[Bug tree-optimization/77399] Poor code generation for vector casts and loads

[rguenth at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=77399

--- Comment #4 from Richard Biener <rguenth at gcc dot gnu.org> ---
Note that this is a patten matching issue that could be quite easily fixed in
tree-ssa-forwprop.c:simplify_vector_constructor (which currently recognizes
a VEC_PERM but it should be easy to handle intermediate conversions meaning
to handle even pack-/unpack-style permuted (float-int) conversions).

Just to give a hint where this can be handled.  [yeah, match.pd but there
we'd need a way to handle variable-length stuff like CONSTRUCTORs first...,
see the "awkward" handling of BIT_FIELD_REF <CONSTRUCTOR, ..> there]