moved utf8::upgrade in dbdimp.c for performance

- and uprade occurs only if imp_dbh->unicode is true so that we can minimize impact on existing applications

dbdimp.c

@@ -586,11 +586,12 @@ sqlite_db_last_insert_id(SV *dbh, imp_dbh_t *imp_dbh, SV *catalog, SV *schema, S
 }
 
 int
-sqlite_st_prepare(SV *sth, imp_sth_t *imp_sth, char *statement, SV *attribs)
+sqlite_st_prepare_sv(SV *sth, imp_sth_t *imp_sth, SV *sv_statement, SV *attribs)
 {
     dTHX;
     int rc = 0;
     const char *extra;
+    char *statement;
     D_imp_dbh_from_sth;
 
     if (!DBIc_ACTIVE(imp_dbh)) {
@@ -598,6 +599,13 @@ sqlite_st_prepare(SV *sth, imp_sth_t *imp_sth, char *statement, SV *attribs)
         return FALSE; /* -> undef in lib/DBD/SQLite.pm */
     }
 
+    /* sqlite3_prepare wants an utf8-encoded SQL statement */
+    if (imp_dbh->unicode) {
+        sv_utf8_upgrade(sv_statement);
+    }
+
+    statement = SvPV_nolen(sv_statement);
+
 #if 0
     if (*statement == '\0') {
         sqlite_error(sth, -2, "attempt to prepare empty statement");

dbdimp.h

@@ -64,7 +64,7 @@ struct imp_sth_st {
 #define dbd_db_STORE_attrib     sqlite_db_STORE_attrib
 #define dbd_db_FETCH_attrib     sqlite_db_FETCH_attrib
 #define dbd_db_last_insert_id   sqlite_db_last_insert_id
-#define dbd_st_prepare          sqlite_st_prepare
+#define dbd_st_prepare_sv       sqlite_st_prepare_sv
 #define dbd_st_rows             sqlite_st_rows
 #define dbd_st_execute          sqlite_st_execute
 #define dbd_st_fetch            sqlite_st_fetch

lib/DBD/SQLite.pm

@@ -196,9 +196,6 @@ sub prepare {
     my $sql = shift;
     $sql = '' unless defined $sql;
 
-    # sqlite3_prepare wants an utf8-encoded SQL statement
-    utf8::upgrade($sql);
-
     my $sth = DBI::_new_sth( $dbh, {
         Statement => $sql,
     } );