Camille Gillot

There is a subtle ICE in `incremental-ignore-spans` mode used by the incremental test suite. This PR is blocked on me fixing that ICE.

The perf impact has to be expected. Perf runs the compiler in incremental+optimizations mode, which is not a typical work case. The faster LLVM optimizations do not happen as often...

@bors try @rust-timer queue

@bors try @rust-timer queue

@bors try @rust-timer queue

@bors try @rust-timer queue

@bors try @rust-timer queue

@bors try @rust-timer queue

r? compiler

Will this also fix the ICE in https://github.com/rust-lang/rust/issues/57404?