diff --git a/openmp/cmake/HandleOpenMPOptions.cmake b/openmp/cmake/HandleOpenMPOptions.cmake
index b0fd0b7de4bf7..201aeabbd3df9 100644
--- a/openmp/cmake/HandleOpenMPOptions.cmake
+++ b/openmp/cmake/HandleOpenMPOptions.cmake
@@ -41,3 +41,12 @@ append_if(OPENMP_HAVE_WMAYBE_UNINITIALIZED_FLAG "-Wno-maybe-uninitialized" CMAKE
 append_if(OPENMP_HAVE_NO_SEMANTIC_INTERPOSITION "-fno-semantic-interposition" CMAKE_C_FLAGS CMAKE_CXX_FLAGS)
 append_if(OPENMP_HAVE_FUNCTION_SECTIONS "-ffunction-section" CMAKE_C_FLAGS CMAKE_CXX_FLAGS)
 append_if(OPENMP_HAVE_DATA_SECTIONS "-fdata-sections" CMAKE_C_FLAGS CMAKE_CXX_FLAGS)
+
+if (MSVC)
+  # Disable "warning C4201: nonstandard extension used: nameless struct/union"
+  append("-wd4201" CMAKE_C_FLAGS CMAKE_CXX_FLAGS)
+  
+  # Disable "warning C4190: '__kmpc_atomic_cmplx8_rd' has C-linkage specified, but returns
+  # UDT '__kmp_cmplx64_t' which is incompatible with C"
+  append("-wd4190" CMAKE_C_FLAGS CMAKE_CXX_FLAGS)
+endif()
diff --git a/openmp/runtime/src/kmp_affinity.cpp b/openmp/runtime/src/kmp_affinity.cpp
index 7009730a49ba7..6a41d34b02372 100644
--- a/openmp/runtime/src/kmp_affinity.cpp
+++ b/openmp/runtime/src/kmp_affinity.cpp
@@ -127,8 +127,12 @@ const char *__kmp_hw_get_catalog_string(kmp_hw_t type, bool plural) {
     return ((plural) ? KMP_I18N_STR(Threads) : KMP_I18N_STR(Thread));
   case KMP_HW_PROC_GROUP:
     return ((plural) ? KMP_I18N_STR(ProcGroups) : KMP_I18N_STR(ProcGroup));
+  case KMP_HW_UNKNOWN:
+  case KMP_HW_LAST:
+    return KMP_I18N_STR(Unknown);
   }
-  return KMP_I18N_STR(Unknown);
+  KMP_ASSERT2(false, "Unhandled kmp_hw_t enumeration");
+  KMP_BUILTIN_UNREACHABLE;
 }
 
 const char *__kmp_hw_get_keyword(kmp_hw_t type, bool plural) {
@@ -157,13 +161,18 @@ const char *__kmp_hw_get_keyword(kmp_hw_t type, bool plural) {
     return ((plural) ? "threads" : "thread");
   case KMP_HW_PROC_GROUP:
     return ((plural) ? "proc_groups" : "proc_group");
+  case KMP_HW_UNKNOWN:
+  case KMP_HW_LAST:
+    return ((plural) ? "unknowns" : "unknown");
   }
-  return ((plural) ? "unknowns" : "unknown");
+  KMP_ASSERT2(false, "Unhandled kmp_hw_t enumeration");
+  KMP_BUILTIN_UNREACHABLE;
 }
 
 const char *__kmp_hw_get_core_type_string(kmp_hw_core_type_t type) {
   switch (type) {
   case KMP_HW_CORE_TYPE_UNKNOWN:
+  case KMP_HW_MAX_NUM_CORE_TYPES:
     return "unknown";
 #if KMP_ARCH_X86 || KMP_ARCH_X86_64
   case KMP_HW_CORE_TYPE_ATOM:
@@ -172,7 +181,8 @@ const char *__kmp_hw_get_core_type_string(kmp_hw_core_type_t type) {
     return "Intel(R) Core(TM) processor";
 #endif
   }
-  return "unknown";
+  KMP_ASSERT2(false, "Unhandled kmp_hw_core_type_t enumeration");
+  KMP_BUILTIN_UNREACHABLE;
 }
 
