implementation of fast track for gettable operations

lapi.c

@@ -1,5 +1,5 @@
 /*
-** $Id: lapi.c,v 2.249 2015/04/06 12:23:48 roberto Exp roberto $
+** $Id: lapi.c,v 2.250 2015/06/18 14:19:52 roberto Exp roberto $
 ** Lua API
 ** See Copyright Notice in lua.h
 */
@@ -579,16 +579,27 @@ LUA_API int lua_pushthread (lua_State *L) {
 */
 
 
+static int auxgetstr (lua_State *L, const TValue *t, const char *k) {
+  const TValue *aux;
+  TString *str = luaS_new(L, k);
+  if (luaV_fastget(L, t, str, aux, luaH_getstr)) {
+    setobj2s(L, L->top, aux);
+    api_incr_top(L);
+  }
+  else {
+    setsvalue2s(L, L->top, str);
+    api_incr_top(L);
+    luaV_finishget(L, t, L->top - 1, L->top - 1, aux);
+  }
+  lua_unlock(L);
+  return ttnov(L->top - 1);
+}
+
+
 LUA_API int lua_getglobal (lua_State *L, const char *name) {
   Table *reg = hvalue(&G(L)->l_registry);
-  const TValue *gt;  /* global table */
   lua_lock(L);
-  gt = luaH_getint(reg, LUA_RIDX_GLOBALS);
-  setsvalue2s(L, L->top, luaS_new(L, name));
-  api_incr_top(L);
-  luaV_gettable(L, gt, L->top - 1, L->top - 1);
-  lua_unlock(L);
-  return ttnov(L->top - 1);
+  return auxgetstr(L, luaH_getint(reg, LUA_RIDX_GLOBALS), name);
 }
 
 
@@ -603,24 +614,25 @@ LUA_API int lua_gettable (lua_State *L, int idx) {
 
 
 LUA_API int lua_getfield (lua_State *L, int idx, const char *k) {
-  StkId t;
   lua_lock(L);
-  t = index2addr(L, idx);
-  setsvalue2s(L, L->top, luaS_new(L, k));
-  api_incr_top(L);
-  luaV_gettable(L, t, L->top - 1, L->top - 1);
-  lua_unlock(L);
-  return ttnov(L->top - 1);
+  return auxgetstr(L, index2addr(L, idx), k);
 }
 
 
 LUA_API int lua_geti (lua_State *L, int idx, lua_Integer n) {
   StkId t;
+  const TValue *aux;
   lua_lock(L);
   t = index2addr(L, idx);
-  setivalue(L->top, n);
-  api_incr_top(L);
-  luaV_gettable(L, t, L->top - 1, L->top - 1);
+  if (luaV_fastget(L, t, n, aux, luaH_getint)) {
+    setobj2s(L, L->top, aux);
+    api_incr_top(L);
+  }
+  else {
+    setivalue(L->top, n);
+    api_incr_top(L);
+    luaV_finishget(L, t, L->top - 1, L->top - 1, aux);
+  }
   lua_unlock(L);
   return ttnov(L->top - 1);
 }

lvm.c

@@ -1,5 +1,5 @@
 /*
-** $Id: lvm.c,v 2.246 2015/06/25 14:00:01 roberto Exp roberto $
+** $Id: lvm.c,v 2.247 2015/07/04 16:31:03 roberto Exp roberto $
 ** Lua virtual machine
 ** See Copyright Notice in lua.h
 */
@@ -153,30 +153,28 @@ static int forlimit (const TValue *obj, lua_Integer *p, lua_Integer step,
 
