Perlin noise benchmark speed

[weaselcat via Digitalmars-d]

On Friday, 20 June 2014 at 12:32:39 UTC, Nick Treleaven wrote:
> Hi,
> A Perlin noise benchmark was quoted in this reddit thread:
>
> http://www.reddit.com/r/rust/comments/289enx/c0de517e_where_is_my_c_replacement/cibn6sr
>
> It apparently shows the 3 main D compilers producing slower 
> code than Go, Rust, gcc, clang, Nimrod:
>
> https://github.com/nsf/pnoise#readme
>
> I initially wondered about std.random, but got this response:
>
> "Yeah, but std.random is not used in that benchmark, it just 
> initializes 256 random vectors and permutates 256 sequential 
> integers. What spins in a loop is just plain FP math and array 
> read/writes. I'm sure it can be done faster, maybe D compilers 
> are bad at automatic inlining or something. "
>
> Obviously this is only one person's benchmark, but I wondered 
> if people would like to check their code and suggest reasons 
> for the speed deficit.

I saw this thread when searching for something on the site, been 
a few months since anyone posted-

I fixed the D flags, gdc is now about 15% faster than the second 
fastest in the benchmark(C - gcc) which obviously puts D in first.
some notes:

LDC is missing _tons_ of inline opportunities, killing it in 
comparison to GDC. I think GDC inlined pretty much everything. 
LDC is about 50% slower.

Also, AFAICT there's no fast-math switch for LDC(enabling this 
for GDC might actually be compromising it though : ) )

I think LDC turns the floor in std.math into the same as the stdc 
one, but GDC does not. std.math.floor is still abysmally slow, I 
thought it was because it was still using reals but that does not 
seem to be the case. GDC slows to a crawl(10-20x slower) if you 
replace the stdc floor with the one in std.math(just remove the 
alias)

I thought this might be interesting to someone(i.e, LDC/GDC folks 
or phobos math folks)

bye.