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Simplification in opcodes for numerical 'for'

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As the control variable is read only, the code doesn't need to keep
an internal copy of it.
This commit is contained in:
Roberto Ierusalimschy 2022-12-21 15:35:40 -03:00
parent b2f7b3b79f
commit 873588dc5f
2 changed files with 27 additions and 27 deletions
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4
lparser.c
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@ -1580,7 +1580,6 @@ static void fornum (LexState *ls, TString *varname, int line) {
int base = fs->freereg;
new_localvarliteral(ls, "(for state)");
new_localvarliteral(ls, "(for state)");
new_localvarliteral(ls, "(for state)");
new_localvarkind(ls, varname, RDKCONST); /* control variable */
checknext(ls, '=');
exp1(ls); /* initial value */
@ -1592,7 +1591,8 @@ static void fornum (LexState *ls, TString *varname, int line) {
luaK_int(fs, fs->freereg, 1);
luaK_reserveregs(fs, 1);
}
adjustlocalvars(ls, 3); /* control variables */
adjustlocalvars(ls, 2); /* start scope for internal state variables */
fs->freereg--; /* OP_FORPREP removes one register from the stack */
forbody(ls, base, line, 1, 0);
}

50
lvm.c
View File

@ -196,12 +196,15 @@ static int forlimit (lua_State *L, lua_Integer init, const TValue *lim,
/*
** Prepare a numerical for loop (opcode OP_FORPREP).
** Before execution, stack is as follows:
** ra : initial value
** ra + 1 : limit
** ra + 2 : step
** Return true to skip the loop. Otherwise,
** after preparation, stack will be as follows:
** ra : internal index (safe copy of the control variable)
** ra + 1 : loop counter (integer loops) or limit (float loops)
** ra + 2 : step
** ra + 3 : control variable
** ra : loop counter (integer loops) or limit (float loops)
** ra + 1 : step
** ra + 2 : control variable
*/
static int forprep (lua_State *L, StkId ra) {
TValue *pinit = s2v(ra);
@ -213,7 +216,6 @@ static int forprep (lua_State *L, StkId ra) {
lua_Integer limit;
if (step == 0)
luaG_runerror(L, "'for' step is zero");
setivalue(s2v(ra + 3), init); /* control variable */
if (forlimit(L, init, plimit, &limit, step))
return 1; /* skip the loop */
else { /* prepare loop counter */
@ -228,9 +230,10 @@ static int forprep (lua_State *L, StkId ra) {
/* 'step+1' avoids negating 'mininteger' */
count /= l_castS2U(-(step + 1)) + 1u;
}
/* store the counter in place of the limit (which won't be
needed anymore) */
setivalue(plimit, l_castU2S(count));
/* use 'chgivalue' for places that for sure had integers */
chgivalue(s2v(ra), l_castU2S(count)); /* change init to count */
setivalue(s2v(ra + 1), step); /* change limit to step */
chgivalue(s2v(ra + 2), init); /* change step to init */
}
}
else { /* try making all values floats */
@ -247,11 +250,10 @@ static int forprep (lua_State *L, StkId ra) {
: luai_numlt(init, limit))
return 1; /* skip the loop */
else {
/* make sure internal values are all floats */
setfltvalue(plimit, limit);
setfltvalue(pstep, step);
setfltvalue(s2v(ra), init); /* internal index */
setfltvalue(s2v(ra + 3), init); /* control variable */
/* make sure all values are floats */
setfltvalue(s2v(ra), limit);
setfltvalue(s2v(ra + 1), step);
setfltvalue(s2v(ra + 2), init); /* control variable */
}
}
return 0;
@ -264,14 +266,13 @@ static int forprep (lua_State *L, StkId ra) {
** written online with opcode OP_FORLOOP, for performance.)
*/
static int floatforloop (StkId ra) {
lua_Number step = fltvalue(s2v(ra + 2));
lua_Number limit = fltvalue(s2v(ra + 1));
lua_Number idx = fltvalue(s2v(ra)); /* internal index */
lua_Number step = fltvalue(s2v(ra + 1));
lua_Number limit = fltvalue(s2v(ra));
lua_Number idx = fltvalue(s2v(ra + 2)); /* control variable */
idx = luai_numadd(L, idx, step); /* increment index */
if (luai_numlt(0, step) ? luai_numle(idx, limit)
: luai_numle(limit, idx)) {
chgfltvalue(s2v(ra), idx); /* update internal index */
setfltvalue(s2v(ra + 3), idx); /* and control variable */
chgfltvalue(s2v(ra + 2), idx); /* update control variable */
return 1; /* jump back */
}
else
@ -1781,15 +1782,14 @@ void luaV_execute (lua_State *L, CallInfo *ci) {
}
vmcase(OP_FORLOOP) {
StkId ra = RA(i);
if (ttisinteger(s2v(ra + 2))) { /* integer loop? */
lua_Unsigned count = l_castS2U(ivalue(s2v(ra + 1)));
if (ttisinteger(s2v(ra + 1))) { /* integer loop? */
lua_Unsigned count = l_castS2U(ivalue(s2v(ra)));
if (count > 0) { /* still more iterations? */
lua_Integer step = ivalue(s2v(ra + 2));
lua_Integer idx = ivalue(s2v(ra)); /* internal index */
chgivalue(s2v(ra + 1), count - 1); /* update counter */
lua_Integer step = ivalue(s2v(ra + 1));
lua_Integer idx = ivalue(s2v(ra + 2)); /* control variable */
chgivalue(s2v(ra), count - 1); /* update counter */
idx = intop(+, idx, step); /* add step to index */
chgivalue(s2v(ra), idx); /* update internal index */
setivalue(s2v(ra + 3), idx); /* and control variable */
chgivalue(s2v(ra + 2), idx); /* update control variable */
pc -= GETARG_Bx(i); /* jump back */
}
}