On Mon, 19 Mar 2007, Shawn O. Pearce wrote:
quoted text
>
> DrNick suggested on #git to try flipping the isspace test around.
> This is a smaller change and generated the same ~3.60 seconds run
> as Dscho's patch.  I like DrNick's version better.  ;-)

For me, the result seems to be in the noise.

It may be due to running on Core 2. It's not very sensitive to 
micro-optimizations like this. It definitely makes sense to test the 
*stable* test first, since that will help branch prediction (the 
"isspace()" test is *not* very predictable), so I don't disagree with the 
patch, but I suspect it depends a lot on the microarchitecture just how 
much it matters.

Do you perhaps have a P4? It has a very bad branch mispredict penalty, so 
putting the predictable branch first could explain the big difference you 
see..

Dscho's bigger patch probably helps more on an in-order architecture, and 
should be equally good on a P4 (or Opteron). On Core 2, neither of the 
patches seem to make a huge difference.

			Linus
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