Another case of DCE deleting live code

[Richard Kenner]

    > Yes.  The tag_set we compute in get_tmt_for must be exactly what
    > get_alias_set returns.  We use that to determine which pointers get the
    > same alias set and other checks.

    Why isn't get_alias_set returning 0 for types with that flag set, which 
    would avoid anything but get_alias_set being modified?

Because the alias set of the *type* isn't zero.  What's zero is the alias
set of anything *dereferenced* via the type.