Used to work with cryengine some time ago. That is by far the worst c++ codebase i've ever seen.
Many very highly performance tuned applications I saw in the wild would fall into the category of "horrible codebase" when looked at through that lens.
I understand that you might think that messy could mean it's fine tuned for performance. In this case, I highly doubt it and think it's more reasonable to think it's messy because they had deadlines.
The messy part isn't about performance optimizations. It's more about things that got crammed in there and only works for a very specific subset of parameters. And even then you can't be sure it'll work...
I don't blame the programmers, it feels they had deadlines to uphold from managment.
https://www.viva64.com/en/b/0417/
https://www.viva64.com/en/b/0495/
https://www.viva64.com/en/b/0574/
I'm not endorsing pvs studio nor am I saying it's bad. Try out some tools and see what works best for you.
This is my own experience. The teams that spent the most time on standards usually had the least pressure, in terms of things like deadlines. Once the focus of the team shifts to having to ship things, there is less time to worry about having 100% code coverage (to pull out an arbitrary number), and so forth. Code review can slip into flagging only things that really matter, and leaving nitpicks for another day.
The issue with games in particular is probably partly due to the performance optimizations being directed at a moving target (it's not just your supercomputer nodes, it's every computer CPU). C++ doesn't really help you much in that regard (or at least better know but certainly not 10 years ago)
If we want the code to be clean or performant, we will likely have to spend time iterating on and pruning the code. Let’s assume that improving performance and improving cleanliness are at best orthogonal, at worst opposing.
The project has a limited amount of time, particularly for games, which often have a relatively low roof for how much maintenance the code will need.
The project has a budget on time to spend between cleanliness and maintenance. Games need high performance and relatively little maintenance, so they are more likely to spend their budget on much more performance than cleanliness.
(Game engines meant for heavy reuse such as Frostbite and Unreal Engine would likely have a much more even split, and similar for games which are likely to receive recurring and invasive updates. I would expect Fortnite’s code to be fairly clean as games go, for example.)
Open source generally leads to better quality code, since it's the best way to attract other developers to contribute to it.
So I'm rarely interested by any accomplished project that opens its code.
For example, if microsoft opened its OS, I doubt developers would really try to do things with it. The windows kernel would obviously be high quality code, but a lot of the rest is probably short lived garbage.
There's terrible code all over the place, although it is definitely true that no one's going to clean up - even source available - proprietary code out of kindness of their heart.
Just as an example, this is why Bitwarden started getting some automated testing - lots of propelled bumping github issues about it in order to get it more visibility
I think you got lost in your triple negative there