Index: cfe/trunk/include/clang/Driver/CLCompatOptions.td
===================================================================
--- cfe/trunk/include/clang/Driver/CLCompatOptions.td
+++ cfe/trunk/include/clang/Driver/CLCompatOptions.td
@@ -138,6 +138,9 @@
 
 // Non-aliases:
 
+def _SLASH_arch : CLCompileJoined<"arch:">,
+  HelpText<"Set architecture for code generation">;
+
 def _SLASH_M_Group : OptionGroup<"</M group>">, Group<cl_compile_Group>;
 
 def _SLASH_EH : CLJoined<"EH">, HelpText<"Exception handling model">;
@@ -207,7 +210,6 @@
 // Unsupported:
 
 def _SLASH_AI : CLJoined<"AI">;
-def _SLASH_arch : CLJoined<"arch:">;
 def _SLASH_bigobj : CLFlag<"bigobj">;
 def _SLASH_clr : CLJoined<"clr">;
 def _SLASH_d2Zi_PLUS : CLFlag<"d2Zi+">;
Index: cfe/trunk/lib/Driver/Tools.cpp
===================================================================
--- cfe/trunk/lib/Driver/Tools.cpp
+++ cfe/trunk/lib/Driver/Tools.cpp
@@ -1423,7 +1423,8 @@
     CmdArgs.push_back(Args.MakeArgString(Twine("-plugin-opt=mcpu=") + CPU));
 }
 
-static void getX86TargetFeatures(const llvm::Triple &Triple,
+static void getX86TargetFeatures(const Driver & D,
+                                 const llvm::Triple &Triple,
                                  const ArgList &Args,
                                  std::vector<const char *> &Features) {
   if (Triple.getArchName() == "x86_64h") {
@@ -1446,6 +1447,31 @@
       Features.push_back("+ssse3");
   }
 
+  // Set features according to the -arch flag on MSVC
+  if (Arg *A = Args.getLastArg(options::OPT__SLASH_arch)) {
+    StringRef Arch = A->getValue();
+    bool ArchUsed = false;
+    // First, look for flags that are shared in x86 and x86-64.
+    if (Triple.getArch() == llvm::Triple::x86_64 ||
+        Triple.getArch() == llvm::Triple::x86) {
+      if (Arch == "AVX" || Arch == "AVX2") {
+        ArchUsed = true;
+        Features.push_back(Args.MakeArgString("+" + Arch.lower()));
+      }
+    }
+    // Then, look for x86-specific flags.
+    if (Triple.getArch() == llvm::Triple::x86) {
+      if (Arch == "IA32") {
+        ArchUsed = true;
+      } else if (Arch == "SSE" || Arch == "SSE2") {
+        ArchUsed = true;
+        Features.push_back(Args.MakeArgString("+" + Arch.lower()));
+      }
+    }
+    if (!ArchUsed)
+      D.Diag(clang::diag::warn_drv_unused_argument) << A->getAsString(Args);
+  }
+
   // Now add any that the user explicitly requested on the command line,
   // which may override the defaults.
   for (arg_iterator it = Args.filtered_begin(options::OPT_m_x86_Features_Group),
@@ -1608,7 +1634,7 @@
     break;
   case llvm::Triple::x86:
   case llvm::Triple::x86_64:
-    getX86TargetFeatures(Triple, Args, Features);
+    getX86TargetFeatures(D, Triple, Args, Features);
     break;
   }
 
Index: cfe/trunk/test/Driver/cl-options.c
===================================================================
--- cfe/trunk/test/Driver/cl-options.c
+++ cfe/trunk/test/Driver/cl-options.c
@@ -198,7 +198,6 @@
 // (/Zs is for syntax-only)
 // RUN: %clang_cl /Zs \
 // RUN:     /AIfoo \
-// RUN:     /arch:sse2 \
 // RUN:     /clr:pure \
 // RUN:     /docname \
 // RUN:     /d2Zi+ \
Index: cfe/trunk/test/Driver/cl-x86-flags.c
===================================================================
--- cfe/trunk/test/Driver/cl-x86-flags.c
+++ cfe/trunk/test/Driver/cl-x86-flags.c
@@ -8,5 +8,76 @@
 // RUN:     -### -- 2>&1 %s | FileCheck -check-prefix=MFLAGS %s
 // MFLAGS-NOT: argument unused during compilation
 
