Add basic hazard recognizer support. noop insertion isn't complete yet though.

llvm-svn: 26558

llvm/lib/CodeGen/SelectionDAG/ScheduleDAGList.cpp

@@ -160,6 +160,52 @@ struct ls_rr_sort : public std::binary_function<SUnit*, SUnit*, bool> {
   }
 };
 
+
+/// HazardRecognizer - This determines whether or not an instruction can be
+/// issued this cycle, and whether or not a noop needs to be inserted to handle
+/// the hazard.
+namespace {
+  class HazardRecognizer {
+  public:
+    virtual ~HazardRecognizer() {}
+    
+    enum HazardType {
+      NoHazard,      // This instruction can be emitted at this cycle.
+      Hazard,        // This instruction can't be emitted at this cycle.
+      NoopHazard,    // This instruction can't be emitted, and needs noops.
+    };
+    
+    /// getHazardType - Return the hazard type of emitting this node.  There are
+    /// three possible results.  Either:
+    ///  * NoHazard: it is legal to issue this instruction on this cycle.
+    ///  * Hazard: issuing this instruction would stall the machine.  If some
+    ///     other instruction is available, issue it first.
+    ///  * NoopHazard: issuing this instruction would break the program.  If
+    ///     some other instruction can be issued, do so, otherwise issue a noop.
+    virtual HazardType getHazardType(SDNode *Node) {
+      return NoHazard;
+    }
+    
+    /// EmitInstruction - This callback is invoked when an instruction is
+    /// emitted, to advance the hazard state.
+    virtual void EmitInstruction(SDNode *Node) {
+    }
+    
+    /// AdvanceCycle - This callback is invoked when no instructions can be
+    /// issued on this cycle without a hazard.  This should increment the
+    /// internal state of the hazard recognizer so that previously "Hazard"
+    /// instructions will now not be hazards.
+    virtual void AdvanceCycle() {
+    }
+    
+    /// EmitNoop - This callback is invoked when a noop was added to the
+    /// instruction stream.
+    virtual void EmitNoop() {
+    }
+  };
+}
+
+
 /// ScheduleDAGList - List scheduler.
 class ScheduleDAGList : public ScheduleDAG {
 private:
@@ -176,14 +222,21 @@ private:
   /// it is top-down.
   bool isBottomUp;
   
+  /// HazardRec - The hazard recognizer to use.
+  HazardRecognizer *HazardRec;
+  
   typedef std::priority_queue<SUnit*, std::vector<SUnit*>, ls_rr_sort>
     AvailableQueueTy;
 
 public:
   ScheduleDAGList(SelectionDAG &dag, MachineBasicBlock *bb,
-                  const TargetMachine &tm, bool isbottomup)
+                  const TargetMachine &tm, bool isbottomup,
+                  HazardRecognizer *HR = 0)
     : ScheduleDAG(listSchedulingBURR, dag, bb, tm),
-      CurrCycle(0), HeadSUnit(NULL), TailSUnit(NULL), isBottomUp(isbottomup) {}
+      CurrCycle(0), HeadSUnit(NULL), TailSUnit(NULL), isBottomUp(isbottomup) {
+      if (HR == 0) HR = new HazardRecognizer();
+        HazardRec = HR;
+    }
 
   ~ScheduleDAGList() {
     SUnit *SU = HeadSUnit;
@@ -192,6 +245,8 @@ public:
       delete SU;
       SU = NextSU;
     }
+    
+    delete HazardRec;
   }
 
   void Schedule();
@@ -411,7 +466,8 @@ void ScheduleDAGList::ListScheduleTopDown() {
   // Emit the entry node first.
   SUnit *Entry = SUnitMap[DAG.getEntryNode().Val];
   ScheduleNodeTopDown(Available, Entry);
-  
+  HazardRec->EmitInstruction(Entry->Node);
+                      
   // All leaves to Available queue.
   for (SUnit *SU = HeadSUnit; SU != NULL; SU = SU->Next) {
     // It is available if it has no predecessors.
@@ -423,23 +479,46 @@ void ScheduleDAGList::ListScheduleTopDown() {
   // priority. If it is not ready put it back.  Schedule the node.
   std::vector<SUnit*> NotReady;
   while (!Available.empty()) {
-    SUnit *CurrNode = Available.top();
+    SUnit *FoundNode = 0;
-    Available.pop();
-    
-    // FIXME: when priorities make sense, reenable this.
-    while (0 && !isReady(CurrNode, CurrCycle)) {
-      NotReady.push_back(CurrNode);
-      CurrNode = Available.top();
-      Available.pop();
-    }
 
+    bool HasNoopHazards = false;
+    do {
+      SUnit *CurrNode = Available.top();
+      Available.pop();
+      HazardRecognizer::HazardType HT =
+        HazardRec->getHazardType(CurrNode->Node);
+      if (HT == HazardRecognizer::NoHazard) {
+        FoundNode = CurrNode;
+        break;
+      }
+      
+      // Remember if this is a noop hazard.
+      HasNoopHazards |= HT == HazardRecognizer::NoopHazard;
+      
+      NotReady.push_back(CurrNode);
+    } while (!Available.empty());
+    
     // Add the nodes that aren't ready back onto the available list.
     while (!NotReady.empty()) {
       Available.push(NotReady.back());
       NotReady.pop_back();
     }
-    
+
-    ScheduleNodeTopDown(Available, CurrNode);
+    // If we found a node to schedule, do it now.
+    if (FoundNode) {
+      ScheduleNodeTopDown(Available, FoundNode);
+      HazardRec->EmitInstruction(FoundNode->Node);
+    } else if (!HasNoopHazards) {
+      // Otherwise, we have a pipeline stall, but no other problem, just advance
+      // the current cycle and try again.
+      HazardRec->AdvanceCycle();
+    } else {
+      // Otherwise, we have no instructions to issue and we have instructions
+      // that will fault if we don't do this right.  This is the case for
+      // processors without pipeline interlocks and other cases.
+      HazardRec->EmitNoop();
+      // FIXME: Add a noop to the schedule!!
+    }
   }
 
 #ifndef NDEBUG
@@ -651,10 +730,20 @@ llvm::ScheduleDAG* llvm::createBURRListDAGScheduler(SelectionDAG &DAG,
   return new ScheduleDAGList(DAG, BB, DAG.getTarget(), true);
 }
 
+/// G5HazardRecognizer - A hazard recognizer for the PowerPC G5 processor.
+/// FIXME: Implement
+/// FIXME: Move to the PowerPC backend.
+class G5HazardRecognizer : public HazardRecognizer {
+public:
+  G5HazardRecognizer() {}
+};
+
+
 /// createTDG5ListDAGScheduler - This creates a top-down list scheduler for
 /// the PowerPC G5.  FIXME: pull the priority function out into the PPC
 /// backend!
 ScheduleDAG* llvm::createTDG5ListDAGScheduler(SelectionDAG &DAG,
                                               MachineBasicBlock *BB) {
-  return new ScheduleDAGList(DAG, BB, DAG.getTarget(), false);
+  return new ScheduleDAGList(DAG, BB, DAG.getTarget(), false,
+                             new G5HazardRecognizer());
 }