 #if KMP_AFFINITY_SUPPORTED
@@ -1238,17 +1248,18 @@ bool kmp_topology_t::filter_hw_subset() {
   struct core_type_indexer {
     int operator()(const kmp_hw_thread_t &t) const {
       switch (t.attrs.get_core_type()) {
+      case KMP_HW_CORE_TYPE_UNKNOWN:
+      case KMP_HW_MAX_NUM_CORE_TYPES:
+        return 0;
 #if KMP_ARCH_X86 || KMP_ARCH_X86_64
       case KMP_HW_CORE_TYPE_ATOM:
         return 1;
       case KMP_HW_CORE_TYPE_CORE:
         return 2;
 #endif
-      case KMP_HW_CORE_TYPE_UNKNOWN:
-        return 0;
       }
-      KMP_ASSERT(0);
-      return 0;
+      KMP_ASSERT2(false, "Unhandled kmp_hw_thread_t enumeration");
+      KMP_BUILTIN_UNREACHABLE;
     }
   };
   struct core_eff_indexer {
diff --git a/openmp/runtime/src/kmp_barrier.cpp b/openmp/runtime/src/kmp_barrier.cpp
index 281b8e9c2883d..e9ab15f1723b6 100644
--- a/openmp/runtime/src/kmp_barrier.cpp
+++ b/openmp/runtime/src/kmp_barrier.cpp
@@ -2403,11 +2403,11 @@ void __kmp_fork_barrier(int gtid, int tid) {
 #if USE_ITT_BUILD
   void *itt_sync_obj = NULL;
 #endif /* USE_ITT_BUILD */
+#ifdef KMP_DEBUG
   if (team)
-
-  KA_TRACE(10, ("__kmp_fork_barrier: T#%d(%d:%d) has arrived\n", gtid,
-                (team != NULL) ? team->t.t_id : -1, tid));
-
+    KA_TRACE(10, ("__kmp_fork_barrier: T#%d(%d:%d) has arrived\n", gtid,
+                  (team != NULL) ? team->t.t_id : -1, tid));
+#endif
   // th_team pointer only valid for primary thread here
   if (KMP_MASTER_TID(tid)) {
 #if USE_ITT_BUILD && USE_ITT_NOTIFY
diff --git a/openmp/runtime/src/kmp_io.cpp b/openmp/runtime/src/kmp_io.cpp
index 578e6e671cdf2..0c52662bc2357 100644
--- a/openmp/runtime/src/kmp_io.cpp
+++ b/openmp/runtime/src/kmp_io.cpp
@@ -50,24 +50,6 @@ static HANDLE __kmp_stderr = NULL;
 static int __kmp_console_exists = FALSE;
 static kmp_str_buf_t __kmp_console_buf;
 
-static int is_console(void) {
-  char buffer[128];
-  DWORD rc = 0;
-  DWORD err = 0;
-  // Try to get console title.
-  SetLastError(0);
-  // GetConsoleTitle does not reset last error in case of success or short
-  // buffer, so we need to clear it explicitly.
-  rc = GetConsoleTitle(buffer, sizeof(buffer));
-  if (rc == 0) {
-    // rc == 0 means getting console title failed. Let us find out why.
-    err = GetLastError();
-    // err == 0 means buffer too short (we suppose console exists).
-    // In Window applications we usually have err == 6 (invalid handle).
-  }
-  return rc > 0 || err == 0;
-}
-
 void __kmp_close_console(void) {
   /* wait until user presses return before closing window */
   /* TODO only close if a window was opened */
@@ -84,7 +66,6 @@ void __kmp_close_console(void) {
 static void __kmp_redirect_output(void) {
   __kmp_acquire_bootstrap_lock(&__kmp_console_lock);
 
-  (void)is_console;
   if (!__kmp_console_exists) {
     HANDLE ho;
     HANDLE he;
diff --git a/openmp/runtime/src/kmp_os.h b/openmp/runtime/src/kmp_os.h
index 6862fd89b6302..a0552dd930a62 100644
--- a/openmp/runtime/src/kmp_os.h
+++ b/openmp/runtime/src/kmp_os.h
@@ -306,6 +306,8 @@ template <> struct traits_t<unsigned long long> {
    !KMP_MIC)
 
 #if KMP_OS_WINDOWS
+// Don't include everything related to NT status code, we'll do that explicitly
+#define WIN32_NO_STATUS
 #include <windows.h>
 
 static inline int KMP_GET_PAGE_SIZE(void) {
@@ -1297,4 +1299,18 @@ extern void *__kmp_lookup_symbol(const char *name, bool next = false);
 #define KMP_DLSYM_NEXT(name) dlsym(RTLD_NEXT, name)
 #endif
 
