What does "32<->64" mean?

vector unsigned long long unpacked;
vector unsigned int packedl, packedr;

unpacked = vec_pack(packedl, packedr);
packedl = vec_unpackh(unpacked);
packedr = vec_unpackl(unpacked);

What should the semantics of this be?  There are four 32-bit elts each
in packedl and packedr, which of those go where in unpacked?

I think what you want to do can be expressed with just two or maybe three
existing builtins, but it's not clear to me exactly what you want.

Oh my bad, I got it backwards

vector unsigned long long unpackedl, unpackedr;
vector unsigned int packed;

packed = vec_pack(unpackedl, unpackedr);
unpackedl = vec_unpackh(packed);
unpackedr = vec_unpackl(packed);

The point is that it is similar to the other pack/unpack unfunctions. Yet somehow this one doesn't exist (probably because there is no hardware instruction for it).

vec_unpack* works on vectors of signed integers only, not unsigned.

You need to target at least power8 (-mcpu=power8) to get the long long
versions of this, i.e. the vpkudum and vupk[hl]sw instructions.

This is all documented correctly, as far as I see?  In the ISA doc,
in the ABI doc, and in the GCC docs?  (Power8 is ISA 2.07, we could add
some clarification for that).

Ahh, sorry for wasting your time. I didn't notice the signed requirement, which is why it didn't work.

Note that vec_pack works for unsigned as well.

For vec_unpack[hl] of unsigned you can do a vec_merge[hl] instead (with the
first arg a zero vector).