From mboxrd@z Thu Jan  1 00:00:00 1970
Message-ID: <775b8d190705032353u1bdf4528ve2e6ec3277017506@mail.gmail.com>
Date: Fri,  4 May 2007 16:53:56 +1000
From: "Bruce Ellis" <bruce.ellis@gmail.com>
To: "Fans of the OS Plan 9 from Bell Labs" <9fans@cse.psu.edu>
Subject: Re: [9fans] speaking of kenc
In-Reply-To: <20070503192201.A22416@orthanc.ca>
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isn't it bleeding obvious by now that asm is dumb.
a function call into something in a *.s file will do.
you'll find a few entry points in your fave l.s.

can i say dumb-asm on this list?

i saw an attempt of ill-informed cleverness where spl() etc
were picked up by the compiler and inlined.

i guess he had nothing else to do with his life.

maybe a 0.02% speedup.

brucee

On 5/4/07, Lyndon Nerenberg <lyndon@orthanc.ca> wrote:
> >> That's called as(1).
> >
> >  On any architecture with a non-trivial register allocation, the above
> > statement does not apply.
> > As far as performance goes you might be better off not using assembler
> > to begin with.
>
> Exactly.  If you want asm, you know where to find it.  These days, the
> cases where raw assembler really matters are significant enough that a few
> in-lines generally don't accomplish anything.  Yes, you can pollute your C
> code with __asm(), but I could also argue for _f77() so that I could
> compile spice (or more importantly, dungeon) with cc.  Where does it end?
>
> > Compilers (at least the ones I work on) are quite smart
> > in how they use precious resource such as registers, and unless you
> > can hide everything away on the other side of the 'call' op you'd
> > be in trouble mixing your code with what compiler had generated for
> > you.
>
> Sure, the compiler can assist with register allocation, but so can reading
> the ABI documentation.  Once upon a time I spent way too much of my life
> optimizing MIPS cycles out of the distributed.net client instead of
> drinking beer.  After watching the compilers blow away almost all of the
> machine code optimizations people proposed, I filed great chunks of
> in-lined cruft in the bin.  The only asm code that mattered was the
> carefully tuned *long* unrolled loop bit-shifting stuff.  And it had an
> execution time that made the call overhead invisible.
>
> > GCC style asm in-lines play nice with things like register
> > allocator and instruction scheduler, where .s files don't.
>
> Only in the cases where asm code doesn't provide enough benefit to be
> worthwhile.
>
> >  What's 3B3 and ESS#5 ? ;-)
>
> A reasonable telephone switch billing system, and the worlds worst
> multi-user UNIX timeshare box.  Perhaps not in that order.  (Or maybe it
> *is* the right order.)
>
>
> --lyndon
>
>   In God we Trust -- all others must submit an X.509 certificate.
>                        -- Charles Forsythe
>