[Bug tree-optimization/87147] [9 Regression] GCC miscompiles at -O3 on valid code

[rguenth at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=87147

--- Comment #2 from Richard Biener <rguenth at gcc dot gnu.org> ---
OK, so the issue is that while non-iterating RPO VN assumes executable
backedges it fails to mark destination blocks as executable.

Testing fix.