Added -misched-regpressure option.

Register pressure tracking is half the complexity of the
scheduler. It's useful to be able to turn it off for compile time and
performance comparisons.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@189987 91177308-0d34-0410-b5e6-96231b3b80d8

include/llvm/CodeGen/MachineScheduler.h

@@ -227,6 +227,7 @@ protected:
   PressureDiffs SUPressureDiffs;
 
   /// Register pressure in this region computed by initRegPressure.
+  bool ShouldTrackPressure;
   IntervalPressure RegPressure;
   RegPressureTracker RPTracker;
 
@@ -259,8 +260,9 @@ public:
   ScheduleDAGMI(MachineSchedContext *C, MachineSchedStrategy *S):
     ScheduleDAGInstrs(*C->MF, *C->MLI, *C->MDT, /*IsPostRA=*/false, C->LIS),
     AA(C->AA), RegClassInfo(C->RegClassInfo), SchedImpl(S), DFSResult(0),
-    Topo(SUnits, &ExitSU), RPTracker(RegPressure), CurrentTop(),
-    TopRPTracker(TopPressure), CurrentBottom(), BotRPTracker(BotPressure),
+    Topo(SUnits, &ExitSU), ShouldTrackPressure(false),
+    RPTracker(RegPressure), CurrentTop(), TopRPTracker(TopPressure),
+    CurrentBottom(), BotRPTracker(BotPressure),
     NextClusterPred(NULL), NextClusterSucc(NULL) {
 #ifndef NDEBUG
     NumInstrsScheduled = 0;

include/llvm/CodeGen/RegisterPressure.h

@@ -288,6 +288,8 @@ public:
     MF(0), TRI(0), RCI(0), LIS(0), MBB(0), P(rp), RequireIntervals(false),
     TrackUntiedDefs(false) {}
 
+  void reset();
+
   void init(const MachineFunction *mf, const RegisterClassInfo *rci,
             const LiveIntervals *lis, const MachineBasicBlock *mbb,
             MachineBasicBlock::const_iterator pos,

lib/CodeGen/MachineScheduler.cpp

@@ -53,6 +53,9 @@ static cl::opt<unsigned> MISchedCutoff("misched-cutoff", cl::Hidden,
 static bool ViewMISchedDAGs = false;
 #endif // NDEBUG
 
+static cl::opt<bool> EnableRegPressure("misched-regpressure", cl::Hidden,
+  cl::desc("Enable register pressure scheduling."), cl::init(true));
+
 static cl::opt<bool> EnableCyclicPath("misched-cyclicpath", cl::Hidden,
   cl::desc("Enable cyclic critical path analysis."), cl::init(false));
 
@@ -477,6 +480,8 @@ void ScheduleDAGMI::enterRegion(MachineBasicBlock *bb,
 {
   ScheduleDAGInstrs::enterRegion(bb, begin, end, regioninstrs);
 
+  ShouldTrackPressure = EnableRegPressure;
+
   // For convenience remember the end of the liveness region.
   LiveRegionEnd =
     (RegionEnd == bb->end()) ? RegionEnd : llvm::next(RegionEnd);
@@ -657,6 +662,13 @@ void ScheduleDAGMI::schedule() {
 
 /// Build the DAG and setup three register pressure trackers.
 void ScheduleDAGMI::buildDAGWithRegPressure() {
+  if (!ShouldTrackPressure) {
+    RPTracker.reset();
+    RegionCriticalPSets.clear();
+    buildSchedGraph(AA);
+    return;
+  }
+
   // Initialize the register pressure tracker used by buildSchedGraph.
   RPTracker.init(&MF, RegClassInfo, LIS, BB, LiveRegionEnd,
                  /*TrackUntiedDefs=*/true);
@@ -820,11 +832,13 @@ void ScheduleDAGMI::initQueues(ArrayRef<SUnit*> TopRoots,
   SchedImpl->registerRoots();
 
   // Advance past initial DebugValues.
-  assert(TopRPTracker.getPos() == RegionBegin && "bad initial Top tracker");
   CurrentTop = nextIfDebug(RegionBegin, RegionEnd);
-  TopRPTracker.setPos(CurrentTop);
-
   CurrentBottom = RegionEnd;
+
+  if (ShouldTrackPressure) {
+    assert(TopRPTracker.getPos() == RegionBegin && "bad initial Top tracker");
+    TopRPTracker.setPos(CurrentTop);
+  }
 }
 
