Scalability in std.parallelism

[Stanislav Blinov]

Don't rely on dmd when making raw performance tests.

On my machine (i3-2100, two cores):

dmd2 -O -release -inline

3.14159 took 368[ms]
3.14159 took 713[ms]
Speedup 1.9375
-5.80829e+09 took 61[ms]
-5.80829e+09 took 201[ms]
Speedup 3.29508

ldc2 -O3 -release

3.14159 took 360[ms]
3.14159 took 718[ms]
Speedup 1.99444
-5.80829e+09 took 0[ms]
-5.80829e+09 took 0[ms]
Speedup -nan

ldc2 -O3 -release -vectorize -vectorize-loops

3.14159 took 193[ms]
3.14159 took 721[ms]
Speedup 3.73575
-5.80829e+09 took 0[ms]
-5.80829e+09 took 0[ms]
Speedup -nan