[Bug tree-optimization/64567] missed optimization: redundant test before clearing bit(s)

[schwab@linux-m68k.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=64567

--- Comment #1 from Andreas Schwab <schwab@linux-m68k.org> ---
This transformation is incorrect if the lvalue may be pointing to a read-only
object.