 /// Move an instruction and update register pressure.
@@ -841,10 +855,12 @@ void ScheduleDAGMI::scheduleMI(SUnit *SU, bool IsTopNode) {
       TopRPTracker.setPos(MI);
     }
 
-    // Update top scheduled pressure.
-    TopRPTracker.advance();
-    assert(TopRPTracker.getPos() == CurrentTop && "out of sync");
-    updateScheduledPressure(TopRPTracker.getPressure().MaxSetPressure);
+    if (ShouldTrackPressure) {
+      // Update top scheduled pressure.
+      TopRPTracker.advance();
+      assert(TopRPTracker.getPos() == CurrentTop && "out of sync");
+      updateScheduledPressure(TopRPTracker.getPressure().MaxSetPressure);
+    }
   }
   else {
     assert(SU->isBottomReady() && "node still has unscheduled dependencies");
@@ -860,12 +876,14 @@ void ScheduleDAGMI::scheduleMI(SUnit *SU, bool IsTopNode) {
       moveInstruction(MI, CurrentBottom);
       CurrentBottom = MI;
     }
-    // Update bottom scheduled pressure.
-    SmallVector<unsigned, 8> LiveUses;
-    BotRPTracker.recede(&LiveUses);
-    assert(BotRPTracker.getPos() == CurrentBottom && "out of sync");
-    updatePressureDiffs(LiveUses);
-    updateScheduledPressure(BotRPTracker.getPressure().MaxSetPressure);
+    if (ShouldTrackPressure) {
+      // Update bottom scheduled pressure.
+      SmallVector<unsigned, 8> LiveUses;
+      BotRPTracker.recede(&LiveUses);
+      assert(BotRPTracker.getPos() == CurrentBottom && "out of sync");
+      updatePressureDiffs(LiveUses);
+      updateScheduledPressure(BotRPTracker.getPressure().MaxSetPressure);
+    }
   }
 }
 

lib/CodeGen/RegisterPressure.cpp

@@ -153,6 +153,24 @@ const LiveInterval *RegPressureTracker::getInterval(unsigned Reg) const {
   return LIS->getCachedRegUnit(Reg);
 }
 
+void RegPressureTracker::reset() {
+  MBB = 0;
+  LIS = 0;
+
+  CurrSetPressure.clear();
+  LiveThruPressure.clear();
+  P.MaxSetPressure.clear();
+
+  if (RequireIntervals)
+    static_cast<IntervalPressure&>(P).reset();
+  else
+    static_cast<RegionPressure&>(P).reset();
+
+  LiveRegs.PhysRegs.clear();
+  LiveRegs.VirtRegs.clear();
+  UntiedDefs.clear();
+}
+
 /// Setup the RegPressureTracker.
 ///
 /// TODO: Add support for pressure without LiveIntervals.
@@ -163,6 +181,8 @@ void RegPressureTracker::init(const MachineFunction *mf,
                               MachineBasicBlock::const_iterator pos,
                               bool ShouldTrackUntiedDefs)
 {
+  reset();
+
   MF = mf;
   TRI = MF->getTarget().getRegisterInfo();
   RCI = rci;
@@ -177,19 +197,11 @@ void RegPressureTracker::init(const MachineFunction *mf,
 
   CurrPos = pos;
   CurrSetPressure.assign(TRI->getNumRegPressureSets(), 0);
-  LiveThruPressure.clear();
 
-  if (RequireIntervals)
-    static_cast<IntervalPressure&>(P).reset();
-  else
-    static_cast<RegionPressure&>(P).reset();
   P.MaxSetPressure = CurrSetPressure;
 
-  LiveRegs.PhysRegs.clear();
   LiveRegs.PhysRegs.setUniverse(TRI->getNumRegs());
-  LiveRegs.VirtRegs.clear();
   LiveRegs.VirtRegs.setUniverse(MRI->getNumVirtRegs());
-  UntiedDefs.clear();
   if (TrackUntiedDefs)
     UntiedDefs.setUniverse(MRI->getNumVirtRegs());
 }