MI Sched: eliminate local vreg copies.

For now, we just reschedule instructions that use the copied vregs and
let regalloc elliminate it. I would really like to eliminate the
copies on-the-fly during scheduling, but we need a complete
implementation of repairIntervalsInRange() first.

The general strategy is for the register coalescer to eliminate as
many global copies as possible and shrink live ranges to be
extended-basic-block local. The coalescer should not have to worry
about resolving local copies (e.g. it shouldn't attemp to reorder
instructions). The scheduler is a much better place to deal with local
interference. The coalescer side of this equation needs work.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@180193 91177308-0d34-0410-b5e6-96231b3b80d8

include/llvm/CodeGen/LiveInterval.h

@@ -399,6 +399,15 @@ namespace llvm {
       return r != end() && r->containsRange(Start, End);
     }
 
+    /// True iff this live range is a single segment that lies between the
+    /// specified boundaries, exclusively. Vregs live across a backedge are not
+    /// considered local. The boundaries are expected to lie within an extended
+    /// basic block, so vregs that are not live out should contain no holes.
+    bool isLocal(SlotIndex Start, SlotIndex End) const {
+      return beginIndex() > Start.getBaseIndex() &&
+        endIndex() < End.getBoundaryIndex();
+    }
+
     /// removeRange - Remove the specified range from this interval.  Note that
     /// the range must be a single LiveRange in its entirety.
     void removeRange(SlotIndex Start, SlotIndex End,

include/llvm/CodeGen/MachineScheduler.h

@@ -274,6 +274,10 @@ public:
     Mutations.push_back(Mutation);
   }
 
+  /// \brief True if an edge can be added from PredSU to SuccSU without creating
+  /// a cycle.
+  bool canAddEdge(SUnit *SuccSU, SUnit *PredSU);
+
   /// \brief Add a DAG edge to the given SU with the given predecessor
   /// dependence data.
   ///

include/llvm/CodeGen/ScheduleDAG.h

@@ -727,9 +727,8 @@ namespace llvm {
     /// IsReachable - Checks if SU is reachable from TargetSU.
     bool IsReachable(const SUnit *SU, const SUnit *TargetSU);
 
-    /// WillCreateCycle - Returns true if adding an edge from SU to TargetSU
-    /// will create a cycle.
-    bool WillCreateCycle(SUnit *SU, SUnit *TargetSU);
+    /// WillCreateCycle - Return true if addPred(TargetSU, SU) creates a cycle.
+    bool WillCreateCycle(SUnit *TargetSU, SUnit *SU);
 
     /// AddPred - Updates the topological ordering to accommodate an edge
     /// to be added from SUnit X to SUnit Y.

include/llvm/CodeGen/ScheduleDAGInstrs.h

@@ -150,6 +150,9 @@ namespace llvm {
 
     virtual ~ScheduleDAGInstrs() {}
 
+    /// \brief Expose LiveIntervals for use in DAG mutators and such.
+    LiveIntervals *getLIS() const { return LIS; }
+
     /// \brief Get the machine model for instruction scheduling.
     const TargetSchedModel *getSchedModel() const { return &SchedModel; }