diff --git a/clang/lib/Driver/ToolChain.cpp b/clang/lib/Driver/ToolChain.cpp
--- a/clang/lib/Driver/ToolChain.cpp
+++ b/clang/lib/Driver/ToolChain.cpp
@@ -786,15 +786,26 @@
     else {
       // Ideally we would check for these flags in
       // CollectArgsForIntegratedAssembler but we can't change the ArchName at
-      // that point. There is no assembler equivalent of -mno-thumb, -marm, or
-      // -mno-arm.
+      // that point.
+      llvm::StringRef WaMArch, WaMCPU;
       for (const auto *A :
            Args.filtered(options::OPT_Wa_COMMA, options::OPT_Xassembler)) {
         for (StringRef Value : A->getValues()) {
+          // There is no assembler equivalent of -mno-thumb, -marm, or -mno-arm.
           if (Value == "-mthumb")
             IsThumb = true;
+          else if (Value.startswith("-march="))
+            WaMArch = Value.substr(7);
+          else if (Value.startswith("-mcpu="))
+            WaMCPU = Value.substr(6);
         }
       }
+
+      if (WaMCPU.size() || WaMArch.size()) {
+        // The way this works means that we prefer -Wa,-mcpu's architecture
+        // over -Wa,-march. Which matches the compiler behaviour.
+        Suffix = tools::arm::getLLVMArchSuffixForARM(WaMCPU, WaMArch, Triple);
+      }
     }
     // Assembly files should start in ARM mode, unless arch is M-profile, or
     // -mthumb has been passed explicitly to the assembler. Windows is always
diff --git a/clang/lib/Driver/ToolChains/Arch/ARM.cpp b/clang/lib/Driver/ToolChains/Arch/ARM.cpp
--- a/clang/lib/Driver/ToolChains/Arch/ARM.cpp
+++ b/clang/lib/Driver/ToolChains/Arch/ARM.cpp
@@ -50,11 +50,14 @@
 
   for (const Arg *A :
        Args.filtered(options::OPT_Wa_COMMA, options::OPT_Xassembler)) {
-    StringRef Value = A->getValue();
-    if (Value.startswith("-mcpu="))
-      CPU = Value.substr(6);
-    if (Value.startswith("-march="))
-      Arch = Value.substr(7);
+    // Use getValues because -Wa can have multiple arguments
+    // e.g. -Wa,-mcpu=foo,-mcpu=bar
+    for (StringRef Value : A->getValues()) {
+      if (Value.startswith("-mcpu="))
+        CPU = Value.substr(6);
+      if (Value.startswith("-march="))
+        Arch = Value.substr(7);
+    }
   }
 }
 
@@ -290,8 +293,8 @@
       Args.hasArg(options::OPT_mkernel, options::OPT_fapple_kext);
   arm::FloatABI ABI = arm::getARMFloatABI(D, Triple, Args);
   arm::ReadTPMode ThreadPointer = arm::getReadTPMode(D, Args);
-  const Arg *WaCPU = nullptr, *WaFPU = nullptr;
-  const Arg *WaHDiv = nullptr, *WaArch = nullptr;
+  llvm::Optional<std::pair<const Arg *, StringRef>> WaCPU, WaFPU, WaHDiv,
+      WaArch;
 
   // This vector will accumulate features from the architecture
   // extension suffixes on -mcpu and -march (e.g. the 'bar' in
@@ -325,15 +328,18 @@
     // to the assembler correctly.
     for (const Arg *A :
          Args.filtered(options::OPT_Wa_COMMA, options::OPT_Xassembler)) {
-      StringRef Value = A->getValue();
-      if (Value.startswith("-mfpu=")) {
-        WaFPU = A;
-      } else if (Value.startswith("-mcpu=")) {
-        WaCPU = A;
-      } else if (Value.startswith("-mhwdiv=")) {
-        WaHDiv = A;
-      } else if (Value.startswith("-march=")) {
-        WaArch = A;
+      // We use getValues here because you can have many options per -Wa
+      // We will keep the last one we find for each of these
+      for (StringRef Value : A->getValues()) {
+        if (Value.startswith("-mfpu=")) {
+          WaFPU = std::make_pair(A, Value.substr(6));
+        } else if (Value.startswith("-mcpu=")) {
+          WaCPU = std::make_pair(A, Value.substr(6));
+        } else if (Value.startswith("-mhwdiv=")) {
+          WaHDiv = std::make_pair(A, Value.substr(8));
+        } else if (Value.startswith("-march=")) {
+          WaArch = std::make_pair(A, Value.substr(7));
+        }
       }
     }
   }
@@ -353,8 +359,8 @@
     if (CPUArg)
       D.Diag(clang::diag::warn_drv_unused_argument)
           << CPUArg->getAsString(Args);
-    CPUName = StringRef(WaCPU->getValue()).substr(6);
-    CPUArg = WaCPU;
+    CPUName = WaCPU->second;
+    CPUArg = WaCPU->first;
   } else if (CPUArg)
     CPUName = CPUArg->getValue();
 
