class templates and static if

[Ali Çehreli]

On 02/27/2012 02:06 PM, Jonathan M Davis wrote:

 > I'm not saying that dmd doesn't ever optimize switch statements. I'm just
 > saying that as I understand it, it doesn't always do so (its 
performance with
 > ranged case statements isn't great for instance). Odds are that it _does_
 > optimize straight integer case statements fairly well, because that's the
 > classic C stuff (and if you've verified that, all the better - I 
haven't).

I have played with this optimization recently. (Could be dmd 2.057.) No, 
dmd did not optimize a straightforward switch statement over a ubyte 
expression with about two hundred ubyte cases.

The assembly contained conditional jump statements, not a table. And 
yes, I did try with -O.

But I am not sure that a lookup table really is an optimization with 
modern CPUs. A series of conditional jumps that fit the CPU's cache 
could be faster than a table that's outside of the cache. I think 
accessing the cache is hundreds of times faster than accessing memory 
outside of the cache.

Ali