Index: flang/include/flang/Common/enum-class.h
===================================================================
--- /dev/null
+++ flang/include/flang/Common/enum-class.h
@@ -0,0 +1,64 @@
+//===-- include/flang/Common/enum-class.h -----------------------*- C++ -*-===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+// The macro
+//   ENUM_CLASS(className, enum1, enum2, ..., enumN)
+// defines
+//   enum class className { enum1, enum2, ... , enumN };
+// as well as the introspective utilities
+//   static constexpr std::size_t className_enumSize{N};
+//   static inline const std::string &EnumToString(className);
+
+#ifndef FORTRAN_COMMON_ENUM_CLASS_H_
+#define FORTRAN_COMMON_ENUM_CLASS_H_
+
+#include <array>
+#include <string>
+
+namespace Fortran::common {
+
+constexpr std::size_t CountEnumNames(const char *p) {
+  std::size_t n{0};
+  std::size_t any{0};
+  for (; *p; ++p) {
+    if (*p == ',') {
+      n += any;
+      any = 0;
+    } else if (*p != ' ') {
+      any = 1;
+    }
+  }
+  return n + any;
+}
+
+template <std::size_t ITEMS>
+constexpr std::array<std::string, ITEMS> EnumNames(const char *p) {
+  std::array<std::string, ITEMS> result{""};
+  std::size_t at{0};
+  for (; *p; ++p) {
+    if (*p == ',') {
+      ++at;
+    } else if (*p != ' ') {
+      result[at] += *p;
+    }
+  }
+  return result;
+}
+
+#define ENUM_CLASS(NAME, ...) \
+  enum class NAME { __VA_ARGS__ }; \
+  [[maybe_unused]] static constexpr std::size_t NAME##_enumSize{ \
+      ::Fortran::common::CountEnumNames(#__VA_ARGS__)}; \
+  [[maybe_unused]] static inline const std::string &EnumToString(NAME e) { \
+    static const auto names{ \
+        ::Fortran::common::EnumNames<NAME##_enumSize>(#__VA_ARGS__)}; \
+    return names[static_cast<std::size_t>(e)]; \
+  }
+
+} // namespace Fortran::common
+#endif // FORTRAN_COMMON_ENUM_CLASS_H_
Index: flang/include/flang/Common/idioms.h
===================================================================
--- flang/include/flang/Common/idioms.h
+++ flang/include/flang/Common/idioms.h
@@ -23,6 +23,7 @@
 #error g++ >= 7.2 is required
 #endif
 
+#include "enum-class.h"
 #include "visit.h"
 #include <array>
 #include <functional>
@@ -125,32 +126,6 @@
   const std::size_t value;
 };
 
-#define ENUM_CLASS(NAME, ...) \
-  enum class NAME { __VA_ARGS__ }; \
-  [[maybe_unused]] static constexpr std::size_t NAME##_enumSize{[] { \
-    enum { __VA_ARGS__ }; \
-    return Fortran::common::ListItemCount{__VA_ARGS__}.value; \
-  }()}; \
-  struct NAME##_struct { \
-    NAME##_struct(const NAME##_struct &) = delete; \
-    NAME##_struct &operator=(const NAME##_struct &) = delete; \
-    static NAME##_struct &instance() { \
-      static NAME##_struct s; \
-      return s; \
-    } \
-    std::array<std::string, NAME##_enumSize> _enumNames; \
-\
-  private: \
-    NAME##_struct() { \
-      Fortran::common::BuildIndexToString( \
-          #__VA_ARGS__, _enumNames.data(), NAME##_enumSize); \
-    } \
-    ~NAME##_struct() {} \
-  }; \
-  [[maybe_unused]] static inline const std::string &EnumToString(NAME e) { \
-    return NAME##_struct::instance()._enumNames[static_cast<int>(e)]; \
-  }
-
 // Check that a pointer is non-null and dereference it
 #define DEREF(p) Fortran::common::Deref(p, __FILE__, __LINE__)
 
Index: flang/lib/Common/idioms.cpp
===================================================================
--- flang/lib/Common/idioms.cpp
+++ flang/lib/Common/idioms.cpp
@@ -10,7 +10,6 @@
 #include <cstdarg>
 #include <cstdio>
 #include <cstdlib>
-#include <regex>
 
 namespace Fortran::common {
 
@@ -24,22 +23,4 @@
   std::abort();
 }
 
-// Converts the comma separated list of enumerators into tokens which are then
-// stored into the provided array of strings. This is intended for use from the
-// expansion of ENUM_CLASS.
-void BuildIndexToString(
-    const char *commaSeparated, std::string enumNames[], int enumSize) {
-  std::string input(commaSeparated);
-  std::regex reg("\\s*,\\s*");
-
-  std::sregex_token_iterator iter(input.begin(), input.end(), reg, -1);
-  std::sregex_token_iterator end;
-  int index = 0;
-  while (iter != end) {
-    enumNames[index] = *iter;
-    iter++;
-    index++;
-  }
-  CHECK(index == enumSize);
-}
 } // namespace Fortran::common