Add a -regalloc=default option that chooses a register allocator based on the -O
optimization level.

This only really affects llc for now because both the llvm-gcc and clang front
ends override the default register allocator. I intend to remove that code later.

llvm-svn: 104904
7 files changed
tree: 5636571fd4c6a9ae72d11d6b206fc54050f9c8f5
  1. clang/
  2. compiler-rt/
  3. libcxx/
  4. llvm/