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

[Andrei Alexandrescu]

On 9/20/13 9:28 AM, Joseph Rushton Wakeling wrote:
> 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.

I think I know how to fix that. I hypothesize it's about using actual 
increment instead of a stored value "step" for the particular case when 
step is 1.

Andrei