This is #3014 with cad5cce reverted for testing.
This is part 2 of 2 of #4801 (which closes #4654). That PR was split in two to allow a stage0 update between declaring the `usize` functions and using them where they are needed.
reset
ResetReuse
We conjecture this is the cause for the segfaults when compiling Mathlib with #4006