diff --git a/clang/lib/Driver/ToolChains/Clang.cpp b/clang/lib/Driver/ToolChains/Clang.cpp
--- a/clang/lib/Driver/ToolChains/Clang.cpp
+++ b/clang/lib/Driver/ToolChains/Clang.cpp
@@ -2304,6 +2304,17 @@
   DumpCompilationDatabase(C, "", Target, Output, Input, Args);
 }
 
+static bool AddARMImplicitITArgs(const ArgList &Args, ArgStringList &CmdArgs,
+                                 StringRef Value) {
+  if (Value == "always" || Value == "never" || Value == "arm" ||
+      Value == "thumb") {
+    CmdArgs.push_back("-mllvm");
+    CmdArgs.push_back(Args.MakeArgString("-arm-implicit-it=" + Value));
+    return true;
+  }
+  return false;
+}
+
 static void CollectArgsForIntegratedAssembler(Compilation &C,
                                               const ArgList &Args,
                                               ArgStringList &CmdArgs,
@@ -2327,14 +2338,9 @@
   case llvm::Triple::thumbeb:
     if (Arg *A = Args.getLastArg(options::OPT_mimplicit_it_EQ)) {
       StringRef Value = A->getValue();
-      if (Value == "always" || Value == "never" || Value == "arm" ||
-          Value == "thumb") {
-        CmdArgs.push_back("-mllvm");
-        CmdArgs.push_back(Args.MakeArgString("-arm-implicit-it=" + Value));
-      } else {
+      if (!AddARMImplicitITArgs(Args, CmdArgs, Value))
         D.Diag(diag::err_drv_unsupported_option_argument)
             << A->getOption().getName() << Value;
-      }
     }
     break;
   default:
@@ -2376,6 +2382,9 @@
       case llvm::Triple::thumbeb:
       case llvm::Triple::arm:
       case llvm::Triple::armeb:
+        if (Value.startswith("-mimplicit-it=") &&
+            AddARMImplicitITArgs(Args, CmdArgs, Value.split("=").second))
+          continue;
         if (Value == "-mthumb")
           // -mthumb has already been processed in ComputeLLVMTriple()
           // recognize but skip over here.
diff --git a/clang/test/Driver/arm-target-as-mimplicit-it.s b/clang/test/Driver/arm-target-as-mimplicit-it.s
new file mode 100644
--- /dev/null
+++ b/clang/test/Driver/arm-target-as-mimplicit-it.s
@@ -0,0 +1,44 @@
+/// Simple tests for valid input.
+/// -Wa,-implicit-it=
+// RUN: %clang -target arm-linux-gnueabi -### -Wa,-mimplicit-it=always %s 2>&1 | FileCheck %s --check-prefix=ALWAYS
+// RUN: %clang -target arm-linux-gnueabi -### -Wa,-mimplicit-it=never %s 2>&1 | FileCheck %s --check-prefix=NEVER
+// RUN: %clang -target arm-linux-gnueabi -### -Wa,-mimplicit-it=arm %s 2>&1 | FileCheck %s --check-prefix=ARM
+// RUN: %clang -target arm-linux-gnueabi -### -Wa,-mimplicit-it=thumb %s 2>&1 | FileCheck %s --check-prefix=THUMB
+/// -Xassembler -mimplicit-it=
+// RUN: %clang -target arm-linux-gnueabi -### -Xassembler -mimplicit-it=always %s 2>&1 | FileCheck %s --check-prefix=ALWAYS
+// RUN: %clang -target arm-linux-gnueabi -### -Xassembler -mimplicit-it=never %s 2>&1 | FileCheck %s --check-prefix=NEVER
+// RUN: %clang -target arm-linux-gnueabi -### -Xassembler -mimplicit-it=arm %s 2>&1 | FileCheck %s --check-prefix=ARM
+// RUN: %clang -target arm-linux-gnueabi -### -Xassembler -mimplicit-it=thumb %s 2>&1 | FileCheck %s --check-prefix=THUMB
+/// Test space separated -Wa,- arguments (latter wins).
