Re: Optimized compilation

[David Schleef <ds@schleef.org>]

On Sat, Oct 12, 2002 at 08:20:13AM +1000, Glenn McGrath wrote:
> It really grates on my nerves to hear people arguing that it only makes
> it a little bit faster so its not worth doing.... its shouldnt be your
> decision, let the user decide if they want to take full advatage of their
> hardware, or run it in 1985 emulation mode.

In case you hadn't noticed, most modern CPUs will execute even
really crappy assembly code optimally.  Most instruction-level
bottlenecks come from data dependencies, which is a direct
result of the way the C code is written.  This is not something
that the compiler can optimize around without breaking the C
standard.

CPU manufacturers have made compiler-based optimizations largely
irrelevant.  A better approach to doing something really
meaningful is to find poorly performing inner loops and rewrite
them with an eye on improving instruction flow through modern
CPUs.



dave...