Changes in opcodes for generic 'for'

Again, as the control variable is read only, the code doesn't need
to keep an internal copy of it.

lparser.c

@@ -1558,6 +1558,7 @@ static void forbody (LexState *ls, int base, int line, int nvars, int isgen) {
   int prep, endfor;
   checknext(ls, TK_DO);
   prep = luaK_codeABx(fs, forprep[isgen], base, 0);
+  fs->freereg--;  /* both 'forprep' remove one register from the stack */
   enterblock(fs, &bl, 0);  /* scope for declared variables */
   adjustlocalvars(ls, nvars);
   luaK_reserveregs(fs, nvars);
@@ -1591,8 +1592,7 @@ static void fornum (LexState *ls, TString *varname, int line) {
     luaK_int(fs, fs->freereg, 1);
     luaK_reserveregs(fs, 1);
   }
-  adjustlocalvars(ls, 2);  /* start scope for internal state variables */
-  fs->freereg--;  /* OP_FORPREP removes one register from the stack */
+  adjustlocalvars(ls, 2);  /* start scope for internal variables */
   forbody(ls, base, line, 1, 0);
 }
 
@@ -1601,14 +1601,13 @@ static void forlist (LexState *ls, TString *indexname) {
   /* forlist -> NAME {,NAME} IN explist forbody */
   FuncState *fs = ls->fs;
   expdesc e;
-  int nvars = 5;  /* gen, state, control, toclose, 'indexname' */
+  int nvars = 4;  /* function, state, closing, control */
   int line;
   int base = fs->freereg;
-  /* create control variables */
-  new_localvarliteral(ls, "(for state)");
-  new_localvarliteral(ls, "(for state)");
-  new_localvarliteral(ls, "(for state)");
-  new_localvarliteral(ls, "(for state)");
+  /* create internal variables */
+  new_localvarliteral(ls, "(for state)");  /* iterator function */
+  new_localvarliteral(ls, "(for state)");  /* state */
+  new_localvarliteral(ls, "(for state)");  /* closing var. (after swap) */
   new_localvarkind(ls, indexname, RDKCONST);  /* control variable */
   /* other declared variables */
   while (testnext(ls, ',')) {
@@ -1618,10 +1617,10 @@ static void forlist (LexState *ls, TString *indexname) {
   checknext(ls, TK_IN);
   line = ls->linenumber;
   adjust_assign(ls, 4, explist(ls, &e), &e);
-  adjustlocalvars(ls, 4);  /* control variables */
-  marktobeclosed(fs);  /* last control var. must be closed */
-  luaK_checkstack(fs, 3);  /* extra space to call generator */
-  forbody(ls, base, line, nvars - 4, 1);
+  adjustlocalvars(ls, 3);  /* start scope for internal variables */
+  marktobeclosed(fs);  /* last internal var. must be closed */
+  luaK_checkstack(fs, 2);  /* extra space to call iterator */
+  forbody(ls, base, line, nvars - 3, 1);
 }
 
 

lvm.c

@@ -1806,26 +1806,38 @@ void luaV_execute (lua_State *L, CallInfo *ci) {
         vmbreak;
       }
       vmcase(OP_TFORPREP) {
+       /* before: 'ra' has the iterator function, 'ra + 1' has the state,
+          'ra + 2' has the initial value for the control variable, and
+          'ra + 3' has the closing variable. This opcode then swaps the
+          control and the closing variables and marks the closing variable
+          as to-be-closed.
+       */
        StkId ra = RA(i);
-        /* create to-be-closed upvalue (if needed) */
-        halfProtect(luaF_newtbcupval(L, ra + 3));
-        pc += GETARG_Bx(i);
-        i = *(pc++);  /* go to next instruction */
+       TValue temp;  /* to swap control and closing variables */
+       setobj(L, &temp, s2v(ra + 3));
+       setobjs2s(L, ra + 3, ra + 2);
+       setobj2s(L, ra + 2, &temp);
+        /* create to-be-closed upvalue (if closing var. is not nil) */
+        halfProtect(luaF_newtbcupval(L, ra + 2));
+        pc += GETARG_Bx(i);  /* go to end of the loop */
+        i = *(pc++);  /* fetch next instruction */
         lua_assert(GET_OPCODE(i) == OP_TFORCALL && ra == RA(i));
         goto l_tforcall;
       }
       vmcase(OP_TFORCALL) {
        l_tforcall: {
-        StkId ra = RA(i);
         /* 'ra' has the iterator function, 'ra + 1' has the state,
-           'ra + 2' has the control variable, and 'ra + 3' has the
-           to-be-closed variable. The call will use the stack after
-           these values (starting at 'ra + 4')
+           'ra + 2' has the closing variable, and 'ra + 3' has the control
+           variable. The call will use the stack starting at 'ra + 3',
+           so that it preserves the first three values, and the first
+           return will be the new value for the control variable.
         */
-        /* push function, state, and control variable */
-        memcpy(ra + 4, ra, 3 * sizeof(*ra));
-        L->top.p = ra + 4 + 3;
-        ProtectNT(luaD_call(L, ra + 4, GETARG_C(i)));  /* do the call */
+        StkId ra = RA(i);
+        setobjs2s(L, ra + 5, ra + 3);  /* copy the control variable */
+        setobjs2s(L, ra + 4, ra + 1);  /* copy state */
+        setobjs2s(L, ra + 3, ra);  /* copy function */
+        L->top.p = ra + 3 + 3;
+        ProtectNT(luaD_call(L, ra + 3, GETARG_C(i)));  /* do the call */
         updatestack(ci);  /* stack may have changed */
         i = *(pc++);  /* go to next instruction */
         lua_assert(GET_OPCODE(i) == OP_TFORLOOP && ra == RA(i));
@@ -1834,10 +1846,8 @@ void luaV_execute (lua_State *L, CallInfo *ci) {
       vmcase(OP_TFORLOOP) {
        l_tforloop: {
         StkId ra = RA(i);
-        if (!ttisnil(s2v(ra + 4))) {  /* continue loop? */
-          setobjs2s(L, ra + 2, ra + 4);  /* save control variable */
+        if (!ttisnil(s2v(ra + 3)))  /* continue loop? */
           pc -= GETARG_Bx(i);  /* jump back */
-        }
         vmbreak;
       }}
       vmcase(OP_SETLIST) {

testes/files.lua

@@ -427,12 +427,12 @@ do   -- testing closing file in line iteration
   -- get the to-be-closed variable from a loop
   local function gettoclose (lv)
     lv = lv + 1
-    local stvar = 0   -- to-be-closed is 4th state variable in the loop
+    local stvar = 0   -- to-be-closed is 3th state variable in the loop
     for i = 1, 1000 do
       local n, v = debug.getlocal(lv, i)
       if n == "(for state)" then
         stvar = stvar + 1
-        if stvar == 4 then return v end
+        if stvar == 3 then return v end
       end
     end
   end