Index: include/clang/Basic/BuiltinsAArch64.def
===================================================================
--- include/clang/Basic/BuiltinsAArch64.def
+++ include/clang/Basic/BuiltinsAArch64.def
@@ -104,6 +104,7 @@
 TARGET_HEADER_BUILTIN(_InterlockedXor64,         "LLiLLiD*LLi", "nh", "intrin.h", ALL_MS_LANGUAGES, "")
 
 TARGET_HEADER_BUILTIN(_ReadWriteBarrier, "v", "nh", "intrin.h", ALL_MS_LANGUAGES, "")
+TARGET_HEADER_BUILTIN(__getReg, "ULLii", "nh", "intrin.h", ALL_MS_LANGUAGES, "")
 
 #undef BUILTIN
 #undef LANGBUILTIN
Index: lib/CodeGen/CGBuiltin.cpp
===================================================================
--- lib/CodeGen/CGBuiltin.cpp
+++ lib/CodeGen/CGBuiltin.cpp
@@ -6576,6 +6576,23 @@
     return Builder.CreateCall(F, {StoreVal, StoreAddr}, "stxr");
   }
 
+  if (BuiltinID == AArch64::BI__getReg) {
+    APSInt Value;
+    if (!E->getArg(0)->EvaluateAsInt(Value, CGM.getContext()))
+      llvm_unreachable("Sema will ensure that the parameter is constant");
+
+    LLVMContext &Context = CGM.getLLVMContext();
+    std::string Reg = Value == 31 ? "sp" : "x" + Value.toString(10);
+
+    llvm::Metadata *Ops[] = {llvm::MDString::get(Context, Reg)};
+    llvm::MDNode *RegName = llvm::MDNode::get(Context, Ops);
+    llvm::Value *Metadata = llvm::MetadataAsValue::get(Context, RegName);
+
+    llvm::Value *F =
+        CGM.getIntrinsic(llvm::Intrinsic::read_register, {Int64Ty});
+    return Builder.CreateCall(F, Metadata);
+  }
+
   if (BuiltinID == AArch64::BI__builtin_arm_clrex) {
     Function *F = CGM.getIntrinsic(Intrinsic::aarch64_clrex);
     return Builder.CreateCall(F);
Index: lib/Headers/intrin.h
===================================================================
--- lib/Headers/intrin.h
+++ lib/Headers/intrin.h
@@ -865,6 +865,13 @@
 #endif
 
 /*----------------------------------------------------------------------------*\
+|* MS AArch64 specific
+\*----------------------------------------------------------------------------*/
+#if defined(__aarch64__)
+unsigned __int64 __getReg(int);
+#endif
+
+/*----------------------------------------------------------------------------*\
 |* Privileged intrinsics
 \*----------------------------------------------------------------------------*/
 #if defined(__i386__) || defined(__x86_64__)
Index: lib/Sema/SemaChecking.cpp
===================================================================
--- lib/Sema/SemaChecking.cpp
+++ lib/Sema/SemaChecking.cpp
@@ -1749,6 +1749,9 @@
       BuiltinID == AArch64::BI__builtin_arm_wsrp)
     return SemaBuiltinARMSpecialReg(BuiltinID, TheCall, 0, 5, true);
 
+  if (BuiltinID == AArch64::BI__getReg)
+    return SemaBuiltinConstantArgRange(TheCall, 0, 0, 31);
+
   if (CheckNeonBuiltinFunctionCall(BuiltinID, TheCall))
     return true;
 
Index: test/CodeGen/arm64-microsoft-intrinsics.c
===================================================================
--- test/CodeGen/arm64-microsoft-intrinsics.c
+++ test/CodeGen/arm64-microsoft-intrinsics.c
@@ -66,3 +66,15 @@
 
 // CHECK-MSVC: fence syncscope("singlethread")
 // CHECK-LINUX: error: implicit declaration of function '_ReadWriteBarrier'
+
+unsigned __int64 check__getReg() {
+  unsigned volatile __int64 reg;
+  reg = __getReg(18);
+  reg = __getReg(31);
+  return reg;
+}
+
+// CHECK-MSVC: call i64 @llvm.read_register.i64(metadata !2)
+// CHECK-MSVC: call i64 @llvm.read_register.i64(metadata !3)
+// CHECK-MSVC: !2 = !{!"x18"}
+// CHECK-MSVC: !3 = !{!"sp"}
Index: test/Sema/builtins-microsoft-arm64.c
===================================================================
--- test/Sema/builtins-microsoft-arm64.c
+++ test/Sema/builtins-microsoft-arm64.c
@@ -0,0 +1,9 @@
+// RUN: %clang_cc1 -triple arm64-windows -fsyntax-only -verify \
+// RUN: -fms-compatibility -ffreestanding -fms-compatibility-version=17.00 %s
+
+#include <intrin.h>
+
+void check__getReg() {
+  __getReg(-1); // expected-error-re {{argument value {{.*}} is outside the valid range}}
+  __getReg(32); // expected-error-re {{argument value {{.*}} is outside the valid range}}
+}