+// RUN: %clang -target arm-linux-gnueabi -### -Wa,-mimplicit-it=never -Wa,-mimplicit-it=always %s 2>&1 | FileCheck %s --check-prefix=ALWAYS
+// RUN: %clang -target arm-linux-gnueabi -### -Wa,-mimplicit-it=always -Wa,-mimplicit-it=never %s 2>&1 | FileCheck %s --check-prefix=NEVER
+// RUN: %clang -target arm-linux-gnueabi -### -Wa,-mimplicit-it=always -Wa,-mimplicit-it=arm %s 2>&1 | FileCheck %s --check-prefix=ARM
+// RUN: %clang -target arm-linux-gnueabi -### -Wa,-mimplicit-it=always -Wa,-mimplicit-it=thumb %s 2>&1 | FileCheck %s --check-prefix=THUMB
+/// Test comma separated -Wa,- arguments (latter wins).
+// RUN: %clang -target arm-linux-gnueabi -### -Wa,-mimplicit-it=never,-mimplicit-it=always %s 2>&1 | FileCheck %s --check-prefix=ALWAYS
+// RUN: %clang -target arm-linux-gnueabi -### -Wa,-mimplicit-it=always,-mimplicit-it=never %s 2>&1 | FileCheck %s --check-prefix=NEVER
+// RUN: %clang -target arm-linux-gnueabi -### -Wa,-mimplicit-it=always,-mimplicit-it=arm %s 2>&1 | FileCheck %s --check-prefix=ARM
+// RUN: %clang -target arm-linux-gnueabi -### -Wa,-mimplicit-it=always,-mimplicit-it=thumb %s 2>&1 | FileCheck %s --check-prefix=THUMB
+
+/// Mix -implicit-it= (compiler) with -Wa,-mimplicit-it= (assembler), assembler
+/// takes priority. -mllvm -arm-implicit-it= will be repeated, with the
+/// assembler flag appearing last (latter wins).
+// RUN: %clang -target arm-linux-gnueabi -### -mimplicit-it=never -Wa,-mimplicit-it=always %S/Inputs/wildcard1.c 2>&1 | FileCheck %s --check-prefix=NEVER_ALWAYS
+// RUN: %clang -target arm-linux-gnueabi -### -mimplicit-it=always -Wa,-mimplicit-it=never %S/Inputs/wildcard1.c 2>&1 | FileCheck %s --check-prefix=ALWAYS_NEVER
+// RUN: %clang -target arm-linux-gnueabi -### -Wa,-mimplicit-it=never -mimplicit-it=always %S/Inputs/wildcard1.c 2>&1 | FileCheck %s --check-prefix=ALWAYS_NEVER
+
+/// Test invalid input.
+// RUN: %clang -target arm-linux-gnueabi -### -Wa,-mimplicit-it=foo %s 2>&1 | FileCheck %s --check-prefix=INVALID
+// RUN: %clang -target arm-linux-gnueabi -### -Xassembler -mimplicit-it=foo %s 2>&1 | FileCheck %s --check-prefix=XINVALID
+// RUN: %clang -target arm-linux-gnueabi -### -Wa,-mimplicit-it=always -Wa,-mimplicit-it=foo %s 2>&1 | FileCheck %s --check-prefix=INVALID
+// RUN: %clang -target arm-linux-gnueabi -### -Wa,-mimplicit-it=always,-mimplicit-it=foo %s 2>&1 | FileCheck %s --check-prefix=INVALID
+
+
+// ALWAYS: "-mllvm" "-arm-implicit-it=always"
+// NEVER: "-mllvm" "-arm-implicit-it=never"
+// ARM: "-mllvm" "-arm-implicit-it=arm"
+// THUMB: "-mllvm" "-arm-implicit-it=thumb"
+// NEVER_ALWAYS: "-mllvm" "-arm-implicit-it=never" "-mllvm" "-arm-implicit-it=always"
+// ALWAYS_NEVER: "-mllvm" "-arm-implicit-it=always" "-mllvm" "-arm-implicit-it=never"
+// INVALID: error: unsupported argument '-mimplicit-it=foo' to option 'Wa,'
+// XINVALID: error: unsupported argument '-mimplicit-it=foo' to option 'Xassembler'