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/Mips/MipsISelDAGToDAG.cpp b/lib/Target/Mips/MipsISelDAGToDAG.cpp
index 099fb53..768ab65 100644
--- a/lib/Target/Mips/MipsISelDAGToDAG.cpp
+++ b/lib/Target/Mips/MipsISelDAGToDAG.cpp
@@ -55,7 +55,7 @@
  
 public:
   explicit MipsDAGToDAGISel(MipsTargetMachine &tm) :
-  SelectionDAGISel(*tm.getTargetLowering()),
+  SelectionDAGISel(tm),
   TM(tm), Subtarget(tm.getSubtarget<MipsSubtarget>()) {}
   
   virtual void InstructionSelect();