SelectionDAG compile time improvement.

One of the phases of SelectionDAG is LegalizeVectors. We don't need to sort the DAG and copy nodes around if there are no vector ops.

Speeds up the compilation time of SelectionDAG on a big scalar workload by ~8%.



git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@175929 91177308-0d34-0410-b5e6-96231b3b80d8
Formatting.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@175931 91177308-0d34-0410-b5e6-96231b3b80d8
Add a TODO and explain when we can get rid of the isMain field.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@175932 91177308-0d34-0410-b5e6-96231b3b80d8
Add a field to the compile unit of where we plan on splitting out
the debug info for -gsplit-dwarf so we can encode that location
in the skeleton cu.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@175933 91177308-0d34-0410-b5e6-96231b3b80d8
Use getSplitDebugFilename when constructing the skeleton cu and
update testcase accordingly to give the correct name to the cu.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@175934 91177308-0d34-0410-b5e6-96231b3b80d8