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
@@ -2366,15 +2366,15 @@
   DumpCompilationDatabase(C, "", Target, Output, Input, Args);
 }
 
-static bool AddARMImplicitITArgs(const ArgList &Args, ArgStringList &CmdArgs,
+static bool CheckARMImplicitITArg(StringRef Value) {
+  return Value == "always" || Value == "never" || Value == "arm" ||
+         Value == "thumb";
+}
+
+static void 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;
+  CmdArgs.push_back("-mllvm");
+  CmdArgs.push_back(Args.MakeArgString("-arm-implicit-it=" + Value));
 }
 
 static void CollectArgsForIntegratedAssembler(Compilation &C,
@@ -2393,22 +2393,6 @@
                    DefaultIncrementalLinkerCompatible))
     CmdArgs.push_back("-mincremental-linker-compatible");
 
-  switch (C.getDefaultToolChain().getArch()) {
-  case llvm::Triple::arm:
-  case llvm::Triple::armeb:
-  case llvm::Triple::thumb:
-  case llvm::Triple::thumbeb:
-    if (Arg *A = Args.getLastArg(options::OPT_mimplicit_it_EQ)) {
-      StringRef Value = A->getValue();
-      if (!AddARMImplicitITArgs(Args, CmdArgs, Value))
-        D.Diag(diag::err_drv_unsupported_option_argument)
-            << A->getOption().getName() << Value;
-    }
-    break;
-  default:
-    break;
-  }
-
   // If you add more args here, also add them to the block below that
   // starts with "// If CollectArgsForIntegratedAssembler() isn't called below".
 
@@ -2422,8 +2406,27 @@
   bool UseRelaxRelocations = C.getDefaultToolChain().useRelaxRelocations();
   bool UseNoExecStack = C.getDefaultToolChain().isNoExecStackDefault();
   const char *MipsTargetFeature = nullptr;
+  StringRef ImplicitIt;
   for (const Arg *A :
-       Args.filtered(options::OPT_Wa_COMMA, options::OPT_Xassembler)) {
+       Args.filtered(options::OPT_Wa_COMMA, options::OPT_Xassembler,
+                     options::OPT_mimplicit_it_EQ)) {
+    if (A->getOption().getID() == options::OPT_mimplicit_it_EQ) {
+      switch (C.getDefaultToolChain().getArch()) {
+      case llvm::Triple::arm:
+      case llvm::Triple::armeb:
+      case llvm::Triple::thumb:
+      case llvm::Triple::thumbeb:
+        // Only store the value; the last value set takes effect.
+        ImplicitIt = A->getValue();
+        if (!CheckARMImplicitITArg(ImplicitIt))
+          D.Diag(diag::err_drv_unsupported_option_argument)
+              << A->getOption().getName() << ImplicitIt;
+        continue;
+      default:
+        break;
+      }
+    }
+
     A->claim();
 
     for (StringRef Value : A->getValues()) {
@@ -2444,9 +2447,12 @@
       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.startswith("-mimplicit-it=")) {
+          // Only store the value; the last value set takes effect.
+          ImplicitIt = Value.split("=").second;
+          if (CheckARMImplicitITArg(ImplicitIt))
+            continue;
+        }
         if (Value == "-mthumb")
           // -mthumb has already been processed in ComputeLLVMTriple()
           // recognize but skip over here.
@@ -2576,6 +2582,8 @@
       }
     }
   }
+  if (ImplicitIt.size())
+    AddARMImplicitITArgs(Args, CmdArgs, ImplicitIt);
   if (UseRelaxRelocations)
     CmdArgs.push_back("--mrelax-relocations");
   if (UseNoExecStack)
diff --git a/clang/test/Driver/arm-target-as-mimplicit-it.s b/clang/test/Driver/arm-target-as-mimplicit-it.s
--- a/clang/test/Driver/arm-target-as-mimplicit-it.s
+++ b/clang/test/Driver/arm-target-as-mimplicit-it.s
@@ -10,22 +10,23 @@
 // 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=always -Wa,-mimplicit-it=always %s 2>&1 | FileCheck %s --check-prefix=ALWAYS
 // 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=always,-mimplicit-it=always %s 2>&1 | FileCheck %s --check-prefix=ALWAYS
 // 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
+/// Mix -implicit-it= (compiler) with -Wa,-mimplicit-it= (assembler), the
+/// last one set takes priority.
+// RUN: %clang -target arm-linux-gnueabi -### -mimplicit-it=always -Wa,-mimplicit-it=always %S/Inputs/wildcard1.c 2>&1 | FileCheck %s --check-prefix=ALWAYS
+// RUN: %clang -target arm-linux-gnueabi -### -mimplicit-it=never -Wa,-mimplicit-it=always %S/Inputs/wildcard1.c 2>&1 | FileCheck %s --check-prefix=ALWAYS
+// RUN: %clang -target arm-linux-gnueabi -### -Wa,-mimplicit-it=never -mimplicit-it=always %S/Inputs/wildcard1.c 2>&1 | FileCheck %s --check-prefix=ALWAYS
 
 /// Test invalid input.
 // RUN: %clang -target arm-linux-gnueabi -### -Wa,-mimplicit-it=foo %s 2>&1 | FileCheck %s --check-prefix=INVALID
@@ -34,11 +35,15 @@
 // RUN: %clang -target arm-linux-gnueabi -### -Wa,-mimplicit-it=always,-mimplicit-it=foo %s 2>&1 | FileCheck %s --check-prefix=INVALID
 
 
+/// Check that there isn't a second -arm-implicit-it before or after the one
+/// that was the indended match.
+// ALWAYS-NOT: "-arm-implicit-it={{.*}}"
 // ALWAYS: "-mllvm" "-arm-implicit-it=always"
+// ALWAYS-NOT: "-arm-implicit-it={{.*}}"
+// NEVER-NOT: "-arm-implicit-it={{.*}}"
 // NEVER: "-mllvm" "-arm-implicit-it=never"
+// NEVER-NOT: "-arm-implicit-it={{.*}}"
 // 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'