AMDGPU: Start to use AV classes for unknown vector class
Use AGPR+VGPR superclasses for gfx90a+. The type used
for the class should be the broadest possible class, to
be contextually restricted later. InstrEmitter clamps these
to the common subclass of the context use instructions, so we're
best off using the broadest possible class for all types.
Note this does very little because we only use VGPR classes
for FP types (though this doesn't particularly make any sense),
and we legalize normal loads and stores to integer.
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