From: "s.ross" <cwdinfo@...>
Date: 2008-01-17T13:38:02+09:00
Subject: Re: any tricks to speed up ruby? -fwhole-program?

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On Jan 16, 2008, at 7:04 PM, John Carter wrote:

> factors up to 2x but usually near 1x for compiler
> optimization tweaks

This is getting off the Ruby topic, but I think you're being unfair to  
optimizers (or rather, those who write them). The great thing about  
optimizers is that we can write clear and expressive code and not  
worry so much about strength reduction or loop unrolling or all those  
other things optimizers do for us. Honestly, does it make sense to you  
to read code like this:

a = (a << 1) + 1;

-or-

a *= 3;

The performance difference in a tight loop would be noticeable, but  
the next person to pick up the code would probably get a quizzical  
look on his or her face reading it. So the benchmark improvement may  
be between 1 and 2 percent, but the maintainability improvement could  
be of far greater benefit.

I'm not too familiar with gcc's global opts, but these are the most  
dangerous, but at the same time least obvious ones. If the optimizer  
gets it wrong, the code can break in the oddest ways; however, when  
the optimizer nails a global opt, it can make a difference you might  
never have predicted.

I am truly a fan of compiler optimizations because they fall into the  
"geez, that really is smart stuff" category. Still, you are absolutely  
correct that a better algorithm will win almost every time.

Just my $.02 :)
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