diff --git a/clang/include/clang/Basic/BuiltinsAArch64.def b/clang/include/clang/Basic/BuiltinsAArch64.def
--- a/clang/include/clang/Basic/BuiltinsAArch64.def
+++ b/clang/include/clang/Basic/BuiltinsAArch64.def
@@ -251,6 +251,11 @@
 
 TARGET_HEADER_BUILTIN(__break, "vi", "nh", "intrin.h", ALL_MS_LANGUAGES, "")
 
+TARGET_HEADER_BUILTIN(__readx18byte,  "UcULi", "nh", "intrin.h", ALL_MS_LANGUAGES, "")
+TARGET_HEADER_BUILTIN(__readx18word,  "UsULi", "nh", "intrin.h", ALL_MS_LANGUAGES, "")
+TARGET_HEADER_BUILTIN(__readx18dword, "ULiULi", "nh", "intrin.h", ALL_MS_LANGUAGES, "")
+TARGET_HEADER_BUILTIN(__readx18qword, "ULLiULi", "nh", "intrin.h", ALL_MS_LANGUAGES, "")
+
 #undef BUILTIN
 #undef LANGBUILTIN
 #undef TARGET_HEADER_BUILTIN
diff --git a/clang/lib/CodeGen/CGBuiltin.cpp b/clang/lib/CodeGen/CGBuiltin.cpp
--- a/clang/lib/CodeGen/CGBuiltin.cpp
+++ b/clang/lib/CodeGen/CGBuiltin.cpp
@@ -9952,6 +9952,30 @@
     return HigherBits;
   }
 
+  if (BuiltinID == AArch64::BI__readx18byte ||
+      BuiltinID == AArch64::BI__readx18word ||
+      BuiltinID == AArch64::BI__readx18dword ||
+      BuiltinID == AArch64::BI__readx18qword) {
+    llvm::Type *IntTy = ConvertType(E->getType());
+
+    // Read x18 as byte ptr, word ptr, dword ptr, or qword ptr
+    LLVMContext &Context = CGM.getLLVMContext();
+    llvm::Metadata *Ops[] = {llvm::MDString::get(Context, "x18")};
+    llvm::MDNode *RegName = llvm::MDNode::get(Context, Ops);
+    llvm::Value *Metadata = llvm::MetadataAsValue::get(Context, RegName);
+    llvm::Function *F =
+        CGM.getIntrinsic(llvm::Intrinsic::read_register, {Int64Ty});
+    llvm::Value *X18 = Builder.CreateCall(F, Metadata);
+    X18 = Builder.CreateIntToPtr(X18, llvm::PointerType::get(IntTy, 256));
+
+    // Load x18 + offset
+    Value *Offset = Builder.CreateZExt(EmitScalarExpr(E->getArg(0)), Int64Ty);
+    Value *Ptr = Builder.CreateGEP(IntTy, X18, Offset);
+    LoadInst *Load = Builder.CreateAlignedLoad(
+        IntTy, Ptr, getContext().getTypeAlignInChars(E->getType()));
+    return Load;
+  }
+
   // Handle MSVC intrinsics before argument evaluation to prevent double
   // evaluation.
   if (Optional<MSVCIntrin> MsvcIntId = translateAarch64ToMsvcIntrin(BuiltinID))
diff --git a/clang/lib/Headers/intrin.h b/clang/lib/Headers/intrin.h
--- a/clang/lib/Headers/intrin.h
+++ b/clang/lib/Headers/intrin.h
@@ -562,6 +562,11 @@
 unsigned __int64 __umulh(unsigned __int64 __a, unsigned __int64 __b);
 
 void __break(int);
+
+unsigned char __readx18byte(unsigned long offset);
+unsigned short __readx18word(unsigned long offset);
+unsigned long __readx18dword(unsigned long offset);
+unsigned __int64 __readx18qword(unsigned long offset);
 #endif
 
 /*----------------------------------------------------------------------------*\
diff --git a/clang/test/CodeGen/arm64-microsoft-intrinsics.c b/clang/test/CodeGen/arm64-microsoft-intrinsics.c
--- a/clang/test/CodeGen/arm64-microsoft-intrinsics.c
+++ b/clang/test/CodeGen/arm64-microsoft-intrinsics.c
@@ -119,5 +119,62 @@
 
