Do not shrink wrap live interval in a mbb if it's livein any of its successor blocks. The mbb can be revisited again after all of the successors are processed.

llvm-svn: 58184

llvm-svn: 58174

If val# def is ~0U, meaning it's defined by a PHI, and it's previously split, spill before the barrier because it's impossible to determine if all the defs are spilled in the same spill slot.

llvm-svn: 58129

llvm-svn: 58102

llvm-svn: 58072

llvm-svn: 58068

Committing a good chunk of the pre-register allocation live interval splitting pass. It's handling simple cases and appear to do good things. Next: avoid splitting an interval multiple times; renumber registers when possible; record stack slot live intervals for coloring; rematerialize defs when possible.

llvm-svn: 58044

llvm-svn: 57847