Re: [Sheflug] c++ & mem

[Will Newton <nospam [at] misconception.org.uk>]

On Tue, 12 Dec 2000, Stephen J. Turnbull wrote:

> Then go find out the history of "Duff's device."  Of course compilers
> can unroll loops.  The point is that unrolling the loop optimally to
> match the spec of a hardware device is something a compiler cannot do,
> because it can't read the spec.  Future compilers, maybe.  Current
> ones, no.

So what does -march and -mcpu do in gcc? Surely scheduling is modified by
these params?

> things that a human would not really be able to do by hand, but if one
> of those optimizations is buggy, it's damn hard to debug.  Sometimes
> you need the speed, but can't trust the compiler, so you do it
> yourself.

A brain damaged architecture like x86 lends itself to hand tuned code,
whereas a more register-full architecture with RISC design (e.g. Ultra
SPARC) it's probably best to let the compiler do it's thing.


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