Undo simplification of tail calls (commit 901d760)

Not that simpler and slower.

ldo.c

@@ -474,33 +474,36 @@ void luaD_poscall (lua_State *L, CallInfo *ci, int nres) {
 
 
 /*
-** In a tail call, move function and parameters to previous call frame.
-** (This is done only when no more errors can occur before entering the
-** new function, to keep debug information always consistent.)
+** Prepare a function for a tail call, building its call info on top
+** of the current call info. 'narg1' is the number of arguments plus 1
+** (so that it includes the function itself).
 */
-static void moveparams (lua_State *L, StkId prevf, StkId func) {
+void luaD_pretailcall (lua_State *L, CallInfo *ci, StkId func, int narg1) {
+  Proto *p = clLvalue(s2v(func))->p;
+  int fsize = p->maxstacksize;  /* frame size */
+  int nfixparams = p->numparams;
   int i;
-  for (i = 0; func + i < L->top; i++)  /* move down function and arguments */
-    setobjs2s(L, prevf + i, func + i);
-  L->top = prevf + i;  /* correct top */
-}
-
-
-static CallInfo *prepCallInfo (lua_State *L, StkId func, int retdel,
-                                             int mask) {
-  CallInfo *ci;
-  if (isdelta(retdel)) {  /* tail call? */
-    ci = L->ci;  /* reuse stack frame */
-    ci->func -= retdel2delta(retdel);  /* correct 'func' */
-    ci->callstatus |= mask | CIST_TAIL;
-    moveparams(L, ci->func, func);
-  }
-  else {  /* regular call */
-    ci = L->ci = next_ci(L);  /* new frame */
-    ci->func = func;
-    ci->nresults = retdel;
-    ci->callstatus = mask;
-  }
+  for (i = 0; i < narg1; i++)  /* move down function and arguments */
+    setobjs2s(L, ci->func + i, func + i);
+  checkstackGC(L, fsize);
+  func = ci->func;  /* moved-down function */
+  for (; narg1 <= nfixparams; narg1++)
+    setnilvalue(s2v(func + narg1));  /* complete missing arguments */
+  ci->top = func + 1 + fsize;  /* top for new function */
+  lua_assert(ci->top <= L->stack_last);
+  ci->u.l.savedpc = p->code;  /* starting point */
+  ci->callstatus |= CIST_TAIL;
+  L->top = func + narg1;  /* set top */
+}
+
+
+static CallInfo *prepCallInfo (lua_State *L, StkId func, int nret,
+                                             int mask, StkId top) {
+  CallInfo *ci = L->ci = next_ci(L);  /* new frame */
+  ci->func = func;
+  ci->nresults = nret;
+  ci->callstatus = mask;
+  ci->top = top;
   return ci;
 }
 
@@ -512,12 +515,8 @@ static CallInfo *prepCallInfo (lua_State *L, StkId func, int retdel,
 ** to be executed, if it was a Lua function. Otherwise (a C function)
 ** returns NULL, with all the results on the stack, starting at the
 ** original function position.
-** For regular calls, 'delta1' is 0. For tail calls, 'delta1' is the
-** 'delta' (correction of base for vararg functions) plus 1, so that it
-** cannot be zero. Like 'moveparams', this correction can only be done
-** when no more errors can occur in the call.
 */
-CallInfo *luaD_precall (lua_State *L, StkId func, int retdel) {
+CallInfo *luaD_precall (lua_State *L, StkId func, int nresults) {
   lua_CFunction f;
  retry:
   switch (ttypetag(s2v(func))) {
@@ -530,8 +529,8 @@ CallInfo *luaD_precall (lua_State *L, StkId func, int retdel) {
       int n;  /* number of returns */
       CallInfo *ci;
       checkstackGCp(L, LUA_MINSTACK, func);  /* ensure minimum stack size */
-      ci = prepCallInfo(L, func, retdel, CIST_C);
-      ci->top = L->top + LUA_MINSTACK;
+      L->ci = ci = prepCallInfo(L, func, nresults, CIST_C,
+                                   L->top + LUA_MINSTACK);
       lua_assert(ci->top <= L->stack_last);
       if (l_unlikely(L->hookmask & LUA_MASKCALL)) {
         int narg = cast_int(L->top - func) - 1;
@@ -551,9 +550,8 @@ CallInfo *luaD_precall (lua_State *L, StkId func, int retdel) {
       int nfixparams = p->numparams;
       int fsize = p->maxstacksize;  /* frame size */
       checkstackGCp(L, fsize, func);
-      ci = prepCallInfo(L, func, retdel, 0);
+      L->ci = ci = prepCallInfo(L, func, nresults, 0, func + 1 + fsize);
       ci->u.l.savedpc = p->code;  /* starting point */
-      ci->top = func + 1 + fsize;
       for (; narg < nfixparams; narg++)
         setnilvalue(s2v(L->top++));  /* complete missing arguments */
       lua_assert(ci->top <= L->stack_last);

ldo.h

@@ -49,18 +49,6 @@
 	luaD_checkstackaux(L, (fsize), luaC_checkGC(L), (void)0)
 
