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Specialize bytecode for pairs()/next() iterator. Speedup: 3.5x.

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Parser predict pairs/next and emits specialized bytecode.
Bytecode is descpecialized at runtime if the prediction was wrong.
Store slot index in hidden control var to avoid key lookups.
This commit is contained in:
Mike Pall
2010-09-30 21:55:32 +02:00
parent fce05fd6e1
commit ac76493df1
9 changed files with 634 additions and 354 deletions
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100
src/lj_parse.c
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@@ -2030,41 +2030,13 @@ static void parse_repeat(LexState *ls, BCLine line)
scope_end(fs); /* End loop scope. */
}
/* Parse body of a 'for' statement. */
static void parse_for_body(LexState *ls, BCReg base, BCLine line,
BCReg nvars, int isnum)
{
FuncScope bl;
FuncState *fs = ls->fs;
BCPos loop, loopend;
var_add(ls, 3); /* Hidden control variables. */
lex_check(ls, TK_do);
loop = isnum ? bcemit_AJ(fs, BC_FORI, base, NO_JMP) :
bcemit_AJ(fs, BC_JMP, fs->freereg, NO_JMP);
scope_begin(fs, &bl, 0); /* Scope for visible variables. */
var_add(ls, nvars);
bcreg_reserve(fs, nvars);
parse_block(ls);
scope_end(fs);
/* Perform loop inversion. Loop control instructions are at the end. */
if (isnum) {
loopend = bcemit_AJ(fs, BC_FORL, base, NO_JMP);
jmp_patchins(fs, loop, fs->pc);
} else {
jmp_patchins(fs, loop, fs->pc);
bcemit_ABC(fs, BC_ITERC, base+3, nvars+1, 2+1);
loopend = bcemit_AJ(fs, BC_ITERL, base+3, NO_JMP);
fs->bcbase[loopend-1].line = line;
}
fs->bcbase[loopend].line = line; /* Fix line for control ins. */
jmp_patchins(fs, loopend, loop+1);
}
/* Parse numeric 'for'. */
static void parse_for_num(LexState *ls, GCstr *varname, BCLine line)
{
FuncState *fs = ls->fs;
BCReg base = fs->freereg;
FuncScope bl;
BCPos loop, loopend;
/* Hidden control variables. */
var_new_lit(ls, FORL_IDX, "(for index)");
var_new_lit(ls, FORL_STOP, "(for limit)");
@@ -2081,7 +2053,51 @@ static void parse_for_num(LexState *ls, GCstr *varname, BCLine line)
bcemit_AD(fs, BC_KSHORT, fs->freereg, 1); /* Default step is 1. */
bcreg_reserve(fs, 1);
}
parse_for_body(ls, base, line, 1, 1);
var_add(ls, 3); /* Hidden control variables. */
lex_check(ls, TK_do);
loop = bcemit_AJ(fs, BC_FORI, base, NO_JMP);
scope_begin(fs, &bl, 0); /* Scope for visible variables. */
var_add(ls, 1);
bcreg_reserve(fs, 1);
parse_block(ls);
scope_end(fs);
/* Perform loop inversion. Loop control instructions are at the end. */
loopend = bcemit_AJ(fs, BC_FORL, base, NO_JMP);
fs->bcbase[loopend].line = line; /* Fix line for control ins. */
jmp_patchins(fs, loopend, loop+1);
jmp_patchins(fs, loop, fs->pc);
}
/* Try to predict whether the iterator is next() and specialize the bytecode.
** Detecting next() and pairs() by name is simplistic, but quite effective.
** The interpreter backs off if the check for the closure fails at runtime.
*/
static int predict_next(LexState *ls, FuncState *fs, BCPos pc)
{
BCIns ins = fs->bcbase[pc].ins;
GCstr *name;
cTValue *o;
switch (bc_op(ins)) {
case BC_MOV:
name = gco2str(gcref(var_get(ls, fs, bc_d(ins)).name));
break;
case BC_UGET:
name = gco2str(gcref(ls->vstack[fs->uvloc[bc_d(ins)].vidx].name));
break;
case BC_GGET:
/* There's no inverse index (yet), so lookup the strings. */
o = lj_tab_getstr(fs->kt, lj_str_newlit(ls->L, "pairs"));
if (o && tvisnum(o) && o->u32.lo == bc_d(ins))
return 1;
o = lj_tab_getstr(fs->kt, lj_str_newlit(ls->L, "next"));
if (o && tvisnum(o) && o->u32.lo == bc_d(ins))
return 1;
return 0;
default:
return 0;
}
return (name->len == 5 && !strcmp(strdata(name), "pairs")) ||
(name->len == 4 && !strcmp(strdata(name), "next"));
}
/* Parse 'for' iterator. */
@@ -2091,7 +2107,10 @@ static void parse_for_iter(LexState *ls, GCstr *indexname)
ExpDesc e;
BCReg nvars = 0;
BCLine line;
BCReg base = fs->freereg;
BCReg base = fs->freereg + 3;
BCPos loop, loopend, exprpc = fs->pc;
FuncScope bl;
int isnext;
/* Hidden control variables. */
var_new_lit(ls, nvars++, "(for generator)");
var_new_lit(ls, nvars++, "(for state)");
@@ -2104,7 +2123,22 @@ static void parse_for_iter(LexState *ls, GCstr *indexname)
line = ls->linenumber;
assign_adjust(ls, 3, expr_list(ls, &e), &e);
bcreg_bump(fs, 3); /* The iterator needs another 3 slots (func + 2 args). */
parse_for_body(ls, base, line, nvars - 3, 0);
isnext = (nvars <= 5 && predict_next(ls, fs, exprpc));
var_add(ls, 3); /* Hidden control variables. */
lex_check(ls, TK_do);
loop = bcemit_AJ(fs, isnext ? BC_ISNEXT : BC_JMP, base, NO_JMP);
scope_begin(fs, &bl, 0); /* Scope for visible variables. */
var_add(ls, nvars-3);
bcreg_reserve(fs, nvars-3);
parse_block(ls);
scope_end(fs);
/* Perform loop inversion. Loop control instructions are at the end. */
jmp_patchins(fs, loop, fs->pc);
bcemit_ABC(fs, isnext ? BC_ITERN : BC_ITERC, base, nvars-3+1, 2+1);
loopend = bcemit_AJ(fs, BC_ITERL, base, NO_JMP);
fs->bcbase[loopend-1].line = line; /* Fix line for control ins. */
fs->bcbase[loopend].line = line;
jmp_patchins(fs, loopend, loop+1);
}
/* Parse 'for' statement. */