[Bug rtl-optimization/63375] [4.8/4.9/5 Regression] reordering of reads across fences

[rguenth at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=63375

--- Comment #15 from Richard Biener <rguenth at gcc dot gnu.org> ---
Note that the technical issue here is that the memory is considered as not
aliased and thus all barriers would need to explicitely reference it as
used and clobbered.