[Bug sanitizer/123873] UBSAN confuses optimizer

[jakub at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=123873

--- Comment #1 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
UBSAN is a development tool, not something meant for production uses.
And obviously it affects lots of optimizations, the added instrumentations
prevent various optimizations and we need to disable other optimizations (most
importantly assumption that no objects appear at address 0), otherwise the
instrumentation is optimized away.