mi-sched: update PressureDiffs on-the-fly for liveness.

This removes all expensive pressure tracking logic from the scheduling
critical path of node comparison.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@189643 91177308-0d34-0410-b5e6-96231b3b80d8

include/llvm/CodeGen/LiveInterval.h

@@ -296,6 +296,12 @@ namespace llvm {
       return r != end() && r->end.getBaseIndex() == BaseIdx;
     }
 
+    /// Return true if a live range starts at the instruction at this index.
+    bool isDefinedByInstr(SlotIndex index) const {
+      const_iterator r = find(index.getDeadSlot());
+      return r != end() && r->end.getBaseIndex() == index.getBaseIndex();
+    }
+
     /// getLiveRangeContaining - Return the live range that contains the
     /// specified index, or null if there is none.
     const LiveRange *getLiveRangeContaining(SlotIndex Idx) const {

include/llvm/CodeGen/MachineScheduler.h

@@ -221,7 +221,9 @@ protected:
 
   MachineBasicBlock::iterator LiveRegionEnd;
 
-  // Map each SU to its summary of pressure changes.
+  // Map each SU to its summary of pressure changes. This array is updated for
+  // liveness during bottom-up scheduling. Top-down scheduling may proceed but
+  // has no affect on the pressure diffs.
   PressureDiffs SUPressureDiffs;
 
   /// Register pressure in this region computed by initRegPressure.
@@ -376,6 +378,8 @@ protected:
 
   void initRegPressure();
 
+  void updatePressureDiffs(ArrayRef<unsigned> LiveUses);
+
   void updateScheduledPressure(const std::vector<unsigned> &NewMaxPressure);
 
   bool checkSchedLimit();

include/llvm/CodeGen/RegisterPressure.h

@@ -311,7 +311,7 @@ public:
   SlotIndex getCurrSlot() const;
 
   /// Recede across the previous instruction.
-  bool recede(PressureDiff *PDiff = 0);
+  bool recede(SmallVectorImpl<unsigned> *LiveUses = 0, PressureDiff *PDiff = 0);
 
   /// Advance across the current instruction.
   bool advance();