[Bug target/86891] [9 Regression] __builtin_sub_overflow incorrect for unsigned types

[jakub at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=86891

--- Comment #6 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
Not everything is optimized during GIMPLE optimizations, we have simplify-rtx.c
and combine.c for a reason.  So, if it is possible to accurately describe the
behavior of the instruction without UNSPECs, it is generally preferable to do
so.