[Bug sanitizer/81387] UBSAN consumes too much memory at -O2

[jakub at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=81387

--- Comment #5 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
Maybe we should just disable the REE pass if we can predict from number of
basic blocks, their sizes or number of edges that DF_UD_CHAIN + DF_DU_CHAIN
computation will be really expensive.