Have the selection dag grab TargetLowering off of the subtarget
inside init rather than have it passed in as an argument.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@219270 91177308-0d34-0410-b5e6-96231b3b80d8
Reset the target options and optimization level as the first
thing we do inside selection dag. This code needs to be
migrated to queries on the function rather than global
data, but this organizes things before we start grabbing
the subtarget.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@219271 91177308-0d34-0410-b5e6-96231b3b80d8
Cache SelectionDAGISel TargetInstrInfo lookups on the class and
propagate. Also use the TargetSubtargetInfo and the MachineFunction
and move TargetRegisterInfo query closer to uses.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@219273 91177308-0d34-0410-b5e6-96231b3b80d8