SchedDFS: Initial support for nested subtrees.

This is mostly refactoring, along with adding an instruction count
within the subtrees and ensuring we only look at data edges.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@173420 91177308-0d34-0410-b5e6-96231b3b80d8
lit/ShUtil.py: Deprecate '!' in shell expression. It is not sh-compatible.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@173421 91177308-0d34-0410-b5e6-96231b3b80d8
whitespace

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@173423 91177308-0d34-0410-b5e6-96231b3b80d8
ArrayRef reverse iterators.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@173424 91177308-0d34-0410-b5e6-96231b3b80d8
MIsched: Improve the interface to SchedDFS analysis (subtrees).

Allow the strategy to select SchedDFS. Allow the results of SchedDFS
to affect initialization of the scheduler state.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@173425 91177308-0d34-0410-b5e6-96231b3b80d8
SchedDFS: Complete support for nested subtrees.

Maintain separate per-node and per-tree book-keeping.
Track all instructions above a DAG node including nested subtrees.
Seperately track instructions within a subtree.
Record subtree parents.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@173426 91177308-0d34-0410-b5e6-96231b3b80d8
ScheduleDAG: Added isBoundaryNode to conveniently detect a common corner case.

This fixes DAG subtree analysis at the boundary.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@173427 91177308-0d34-0410-b5e6-96231b3b80d8