Move a few containers out of ScheduleDAGInstrs::BuildSchedGraph
and into the ScheduleDAGInstrs class, so that they don't get
destructed and re-constructed for each block. This fixes a
compile-time hot spot in the post-pass scheduler.

To help facilitate this, tidy and do some minor reorganization
in the scheduler constructor functions.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@62275 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/Target/PowerPC/PPCISelDAGToDAG.cpp b/lib/Target/PowerPC/PPCISelDAGToDAG.cpp
index fdbd126..a86604b 100644
--- a/lib/Target/PowerPC/PPCISelDAGToDAG.cpp
+++ b/lib/Target/PowerPC/PPCISelDAGToDAG.cpp
@@ -44,7 +44,7 @@
     unsigned GlobalBaseReg;
   public:
     explicit PPCDAGToDAGISel(PPCTargetMachine &tm)
-      : SelectionDAGISel(*tm.getTargetLowering()), TM(tm),
+      : SelectionDAGISel(tm), TM(tm),
         PPCLowering(*TM.getTargetLowering()),
         PPCSubTarget(*TM.getSubtargetImpl()) {}