commit 873588dc5f04bfc37006c3dc6ceb9a495ea503f2
parent b2f7b3b79f3117885b265575f6c5dbf934757797
Author: Roberto Ierusalimschy <roberto@inf.puc-rio.br>
Date: Wed, 21 Dec 2022 15:35:13 -0300
Simplification in opcodes for numerical 'for'
As the control variable is read only, the code doesn't need to keep
an internal copy of it.
Diffstat:
M | lparser.c | | | 4 | ++-- |
M | lvm.c | | | 50 | +++++++++++++++++++++++++------------------------- |
2 files changed, 27 insertions(+), 27 deletions(-)
diff --git a/lparser.c b/lparser.c
@@ -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);
}
diff --git a/lvm.c b/lvm.c
@@ -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 */
}
}