Rebased all three patches and made some small changes to the second one:
- removed sub and abd optabs from commutative_optab_p, I suspect this 
was a copy paste mistake,
- removed what I believe to be a superfluous switch case in vectorizable 
conversion, the one that was here:
+  if (code.is_fn_code ())
+     {
+      internal_fn ifn = as_internal_fn (code.as_fn_code ());
+      int ecf_flags = internal_fn_flags (ifn);
+      gcc_assert (ecf_flags & ECF_MULTI);
+
+      switch (code.as_fn_code ())
+	{
+	case CFN_VEC_WIDEN_PLUS:
+	  break;
+	case CFN_VEC_WIDEN_MINUS:
+	  break;
+	case CFN_LAST:
+	default:
+	  return false;
+	}
+
+      internal_fn lo, hi;
+      lookup_multi_internal_fn (ifn, &lo, &hi);
+      *code1 = as_combined_fn (lo);
+      *code2 = as_combined_fn (hi);
+      optab1 = lookup_multi_ifn_optab (lo, !TYPE_UNSIGNED (vectype));
+      optab2 = lookup_multi_ifn_optab (hi, !TYPE_UNSIGNED (vectype));
      }

I don't think we need to check they are a specfic fn code, as we look-up 
optabs and if they succeed then surely we can vectorize?

OK for trunk?

Kind regards,
Andre