You're right -- I got nerd-sniped by this, and ended up rewriting the benchmarks in Rust. The compiler successfully inlines the square root operation, simplifies the exponentiation into multiplication and then does common-subexpression elimination over it, but no induction variable analysis, and therefore also no loop-invariant code motion. Here's it is in Godbolt:

https://godbolt.org/z/Pa6cqd1fb

But the funny thing is, I tried it on my machine, and guess what, the "unoptimised" version is consistently between 4 and 5 times faster than the hand-optimised variants:

https://gist.github.com/amnn/4be5c05975c250d0ea88b62c03f1719...

So that's fun.