misched: ILP scheduler for experimental heuristics.

llvm-svn: 165950

llvm/include/llvm/CodeGen/MachineScheduler.h

@@ -110,6 +110,10 @@ public:
   /// Initialize the strategy after building the DAG for a new region.
   virtual void initialize(ScheduleDAGMI *DAG) = 0;
 
+  /// Notify this strategy that all roots have been released (including those
+  /// that depend on EntrySU or ExitSU).
+  virtual void registerRoots() {}
+
   /// Pick the next node to schedule, or return NULL. Set IsTopNode to true to
   /// schedule the node at the top of the unscheduled region. Otherwise it will
   /// be scheduled at the bottom.

llvm/include/llvm/CodeGen/ScheduleDAGILP.h

@@ -0,0 +1,86 @@
+//===- ScheduleDAGILP.h - ILP metric for ScheduleDAGInstrs ------*- C++ -*-===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+//
+// Definition of an ILP metric for machine level instruction scheduling.
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef LLVM_CODEGEN_SCHEDULEDAGILP_H
+#define LLVM_CODEGEN_SCHEDULEDAGILP_H
+
+#include "llvm/Support/DataTypes.h"
+#include <vector>
+
+namespace llvm {
+
+class raw_ostream;
+class ScheduleDAGInstrs;
+class SUnit;
+
+/// \brief Represent the ILP of the subDAG rooted at a DAG node.
+struct ILPValue {
+  unsigned InstrCount;
+  unsigned Cycles;
+
+  ILPValue(): InstrCount(0), Cycles(0) {}
+
+  ILPValue(unsigned count, unsigned cycles):
+    InstrCount(count), Cycles(cycles) {}
+
+  bool isValid() const { return Cycles > 0; }
+
+  // Order by the ILP metric's value.
+  bool operator<(ILPValue RHS) const {
+    return (uint64_t)InstrCount * RHS.Cycles
+      < (uint64_t)Cycles * RHS.InstrCount;
+  }
+  bool operator>(ILPValue RHS) const {
+    return RHS < *this;
+  }
+  bool operator<=(ILPValue RHS) const {
+    return (uint64_t)InstrCount * RHS.Cycles
+      <= (uint64_t)Cycles * RHS.InstrCount;
+  }
+  bool operator>=(ILPValue RHS) const {
+    return RHS <= *this;
+  }
+
+#if !defined(NDEBUG) || defined(LLVM_ENABLE_DUMP)
+  void print(raw_ostream &OS) const;
+
+  void dump() const;
+#endif
+};
+
+/// \brief Compute the values of each DAG node for an ILP metric.
+///
+/// This metric assumes that the DAG is a forest of trees with roots at the
+/// bottom of the schedule.
+class ScheduleDAGILP {
+  bool IsBottomUp;
+  std::vector<ILPValue> ILPValues;
+
+public:
+  ScheduleDAGILP(bool IsBU): IsBottomUp(IsBU) {}
+
+  /// \brief Initialize the result data with the size of the DAG.
+  void resize(unsigned NumSUnits);
+
+  /// \brief Compute the ILP metric for the subDAG at this root.
+  void computeILP(const SUnit *Root);
+
+  /// \brief Get the ILP value for a DAG node.
+  ILPValue getILP(const SUnit *SU);
+};
+
+raw_ostream &operator<<(raw_ostream &OS, const ILPValue &Val);
+
+} // namespace llvm
+
+#endif

llvm/lib/CodeGen/MachineScheduler.cpp

@@ -18,6 +18,7 @@
 #include "llvm/CodeGen/MachineScheduler.h"
 #include "llvm/CodeGen/Passes.h"
 #include "llvm/CodeGen/RegisterClassInfo.h"
+#include "llvm/CodeGen/ScheduleDAGILP.h"
 #include "llvm/CodeGen/ScheduleHazardRecognizer.h"
 #include "llvm/Analysis/AliasAnalysis.h"
 #include "llvm/Support/CommandLine.h"
@@ -451,26 +452,6 @@ updateScheduledPressure(std::vector<unsigned> NewMaxPressure) {
   }
 }
 
