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
diff --git a/lib/CodeGen/MachineScheduler.cpp b/lib/CodeGen/MachineScheduler.cpp
index b088d1a..badc0e5 100644
--- a/lib/CodeGen/MachineScheduler.cpp
+++ b/lib/CodeGen/MachineScheduler.cpp
@@ -464,7 +464,7 @@
// Close the RPTracker to finalize live ins.
RPTracker.closeRegion();
- DEBUG(RPTracker.getPressure().dump(TRI));
+ DEBUG(RPTracker.dump());
// Initialize the live ins and live outs.
TopRPTracker.addLiveRegs(RPTracker.getPressure().LiveInRegs);
@@ -476,6 +476,13 @@
TopRPTracker.closeTop();
BotRPTracker.closeBottom();
+ BotRPTracker.initLiveThru(RPTracker);
+ if (!BotRPTracker.getLiveThru().empty()) {
+ TopRPTracker.initLiveThru(BotRPTracker.getLiveThru());
+ DEBUG(dbgs() << "Live Thru: ";
+ dumpRegSetPressure(BotRPTracker.getLiveThru(), TRI));
+ };
+
// Account for liveness generated by the region boundary.
if (LiveRegionEnd != RegionEnd)
BotRPTracker.recede();
@@ -579,7 +586,8 @@
/// Build the DAG and setup three register pressure trackers.
void ScheduleDAGMI::buildDAGWithRegPressure() {
// Initialize the register pressure tracker used by buildSchedGraph.
- RPTracker.init(&MF, RegClassInfo, LIS, BB, LiveRegionEnd);
+ RPTracker.init(&MF, RegClassInfo, LIS, BB, LiveRegionEnd,
+ /*TrackUntiedDefs=*/true);
// Account for liveness generate by the region boundary.
if (LiveRegionEnd != RegionEnd)
diff --git a/lib/CodeGen/RegisterPressure.cpp b/lib/CodeGen/RegisterPressure.cpp
index 4175a4f..b7ab138 100644
--- a/lib/CodeGen/RegisterPressure.cpp
+++ b/lib/CodeGen/RegisterPressure.cpp
@@ -76,17 +76,22 @@
}
#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 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 @@
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 @@
CurrPos = pos;
CurrSetPressure.assign(TRI->getNumRegPressureSets(), 0);
+ LiveThruPressure.clear();
if (RequireIntervals)
static_cast<IntervalPressure&>(P).reset();
@@ -226,6 +236,9 @@
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 @@
// 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 @@
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 @@
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 @@
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 @@
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 @@
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 &&