-cpu" "atmega16a"
-
 // RUN: %clang -### --target=avr -mmcu=atmega128a -save-temps %s 2>&1 | FileCheck -check-prefix=CHECKc %s
 // CHECKc: "-cc1" {{.*}} "-target-cpu" "atmega128a"
 // CHECKc: "-cc1as" {{.*}} "-target-cpu" "atmega128a"
@@ -72,10 +59,15 @@
 // CHECKh: "-cc1" {{.*}} "-target-cpu" "atxmega64a1u"
 // CHECKh: "-cc1as" {{.*}} "-target-cpu" "atxmega64a1u"
 
+// RUN: %clang -### --target=avr -mcpu=atxmega128a3u -save-temps %s 2>&1 | FileCheck -check-prefix=CHECKj %s
 // RUN: %clang -### --target=avr -mmcu=atxmega128a3u -save-temps %s 2>&1 | FileCheck -check-prefix=CHECKj %s
 // CHECKj: "-cc1" {{.*}} "-target-cpu" "atxmega128a3u"
 // CHECKj: "-cc1as" {{.*}} "-target-cpu" "atxmega128a3u"
 
+// RUN: %clang -### --target=avr -mcpu=atxmega128a4u -save-temps %s 2>&1 | FileCheck -check-prefix=CHECKi %s
 // RUN: %clang -### --target=avr -mmcu=atxmega128a4u -save-temps %s 2>&1 | FileCheck -check-prefix=CHECKi %s
 // CHECKi: "-cc1" {{.*}} "-target-cpu" "atxmega128a4u"
 // CHECKi: "-cc1as" {{.*}} "-target-cpu" "atxmega128a4u"
+
+// RUN: %clang --target=avr -mcpu=atmega328 -mmcu=atmega168 -c %s 2>&1 | FileCheck -check-prefix=CHECKz %s
+// CHECKz: warning: argument unused during compilation: '-mmcu=atmega168'