+// -arch:IA32 is no-op.
+// RUN: %clang_cl -m32 -arch:IA32 -### -- 2>&1 %s | FileCheck -check-prefix=IA32 %s
+// IA32-NOT: argument unused during compilation
+// IA32-NOT: -target-feature
+
+// RUN: %clang_cl -m32 -arch:ia32 -### -- 2>&1 %s | FileCheck -check-prefix=ia32 %s
+// ia32: argument unused during compilation
+// ia32-NOT: -target-feature
+
+// RUN: %clang_cl -m64 -arch:IA32 -### -- 2>&1 %s | FileCheck -check-prefix=IA3264 %s
+// IA3264: argument unused during compilation
+// IA3264-NOT: -target-feature
+
+// RUN: %clang_cl -m32 -arch:SSE -### -- 2>&1 %s | FileCheck -check-prefix=SSE %s
+// SSE: -target-feature
+// SSE: +sse
+// SSE-NOT: argument unused during compilation
+
+// RUN: %clang_cl -m32 -arch:sse -### -- 2>&1 %s | FileCheck -check-prefix=sse %s
+// sse: argument unused during compilation
+// sse-NOT: -target-feature
+
+// RUN: %clang_cl -m32 -arch:SSE2 -### -- 2>&1 %s | FileCheck -check-prefix=SSE2 %s
+// SSE2: -target-feature
+// SSE2: +sse2
+// SSE2-NOT: argument unused during compilation
+
+// RUN: %clang_cl -m32 -arch:sse2 -### -- 2>&1 %s | FileCheck -check-prefix=sse %s
+// sse2: argument unused during compilation
+// sse2-NOT: -target-feature
+
+// RUN: %clang_cl -m64 -arch:SSE -### -- 2>&1 %s | FileCheck -check-prefix=SSE64 %s
+// SSE64: argument unused during compilation
+// SSE64-NOT: -target-feature
+
+// RUN: %clang_cl -m64 -arch:SSE2 -### -- 2>&1 %s | FileCheck -check-prefix=SSE264 %s
+// SSE264: argument unused during compilation
+// SSE264-NOT: -target-feature
+
+// RUN: %clang_cl -m32 -arch:AVX -### -- 2>&1 %s | FileCheck -check-prefix=AVX %s
+// AVX: -target-feature
+// AVX: +avx
+
+// RUN: %clang_cl -m32 -arch:avx -### -- 2>&1 %s | FileCheck -check-prefix=avx %s
+// avx: argument unused during compilation
+// avx-NOT: -target-feature
+
+// RUN: %clang_cl -m32 -arch:AVX2 -### -- 2>&1 %s | FileCheck -check-prefix=AVX2 %s
+// AVX2: -target-feature
+// AVX2: +avx2
+
+// RUN: %clang_cl -m32 -arch:avx2 -### -- 2>&1 %s | FileCheck -check-prefix=avx2 %s
+// avx2: argument unused during compilation
+// avx2-NOT: -target-feature
+
+// RUN: %clang_cl -m64 -arch:AVX -### -- 2>&1 %s | FileCheck -check-prefix=AVX64 %s
+// AVX64: -target-feature
+// AVX64: +avx
+
+// RUN: %clang_cl -m64 -arch:avx -### -- 2>&1 %s | FileCheck -check-prefix=avx64 %s
+// avx64: argument unused during compilation
+// avx64-NOT: -target-feature
+
+// RUN: %clang_cl -m64 -arch:AVX2 -### -- 2>&1 %s | FileCheck -check-prefix=AVX264 %s
+// AVX264: -target-feature
+// AVX264: +avx2
+
+// RUN: %clang_cl -m64 -arch:avx2 -### -- 2>&1 %s | FileCheck -check-prefix=avx264 %s
+// avx264: argument unused during compilation
+// avx264-NOT: -target-feature
+
 void f() {
 }