@@ -363,11 +369,12 @@
     if (ArchArg)
       D.Diag(clang::diag::warn_drv_unused_argument)
           << ArchArg->getAsString(Args);
-    ArchName = StringRef(WaArch->getValue()).substr(7);
-    checkARMArchName(D, WaArch, Args, ArchName, CPUName, ExtensionFeatures,
-                     Triple, ArchArgFPUID);
-    // FIXME: Set Arch.
-    D.Diag(clang::diag::warn_drv_unused_argument) << WaArch->getAsString(Args);
+    ArchName = WaArch->second;
+    // This will set any features after the base architecture.
+    checkARMArchName(D, WaArch->first, Args, ArchName, CPUName,
+                     ExtensionFeatures, Triple, ArchArgFPUID);
+    // The base architecture was handled in ToolChain::ComputeLLVMTriple because
+    // triple is read only by this point.
   } else if (ArchArg) {
     ArchName = ArchArg->getValue();
     checkARMArchName(D, ArchArg, Args, ArchName, CPUName, ExtensionFeatures,
@@ -399,8 +406,7 @@
     if (FPUArg)
       D.Diag(clang::diag::warn_drv_unused_argument)
           << FPUArg->getAsString(Args);
-    (void)getARMFPUFeatures(D, WaFPU, Args, StringRef(WaFPU->getValue()).substr(6),
-                            Features);
+    (void)getARMFPUFeatures(D, WaFPU->first, Args, WaFPU->second, Features);
   } else if (FPUArg) {
     FPUID = getARMFPUFeatures(D, FPUArg, Args, FPUArg->getValue(), Features);
   } else if (Triple.isAndroid() && getARMSubArchVersionNumber(Triple) >= 7) {
@@ -423,8 +429,7 @@
     if (HDivArg)
       D.Diag(clang::diag::warn_drv_unused_argument)
           << HDivArg->getAsString(Args);
-    getARMHWDivFeatures(D, WaHDiv, Args,
-                        StringRef(WaHDiv->getValue()).substr(8), Features);
+    getARMHWDivFeatures(D, WaHDiv->first, Args, WaHDiv->second, Features);
   } else if (HDivArg)
     getARMHWDivFeatures(D, HDivArg, Args, HDivArg->getValue(), Features);
 
