diff --git a/openmp/cmake/HandleOpenMPOptions.cmake b/openmp/cmake/HandleOpenMPOptions.cmake
index 201aeabbd3df9..b0fd0b7de4bf7 100644
--- a/openmp/cmake/HandleOpenMPOptions.cmake
+++ b/openmp/cmake/HandleOpenMPOptions.cmake
@@ -41,12 +41,3 @@ 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 d9e53bf946aff..7009730a49ba7 100644
--- a/openmp/runtime/src/kmp_affinity.cpp
+++ b/openmp/runtime/src/kmp_affinity.cpp
@@ -28,8 +28,6 @@
 #endif
 #include <ctype.h>
 
-#include "llvm/Support/Compiler.h"
-
 // The machine topology
 kmp_topology_t *__kmp_topology = nullptr;
 // KMP_HW_SUBSET environment variable
@@ -129,12 +127,8 @@ 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);
   }
-  KMP_ASSERT2(false, "Unhandled kmp_hw_t enumeration");
-  LLVM_BUILTIN_UNREACHABLE;
+  return KMP_I18N_STR(Unknown);
 }
 
 const char *__kmp_hw_get_keyword(kmp_hw_t type, bool plural) {
@@ -163,18 +157,13 @@ 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");
   }
-  KMP_ASSERT2(false, "Unhandled kmp_hw_t enumeration");
-  LLVM_BUILTIN_UNREACHABLE;
+  return ((plural) ? "unknowns" : "unknown");
 }
 
 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:
@@ -183,8 +172,7 @@ const char *__kmp_hw_get_core_type_string(kmp_hw_core_type_t type) {
     return "Intel(R) Core(TM) processor";
 #endif
   }
-  KMP_ASSERT2(false, "Unhandled kmp_hw_core_type_t enumeration");
-  LLVM_BUILTIN_UNREACHABLE;
+  return "unknown";
 }
 
 #if KMP_AFFINITY_SUPPORTED
@@ -1250,18 +1238,17 @@ 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_ASSERT2(false, "Unhandled kmp_hw_thread_t enumeration");
-      LLVM_BUILTIN_UNREACHABLE;
+      KMP_ASSERT(0);
+      return 0;
     }
   };
   struct core_eff_indexer {
diff --git a/openmp/runtime/src/kmp_barrier.cpp b/openmp/runtime/src/kmp_barrier.cpp
index e9ab15f1723b6..281b8e9c2883d 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));
-#endif
+
+  KA_TRACE(10, ("__kmp_fork_barrier: T#%d(%d:%d) has arrived\n", gtid,
+                (team != NULL) ? team->t.t_id : -1, tid));
+
   // 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 0c52662bc2357..578e6e671cdf2 100644
--- a/openmp/runtime/src/kmp_io.cpp
+++ b/openmp/runtime/src/kmp_io.cpp
@@ -50,6 +50,24 @@ 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 */
@@ -66,6 +84,7 @@ 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 025304caf8724..6862fd89b6302 100644
--- a/openmp/runtime/src/kmp_os.h
+++ b/openmp/runtime/src/kmp_os.h
@@ -306,8 +306,6 @@ 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) {
diff --git a/openmp/runtime/src/kmp_settings.cpp b/openmp/runtime/src/kmp_settings.cpp
index a9bbfdaf841bf..30a4c05fe76b3 100644
--- a/openmp/runtime/src/kmp_settings.cpp
+++ b/openmp/runtime/src/kmp_settings.cpp
@@ -29,8 +29,6 @@
 #include "ompd-specific.h"
 #endif
 
-#include "llvm/Support/Compiler.h"
-
 static int __kmp_env_toPrint(char const *name, int flag);
 
 bool __kmp_env_format = 0; // 0 - old format; 1 - new format
@@ -875,10 +873,6 @@ 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) {
@@ -891,9 +885,6 @@ 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) {
@@ -2013,7 +2004,6 @@ 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:
@@ -2022,8 +2012,7 @@ __kmp_hw_get_core_type_keyword(kmp_hw_core_type_t type) {
     return "intel_core";
 #endif
   }
-  KMP_ASSERT2(false, "Unhandled kmp_hw_core_type_t enumeration");
-  LLVM_BUILTIN_UNREACHABLE;
+  return "unknown";
 }
 
 #if KMP_AFFINITY_SUPPORTED
@@ -4439,10 +4428,6 @@ 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");
-      LLVM_BUILTIN_UNREACHABLE;
-      break;
     }
   } else {
     switch (sched) {
@@ -4468,10 +4453,6 @@ 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");
-      LLVM_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 c1a4c778b4b41..3fcae5687d124 100644
--- a/openmp/runtime/src/kmp_wait_release.h
+++ b/openmp/runtime/src/kmp_wait_release.h
@@ -20,8 +20,6 @@
 #include "ompt-specific.h"
 #endif
 
-#include "llvm/Support/Compiler.h"
-
 /*!
 @defgroup WAIT_RELEASE Wait/Release operations
 
@@ -1040,6 +1038,7 @@ 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;
@@ -1047,7 +1046,7 @@ static inline void __kmp_null_resume_wrapper(kmp_info_t *thr) {
     KF_TRACE(100, ("__kmp_null_resume_wrapper: flag type %d does not match any "
                    "known flag type\n",
                    type));
-    LLVM_BUILTIN_UNREACHABLE;
+#endif
   }
 }
 
diff --git a/openmp/runtime/src/z_Windows_NT_util.cpp b/openmp/runtime/src/z_Windows_NT_util.cpp
index d75b48b2c1bcf..9e264ab45b87f 100644
--- a/openmp/runtime/src/z_Windows_NT_util.cpp
+++ b/openmp/runtime/src/z_Windows_NT_util.cpp
@@ -22,7 +22,6 @@
    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
@@ -1636,7 +1635,7 @@ 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 (ULONG i = 0; i < num; ++i) {
+      for (int 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???