Why is D slower than LuaJIT?

[Pelle Månsson]

On 12/22/2010 11:04 PM, Andreas Mayer wrote:
> To see what performance advantage D would give me over using a scripting language, I made a small benchmark. It consists of this code:
>
>>     auto L = iota(0.0, 10000000.0);
>>     auto L2 = map!"a / 2"(L);
>>     auto L3 = map!"a + 2"(L2);
>>     auto V = reduce!"a + b"(L3);
>
> It runs in 281 ms on my computer.
>
> The same code in Lua (using LuaJIT) runs in 23 ms.
>
> That's about 10 times faster. I would have expected D to be faster. Did I do something wrong?
>
> The first Lua version uses a simplified design. I thought maybe that is unfair to ranges, which are more complicated. You could argue ranges have more features and do more work. To make it fair, I made a second Lua version of the above benchmark that emulates ranges. It is still 29 ms fast.
>
> The full D version is here: http://pastebin.com/R5AGHyPx
> The Lua version: http://pastebin.com/Sa7rp6uz
> Lua version that emulates ranges: http://pastebin.com/eAKMSWyr
>
> Could someone help me solving this mystery?
>
> Or is D, unlike I thought, not suitable for high performance computing? What should I do?
>

I changed the code to this:

     auto L = iota(0, 10000000);
     auto L2 = map!"a / 2.0"(L);
     auto L3 = map!"a + 2"(L2);
     auto V = reduce!"a + b"(L3);

and ripped the caching out of std.algorithm.map. :-)

This made it go from about 1.4 seconds to about 0.4 seconds on my 
machine. Note that I did no rigorous or scientific testing.

Also, if you really really need the performance you can change it all to 
lower level code, should you want to.