Re: optimisation question

[Marcin Dalecki <martin at dalecki dot de>]

On 2005-02-01, at 00:43, Joe Buck wrote:
> Unless you've done profiling and determined that you have a critical 
> inner
> loop, it's best to optimize your code's form for readability and
> maintainability, rather than to tweak it based on a belief you haven't
> tested that compilers will "like it better".

Optimization without profiling and measurement is like swimming without
water. Code optimization can give you only linearly better results. If 
you
really want to work miracles you should look at an *much* higher 
abstraction
level. Most of micro optimization which applied 10 years ago will 
frequently
do no good those days due to changes in hardware as well. Thus caches 
for example.
Or instruction scheduling - turns out it's best done at runtime by the 
CPU
instead of the compiler. Yea. I know there is a CPU from intel 
promising miracles
by the still to be developer compiler to start working at full gear 
frequently
called Itanic. It will sink. Static code analysis just can't get you
around fundamental complexities of the underlying theory. Most stuff 
simply can't
be analyzed in reasonable time. Thus most compilers simple end up as a 
heap
of heuristics applied after each other. However the set of heuristics 
used by
commercial grade products is really HUGE those days. It's hard to beat 
them
by just looking at the assembler code for yourself.