https://gcc.gnu.org/bugzilla/show_bug.cgi?id=69896
--- Comment #9 from Jakub Jelinek <jakub at gcc dot gnu.org> --- Created attachment 37810 --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=37810&action=edit gcc6-pr69896.patch And here is the unfinished BIT_FIELD_REF folding patch. This fixes one issue, where we are asking for a 1x vector out of say 2x vector, and we get incorrectly the element instead of { element }. But that just seems to be a tip of an iceberg - we can then end up with say VECTOR_CST with a single element inside of a CONSTRUCTOR and might be assuming that we get the element type instead of the 1x vector, etc. I'd say we really should avoid the 1x vectors at the tree/gimple levels as much as possible.
