avoid copying when the original string comes with MRB_STR_NOFREE

include/mruby/string.h

@@ -32,6 +32,9 @@ struct RString {
 #define RSTRING_CAPA(s)   (RSTRING(s)->aux.capa)
 #define RSTRING_END(s)    (RSTRING(s)->ptr + RSTRING(s)->len)
 
+#define MRB_STR_SHARED    1
+#define MRB_STR_NOFREE    2
+
 void mrb_gc_free_str(mrb_state*, struct RString*);
 void mrb_str_modify(mrb_state*, struct RString*);
 mrb_value mrb_str_literal(mrb_state*, mrb_value);

src/state.c

@@ -136,7 +136,9 @@ mrb_irep_free(mrb_state *mrb, mrb_irep *irep)
     mrb_free(mrb, irep->iseq);
   for (i=0; i<irep->plen; i++) {
     if (mrb_type(irep->pool[i]) == MRB_TT_STRING) {
+      if (mrb_str_ptr(irep->pool[i])->flags & MRB_STR_NOFREE == 0) {
         mrb_free(mrb, mrb_str_ptr(irep->pool[i])->ptr);
+      }
       mrb_free(mrb, mrb_obj_ptr(irep->pool[i]));
     }
 #ifdef MRB_WORD_BOXING
@@ -170,12 +172,17 @@ mrb_str_pool(mrb_state *mrb, mrb_value str)
 
   len = s->len;
   ns->len = len;
+  if (s->flags & MRB_STR_NOFREE) {
+    ns->ptr = s->ptr;
+    ns->flags = MRB_STR_NOFREE;
+  }
+  else {
     ns->ptr = (char *)mrb_malloc(mrb, (size_t)len+1);
     if (s->ptr) {
       memcpy(ns->ptr, s->ptr, len);
     }
     ns->ptr[len] = '\0';
-
+  }
   return mrb_obj_value(ns);
 }
 

src/string.c

@@ -30,9 +30,6 @@ typedef struct mrb_shared_string {
   mrb_int len;
 } mrb_shared_string;
 
-#define MRB_STR_SHARED    1
-#define MRB_STR_NOFREE    2
-
 static mrb_value str_replace(mrb_state *mrb, struct RString *s1, struct RString *s2);
 static mrb_value mrb_str_subseq(mrb_state *mrb, mrb_value str, mrb_int beg, mrb_int len);