Slow performance compared to C++, ideas?

[nazriel]

On Friday, 31 May 2013 at 01:26:13 UTC, finalpatch wrote:
> Recently I ported a simple ray tracer I wrote in C++11 to D. 
> Thanks to the similarity between D and C++ it was almost a line 
> by line translation, in other words, very very close. However, 
> the D verson runs much slower than the C++11 version. On 
> Windows, with MinGW GCC and GDC, the C++ version is twice as 
> fast as the D version. On OSX, I used Clang++ and LDC, and the 
> C++11 version was 4x faster than D verson.  Since the 
> comparison were between compilers that share the same codegen 
> backends I suppose that's a relatively fair comparison.  (flags 
> used for GDC: -O3 -fno-bounds-check -frelease,  flags used for 
> LDC: -O3 -release)
>
> I really like the features offered by D but it's the raw 
> performance that's worrying me. From what I read D should offer 
> similar performance when doing similar things but my own test 
> results is not consistent with this claim. I want to know 
> whether this slowness is inherent to the language or it's 
> something I was not doing right (very possible because I have 
> only a few days of experience with D).
>
> Below is the link to the D and C++ code, in case anyone is 
> interested to have a look.
>
> https://dl.dropboxusercontent.com/u/974356/raytracer.d
> https://dl.dropboxusercontent.com/u/974356/raytracer.cpp

Greetings.

After few fast changes I manage to get such results:
[raz at d3 tmp]$ ./a.out
rendering time 276 ms
[raz at d3 tmp]$ ./test
346 ms, 814 μs, and 5 hnsecs


./a.out being binary compiled with clang++ ./test.cxx -std=c++11 
-lSDL -O3
./test being binary compiled with ldmd2 -O3 -release -inline 
-noboundscheck ./test.d (Actually I used rdmd with 
--compiler=ldmd2 but I omitted it because it was rather long cmd 
line :p)


Here is source code with changes I applied to D-code (I hope you 
don't mind repasting it): http://dpaste.dzfl.pl/84bb308d

I am sure there is way more room for improvements and at minimum 
achieving C++ performance.