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/X86/X86ISelDAGToDAG.cpp b/lib/Target/X86/X86ISelDAGToDAG.cpp
index 907aa69..44c43a2 100644
--- a/lib/Target/X86/X86ISelDAGToDAG.cpp
+++ b/lib/Target/X86/X86ISelDAGToDAG.cpp
@@ -126,7 +126,7 @@
 
   public:
     X86DAGToDAGISel(X86TargetMachine &tm, bool fast)
-      : SelectionDAGISel(*tm.getTargetLowering(), fast),
+      : SelectionDAGISel(tm, fast),
         TM(tm), X86Lowering(*TM.getTargetLowering()),
         Subtarget(&TM.getSubtarget<X86Subtarget>()),
         OptForSize(false) {}