Why DMD is so slow?

[Frits van Bommel]

Marco wrote:
> I have written the code reported below to test execution speed of D in Windows and I have found that the same code is about 10 times slower if compiled using DMD w.r.t. GCD: 1.9 minutes in DMD vs 1.84 seconds in GDC ! Is there perhaps something wrong? why such a difference?
[snip]
>  cdouble a, b, c, z;
>  double mand_re = 0, mand_im = 0;
[snip]

IIRC DMD's backend is just not as good at optimizing floating-point code 
as GDC's backend (GCC) is.