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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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48
ldo.c
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@@ -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);
ci->nresults = nresults;
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 */
}