Why is D slower than LuaJIT?

[Marco Leise]

Am Wed, 22 Dec 2010 17:04:21 -0500
schrieb Andreas Mayer <spam at bacon.eggs>:

> 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?


Actually "D" is 1.5 times faster on my computer*:

LDC**           ========     18 ms
GDC***          ===========  25 ms
LuaJIT 2.0.0 b7 ============ 27 ms
DMD             ========================================= 93 ms

All compilers based on DMD 2.062 front-end.
* 64-bit Linux, 2.0 Ghz Mobile Core 2 Duo.
** based on LLVM 3.2
*** based on GCC 4.7.2

I modified the iota template to more closely reflect the one
used in the original Lua code: ---------------------

import std.algorithm;
import std.stdio;
import std.traits;

auto iota(B, E)(B begin, E end)	if (isFloatingPoint!(CommonType!(B, E))) {
	alias CommonType!(B, E) Value;
	static struct Result
	{
		private Value start, end;
		@property bool empty() const { return start >= end; }
		@property Value front() const { return start; }
		void popFront() { start++; }
	}
	return Result(begin, end);
}

void main() {
	auto L  = iota(0.0, 10000000.0),
	     L2 = map!(a => a / 2)(L),
	     L3 = map!(a => a + 2)(L2),
	     V  = reduce!((a, b) => a + b)(L3);

	writefln("%f", V);
}

-- 
Marco