I'm not entirely sure whether this belongs to LLVM or rust (I haven't triaged), but let's start here.

I tried this code: https://godbolt.org/z/E5W74re7v
which could potentially folded to a single constant, but the optimizer fails to recognize.

Changing the inner if condition from t + s + r == 10 to t + s == 10 results into the LLVM IR being a single line function:
ret i64 63000000000. In godbolt: https://godbolt.org/z/zfchrszbW

I would expect both cases to fold to a constant, but maybe I'm missing something here.