 // CHECK-MSVC: call i64 @llvm.read_register.i64(metadata ![[MD2:.*]])
 // CHECK-MSVC: call i64 @llvm.read_register.i64(metadata ![[MD3:.*]])
+
+unsigned char check__readx18byte(unsigned long offset) {
+  return __readx18byte(offset);
+}
+
+// CHECK-MSVC: %[[OFFSET_ADDR:.*]] = alloca i32, align 4
+// CHECK-MSVC: store i32 %offset, i32* %[[OFFSET_ADDR]], align 4
+// CHECK-MSVC: %[[X18:.*]] = call i64 @llvm.read_register.i64(metadata ![[MD2]])
+// CHECK-MSVC: %[[X18_AS_PTR:.*]] = inttoptr i64 %[[X18]] to i8 addrspace(256)*
+// CHECK-MSVC: %[[OFFSET:.*]] = load i32, i32* %[[OFFSET_ADDR]], align 4
+// CHECK-MSVC: %[[ZEXT_OFFSET:.*]] = zext i32 %[[OFFSET]] to i64
+// CHECK-MSVC: %[[PTR:.*]] = getelementptr i8, i8 addrspace(256)* %[[X18_AS_PTR]], i64 %[[ZEXT_OFFSET]]
+// CHECK-MSVC: %[[RETVAL:.*]] = load i8, i8 addrspace(256)* %[[PTR]], align 1
+// CHECK-MSVC: ret i8 %[[RETVAL]]
+
+unsigned short check__readx18word(unsigned long offset) {
+  return __readx18word(offset);
+}
+
+// CHECK-MSVC: %[[OFFSET_ADDR:.*]] = alloca i32, align 4
+// CHECK-MSVC: store i32 %offset, i32* %[[OFFSET_ADDR]], align 4
+// CHECK-MSVC: %[[X18:.*]] = call i64 @llvm.read_register.i64(metadata ![[MD2]])
+// CHECK-MSVC: %[[X18_AS_PTR:.*]] = inttoptr i64 %[[X18]] to i16 addrspace(256)*
+// CHECK-MSVC: %[[OFFSET:.*]] = load i32, i32* %[[OFFSET_ADDR]], align 4
+// CHECK-MSVC: %[[ZEXT_OFFSET:.*]] = zext i32 %[[OFFSET]] to i64
+// CHECK-MSVC: %[[PTR:.*]] = getelementptr i16, i16 addrspace(256)* %[[X18_AS_PTR]], i64 %[[ZEXT_OFFSET]]
+// CHECK-MSVC: %[[RETVAL:.*]] = load i16, i16 addrspace(256)* %[[PTR]], align 2
+// CHECK-MSVC: ret i16 %[[RETVAL]]
+
+unsigned long check__readx18dword(unsigned long offset) {
+  return __readx18dword(offset);
+}
+
+// CHECK-MSVC: %[[OFFSET_ADDR:.*]] = alloca i32, align 4
+// CHECK-MSVC: store i32 %offset, i32* %[[OFFSET_ADDR]], align 4
+// CHECK-MSVC: %[[X18:.*]] = call i64 @llvm.read_register.i64(metadata ![[MD2]])
+// CHECK-MSVC: %[[X18_AS_PTR:.*]] = inttoptr i64 %[[X18]] to i32 addrspace(256)*
+// CHECK-MSVC: %[[OFFSET:.*]] = load i32, i32* %[[OFFSET_ADDR]], align 4
+// CHECK-MSVC: %[[ZEXT_OFFSET:.*]] = zext i32 %[[OFFSET]] to i64
+// CHECK-MSVC: %[[PTR:.*]] = getelementptr i32, i32 addrspace(256)* %[[X18_AS_PTR]], i64 %[[ZEXT_OFFSET]]
+// CHECK-MSVC: %[[RETVAL:.*]] = load i32, i32 addrspace(256)* %[[PTR]], align 4
+// CHECK-MSVC: ret i32 %[[RETVAL]]
+
+unsigned __int64 check__readx18qword(unsigned long offset) {
+  return __readx18qword(offset);
+}
+
+// CHECK-MSVC: %[[OFFSET_ADDR:.*]] = alloca i32, align 4
+// CHECK-MSVC: store i32 %offset, i32* %[[OFFSET_ADDR]], align 4
+// CHECK-MSVC: %[[X18:.*]] = call i64 @llvm.read_register.i64(metadata ![[MD2]])
+// CHECK-MSVC: %[[X18_AS_PTR:.*]] = inttoptr i64 %[[X18]] to i64 addrspace(256)*
+// CHECK-MSVC: %[[OFFSET:.*]] = load i32, i32* %[[OFFSET_ADDR]], align 4
+// CHECK-MSVC: %[[ZEXT_OFFSET:.*]] = zext i32 %[[OFFSET]] to i64
+// CHECK-MSVC: %[[PTR:.*]] = getelementptr i64, i64 addrspace(256)* %[[X18_AS_PTR]], i64 %[[ZEXT_OFFSET]]
+// CHECK-MSVC: %[[RETVAL:.*]] = load i64, i64 addrspace(256)* %[[PTR]], align 8
+// CHECK-MSVC: ret i64 %[[RETVAL]]
+
 // CHECK-MSVC: ![[MD2]] = !{!"x18"}
 // CHECK-MSVC: ![[MD3]] = !{!"sp"}