[Bug c++/118817] [14/15 Regression] stringop-overflow and array-bound error with LTO/O3

[rguenth at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=118817

--- Comment #7 from Richard Biener <rguenth at gcc dot gnu.org> ---
Oh, and we _do_ fold the stmt, but only w/o following SSA edges by means of
gimple_build which is restricted.  We fold the last stmt "extra" but only
inplace and w/o following any edges.

We are also not folding the NARY in place when PHI-translating it, we only
try to simplify it down to a constant or SSA name.  During VN itself we
assume folded stmts, so there that's OK, but PHI translation should
possibly re-fold before the lookup, so it probably should work more like
vn_nary_build_or_lookup_1, mapping back a NARY result to the nary.
fully_constant_expression via vn_nary_simplify does already all the hard work,
we just throw away the result.