 
-/*
-** 'luaD_precall' is used for regular calls, when it needs the
-** number of results, and in tail calls, when it needs the 'delta'
-** (correction of base for vararg functions). The argument 'retdel'
-** codes these two options. A number of results is represented by
-** itself, while a delta is represented by 'delta2retdel(delta)'
-*/
-#define delta2retdel(d) 	(-(d) + LUA_MULTRET - 1)
-#define retdel2delta(d) 	(-(d) + LUA_MULTRET - 1)
-#define isdelta(rd)	((rd) < LUA_MULTRET)
-
-
 /* type of protected functions, to be ran by 'runprotected' */
 typedef void (*Pfunc) (lua_State *L, void *ud);
 
@@ -70,7 +58,8 @@ LUAI_FUNC int luaD_protectedparser (lua_State *L, ZIO *z, const char *name,
 LUAI_FUNC void luaD_hook (lua_State *L, int event, int line,
                                         int fTransfer, int nTransfer);
 LUAI_FUNC void luaD_hookcall (lua_State *L, CallInfo *ci);
-LUAI_FUNC CallInfo *luaD_precall (lua_State *L, StkId func, int retdel);
+LUAI_FUNC void luaD_pretailcall (lua_State *L, CallInfo *ci, StkId func, int n);
+LUAI_FUNC CallInfo *luaD_precall (lua_State *L, StkId func, int nResults);
 LUAI_FUNC void luaD_call (lua_State *L, StkId func, int nResults);
 LUAI_FUNC void luaD_callnoyield (lua_State *L, StkId func, int nResults);
 LUAI_FUNC void luaD_tryfuncTM (lua_State *L, StkId func);

lvm.c

@@ -768,6 +768,7 @@ lua_Number luaV_modf (lua_State *L, lua_Number m, lua_Number n) {
 */
 #define luaV_shiftr(x,y)	luaV_shiftl(x,intop(-, 0, y))
 
+
 lua_Integer luaV_shiftl (lua_Integer x, lua_Integer y) {
   if (y < 0) {  /* shift right? */
     if (y <= -NBITS) return 0;
@@ -1647,19 +1648,31 @@ void luaV_execute (lua_State *L, CallInfo *ci) {
         int delta = (nparams1) ? ci->u.l.nextraargs + nparams1 : 0;
         if (b != 0)
           L->top = ra + b;
-        /* else previous instruction set top */
+        else  /* previous instruction set top */
+          b = cast_int(L->top - ra);
         savepc(ci);  /* several calls here can raise errors */
         if (TESTARG_k(i)) {
           luaF_closeupval(L, base);  /* close upvalues from current call */
           lua_assert(L->tbclist < base);  /* no pending tbc variables */
           lua_assert(base == ci->func + 1);
         }
-        if (luaD_precall(L, ra, delta2retdel(delta)))  /* Lua function? */
-          goto startfunc;  /* execute the callee */
-        else {  /* C function */
+        while (!ttisfunction(s2v(ra))) {  /* not a function? */
+          luaD_tryfuncTM(L, ra);  /* try '__call' metamethod */
+          b++;  /* there is now one extra argument */
+          checkstackGCp(L, 1, ra);
+        }
+        if (!ttisLclosure(s2v(ra))) {  /* C function? */
+          luaD_precall(L, ra, LUA_MULTRET);  /* call it */
           updatetrap(ci);
+          updatestack(ci);  /* stack may have been relocated */
+          ci->func -= delta;  /* restore 'func' (if vararg) */
+          luaD_poscall(L, ci, cast_int(L->top - ra));  /* finish caller */
+          updatetrap(ci);  /* 'luaD_poscall' can change hooks */
           goto ret;  /* caller returns after the tail call */
         }
+        ci->func -= delta;  /* restore 'func' (if vararg) */
+        luaD_pretailcall(L, ci, ra, b);  /* prepare call frame */
+        goto startfunc;  /* execute the callee */
       }
       vmcase(OP_RETURN) {
         int n = GETARG_B(i) - 1;  /* number of results */