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Simpler implementation for tail calls

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Tail calls handled by 'luaD_precall', like regular calls, to avoid
code duplication.
This commit is contained in:
Roberto Ierusalimschy 2021-06-11 13:41:07 -03:00
parent c0ed74c1e1
commit 901d760093
3 changed files with 33 additions and 39 deletions
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46
ldo.c
View File

@ -474,26 +474,16 @@ void luaD_poscall (lua_State *L, CallInfo *ci, int nres) {
/*
** 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).
** 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.)
*/
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;
static void moveparams (lua_State *L, StkId prevf, StkId func, int narg) {
int i;
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 */
narg++; /* function itself will be moved, too */
for (i = 0; i < narg; i++) /* move down function and arguments */
setobjs2s(L, prevf + i, func + i);
L->top = prevf + narg; /* correct top */
}
@ -504,8 +494,12 @@ void luaD_pretailcall (lua_State *L, CallInfo *ci, StkId func, int narg1) {
** 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 nresults) {
CallInfo *luaD_precall (lua_State *L, StkId func, int nresults, int delta1) {
lua_CFunction f;
retry:
switch (ttypetag(s2v(func))) {
@ -542,12 +536,18 @@ CallInfo *luaD_precall (lua_State *L, StkId func, int nresults) {
int nfixparams = p->numparams;
int fsize = p->maxstacksize; /* frame size */
checkstackGCp(L, fsize, func);
L->ci = ci = next_ci(L);
if (delta1) { /* tail call? */
ci = L->ci; /* reuse stack frame */
ci->func -= delta1 - 1; /* correct 'func' */
moveparams(L, ci->func, func, narg);
}
else { /* regular call */
L->ci = ci = next_ci(L); /* new frame */
ci->func = func;
ci->nresults = nresults;
}
ci->u.l.savedpc = p->code; /* starting point */
ci->top = func + 1 + fsize;
ci->func = func;
L->ci = ci;
for (; narg < nfixparams; narg++)
setnilvalue(s2v(L->top++)); /* complete missing arguments */
lua_assert(ci->top <= L->stack_last);
@ -572,7 +572,7 @@ static void ccall (lua_State *L, StkId func, int nResults, int inc) {
L->nCcalls += inc;
if (l_unlikely(getCcalls(L) >= LUAI_MAXCCALLS))
luaE_checkcstack(L);
if ((ci = luaD_precall(L, func, nResults)) != NULL) { /* Lua function? */
if ((ci = luaD_precall(L, func, nResults, 0)) != NULL) { /* Lua function? */
ci->callstatus = CIST_FRESH; /* mark that it is a "fresh" execute */
luaV_execute(L, ci); /* call it */
}

4
ldo.h
View File

@ -58,8 +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 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 CallInfo *luaD_precall (lua_State *L, StkId func, int nresults,
int delta1);
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);

20
lvm.c
View File

@ -1632,11 +1632,11 @@ void luaV_execute (lua_State *L, CallInfo *ci) {
L->top = ra + b; /* top signals number of arguments */
/* else previous instruction set top */
savepc(L); /* in case of errors */
if ((newci = luaD_precall(L, ra, nresults)) == NULL)
if ((newci = luaD_precall(L, ra, nresults, 0)) == NULL)
updatetrap(ci); /* C call; nothing else to be done */
else { /* Lua call: run function in this same C frame */
ci = newci;
ci->callstatus = 0; /* call re-uses 'luaV_execute' */
ci->callstatus = 0;
goto startfunc;
}
vmbreak;
@ -1648,21 +1648,18 @@ 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 */
b = cast_int(L->top - ra);
/* else previous instruction set top */
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);
}
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 (luaD_precall(L, ra, LUA_MULTRET, delta + 1)) { /* Lua function? */
ci->callstatus |= CIST_TAIL;
goto startfunc; /* execute the callee */
}
if (!ttisLclosure(s2v(ra))) { /* C function? */
luaD_precall(L, ra, LUA_MULTRET); /* call it */
else { /* C function */
updatetrap(ci);
updatestack(ci); /* stack may have been relocated */
ci->func -= delta; /* restore 'func' (if vararg) */
@ -1670,9 +1667,6 @@ void luaV_execute (lua_State *L, CallInfo *ci) {
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 */