perf(api): avoid spurious allocations when converting small objects

Converter functions use a heap-allocated stack to handle complex
nested objects. However, these are often called with simple,
primitive values like integers or bools wrapped in an Object.
Avoid the memory allocation in this case using kvec_withinit_t

1 files changed, 21 insertions, 19 deletions

diff --git a/src/nvim/lua/converter.c b/src/nvim/lua/converter.c
index ce8c9b0d06..1a59cd94ae 100644
--- a/src/nvim/lua/converter.c
+++ b/src/nvim/lua/converter.c
@@ -196,8 +196,9 @@ bool nlua_pop_typval(lua_State *lstate, typval_T *ret_tv)
 {
   bool ret = true;
   const int initial_size = lua_gettop(lstate);
-  kvec_t(TVPopStackItem) stack = KV_INITIAL_VALUE;
-  kv_push(stack, ((TVPopStackItem) { ret_tv, false, false, 0 }));
+  kvec_withinit_t(TVPopStackItem, 2) stack = KV_INITIAL_VALUE;
+  kvi_init(stack);
+  kvi_push(stack, ((TVPopStackItem) { ret_tv, false, false, 0 }));
   while (ret && kv_size(stack)) {
     if (!lua_checkstack(lstate, lua_gettop(lstate) + 3)) {
       emsgf(_("E1502: Lua failed to grow stack to %i"), lua_gettop(lstate) + 3);
@@ -234,7 +235,7 @@ bool nlua_pop_typval(lua_State *lstate, typval_T *ret_tv)
             tv_list_append_owned_tv(kv_pair, (typval_T) {
               .v_type = VAR_UNKNOWN,
             });
-            kv_push(stack, cur);
+            kvi_push(stack, cur);
             tv_list_append_list(cur.tv->vval.v_list, kv_pair);
             cur = (TVPopStackItem) {
               .tv = TV_LIST_ITEM_TV(tv_list_last(kv_pair)),
@@ -247,7 +248,7 @@ bool nlua_pop_typval(lua_State *lstate, typval_T *ret_tv)
             if (tv_dict_add(cur.tv->vval.v_dict, di) == FAIL) {
               abort();
             }
-            kv_push(stack, cur);
+            kvi_push(stack, cur);
             cur = (TVPopStackItem) { &di->di_tv, false, false, 0 };
           }
         } else {
@@ -265,7 +266,7 @@ bool nlua_pop_typval(lua_State *lstate, typval_T *ret_tv)
         tv_list_append_owned_tv(cur.tv->vval.v_list, (typval_T) {
           .v_type = VAR_UNKNOWN,
         });
-        kv_push(stack, cur);
+        kvi_push(stack, cur);
         // TODO(ZyX-I): Use indexes, here list item *will* be reallocated.
         cur = (TVPopStackItem) {
           .tv = TV_LIST_ITEM_TV(tv_list_last(cur.tv->vval.v_list)),
@@ -343,7 +344,7 @@ bool nlua_pop_typval(lua_State *lstate, typval_T *ret_tv)
             if (table_props.maxidx != 0) {
               cur.container = true;
               cur.idx = lua_gettop(lstate);
-              kv_push(stack, cur);
+              kvi_push(stack, cur);
             }
             break;
           }
@@ -373,7 +374,7 @@ bool nlua_pop_typval(lua_State *lstate, typval_T *ret_tv)
               }
               cur.container = true;
               cur.idx = lua_gettop(lstate);
-              kv_push(stack, cur);
+              kvi_push(stack, cur);
               lua_pushnil(lstate);
             }
             break;
@@ -434,7 +435,7 @@ nlua_pop_typval_table_processing_end:
       lua_pop(lstate, 1);
     }
   }
-  kv_destroy(stack);
+  kvi_destroy(stack);
   if (!ret) {
     tv_clear(ret_tv);
     *ret_tv = (typval_T) {
@@ -1060,15 +1061,16 @@ Object nlua_pop_Object(lua_State *const lstate, bool ref, Error *const err)
 {
   Object ret = NIL;
   const int initial_size = lua_gettop(lstate);
-  kvec_t(ObjPopStackItem) stack = KV_INITIAL_VALUE;
-  kv_push(stack, ((ObjPopStackItem) { &ret, false }));
+  kvec_withinit_t(ObjPopStackItem, 2) stack = KV_INITIAL_VALUE;
+  kvi_init(stack);
+  kvi_push(stack, ((ObjPopStackItem) { &ret, false }));
   while (!ERROR_SET(err) && kv_size(stack)) {
-    if (!lua_checkstack(lstate, lua_gettop(lstate) + 3)) {
-      api_set_error(err, kErrorTypeException, "Lua failed to grow stack");
-      break;
-    }
     ObjPopStackItem cur = kv_pop(stack);
     if (cur.container) {
+      if (!lua_checkstack(lstate, lua_gettop(lstate) + 3)) {
+        api_set_error(err, kErrorTypeException, "Lua failed to grow stack");
+        break;
+      }
       if (cur.obj->type == kObjectTypeDictionary) {
         // stack: …, dict, key
         if (cur.obj->data.dictionary.size
@@ -1095,7 +1097,7 @@ Object nlua_pop_Object(lua_State *const lstate, bool ref, Error *const err)
             .data = xmemdupz(s, len),
             .size = len,
           };
-          kv_push(stack, cur);
+          kvi_push(stack, cur);
           cur = (ObjPopStackItem) {
             .obj = &cur.obj->data.dictionary.items[idx].value,
             .container = false,
@@ -1117,7 +1119,7 @@ Object nlua_pop_Object(lua_State *const lstate, bool ref, Error *const err)
           lua_pop(lstate, 2);
           continue;
         }
-        kv_push(stack, cur);
+        kvi_push(stack, cur);
         cur = (ObjPopStackItem) {
           .obj = &cur.obj->data.array.items[idx],
           .container = false,
@@ -1169,7 +1171,7 @@ Object nlua_pop_Object(lua_State *const lstate, bool ref, Error *const err)
                           sizeof(cur.obj->data.array.items[0]));
               cur.obj->data.array.capacity = table_props.maxidx;
               cur.container = true;
-              kv_push(stack, cur);
+              kvi_push(stack, cur);
             }
             break;
           }
@@ -1185,7 +1187,7 @@ Object nlua_pop_Object(lua_State *const lstate, bool ref, Error *const err)
                           sizeof(cur.obj->data.dictionary.items[0]));
               cur.obj->data.dictionary.capacity = table_props.string_keys_num;
               cur.container = true;
-              kv_push(stack, cur);
+              kvi_push(stack, cur);
               lua_pushnil(lstate);
             }
             break;
@@ -1239,7 +1241,7 @@ type_error:
       lua_pop(lstate, 1);
     }
   }
-  kv_destroy(stack);
+  kvi_destroy(stack);
   if (ERROR_SET(err)) {
     api_free_object(ret);
     ret = NIL;