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C functions can be tail called, too

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A tail call to a C function can have the behavior of a "real" tail
call, reusing the stack frame of the caller.
This commit is contained in:
Roberto Ierusalimschy
2021-06-14 13:28:21 -03:00
parent 901d760093
commit 04e19712a5
4 changed files with 29 additions and 29 deletions
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43
ldo.c
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@@ -478,12 +478,31 @@ void luaD_poscall (lua_State *L, CallInfo *ci, int nres) {
** (This is done only when no more errors can occur before entering the
** new function, to keep debug information always consistent.)
*/
static void moveparams (lua_State *L, StkId prevf, StkId func, int narg) {
static void moveparams (lua_State *L, StkId prevf, StkId func) {
int i;
narg++; /* function itself will be moved, too */
for (i = 0; i < narg; i++) /* move down function and arguments */
for (i = 0; func + i < L->top; i++) /* move down function and arguments */
setobjs2s(L, prevf + i, func + i);
L->top = prevf + narg; /* correct top */
L->top = prevf + i; /* correct top */
}
static CallInfo *prepCallInfo (lua_State *L, StkId func, int nresults,
int delta1, int mask) {
CallInfo *ci;
if (delta1) { /* tail call? */
ci = L->ci; /* reuse stack frame */
ci->func -= delta1 - 1; /* 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 = nresults;
ci->callstatus = mask;
}
return ci;
}
@@ -512,11 +531,8 @@ CallInfo *luaD_precall (lua_State *L, StkId func, int nresults, int delta1) {
int n; /* number of returns */
CallInfo *ci;
checkstackGCp(L, LUA_MINSTACK, func); /* ensure minimum stack size */
L->ci = ci = next_ci(L);
ci->nresults = nresults;
ci->callstatus = CIST_C;
ci = prepCallInfo(L, func, nresults, delta1, CIST_C);
ci->top = L->top + LUA_MINSTACK;
ci->func = func;
lua_assert(ci->top <= L->stack_last);
if (l_unlikely(L->hookmask & LUA_MASKCALL)) {
int narg = cast_int(L->top - func) - 1;
@@ -536,16 +552,7 @@ CallInfo *luaD_precall (lua_State *L, StkId func, int nresults, int delta1) {
int nfixparams = p->numparams;
int fsize = p->maxstacksize; /* frame size */
checkstackGCp(L, fsize, func);
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 = prepCallInfo(L, func, nresults, delta1, 0);
ci->u.l.savedpc = p->code; /* starting point */
ci->top = func + 1 + fsize;
for (; narg < nfixparams; narg++)