diff --git a/clang/test/Driver/arm-target-as-march-mcpu.s b/clang/test/Driver/arm-target-as-march-mcpu.s
new file mode 100644
--- /dev/null
+++ b/clang/test/Driver/arm-target-as-march-mcpu.s
@@ -0,0 +1,104 @@
+/// These tests make sure that options passed to the assembler
+/// via -Wa or -Xassembler are applied correctly to assembler inputs.
+/// Also we check that the same priority rules apply to compiler and
+/// assembler options.
+///
+/// Note that the cortex-a8 is armv7-a, the cortex-a32 is armv8-a
+/// and clang's default Arm architecture is armv4t.
+
+/// Sanity check how the options behave when passed to the compiler
+// RUN: %clang -target arm-linux-gnueabi -### -c -march=armv7-a %s 2>&1 | \
+// RUN: FileCheck --check-prefix=TRIPLE-ARMV7 %s
+// RUN: %clang -target arm-linux-gnueabi -### -c -march=armv7-a+crc %s 2>&1 | \
+// RUN: FileCheck --check-prefixes=TRIPLE-ARMV7,EXT-CRC %s
+
+/// -Wa/-Xassembler doesn't apply to non assembly files
+// RUN: %clang -target arm-linux-gnueabi -### -c -Wa,-march=armv7-a \
+// RUN: %S/Inputs/wildcard1.c 2>&1 | FileCheck --check-prefix=TRIPLE-ARMV4 %s
+// RUN: %clang -target arm-linux-gnueabi -### -c -Xassembler -march=armv7-a \
+// RUN: %S/Inputs/wildcard1.c 2>&1 | FileCheck --check-prefix=TRIPLE-ARMV4 %s
+
+/// -Wa/-Xassembler does apply to assembler input
+// RUN: %clang -target arm-linux-gnueabi -### -c -Wa,-march=armv7-a %s 2>&1 | \
+// RUN: FileCheck --check-prefix=TRIPLE-ARMV7 %s
+// RUN: %clang -target arm-linux-gnueabi -### -c -Wa,-march=armv7-a+crc %s 2>&1 | \
+// RUN: FileCheck --check-prefixes=TRIPLE-ARMV7,EXT-CRC %s
+// RUN: %clang -target arm-linux-gnueabi -### -c -Xassembler -march=armv7-a %s 2>&1 | \
+// RUN: FileCheck --check-prefix=TRIPLE-ARMV7 %s
+// RUN: %clang -target arm-linux-gnueabi -### -c -Xassembler -march=armv7-a+crc %s 2>&1 | \
+// RUN: FileCheck --check-prefixes=TRIPLE-ARMV7,EXT-CRC %s
+
+/// Check that arch name is still canonicalised
+// RUN: %clang -target arm-linux-gnueabi -### -c -Wa,-march=armv7a %s 2>&1 | \
+// RUN: FileCheck --check-prefix=TRIPLE-ARMV7 %s
+// RUN: %clang -target arm-linux-gnueabi -### -c -Xassembler -march=armv7 %s 2>&1 | \
+// RUN: FileCheck --check-prefix=TRIPLE-ARMV7 %s
+
+/// march to compiler and assembler, we choose the one suited to the input file type
+// RUN: %clang -target arm-linux-gnueabi -### -c -march=armv8-a -Wa,-march=armv7a %s 2>&1 | \
+// RUN: FileCheck --check-prefix=TRIPLE-ARMV7 %s
+// RUN: %clang -target arm-linux-gnueabi -### -c -march=armv7-a -Wa,-march=armv8-a \
+// RUN: %S/Inputs/wildcard1.c 2>&1 | FileCheck --check-prefix=TRIPLE-ARMV7 %s
+
+/// mcpu to compiler and march to assembler, we use the assembler's architecture for assembly files.
+/// We use the target CPU for both.
+// RUN: %clang -target arm-linux-gnueabi -### -c -mcpu=cortex-a8 -Wa,-march=armv8a %s 2>&1 | \
+// RUN: FileCheck --check-prefixes=TRIPLE-ARMV8,CPU-A8 %s
+// RUN: %clang -target arm-linux-gnueabi -### -c -mcpu=cortex-a8 -Wa,-march=armv8-a \
+// RUN: %S/Inputs/wildcard1.c 2>&1 | FileCheck --check-prefixes=TRIPLE-ARMV7,CPU-A8 %s
+
+/// march to compiler and mcpu to assembler, we use the one that matches the file type
+/// (again both get the target-cpu option either way)
+// RUN: %clang -target arm-linux-gnueabi -### -c -march=armv8a -Wa,-mcpu=cortex-a8 %s 2>&1 | \
+// RUN: FileCheck --check-prefixes=TRIPLE-ARMV7,CPU-A8 %s
+// RUN: %clang -target arm-linux-gnueabi -### -c -march=armv8a -Wa,-mcpu=cortex-a8 \
+// RUN: %S/Inputs/wildcard1.c 2>&1 | FileCheck --check-prefix=TRIPLE-ARMV8 %s
+
+/// march and mcpu to the compiler, mcpu wins
+// RUN: %clang -target arm-linux-gnueabi -### -c -mcpu=cortex-a8 -march=armv8-a %s 2>&1 | \
+// RUN: FileCheck --check-prefixes=TRIPLE-ARMV7,CPU-A8 %s
+/// not dependent on order
+// RUN: %clang -target arm-linux-gnueabi -### -c -march=armv8-a -mcpu=cortex-a8 %s 2>&1 | \
