It would be useful to have a tool that can simulate the impact of a hypothetical optimization to a function/query. For example, let's say someone has an idea that allows speeding up typeck_tables_of by 10% but it's kind of complicated and they don't know if they should put in the effort of implementing it. With all the caching going on in the compiler it is non-trivial to predict the effect of such an optimization on total compilation time.

However, given a concrete profile, it should be possible to compute an approximation of the same profile with the hypothetical speed-up applied. For the single-threaded case it should be pretty accurate even.