[Bug target/79218] Missed swap optimization on powerpc64le simple test case

[wschmidt at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=79218

--- Comment #2 from Bill Schmidt <wschmidt at gcc dot gnu.org> ---
At the moment, swap optimization doesn't attempt to handle __int128 values, for
which swaps don't deal with elements of a vector, but pieces of a cohesive
integer value.  This may be overly conservative, and we may want to see what
breaks if this is relaxed by now.  But I wouldn't do this before GCC 8, because
it's a large change.