+// RUN: FileCheck --check-prefixes=TRIPLE-ARMV7,CPU-A8 %s
+/// or file type
+// RUN: %clang -target arm-linux-gnueabi -### -c -march=armv8a -mcpu=cortex-a8 \
+// RUN: %S/Inputs/wildcard1.c 2>&1 | FileCheck --check-prefixes=TRIPLE-ARMV7,CPU-A8 %s
+
+/// If we pass mcpu and march to the assembler then mcpu's arch wins
+/// (matches the compiler behaviour)
+// RUN: %clang -target arm-linux-gnueabi -### -c -Wa,-mcpu=cortex-a8 -Wa,-march=armv8-a %s 2>&1 | \
+// RUN: FileCheck --check-prefixes=TRIPLE-ARMV7,CPU-A8 %s
+// RUN: %clang -target arm-linux-gnueabi -### -c -Wa,-mcpu=cortex-a8,-march=armv8-a %s 2>&1 | \
+// RUN: FileCheck --check-prefixes=TRIPLE-ARMV7,CPU-A8 %s
+// RUN: %clang -target arm-linux-gnueabi -### -c -Xassembler -march=armv8-a -Xassembler -mcpu=cortex-a8 \
+// RUN: %s 2>&1 | FileCheck --check-prefixes=TRIPLE-ARMV7,CPU-A8 %s
+
+/// Last mcpu to assembler wins
+// RUN: %clang -target arm-linux-gnueabi -### -c -Wa,-mcpu=cortex-a32,-mcpu=cortex-a8 %s 2>&1 | \
+// RUN: FileCheck --check-prefixes=TRIPLE-ARMV7,CPU-A8 %s
+// RUN: %clang -target arm-linux-gnueabi -### -c -Wa,-mcpu=cortex-a32 -Wa,-mcpu=cortex-a8 %s 2>&1 | \
+// RUN: FileCheck --check-prefix=TRIPLE-ARMV7 --check-prefix=CPU-A8 %s
+// RUN: %clang -target arm-linux-gnueabi -### -c -Xassembler -mcpu=cortex-a32 -Xassembler -mcpu=cortex-a8 \
+// RUN: %s 2>&1 | FileCheck --check-prefixes=TRIPLE-ARMV7,CPU-A8 %s
+
+/// Last mcpu to compiler wins
+// RUN: %clang -target arm-linux-gnueabi -### -c -mcpu=cortex-a32 -mcpu=cortex-a8 %s 2>&1 | \
+// RUN: FileCheck --check-prefixes=TRIPLE-ARMV7,CPU-A8 %s
+
+/// Last march to assembler wins
+// RUN: %clang -target arm-linux-gnueabi -### -c -Wa,-march=armv8-a,-march=armv7-a %s 2>&1 | \
+// RUN: FileCheck --check-prefix=TRIPLE-ARMV7 %s
+// RUN: %clang -target arm-linux-gnueabi -### -c -Wa,-march=armv8-a -Wa,-march=armv7-a %s 2>&1 | \
+// RUN: FileCheck --check-prefix=TRIPLE-ARMV7 %s
+// RUN: %clang -target arm-linux-gnueabi -### -c -Xassembler -march=armv8-a -Xassembler -march=armv7-a \
+// RUN: %s 2>&1 | FileCheck --check-prefix=TRIPLE-ARMV7 %s
+
+/// Last march to compiler wins
+// RUN: %clang -target arm-linux-gnueabi -### -c -march=armv8-a -march=armv7-a %s 2>&1 | \
+// RUN: FileCheck --check-prefix=TRIPLE-ARMV7 %s
+
+// TRIPLE-ARMV4: "-triple" "armv4t-unknown-linux-gnueabi"
+// TRIPLE-ARMV7: "-triple" "armv7-unknown-linux-gnueabi"
+// TRIPLE-ARMV8: "-triple" "armv8-unknown-linux-gnueabi"
+// CPU-A8: "-target-cpu" "cortex-a8"
+// EXT-CRC: "-target-feature" "+crc"
diff --git a/clang/test/Driver/arm-target-as-mthumb.s b/clang/test/Driver/arm-target-as-mthumb.s
--- a/clang/test/Driver/arm-target-as-mthumb.s
+++ b/clang/test/Driver/arm-target-as-mthumb.s
@@ -5,12 +5,18 @@
 // RUN: %clang -target armv7a-linux-gnueabi -### -c -mthumb %s 2>&1 | \
 // RUN: FileCheck -check-prefix=TRIPLE-ARM %s
 // RUN: %clang -target armv7a-linux-gnueabi -### -c -Wa,-mthumb \
-// RUN: %S/Inputs/wildcard1.c  2>&1 | FileCheck -check-prefix=TRIPLE-ARM %s
+// RUN: %S/Inputs/wildcard1.c 2>&1 | FileCheck -check-prefix=TRIPLE-ARM %s
+// RUN: %clang -target armv7a-linux-gnueabi -### -c -Wa,-mcpu=cortex-a8,-mthumb \
+// RUN: %S/Inputs/wildcard1.c 2>&1 | FileCheck -check-prefix=TRIPLE-ARM %s
 
 // TRIPLE-ARM: "-triple" "armv7-unknown-linux-gnueabi"
 
 // RUN: %clang -target armv7a-linux-gnueabi -### -c -Wa,-mthumb %s 2>&1 | \
 // RUN: FileCheck -check-prefix=TRIPLE-THUMB %s
+// RUN: %clang -target armv7a-linux-gnueabi -### -c -Wa,-mcpu=cortex-a8,-mthumb %s 2>&1 | \
+// RUN: FileCheck -check-prefix=TRIPLE-THUMB %s
+// RUN: %clang -target armv7a-linux-gnueabi -### -c -Wa,-mcpu=cortex-a8 -Wa,-mthumb %s 2>&1 | \
+// RUN: FileCheck -check-prefix=TRIPLE-THUMB %s
 // RUN: %clang -target armv7a-linux-gnueabi -### -c -Xassembler -mthumb %s \
 // RUN: 2>&1 | FileCheck -check-prefix=TRIPLE-THUMB %s