-// Release all DAG roots for scheduling.
-void ScheduleDAGMI::releaseRoots() {
-  SmallVector<SUnit*, 16> BotRoots;
-
-  for (std::vector<SUnit>::iterator
-         I = SUnits.begin(), E = SUnits.end(); I != E; ++I) {
-    // A SUnit is ready to top schedule if it has no predecessors.
-    if (I->Preds.empty())
-      SchedImpl->releaseTopNode(&(*I));
-    // A SUnit is ready to bottom schedule if it has no successors.
-    if (I->Succs.empty())
-      BotRoots.push_back(&(*I));
-  }
-  // Release bottom roots in reverse order so the higher priority nodes appear
-  // first. This is more natural and slightly more efficient.
-  for (SmallVectorImpl<SUnit*>::const_reverse_iterator
-         I = BotRoots.rbegin(), E = BotRoots.rend(); I != E; ++I)
-    SchedImpl->releaseBottomNode(*I);
-}
-
 /// schedule - Called back from MachineScheduler::runOnMachineFunction
 /// after setting up the current scheduling region. [RegionBegin, RegionEnd)
 /// only includes instructions that have DAG nodes, not scheduling boundaries.
@@ -532,8 +513,29 @@ void ScheduleDAGMI::postprocessDAG() {
   }
 }
 
+// Release all DAG roots for scheduling.
+void ScheduleDAGMI::releaseRoots() {
+  SmallVector<SUnit*, 16> BotRoots;
+
+  for (std::vector<SUnit>::iterator
+         I = SUnits.begin(), E = SUnits.end(); I != E; ++I) {
+    // A SUnit is ready to top schedule if it has no predecessors.
+    if (I->Preds.empty())
+      SchedImpl->releaseTopNode(&(*I));
+    // A SUnit is ready to bottom schedule if it has no successors.
+    if (I->Succs.empty())
+      BotRoots.push_back(&(*I));
+  }
+  // Release bottom roots in reverse order so the higher priority nodes appear
+  // first. This is more natural and slightly more efficient.
+  for (SmallVectorImpl<SUnit*>::const_reverse_iterator
+         I = BotRoots.rbegin(), E = BotRoots.rend(); I != E; ++I)
+    SchedImpl->releaseBottomNode(*I);
+}
+
 /// Identify DAG roots and setup scheduler queues.
 void ScheduleDAGMI::initQueues() {
+
   // Initialize the strategy before modifying the DAG.
   SchedImpl->initialize(this);
 
@@ -544,6 +546,8 @@ void ScheduleDAGMI::initQueues() {
   // Release all DAG roots for scheduling.
   releaseRoots();
 
+  SchedImpl->registerRoots();
+
   CurrentTop = nextIfDebug(RegionBegin, RegionEnd);
   CurrentBottom = RegionEnd;
 }
@@ -1197,6 +1201,86 @@ static MachineSchedRegistry
 ConvergingSchedRegistry("converge", "Standard converging scheduler.",
                         createConvergingSched);
 
