Micro optimization in OP_RETURN and OP_TAILCALL

Many functions are vararg but create no upvalues, so it is better
to separate the tests for these two kinds of "extra work".

lcode.c

@@ -1745,10 +1745,10 @@ void luaK_finish (FuncState *fs) {
         SET_OPCODE(*pc, OP_RETURN);
       }  /* FALLTHROUGH */
       case OP_RETURN: case OP_TAILCALL: {
-        if (fs->needclose || p->is_vararg) {
-          SETARG_C(*pc, p->is_vararg ? p->numparams + 1 : 0);
-          SETARG_k(*pc, 1);  /* signal that there is extra work */
-        }
+        if (fs->needclose)
+          SETARG_k(*pc, 1);  /* signal that it needs to close */
+        if (p->is_vararg)
+          SETARG_C(*pc, p->numparams + 1);  /* signal that it is vararg */
         break;
       }
       case OP_JMP: {

lopcodes.h

@@ -338,10 +338,9 @@ OP_EXTRAARG/*	Ax	extra (larger) argument for previous opcode	*/
   (*) All 'skips' (pc++) assume that next instruction is a jump.
 
   (*) In instructions OP_RETURN/OP_TAILCALL, 'k' specifies that the
-  function either builds upvalues, which may need to be closed, or is
-  vararg, which must be corrected before returning. When 'k' is true,
-  C > 0 means the function is vararg and (C - 1) is its number of
-  fixed parameters.
+  function builds upvalues, which may need to be closed. C > 0 means
+  the function is vararg, so that its 'func' must be corrected before
+  returning; in this case, (C - 1) is its number of fixed parameters.
 
   (*) In comparisons with an immediate operand, C signals whether the
   original operand was a float.

lvm.c

@@ -1564,16 +1564,15 @@ void luaV_execute (lua_State *L, CallInfo *ci) {
       }
       vmcase(OP_TAILCALL) {
         int b = GETARG_B(i);  /* number of arguments + 1 (function) */
-        int delta = 0;  /* virtual 'func' - real 'func' (vararg functions) */
+        int nparams1 = GETARG_C(i);
+        /* delat is virtual 'func' - real 'func' (vararg functions) */
+        int delta = (nparams1) ? ci->u.l.nextraargs + nparams1 : 0;
         if (b != 0)
           L->top = ra + b;
         else  /* previous instruction set top */
           b = cast_int(L->top - ra);
         savepc(ci);  /* some calls here can raise errors */
         if (TESTARG_k(i)) {
-          int nparams1 = GETARG_C(i);
-          if (nparams1)  /* vararg function? */
-            delta = ci->u.l.nextraargs + nparams1;
           /* close upvalues from current call; the compiler ensures
              that there are no to-be-closed variables here */
           luaF_close(L, base, NOCLOSINGMETH);
@@ -1599,18 +1598,18 @@ void luaV_execute (lua_State *L, CallInfo *ci) {
       }
       vmcase(OP_RETURN) {
         int n = GETARG_B(i) - 1;  /* number of results */
+        int nparams1 = GETARG_C(i);
         if (n < 0)  /* not fixed? */
           n = cast_int(L->top - ra);  /* get what is available */
         savepc(ci);
         if (TESTARG_k(i)) {
-          int nparams1 = GETARG_C(i);
           if (L->top < ci->top)
             L->top = ci->top;
           luaF_close(L, base, LUA_OK);  /* there may be open upvalues */
           updatestack(ci);
-          if (nparams1)  /* vararg function? */
-            ci->func -= ci->u.l.nextraargs + nparams1;
         }
+        if (nparams1)  /* vararg function? */
+          ci->func -= ci->u.l.nextraargs + nparams1;
         L->top = ra + n;  /* set call for 'luaD_poscall' */
         luaD_poscall(L, ci, n);
         return;