static Map<S, java.util.regex.Pattern> compileRegexpIC_cache = syncMRUCache(10);

static java.util.regex.Pattern compileRegexpIC(S pat) {
  java.util.regex.Pattern p = compileRegexpIC_cache.get(pat);
  if (p == null) {
    ifdef compileRegexp_debug
      print("Compiling regexp (IC): " + pat);
    endifdef
    try {
      compileRegexpIC_cache.put(pat, p = java.util.regex.Pattern.compile(pat, Pattern.CASE_INSENSITIVE));
    } catch (PatternSyntaxException e) {
      throw rethrow(wrapPatternSyntaxException(e));
    }
  }
  ret p;
}

Began life as a copy of #1007003