How are 2D static arrays allocated?

[Lars Kyllingstad]

Jarrett Billingsley wrote:
> Performance of dynamic arrays is the same no matter where their data
> is.  Fixed-size 2D arrays are not faster _because_ they are on the
> stack, they just happen to be allocated on the stack.  They are faster
> (usually) because they don't need two pointer dereferences.  You can
> allocated a fixed-size 2D array on the heap (well.. inside a struct or
> class anyway) and it will be just as fast.

Your "usually" interests me. I was under the impression, and it seems 
quite logical, that static arrays are faster than dynamic ones. However, 
recently I did some simple experiments with matrix operations 
(multiplication, etc.), in which performance was actually a little bit 
better for dynamic arrays.

Is there a general "rule" for when dynamic arrays are faster than static 
ones, and vice versa?

Also, I tried multiplying large matrices both using arrays in D and 
using a C BLAS implementation. The BLAS algorithm is the same as the one 
I've written in D, and additionally includes a lot of runtime checks. 
Still, multiplication using BLAS was about four times faster. Is this 
simply because C compilers are a lot better at optimisation than the D 
compilers?

-Lars