MI Sched: Track live-thru registers.

When registers must be live throughout the scheduling region, increase
the limit for the register class. Once we exceed the original limit,
they will be spilled, and there's no point further reducing pressure.

This isn't a perfect heuristics but avoids a situation where the
scheduler could become trapped by trying to achieve the impossible.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@187436 91177308-0d34-0410-b5e6-96231b3b80d8

1 files changed, 57 insertions, 10 deletions

diff --git a/lib/CodeGen/RegisterPressure.cpp b/lib/CodeGen/RegisterPressure.cpp
index 4175a4ff85..b7ab138bf1 100644
--- a/lib/CodeGen/RegisterPressure.cpp
+++ b/lib/CodeGen/RegisterPressure.cpp
@@ -76,17 +76,22 @@ void RegisterPressure::decrease(unsigned Reg, const TargetRegisterInfo *TRI,
 }
 
 #if !defined(NDEBUG) || defined(LLVM_ENABLE_DUMP)
-static void dumpSetPressure(const std::vector<unsigned> &SetPressure,
-                            const TargetRegisterInfo *TRI) {
+void llvm::dumpRegSetPressure(ArrayRef<unsigned> SetPressure,
+                              const TargetRegisterInfo *TRI) {
+  bool Empty = true;
   for (unsigned i = 0, e = SetPressure.size(); i < e; ++i) {
-    if (SetPressure[i] != 0)
+    if (SetPressure[i] != 0) {
       dbgs() << TRI->getRegPressureSetName(i) << "=" << SetPressure[i] << '\n';
+      Empty = false;
+    }
   }
+  if (Empty)
+    dbgs() << "\n";
 }
 
 void RegisterPressure::dump(const TargetRegisterInfo *TRI) const {
   dbgs() << "Max Pressure: ";
-  dumpSetPressure(MaxSetPressure, TRI);
+  dumpRegSetPressure(MaxSetPressure, TRI);
   dbgs() << "Live In: ";
   for (unsigned i = 0, e = LiveInRegs.size(); i < e; ++i)
     dbgs() << PrintReg(LiveInRegs[i], TRI) << " ";
@@ -98,8 +103,10 @@ void RegisterPressure::dump(const TargetRegisterInfo *TRI) const {
 }
 
 void RegPressureTracker::dump() const {
-  dbgs() << "Curr Pressure: ";
-  dumpSetPressure(CurrSetPressure, TRI);
+  if (!isTopClosed() || !isBottomClosed()) {
+    dbgs() << "Curr Pressure: ";
+    dumpRegSetPressure(CurrSetPressure, TRI);
+  }
   P.dump(TRI);
 }
 #endif
@@ -200,13 +207,15 @@ void RegPressureTracker::init(const MachineFunction *mf,
                               const RegisterClassInfo *rci,
                               const LiveIntervals *lis,
                               const MachineBasicBlock *mbb,
-                              MachineBasicBlock::const_iterator pos)
+                              MachineBasicBlock::const_iterator pos,
+                              bool ShouldTrackUntiedDefs)
 {
   MF = mf;
   TRI = MF->getTarget().getRegisterInfo();
   RCI = rci;
   MRI = &MF->getRegInfo();
   MBB = mbb;
+  TrackUntiedDefs = ShouldTrackUntiedDefs;
 
   if (RequireIntervals) {
     assert(lis && "IntervalPressure requires LiveIntervals");
@@ -215,6 +224,7 @@ void RegPressureTracker::init(const MachineFunction *mf,
 
   CurrPos = pos;
   CurrSetPressure.assign(TRI->getNumRegPressureSets(), 0);
+  LiveThruPressure.clear();
 
   if (RequireIntervals)
     static_cast<IntervalPressure&>(P).reset();
@@ -226,6 +236,9 @@ void RegPressureTracker::init(const MachineFunction *mf,
   LiveRegs.PhysRegs.setUniverse(TRI->getNumRegs());
   LiveRegs.VirtRegs.clear();
   LiveRegs.VirtRegs.setUniverse(MRI->getNumVirtRegs());
+  UntiedDefs.clear();
+  if (TrackUntiedDefs)
+    UntiedDefs.setUniverse(MRI->getNumVirtRegs());
 }
 
 /// Does this pressure result have a valid top position and live ins.
@@ -304,6 +317,25 @@ void RegPressureTracker::closeRegion() {
   // If both top and bottom are closed, do nothing.
 }
 
