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More uniform implementation for tail calls

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'luaD_pretailcall' mimics 'luaD_precall', handling call metamethods
and calling C functions directly. That makes the code in the
interpreter loop simpler.

This commit also goes back to emulating the tail call in 'luaD_precall'
with a goto, as C compilers may not do proper tail calls and the C
stack can overflow much sooner than the Lua stack (which grows as the
metamethod is added to it).
This commit is contained in:
Roberto Ierusalimschy
2021-10-29 13:41:24 -03:00
parent 3699446aaf
commit 1fce5bea81
3 changed files with 58 additions and 44 deletions
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19
lvm.c
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@@ -1643,6 +1643,7 @@ void luaV_execute (lua_State *L, CallInfo *ci) {
}
vmcase(OP_TAILCALL) {
int b = GETARG_B(i); /* number of arguments + 1 (function) */
int n; /* number of results when calling a C function */
int nparams1 = GETARG_C(i);
/* delta is virtual 'func' - real 'func' (vararg functions) */
int delta = (nparams1) ? ci->u.l.nextraargs + nparams1 : 0;
@@ -1656,24 +1657,14 @@ void luaV_execute (lua_State *L, CallInfo *ci) {
lua_assert(L->tbclist < base); /* no pending tbc variables */
lua_assert(base == ci->func + 1);
}
while (!ttisfunction(s2v(ra))) { /* not a function? */
ra = luaD_tryfuncTM(L, ra); /* try '__call' metamethod */
b++; /* there is now one extra argument */
}
if (!ttisLclosure(s2v(ra))) { /* C function? */
luaD_precall(L, ra, LUA_MULTRET); /* call it */
updatetrap(ci);
updatestack(ci); /* stack may have been relocated */
if ((n = luaD_pretailcall(L, ci, ra, b, delta)) < 0) /* Lua function? */
goto startfunc; /* execute the callee */
else { /* C function? */
ci->func -= delta; /* restore 'func' (if vararg) */
luaD_poscall(L, ci, cast_int(L->top - ra)); /* finish caller */
luaD_poscall(L, ci, n); /* finish caller */
updatetrap(ci); /* 'luaD_poscall' can change hooks */
goto ret; /* caller returns after the tail call */
}
else { /* Lua function */
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 */