+//===----------------------------------------------------------------------===//
+// ILP Scheduler. Currently for experimental analysis of heuristics.
+//===----------------------------------------------------------------------===//
+
+namespace {
+/// \brief Order nodes by the ILP metric.
+struct ILPOrder {
+  ScheduleDAGILP *ILP;
+  bool MaximizeILP;
+
+  ILPOrder(ScheduleDAGILP *ilp, bool MaxILP): ILP(ilp), MaximizeILP(MaxILP) {}
+
+  /// \brief Apply a less-than relation on node priority.
+  bool operator()(const SUnit *A, const SUnit *B) const {
+    // Return true if A comes after B in the Q.
+    if (MaximizeILP)
+      return ILP->getILP(A) < ILP->getILP(B);
+    else
+      return ILP->getILP(A) > ILP->getILP(B);
+  }
+};
+
+/// \brief Schedule based on the ILP metric.
+class ILPScheduler : public MachineSchedStrategy {
+  ScheduleDAGILP ILP;
+  ILPOrder Cmp;
+
+  std::vector<SUnit*> ReadyQ;
+public:
+  ILPScheduler(bool MaximizeILP)
+  : ILP(/*BottomUp=*/true), Cmp(&ILP, MaximizeILP) {}
+
+  virtual void initialize(ScheduleDAGMI *DAG) {
+    ReadyQ.clear();
+    ILP.resize(DAG->SUnits.size());
+  }
+
+  virtual void registerRoots() {
+    for (std::vector<SUnit*>::const_iterator
+           I = ReadyQ.begin(), E = ReadyQ.end(); I != E; ++I) {
+      ILP.computeILP(*I);
+    }
+  }
+
+  /// Implement MachineSchedStrategy interface.
+  /// -----------------------------------------
+
+  virtual SUnit *pickNode(bool &IsTopNode) {
+    if (ReadyQ.empty()) return NULL;
+    pop_heap(ReadyQ.begin(), ReadyQ.end(), Cmp);
+    SUnit *SU = ReadyQ.back();
+    ReadyQ.pop_back();
+    IsTopNode = false;
+    DEBUG(dbgs() << "*** Scheduling " << *SU->getInstr()
+          << " ILP: " << ILP.getILP(SU) << '\n');
+    return SU;
+  }
+
+  virtual void schedNode(SUnit *, bool) {}
+
+  virtual void releaseTopNode(SUnit *) { /*only called for top roots*/ }
+
+  virtual void releaseBottomNode(SUnit *SU) {
+    ReadyQ.push_back(SU);
+    std::push_heap(ReadyQ.begin(), ReadyQ.end(), Cmp);
+  }
+};
+} // namespace
+
+static ScheduleDAGInstrs *createILPMaxScheduler(MachineSchedContext *C) {
+  return new ScheduleDAGMI(C, new ILPScheduler(true));
+}
+static ScheduleDAGInstrs *createILPMinScheduler(MachineSchedContext *C) {
+  return new ScheduleDAGMI(C, new ILPScheduler(false));
+}
+static MachineSchedRegistry ILPMaxRegistry(
+  "ilpmax", "Schedule bottom-up for max ILP", createILPMaxScheduler);
+static MachineSchedRegistry ILPMinRegistry(
+  "ilpmin", "Schedule bottom-up for min ILP", createILPMinScheduler);
+
 //===----------------------------------------------------------------------===//
 // Machine Instruction Shuffler for Correctness Testing
 //===----------------------------------------------------------------------===//

