Index: include/clang/Basic/Builtins.def
===================================================================
--- include/clang/Basic/Builtins.def
+++ include/clang/Basic/Builtins.def
@@ -778,6 +778,7 @@
 LANGBUILTIN(__abnormal_termination, "i", "n", ALL_MS_LANGUAGES)
 LANGBUILTIN(_abnormal_termination,  "i", "n", ALL_MS_LANGUAGES)
 LANGBUILTIN(__GetExceptionInfo, "v*.", "ntu", ALL_MS_LANGUAGES)
+LANGBUILTIN(_InterlockedAdd,    "NiNiD*Ni",     "n", ALL_MS_LANGUAGES)
 LANGBUILTIN(_InterlockedAnd8,   "ccD*c",        "n", ALL_MS_LANGUAGES)
 LANGBUILTIN(_InterlockedAnd16,  "ssD*s",        "n", ALL_MS_LANGUAGES)
 LANGBUILTIN(_InterlockedAnd,    "NiNiD*Ni",     "n", ALL_MS_LANGUAGES)
Index: lib/CodeGen/CGBuiltin.cpp
===================================================================
--- lib/CodeGen/CGBuiltin.cpp
+++ lib/CodeGen/CGBuiltin.cpp
@@ -737,6 +737,7 @@
 enum class CodeGenFunction::MSVCIntrin {
   _BitScanForward,
   _BitScanReverse,
+  _InterlockedAdd,
   _InterlockedAnd,
   _InterlockedDecrement,
   _InterlockedExchange,
@@ -799,6 +800,8 @@
     Builder.SetInsertPoint(End);
     return Result;
   }
+  case MSVCIntrin::_InterlockedAdd:
+    return MakeBinaryAtomicValue(*this, AtomicRMWInst::Add, E);
   case MSVCIntrin::_InterlockedAnd:
     return MakeBinaryAtomicValue(*this, AtomicRMWInst::And, E);
   case MSVCIntrin::_InterlockedExchange:
@@ -3048,6 +3051,8 @@
   case Builtin::BI_InterlockedDecrement:
     return RValue::get(
         EmitMSVCBuiltinExpr(MSVCIntrin::_InterlockedDecrement, E));
+  case Builtin::BI_InterlockedAdd:
+    return RValue::get(EmitMSVCBuiltinExpr(MSVCIntrin::_InterlockedAdd, E));
   case Builtin::BI_InterlockedAnd8:
   case Builtin::BI_InterlockedAnd16:
   case Builtin::BI_InterlockedAnd:
Index: test/CodeGen/ms-intrinsics.c
===================================================================
--- test/CodeGen/ms-intrinsics.c
+++ test/CodeGen/ms-intrinsics.c
@@ -370,6 +370,15 @@
 // CHECK:   ret i32 [[RESULT:%[0-9]+]]
 // CHECK: }
 
+long test_InterlockedAdd(long volatile *value, long mask) {
+  return _InterlockedAdd(value, mask);
+}
+
+// CHECK: define{{.*}}i32 @test_InterlockedAdd(i32*{{[a-z_ ]*}}%value, i32{{[a-z_ ]*}}%mask){{.*}}{
+// CHECK:   [[RESULT:%[0-9]+]] = atomicrmw add i32* %value, i32 %mask seq_cst
+// CHECK:   ret i32 [[RESULT:%[0-9]+]]
+// CHECK: }
+
 char test_InterlockedAnd8(char volatile *value, char mask) {
   return _InterlockedAnd8(value, mask);
 }