The machine scheduler currently biases register copies to/from
physical registers to be closer to their point of use / def to
minimize their live ranges. This change extends this to also physical
register assignments from immediate values.
This causes a reduction in reduction in overall register pressure and
minor reduction in spills and indirectly fixes an out of register assertion (PR39391).
Most test changes are from minor instruction reorderings and register
name selection changes and direct consequences of that.