llvm/lib/CodeGen/ScheduleDAGInstrs.cpp

@@ -22,6 +22,7 @@
 #include "llvm/CodeGen/MachineRegisterInfo.h"
 #include "llvm/CodeGen/PseudoSourceValue.h"
 #include "llvm/CodeGen/RegisterPressure.h"
+#include "llvm/CodeGen/ScheduleDAGILP.h"
 #include "llvm/CodeGen/ScheduleDAGInstrs.h"
 #include "llvm/MC/MCInstrItineraries.h"
 #include "llvm/Target/TargetMachine.h"
@@ -30,6 +31,7 @@
 #include "llvm/Target/TargetSubtargetInfo.h"
 #include "llvm/Support/CommandLine.h"
 #include "llvm/Support/Debug.h"
+#include "llvm/Support/Format.h"
 #include "llvm/Support/raw_ostream.h"
 #include "llvm/ADT/SmallSet.h"
 #include "llvm/ADT/SmallPtrSet.h"
@@ -933,3 +935,94 @@ std::string ScheduleDAGInstrs::getGraphNodeLabel(const SUnit *SU) const {
 std::string ScheduleDAGInstrs::getDAGName() const {
   return "dag." + BB->getFullName();
 }
+
+namespace {
+/// \brief Manage the stack used by a reverse depth-first search over the DAG.
+class SchedDAGReverseDFS {
+  std::vector<std::pair<const SUnit*, SUnit::const_pred_iterator> > DFSStack;
+public:
+  bool isComplete() const { return DFSStack.empty(); }
+
+  void follow(const SUnit *SU) {
+    DFSStack.push_back(std::make_pair(SU, SU->Preds.begin()));
+  }
+  void advance() { ++DFSStack.back().second; }
+
+  void backtrack() { DFSStack.pop_back(); }
+
+  const SUnit *getCurr() const { return DFSStack.back().first; }
+
+  SUnit::const_pred_iterator getPred() const { return DFSStack.back().second; }
+
+  SUnit::const_pred_iterator getPredEnd() const {
+    return getCurr()->Preds.end();
+  }
+};
+} // anonymous
+
+void ScheduleDAGILP::resize(unsigned NumSUnits) {
+  ILPValues.resize(NumSUnits);
+}
+
+ILPValue ScheduleDAGILP::getILP(const SUnit *SU) {
+  return ILPValues[SU->NodeNum];
+}
+
+// A leaf node has an ILP of 1/1.
+static ILPValue initILP(const SUnit *SU) {
+  unsigned Cnt = SU->getInstr()->isTransient() ? 0 : 1;
+  return ILPValue(Cnt, 1 + SU->getDepth());
+}
+
+/// Compute an ILP metric for all nodes in the subDAG reachable via depth-first
+/// search from this root.
+void ScheduleDAGILP::computeILP(const SUnit *Root) {
+  if (!IsBottomUp)
+    llvm_unreachable("Top-down ILP metric is unimplemnted");
+
+  SchedDAGReverseDFS DFS;
+  // Mark a node visited by validating it.
+  ILPValues[Root->NodeNum] = initILP(Root);
+  DFS.follow(Root);
+  for (;;) {
+    // Traverse the leftmost path as far as possible.
+    while (DFS.getPred() != DFS.getPredEnd()) {
+      const SUnit *PredSU = DFS.getPred()->getSUnit();
+      DFS.advance();
+      // If the pred is already valid, skip it.
+      if (ILPValues[PredSU->NodeNum].isValid())
+        continue;
+      ILPValues[PredSU->NodeNum] = initILP(PredSU);
+      DFS.follow(PredSU);
+    }
+    // Visit the top of the stack in postorder and backtrack.
+    unsigned PredCount = ILPValues[DFS.getCurr()->NodeNum].InstrCount;
+    DFS.backtrack();
+    if (DFS.isComplete())
+      break;
+    // Add the recently finished predecessor's bottom-up descendent count.
+    ILPValues[DFS.getCurr()->NodeNum].InstrCount += PredCount;
+  }
+}
+
+#if !defined(NDEBUG) || defined(LLVM_ENABLE_DUMP)
+void ILPValue::print(raw_ostream &OS) const {
+  if (!isValid())
+    OS << "BADILP";
+  OS << InstrCount << " / " << Cycles << " = "
+     << format("%g", ((double)InstrCount / Cycles));
+}
+
+void ILPValue::dump() const {
+  dbgs() << *this << '\n';
+}
+
+namespace llvm {
+
+raw_ostream &operator<<(raw_ostream &OS, const ILPValue &Val) {
+  Val.print(OS);
+  return OS;
+}
+
+} // namespace llvm
+#endif // !NDEBUG || LLVM_ENABLE_DUMP

llvm/test/CodeGen/X86/misched-ilp.ll

@@ -0,0 +1,25 @@
+; RUN: llc < %s -march=x86-64 -mcpu=core2 -enable-misched -misched=ilpmax | FileCheck -check-prefix=MAX %s
+; RUN: llc < %s -march=x86-64 -mcpu=core2 -enable-misched -misched=ilpmin | FileCheck -check-prefix=MIN %s
+;
+; Basic verification of the ScheduleDAGILP metric.
+;
+; MAX: addss
+; MAX: addss
+; MAX: addss
+; MAX: subss
+; MAX: addss
+;
+; MIN: addss
+; MIN: addss
+; MIN: subss
+; MIN: addss
+; MIN: addss
+define float @ilpsched(float %a, float %b, float %c, float %d, float %e, float %f) nounwind uwtable readnone ssp {
+entry:
+  %add = fadd float %a, %b
+  %add1 = fadd float %c, %d
+  %add2 = fadd float %e, %f
+  %add3 = fsub float %add1, %add2
+  %add4 = fadd float %add, %add3
+  ret float %add4
+}