The code-generator is currently not able to handle scalable vectors of
<vscale x 1 x eltty>. The usual "fix" for this until it is supported is
to mark the costs of loads/stores with an invalid cost, preventing the
vectorizer from vectorizing at those factors. But on rare occasions
loops do not contain load/stores, only reductions.
So whilst this is still unsupported return an invalid cost to avoid
selecting vscale x 1 VFs. The cost of a reduction is not currently used
by the vectorizer so this adds the cost to the add/mul/and/or/xor or
min/max that should feed the reduction. It includes reduction costs
too, for completeness. This change will be removed when code-generation
for these types is sufficiently reliable.
Fixes#99760
0b745a1084