Ppxlib Performance [ppxlib-perf]

In Ppxlib issue 436, Sonja described a performance analysis related to Ppxlib's derivers.

Why do very simple AST passes take so long? E.g., for drivers containing derivers, why do the AST passes turning off the warnings w32 and w60 take so long?

Why do very simple AST passes take so long? E.g., for drivers containing derivers, why do the AST passes turning off the warnings w32 and w60 take so long?

I decide to take a look and report my findings here.