Bias physical register immediate assignments

Bias physical register immediate assignments

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-registers
assertion (PR39391).

Most test changes are from minor instruction reorderings and register
name selection changes and direct consequences of that.

Reviewers: MatzeB, qcolombet, myatsina, pcc

Subscribers: nemanjai, jvesely, nhaehnle, eraman, hiraditya,
  javed.absar, arphaman, jfb, jsji, llvm-commits

Differential Revision: https://reviews.llvm.org/D54218

llvm-svn: 346894