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Postings from July 2001
Vadim Vladimirovich Konovalov <vkonovalov@lucent.com> writes:
>> >Additionally, there are several places where local temporary
>> variables assigned just to make further assignment less verbose.
>> >("buf" in PerlIOStdio_read function is an example).
>>
>> That is not the reason. The reason is to get the
>> function/macro calls out of the
>> inner loop.
>
>Sorry, I can't see any loops there:
>
>SSize_t
>PerlIOStdio_read(PerlIO *f, void *vbuf, Size_t count)
>{
> dSYS;
> FILE *s = PerlIOSelf(f,PerlIOStdio)->stdio;
> SSize_t got = 0;
> if (count == 1)
> {
> STDCHAR *buf = (STDCHAR *) vbuf;
> /* Perl is expecting PerlIO_getc() to fill the buffer
> * Linux's stdio does not do that for fread()
> */
> int ch = PerlSIO_fgetc(s);
> if (ch != EOF)
> {
> *buf = ch;
> got = 1;
> }
> }
> else
> got = PerlSIO_fread(vbuf,1,count,s);
> return got;
>}
But s is used in both branches of the if - so factoring it out saves code
size.
Sorry this is my style, it isn't completely pointless - having "loads"
at the top of the function tends help instruction schedulers put them
in the "right place". GCC at least used to fail to put "loads" like
that in the delay slot of the jump that implements the if() - it did
not spot that there was a "common" instruction in the two basic blocks.
>
>
>
>Anyway, that tiny snippet of code is not essential, so it does not worth much debating...
>
>
>> >IMHO while idea of perlio.c is good, and it allows cool
>> things, it's implementation could be cleaned greatly.
>>
>> Patches welcome.
>
>Okay.
>Here is a tiny-optimization patch. Although patch is obvious, I checked for perl to pass tests after applying it.
>
>--- d:\WORK\PerlCompile\perl@11148-orig\perlio.c Sat Jun 30 22:41:57 2001
>+++ d:\WORK\PerlCompile\perl@11148\perlio.c Fri Jul 6 17:07:24 2001
>@@ -2278,14 +2278,13 @@
> SSize_t got = 0;
> if (count == 1)
> {
>- STDCHAR *buf = (STDCHAR *) vbuf;
> /* Perl is expecting PerlIO_getc() to fill the buffer
> * Linux's stdio does not do that for fread()
> */
> int ch = PerlSIO_fgetc(s);
> if (ch != EOF)
> {
>- *buf = ch;
>+ *((STDCHAR *)vbuf) = ch;
> got = 1;
> }
> }
Does that actually change the generated code at all?
IIRC there is at least one compiler which is used for perl which
does not like lvalue casts. I seem to remember doing the inverse of your
patch to fix that.
>
>
>I'm not sure that I am able to produce more essential patches, but I'll try.
>
>Best wishes,
><!ENTITY Vadim REALLIFE "Vadim V.Konovalov, St.Petersburg, Russia">
>&Vadim;
--
Nick Ing-Simmons
http://www.ni-s.u-net.com/
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