Introducing a new method of tracking register pressure. We can't

precisely track pressure on a selection DAG, but we can at least keep
it balanced. This design accounts for various interesting aspects of
selection DAGS: register and subregister copies, glued nodes, dead
nodes, unused registers, etc.

Added SUnit::NumRegDefsLeft and ScheduleDAGSDNodes::RegDefIter.

Note: I disabled PrescheduleNodesWithMultipleUses when register
pressure is enabled, based on no evidence other than I don't think it
makes sense to have both enabled.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@124853 91177308-0d34-0410-b5e6-96231b3b80d8

lib/CodeGen/SelectionDAG/ScheduleDAGSDNodes.h

@@ -20,7 +20,7 @@
 
 namespace llvm {
   /// ScheduleDAGSDNodes - A ScheduleDAG for scheduling SDNode-based DAGs.
-  /// 
+  ///
   /// Edges between SUnits are initially based on edges in the SelectionDAG,
   /// and additional edges can be added by the schedulers as heuristics.
   /// SDNodes such as Constants, Registers, and a few others that are not
@@ -73,13 +73,17 @@ namespace llvm {
     /// predecessors / successors info nor the temporary scheduling states.
     ///
     SUnit *Clone(SUnit *N);
-    
+
     /// BuildSchedGraph - Build the SUnit graph from the selection dag that we
     /// are input.  This SUnit graph is similar to the SelectionDAG, but
     /// excludes nodes that aren't interesting to scheduling, and represents
     /// flagged together nodes with a single SUnit.
     virtual void BuildSchedGraph(AliasAnalysis *AA);
 
+    /// InitNumRegDefsLeft - Determine the # of regs defined by this node.
+    ///
+    void InitNumRegDefsLeft(SUnit *SU);
+
     /// ComputeLatency - Compute node latency.
     ///
     virtual void ComputeLatency(SUnit *SU);
@@ -106,6 +110,30 @@ namespace llvm {
 
     virtual void getCustomGraphFeatures(GraphWriter<ScheduleDAG*> &GW) const;
 
+    /// RegDefIter - In place iteration over the values defined by an
+    /// SUnit. This does not need copies of the iterator or any other STLisms.
+    /// The iterator creates itself, rather than being provided by the SchedDAG.
+    class RegDefIter {
+      const ScheduleDAGSDNodes *SchedDAG;
+      const SDNode *Node;
+      unsigned DefIdx;
+      unsigned NodeNumDefs;
+      EVT ValueType;
+    public:
+      RegDefIter(const SUnit *SU, const ScheduleDAGSDNodes *SD);
+
+      bool IsValid() const { return Node != NULL; }
+
+      EVT GetValue() const {
+        assert(IsValid() && "bad iterator");
+        return ValueType;
+      }
+
+      void Advance();
+    private:
+      void InitNodeNumDefs();
+    };
+
   private:
     /// ClusterNeighboringLoads - Cluster loads from "near" addresses into
     /// combined SUnits.