+/// The register tracker is unaware of global liveness so ignores normal
+/// live-thru ranges. However, two-address or coalesced chains can also lead
+/// to live ranges with no holes. Count these to inform heuristics that we
+/// can never drop below this pressure.
+void RegPressureTracker::initLiveThru(const RegPressureTracker &RPTracker) {
+  LiveThruPressure.assign(TRI->getNumRegPressureSets(), 0);
+  assert(isBottomClosed() && "need bottom-up tracking to intialize.");
+  for (unsigned i = 0, e = P.LiveOutRegs.size(); i < e; ++i) {
+    unsigned Reg = P.LiveOutRegs[i];
+    if (TargetRegisterInfo::isVirtualRegister(Reg)
+        && !RPTracker.hasUntiedDef(Reg)) {
+      const TargetRegisterClass *RC = MRI->getRegClass(Reg);
+      increaseSetPressure(LiveThruPressure, LiveThruPressure,
+                          TRI->getRegClassPressureSets(RC),
+                          TRI->getRegClassWeight(RC).RegWeight);
+    }
+  }
+}
+
 /// \brief Convenient wrapper for checking membership in RegisterOperands.
 static bool containsReg(ArrayRef<unsigned> Regs, unsigned Reg) {
   return std::find(Regs.begin(), Regs.end(), Reg) != Regs.end();
@@ -459,11 +491,20 @@ bool RegPressureTracker::recede() {
       LiveRegs.insert(Reg);
     }
   }
+  if (TrackUntiedDefs) {
+    for (unsigned i = 0, e = RegOpers.Defs.size(); i < e; ++i) {
+      unsigned Reg = RegOpers.Defs[i];
+      if (TargetRegisterInfo::isVirtualRegister(Reg) && !LiveRegs.contains(Reg))
+        UntiedDefs.insert(Reg);
+    }
+  }
   return true;
 }
 
 /// Advance across the current instruction.
 bool RegPressureTracker::advance() {
+  assert(!TrackUntiedDefs && "unsupported mode");
+
   // Check for the bottom of the analyzable region.
   if (CurrPos == MBB->end()) {
     closeRegion();
@@ -533,7 +574,8 @@ bool RegPressureTracker::advance() {
 static void computeExcessPressureDelta(ArrayRef<unsigned> OldPressureVec,
                                        ArrayRef<unsigned> NewPressureVec,
                                        RegPressureDelta &Delta,
-                                       const RegisterClassInfo *RCI) {
+                                       const RegisterClassInfo *RCI,
+                                       ArrayRef<unsigned> LiveThruPressureVec) {
   int ExcessUnits = 0;
   unsigned PSetID = ~0U;
   for (unsigned i = 0, e = OldPressureVec.size(); i < e; ++i) {
@@ -544,6 +586,9 @@ static void computeExcessPressureDelta(ArrayRef<unsigned> OldPressureVec,
       continue;
     // Only consider change beyond the limit.
     unsigned Limit = RCI->getRegPressureSetLimit(i);
+    if (!LiveThruPressureVec.empty())
+      Limit += LiveThruPressureVec[i];
+
     if (Limit > POld) {
       if (Limit > PNew)
         PDiff = 0;            // Under the limit
@@ -665,7 +710,8 @@ getMaxUpwardPressureDelta(const MachineInstr *MI, RegPressureDelta &Delta,
 
   bumpUpwardPressure(MI);
 
-  computeExcessPressureDelta(SavedPressure, CurrSetPressure, Delta, RCI);
+  computeExcessPressureDelta(SavedPressure, CurrSetPressure, Delta, RCI,
+                             LiveThruPressure);
   computeMaxPressureDelta(SavedMaxPressure, P.MaxSetPressure, CriticalPSets,
                           MaxPressureLimit, Delta);
   assert(Delta.CriticalMax.UnitIncrease >= 0 &&
@@ -755,7 +801,8 @@ getMaxDownwardPressureDelta(const MachineInstr *MI, RegPressureDelta &Delta,
 
   bumpDownwardPressure(MI);
 
-  computeExcessPressureDelta(SavedPressure, CurrSetPressure, Delta, RCI);
+  computeExcessPressureDelta(SavedPressure, CurrSetPressure, Delta, RCI,
+                             LiveThruPressure);
   computeMaxPressureDelta(SavedMaxPressure, P.MaxSetPressure, CriticalPSets,
                           MaxPressureLimit, Delta);
   assert(Delta.CriticalMax.UnitIncrease >= 0 &&