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On Monday 30 July 2007 03:45:42 James Richard Tyrer wrote:
> Profiling is used for macro-optimization, it has no place in peephole
> optimization.

In my experience, your point about micro-optimizations (or "peephole=20
optimizations", or whatever you want to call them) is simply wrong.

I've run into a number of situations in my work projects where I'll perform=
=20
some "obvious" micro-optimization (such as the one you are suggesting) only=
=20
to have the profile numbers become significantly *worse*.  (Unfortunately I=
=20
can't give a specific example -- employer confidentiality and whatnot.)

So Knuth's point about premature optimization definitely applies here --=20
profile *first*, to make sure the problem's where you think it is.  Only=20
after you've profiled should you even begin to discuss how to fix it. =20
Then, once you've come up with a solution, profile *again* to test your=20
solution and make sure it actually works.

Otherwise, you have no idea what is going on.

Really, this is standard software engineering practice -- you have to=20
identify and confirm the problem before you fix it (profiling beforehand),=
=20
fix it, then test to make sure you actually did (profiling afterward).

You wouldn't close a bug without having tested to make sure your patch=20
works, would you?  So why would you discount the importance of profiling=20
when performing optimizations?


=2D-=20
Joshua J. Berry

"I haven't lost my mind -- it's backed up on tape somewhere."
    -- /usr/games/fortune

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