GHC 8.4.1-rc1 is slower on a ray-tracer project

[Vassil Ognyanov Keremidchiev]

Hello!

I have a small ray-tracer project: https://bitbucket.org/varosi/cgraytrace
>From time to time I'm testing it with different GHC versions including ARM.

Yesterday I successfully compiled it with GHC 8.4.1-rc1. I got compiled it
with 8.2.2 and 8.0.2 as well and ran tests for about a minute each on my
Intel Core i7 machine on Windows 10 x64.

I got this results:

GHC 8.4.1-rc1
Average time: 61.87s

GHC 8.2.2
Average time: 60.09s

GHC 8.0.2
Average time: 67.07s

Application is doing multi-threaded brute-force ray-tracing with GI, so a
lot of rays are shot around.
It seems that previous GHC 8.2.2 is doing better on a high-performance
application. I know that this test is too simple, but it is on a real world
problem and application and not one for whole purpose of benchmarking.

Any thoughts are welcome!
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