+// MSVC doesn't have this, but clang/clang-cl does.
+#ifndef __has_builtin
+#define __has_builtin(x) 0
+#endif
+
+// Same as LLVM_BUILTIN_UNREACHABLE. States that it is UB to reach this point.
+#if __has_builtin(__builtin_unreachable) || defined(__GNUC__)
+#define KMP_BUILTIN_UNREACHABLE __builtin_unreachable()
+#elif defined(_MSC_VER)
+#define KMP_BUILTIN_UNREACHABLE __assume(false)
+#else
+#define KMP_BUILTIN_UNREACHABLE
+#endif
+
 #endif /* KMP_OS_H */
diff --git a/openmp/runtime/src/kmp_settings.cpp b/openmp/runtime/src/kmp_settings.cpp
index 30a4c05fe76b3..d2157b10b7819 100644
--- a/openmp/runtime/src/kmp_settings.cpp
+++ b/openmp/runtime/src/kmp_settings.cpp
@@ -873,6 +873,10 @@ static void __kmp_stg_print_wait_policy(kmp_str_buf_t *buffer, char const *name,
     case library_throughput: {
       value = "PASSIVE";
     } break;
+    case library_none:
+    case library_serial: {
+      value = NULL;
+    } break;
     }
   } else {
     switch (__kmp_library) {
@@ -885,6 +889,9 @@ static void __kmp_stg_print_wait_policy(kmp_str_buf_t *buffer, char const *name,
     case library_throughput: {
       value = "throughput";
     } break;
+    case library_none: {
+      value = NULL;
+    } break;
     }
   }
   if (value != NULL) {
@@ -2004,6 +2011,7 @@ static inline const char *
 __kmp_hw_get_core_type_keyword(kmp_hw_core_type_t type) {
   switch (type) {
   case KMP_HW_CORE_TYPE_UNKNOWN:
+  case KMP_HW_MAX_NUM_CORE_TYPES:
     return "unknown";
 #if KMP_ARCH_X86 || KMP_ARCH_X86_64
   case KMP_HW_CORE_TYPE_ATOM:
@@ -2012,7 +2020,8 @@ __kmp_hw_get_core_type_keyword(kmp_hw_core_type_t type) {
     return "intel_core";
 #endif
   }
-  return "unknown";
+  KMP_ASSERT2(false, "Unhandled kmp_hw_core_type_t enumeration");
+  KMP_BUILTIN_UNREACHABLE;
 }
 
 #if KMP_AFFINITY_SUPPORTED
@@ -4428,6 +4437,10 @@ static void __kmp_stg_print_omp_schedule(kmp_str_buf_t *buffer,
     case kmp_sch_auto:
       __kmp_str_buf_print(buffer, "%s,%d'\n", "auto", __kmp_chunk);
       break;
+    default:
+      KMP_ASSERT2(false, "Unhandled sched_type enumeration");
+      KMP_BUILTIN_UNREACHABLE;
+      break;
     }
   } else {
     switch (sched) {
@@ -4453,6 +4466,10 @@ static void __kmp_stg_print_omp_schedule(kmp_str_buf_t *buffer,
     case kmp_sch_auto:
       __kmp_str_buf_print(buffer, "%s'\n", "auto");
       break;
+    default:
+      KMP_ASSERT2(false, "Unhandled sched_type enumeration");
+      KMP_BUILTIN_UNREACHABLE;
+      break;
     }
   }
 } // __kmp_stg_print_omp_schedule
diff --git a/openmp/runtime/src/kmp_wait_release.h b/openmp/runtime/src/kmp_wait_release.h
index 3fcae5687d124..12d5d0677a90a 100644
--- a/openmp/runtime/src/kmp_wait_release.h
+++ b/openmp/runtime/src/kmp_wait_release.h
@@ -1038,15 +1038,9 @@ static inline void __kmp_null_resume_wrapper(kmp_info_t *thr) {
   case flag_oncore:
     __kmp_resume_oncore(gtid, RCAST(kmp_flag_oncore *, flag));
     break;
-#ifdef KMP_DEBUG
   case flag_unset:
     KF_TRACE(100, ("__kmp_null_resume_wrapper: flag type %d is unset\n", type));
     break;
-  default:
-    KF_TRACE(100, ("__kmp_null_resume_wrapper: flag type %d does not match any "
-                   "known flag type\n",
-                   type));
-#endif
   }
 }
 
diff --git a/openmp/runtime/src/z_Windows_NT_util.cpp b/openmp/runtime/src/z_Windows_NT_util.cpp
index 9e264ab45b87f..d75b48b2c1bcf 100644
--- a/openmp/runtime/src/z_Windows_NT_util.cpp
+++ b/openmp/runtime/src/z_Windows_NT_util.cpp
@@ -22,6 +22,7 @@
    number of running threads in the system. */
 
 #include <ntsecapi.h> // UNICODE_STRING
+#undef WIN32_NO_STATUS
 #include <ntstatus.h>
 #include <psapi.h>
 #ifdef _MSC_VER
@@ -1635,7 +1636,7 @@ int __kmp_get_load_balance(int max) {
     // threads on all cores. So, we don't consider the running threads of this
     // process.
     if (pid != 0) {
-      for (int i = 0; i < num; ++i) {
+      for (ULONG i = 0; i < num; ++i) {
         THREAD_STATE state = spi->Threads[i].State;
         // Count threads that have Ready or Running state.
         // !!! TODO: Why comment does not match the code???