introduce name cache to lexer

gcc/cobol/scan_ante.h

@@ -410,6 +410,27 @@ static int symbol_function_token( const char name[] ) {
   return e ? symbol_index(e) : 0;
 }
 
+static symbol_elem_t *
+symbol_exists( const char name[] ) {
+  typedef std::map <std::string, size_t> name_cache_t;
+  static std::map <size_t, name_cache_t> cachemap;
+
+  cbl_name_t lname;
+  std::transform( name, name + strlen(name) + 1, lname, tolower );
+  auto& cache = cachemap[PROGRAM];
+  auto p = cache.find(lname);
+  
+  if( p == cache.end() ) {
+    symbol_elem_t * e = symbol_field( PROGRAM, 0, name );
+    if( !e ) return NULL;
+    cache[lname] = symbol_index(e);
+    return e;
+  }
+
+  size_t isym = p->second;
+  return symbol_at(cache[lname] = isym);
+}
+
 static int
 typed_name( const char name[] ) {
   if( 0 == PROGRAM ) return NAME;
@@ -421,7 +442,7 @@ typed_name( const char name[] ) {
   struct symbol_elem_t *e = symbol_special( PROGRAM, name );
   if( e ) return  cbl_special_name_of(e)->token;
 
-  e = symbol_field( PROGRAM, 0, name );
+  e = symbol_exists( name );
 
   auto type = e && e->type == SymField? cbl_field_of(e)->type : FldInvalid;
 
@@ -567,7 +588,7 @@ might_be(void) {
   assert(yyleng > 0);
   for( char *name = yytext + yyleng  - 1; name > yytext; name-- ) {
     if( isspace(*name) ) {
-	symbol_elem_t *e =  symbol_field(PROGRAM, 0, ++name);
+	symbol_elem_t *e =  symbol_exists(++name);
       // TRUE if the input names a field that isn't a level 88 or switch
       return e && e->type == SymField &&
 	cbl_field_of(e)->type != FldSwitch && cbl_field_of(e)->level != 88;