986d9f104b
For things with easily pre-checked overflow conditions -- shifts and unsigned subtraction -- write then checked methods in such a way that we stop emitting wrapping versions of them. For example, today <https://rust.godbolt.org/z/qM9YK8Txb> neither ```rust a.checked_sub(b).unwrap() ``` nor ```rust a.checked_sub(b).unwrap_unchecked() ``` actually optimizes to `sub nuw`. After this PR they do.
The goal of this directory is to track the quality of MIR that is given to codegen in a standard -O condiguration.
As such, feel free to --bless whatever changes you get here, so long as doing so doesn't add substantially more MIR.