Moving to D

[bearophile]

Adrian Mercieca:

> How does D square up, performance-wise, to C and C++ ?
> Has anyone got any benchmark figures?

DMD has an old back-end, it doesn't use SSE (or AVX) registers yet (64 bit version will use 8 or more SSE registers), and sometimes it's slower for integer programs too. I've seen DMD programs slow down if you nest two foreach inside each other. There is a collection of different slow microbenchmarks.

But LDC1 is able to run D1 code that looks like C about equally fast as C or sometimes a bit faster.

DMD2 uses thread local memory on default that in theory slows code down a bit if you use global data, but I have never seen a benchmark that shows this slowdown clearly (an there is __gshared too, but sometimes it seems a placebo).

If you use higher level constructs your program will often go slower.

Often one of the most important things for speed is memory management, D encourages to heap allocate a lot (class instances are usually on the heap), and this is very bad for performance, also because the built-in GC doesn't have an Eden generation managed as a stack. So if you want more performance you must program like in Pascal/Ada, stack-allocating a lot, or using memory pools, etc. It's a lot a matter of self-discipline while you program.


> Also, is D more of a Windows oriented language?
> Do the Linux and OSX versions get as much attention as the Windows one?

The Windows version is receiving enough attention, it's not ignored by Walter. But I think for some time the 64 bit version will not be Windows too.

Bye,
bearophile