[Bug rtl-optimization/94864] Failure to combine vunpckhpd+movsd into single vunpckhpd

[segher at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=94864

--- Comment #3 from Segher Boessenkool <segher at gcc dot gnu.org> ---
vec_duplicate of vec_select is just a vec_select.  Any vec_merge is a
vec_select as well, as you say.

Canonicalisation should make vec_select always.

We probably should have canonicalisation rules for this, so that we do
not get all those rtxes in the instruction stream at all.