The SLP-Vectorizer can merge a set of scalar stores into a single vectorized store. Merge DIAssignID intrinsics from the scalar stores onto the new vectorized store.
The test currently requires x86 - if anyone knows any command line options to tell opt to enable the vectorization in the test without the triple please let me know.
This raises the tantalising question of why the store goes in the middle of the dbg.assigns, and whether that's going to mean we generate a different location list.
(Not a big deal IMO).