Bartosz Milewski seems to like D more than C++ now :)

[Joseph Rushton Wakeling]

On 20/09/13 18:01, Walter Bright wrote:
> I know that, at least with dmd's back end, it's because the optimizer was built
> around the kinds of things that C++ programmers tend to write. The D
> range/algorithm generates unusual code (for the back end) that the back end
> doesn't optimize for.
>
> For example, ranges tend to lump several variables together and call them a
> 'struct'. The back end is not tuned to deal with structs as an aggregate of
> discreet 'variables', meaning that such variables don't get assigned to
> registers. Structs are treated as a lump.
>
> This is not a fundamental performance problem with D.
>
> The back end needs to be improved to "dis-aggregate" structs back into discreet
> variables.

I wouldn't single out DMD for criticism -- I don't know to what extent the 
underlying reasons overlap, but all the compilers cope less well with 
range-based material than they might in theory.

The canonical example would be something like,

     foreach (i; iota(10)) { ... }

which in theory shouldn't be any slower than,

     foreach (i; 0 .. 10) { ... }

but in practice is, no matter what the compiler.