The artifact's executions speed doesn't seem to be Cranelift's priority. They're instead focusing on compilation speed and security. Those are still useful in Rust for debug builds at least. That's when we need a quick turnaround time and as much verification as possible.
> The resulting code performs on average 14% better than LLVM -O0, 22% slower than LLVM -O1, 25% slower than LLVM -O2, and 24% slower than LLVM -O3
So it is more like 24% slower, not 14%. Perhaps a typo (24/14), or they got the direction mixed up (it is +14 vs -24), or I'm reading that wrong?
Regardless, those numbers are on a particular set of database benchmarks (TPC-H), and I wouldn't read too much into them.