On Mon, 2005-05-02 at 08:58 +0200, Leopold Toetsch wrote:
> Nicholas Clark <[EMAIL PROTECTED]> wrote:
> > 1 bit for SVf_IOK
> > 1 bit for SVf_NOK
> > 1 bit for SVf_POK
> > 1 bit for SVf_ROK
>
> I'd not mess around with (or introduce) flag bits. The more that this
> would only cover perl5 PMCs. Presuming that the Perl5 PMCs are subtypes
> of Parrot core PMCs, I'd do ...
[... code doing a string "isa" check on the type ...]
> The vtable functions C<isa> and C<does>, which take now a string, are a
> bit heavy-weighted and might get an extension in the log run that take
> an integer flag.
Unless this happens, this would be a HUGE performance hit. After all,
Sv*OK is called all over the place in the Perl 5 code, including many
places where performance is an issue.
[...]
> > 2 bits to say what we're storing in the union
>
> The vtable is that information:
>
> INTVAL i = VTABLE_get_integer(interpreter, pmc);
> FLOATVAL n = VTABLE_get_number(interpreter, pmc);
Here is some example P5 source from pp_pow in pp.c:
if (SvIOK(TOPm1s)) {
bool baseuok = SvUOK(TOPm1s);
UV baseuv;
if (baseuok) {
baseuv = SvUVX(TOPm1s);
} else {
IV iv = SvIVX(TOPm1s);
and here that is, run through the C pre-processor: pre-processor:
if ((((*(sp-1)))->sv_flags & 0x00010000)) {
char baseuok = ((((*(sp-1)))->sv_flags & (0x00010000|0x80000000))
== (0x00010000|0x80000000));
UV baseuv;
if (baseuok) {
baseuv = ((XPVUV*) ((*(sp-1)))->sv_any)->xuv_uv;
} else {
IV iv = ((XPVIV*) ((*(sp-1)))->sv_any)->xiv_iv;
Notice that there is exactly no function calling going on there. To
change that to (pseudocode):
if (isa_int_test(TOPm1s)) {
bool baseuok = isa_uint_test(TOPm1s);
UV baseuv;
if (baseuok) {
baseuv = invoke_uint_vtable_get(TOPm1s);
} else {
IV iv = invoke_int_vtable_get(TOPm1s);
Well... even after JIT compilation, function call overhead is function
call overhead, no?
> just do the right thing. Usually there is no need to query the PMC what
> it is.
If you're writing a compiler from scratch, I can see that being mostly
true. However, in trying to port Perl 5 guts over to Parrot, there's a
lot of code that relies on knowing what's going on (e.g. if a value has
ever been a number, etc.)
