Index: lib/Driver/ToolChains/Arch/X86.cpp
===================================================================
--- lib/Driver/ToolChains/Arch/X86.cpp
+++ lib/Driver/ToolChains/Arch/X86.cpp
@@ -43,19 +43,20 @@
   if (const Arg *A = Args.getLastArgNoClaim(options::OPT__SLASH_arch)) {
     // Mapping built by looking at lib/Basic's X86TargetInfo::initFeatureMap().
     StringRef Arch = A->getValue();
-    const char *CPU;
-    if (Triple.getArch() == llvm::Triple::x86) {
+    const char *CPU = nullptr;
+    if (Triple.getArch() == llvm::Triple::x86) {  // 32-bit-only /arch: flags.
       CPU = llvm::StringSwitch<const char *>(Arch)
                 .Case("IA32", "i386")
                 .Case("SSE", "pentium3")
                 .Case("SSE2", "pentium4")
-                .Case("AVX", "sandybridge")
-                .Case("AVX2", "haswell")
                 .Default(nullptr);
-    } else {
+    }
+    if (CPU == nullptr) {  // 32-bit and 64-bit /arch: flags.
       CPU = llvm::StringSwitch<const char *>(Arch)
                 .Case("AVX", "sandybridge")
                 .Case("AVX2", "haswell")
+                .Case("AVX512F", "knl")
+                .Case("AVX512", "skylake-avx512")
                 .Default(nullptr);
     }
     if (CPU) {
Index: test/Driver/cl-x86-flags.c
===================================================================
--- test/Driver/cl-x86-flags.c
+++ test/Driver/cl-x86-flags.c
@@ -68,6 +68,26 @@
 // RUN: %clang_cl -m32 -arch:avx2 --target=i386-pc-windows -### -- 2>&1 %s | FileCheck -check-prefix=avx2 %s
 // avx2: argument unused during compilation
 
+// RUN: %clang_cl -m32 -arch:AVX512F --target=i386-pc-windows /c -Xclang -verify -DTEST_32_ARCH_AVX512F -- %s
+#if defined(TEST_32_ARCH_AVX512F)
+#if _M_IX86_FP != 2 || !__AVX__ || !__AVX2__ || !__AVX512F__  || __AVX512BW__
+#error fail
+#endif
+#endif
+
+// RUN: %clang_cl -m32 -arch:avx512f --target=i386-pc-windows -### -- 2>&1 %s | FileCheck -check-prefix=avx512f %s
+// avx512f: argument unused during compilation
+
+// RUN: %clang_cl -m32 -arch:AVX512 --target=i386-pc-windows /c -Xclang -verify -DTEST_32_ARCH_AVX512 -- %s
+#if defined(TEST_32_ARCH_AVX512)
+#if _M_IX86_FP != 2 || !__AVX__ || !__AVX2__ || !__AVX512F__  || !__AVX512BW__
+#error fail
+#endif
+#endif
+
+// RUN: %clang_cl -m32 -arch:avx512 --target=i386-pc-windows -### -- 2>&1 %s | FileCheck -check-prefix=avx512 %s
+// avx512: argument unused during compilation
+
 // RUN: %clang_cl -m64 -arch:AVX --target=x86_64-pc-windows /c -Xclang -verify -DTEST_64_ARCH_AVX -- %s
 #if defined(TEST_64_ARCH_AVX)
 #if _M_IX86_FP || !__AVX__ || __AVX2__ || __AVX512F__  || __AVX512BW__
@@ -88,5 +108,25 @@
 // RUN: %clang_cl -m64 -arch:avx2 --target=x86_64-pc-windows -### -- 2>&1 %s | FileCheck -check-prefix=avx264 %s
 // avx264: argument unused during compilation
 
+// RUN: %clang_cl -m64 -arch:AVX512F --target=i386-pc-windows /c -Xclang -verify -DTEST_64_ARCH_AVX512F -- %s
+#if defined(TEST_64_ARCH_AVX512F)
+#if _M_IX86_FP || !__AVX__ || !__AVX2__ || !__AVX512F__  || __AVX512BW__
+#error fail
+#endif
+#endif
+
+// RUN: %clang_cl -m64 -arch:avx512f --target=i386-pc-windows -### -- 2>&1 %s | FileCheck -check-prefix=avx512f64 %s
+// avx512f64: argument unused during compilation
+
+// RUN: %clang_cl -m64 -arch:AVX512 --target=i386-pc-windows /c -Xclang -verify -DTEST_64_ARCH_AVX512 -- %s
+#if defined(TEST_64_ARCH_AVX512)
+#if _M_IX86_FP || !__AVX__ || !__AVX2__ || !__AVX512F__  || !__AVX512BW__
+#error fail
+#endif
+#endif
+
+// RUN: %clang_cl -m64 -arch:avx512 --target=i386-pc-windows -### -- 2>&1 %s | FileCheck -check-prefix=avx51264 %s
+// avx51264: argument unused during compilation
+
 void f() {
 }