- Prevent some functions from being inlined to eliminate the code size bloat

- Prevent some functions from being inlined to eliminate the code size bloat
  introduced by previous commit.
- SelectCode now returns a SDNode*. If it is not null, the selected node
  produces the same number of results as the input node. The seletion loop
  is responsible for calling ReplaceAllUsesWith() to replace the input node
  with the output target node. For other cases, e.g. when load is folded,
  the selection code is responsible for calling ReplaceAllUsesOfValueWith()
  and SelectCode returns NULL.
- Other clean ups.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@29602 91177308-0d34-0410-b5e6-96231b3b80d8