string::find complexity.

[Paolo Carlini]

Ian Lance Taylor wrote:

> Eventually we are going to hit the point where the choices between
> optimizations are going to be harder to make--where the function runs
> somewhat faster, but gets noticeably bigger, so you have to consider
> whether the effect on the instruction cache outweighs the other
> performance gain.

By the way, *methodological* help would be also appreciated! For instance:
in case we don't have available a large testcase, comparing also codesize
besides performance, helps, right? Usually, I do that too, but I have to
remember to post the numbers more often (I did, sometimes)

Paolo.