Unaligned block moves and MEM_ALIGN re-broken

[Richard Kenner]

    However, set_mem_attributes() looks to MEM_ALIGN for its preliminary
    guess at the alignment, which uses the default MODE alignment because
    memattrs is not yet set!  When we compare the preliminary alignment
    against the alignment specified by the tree, it is smaller and we
    prefer the alignment specified by the MODE.  

How can the alignment in the tree be smaller and yet DImode be assigned
as its mode?  You can't have DImode unless the alignment is at least 64.