Error running concurrent process and storing results in array

[data pulverizer]

On Wednesday, 6 May 2020 at 23:10:05 UTC, data pulverizer wrote:
> The -O3 -O5 optimization on the ldc compiler is instrumental in 
> bringing the times down, going with -02 based optimization even 
> with the other flags gives us ~ 13 seconds for the 10,000 
> dataset rather than the very nice 1.5 seconds.

What is the difference between -O2 and -O3 ldc2 compiler 
optimizations?