 
 /*
-** Main function for table access (invoking metamethods if needed).
-** Compute 'val = t[key]'
+** Complete a table access: if 't' is a table, 'tm' has its metamethod;
+** otherwise, 'tm' is NULL.
 */
-void luaV_gettable (lua_State *L, const TValue *t, TValue *key, StkId val) {
+void luaV_finishget (lua_State *L, const TValue *t, TValue *key, StkId val,
+                      const TValue *tm) {
   int loop;  /* counter to avoid infinite loops */
+  lua_assert(tm != NULL || !ttistable(t));
   for (loop = 0; loop < MAXTAGLOOP; loop++) {
-    const TValue *tm;
-    if (ttistable(t)) {  /* 't' is a table? */
-      Table *h = hvalue(t);
-      const TValue *res = luaH_get(h, key); /* do a primitive get */
-      if (!ttisnil(res) ||  /* result is not nil? */
-          (tm = fasttm(L, h->metatable, TM_INDEX)) == NULL) { /* or no TM? */
-        setobj2s(L, val, res);  /* result is the raw get */
-        return;
-      }
-      /* else will try metamethod */
+    if (tm == NULL) {  /* no metamethod (from a table)? */
+      if (ttisnil(tm = luaT_gettmbyobj(L, t, TM_INDEX)))
+        luaG_typeerror(L, t, "index");  /* no metamethod */
     }
-    else if (ttisnil(tm = luaT_gettmbyobj(L, t, TM_INDEX)))
-      luaG_typeerror(L, t, "index");  /* no metamethod */
     if (ttisfunction(tm)) {  /* metamethod is a function */
-      luaT_callTM(L, tm, t, key, val, 1);
+      luaT_callTM(L, tm, t, key, val, 1);  /* call it */
       return;
     }
     t = tm;  /* else repeat access over 'tm' */
+    if (luaV_fastget(L,t,key,tm,luaH_get)) {  /* try fast track */
+      setobj2s(L, val, tm);  /* done */
+      return;
+    }
+    /* else repeat */
   }
   luaG_runerror(L, "gettable chain too long; possible loop");
 }

lvm.h

@@ -1,5 +1,5 @@
 /*
-** $Id: lvm.h,v 2.34 2014/08/01 17:24:02 roberto Exp roberto $
+** $Id: lvm.h,v 2.35 2015/02/20 14:27:53 roberto Exp roberto $
 ** Lua virtual machine
 ** See Copyright Notice in lua.h
 */
@@ -48,13 +48,35 @@
 #define luaV_rawequalobj(t1,t2)		luaV_equalobj(NULL,t1,t2)
 
 
+/*
+** fast track for 'gettable': 1 means 'aux' points to resulted value;
+** 0 means 'aux' is metamethod (if 't' is a table) or NULL. 'f' is
+** the raw get function to use.
+*/
+#define luaV_fastget(L,t,k,aux,f) \
+  (!ttistable(t)  \
+   ? (aux = NULL, 0)  /* not a table; 'aux' is NULL and result is 0 */  \
+   : (aux = f(hvalue(t), k),  /* else, do raw access */  \
+      !ttisnil(aux) ? 1  /* result not nil? 'aux' has it */  \
+      : (aux = fasttm(L, hvalue(t)->metatable, TM_INDEX),  /* get metamethod */\
+         aux != NULL  ? 0  /* has metamethod? must call it */  \
+         : (aux = luaO_nilobject, 1))))  /* else, final result is nil */
+
+/*
+** standard implementation for 'gettable'
+*/
+#define luaV_gettable(L,t,k,v) { const TValue *aux; \
+  if (luaV_fastget(L,t,k,aux,luaH_get)) { setobj2s(L, v, aux); } \
+  else luaV_finishget(L,t,k,v,aux); }
+
+
 LUAI_FUNC int luaV_equalobj (lua_State *L, const TValue *t1, const TValue *t2);
 LUAI_FUNC int luaV_lessthan (lua_State *L, const TValue *l, const TValue *r);
 LUAI_FUNC int luaV_lessequal (lua_State *L, const TValue *l, const TValue *r);
 LUAI_FUNC int luaV_tonumber_ (const TValue *obj, lua_Number *n);
 LUAI_FUNC int luaV_tointeger (const TValue *obj, lua_Integer *p, int mode);
-LUAI_FUNC void luaV_gettable (lua_State *L, const TValue *t, TValue *key,
-                                            StkId val);
+LUAI_FUNC void luaV_finishget (lua_State *L, const TValue *t, TValue *key,
+                               StkId val, const TValue *tm);
 LUAI_FUNC void luaV_settable (lua_State *L, const TValue *t, TValue *key,
                                             StkId val);
 LUAI_FUNC void luaV_finishOp (lua_State *L);