mi-sched: Don't call MBB.size() in initSUnits. The driver already has instr count.

This fixes a pathological compile time problem with very large blocks
and lots of scheduling boundaries.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@189116 91177308-0d34-0410-b5e6-96231b3b80d8

include/llvm/CodeGen/MachineScheduler.h

@@ -293,8 +293,7 @@ public:
   void enterRegion(MachineBasicBlock *bb,
                    MachineBasicBlock::iterator begin,
                    MachineBasicBlock::iterator end,
-                   unsigned endcount);
-
+                   unsigned regioninstrs) LLVM_OVERRIDE;
 
   /// Implement ScheduleDAGInstrs interface for scheduling a sequence of
   /// reorderable instructions.

include/llvm/CodeGen/ScheduleDAGInstrs.h

@@ -104,12 +104,8 @@ namespace llvm {
     /// The end of the range to be scheduled.
     MachineBasicBlock::iterator RegionEnd;
 
-    /// The index in BB of RegionEnd.
-    ///
-    /// This is the instruction number from the top of the current block, not
-    /// the SlotIndex. It is only used by the AntiDepBreaker and should be
-    /// removed once that client is obsolete.
-    unsigned EndIndex;
+    /// Instructions in this region (distance(RegionBegin, RegionEnd)).
+    unsigned NumRegionInstrs;
 
     /// After calling BuildSchedGraph, each machine instruction in the current
     /// scheduling region is mapped to an SUnit.
@@ -185,7 +181,7 @@ namespace llvm {
     virtual void enterRegion(MachineBasicBlock *bb,
                              MachineBasicBlock::iterator begin,
                              MachineBasicBlock::iterator end,
-                             unsigned endcount);
+                             unsigned regioninstrs);
 
     /// Notify that the scheduler has finished scheduling the current region.
     virtual void exitRegion();