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llvm-project/llvm/lib/CodeGen/RegisterPressure.cpp

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//===-- RegisterPressure.cpp - Dynamic Register Pressure ------------------===//
//
// The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
//
// This file implements the RegisterPressure class which can be used to track
// MachineInstr level register pressure.
//
//===----------------------------------------------------------------------===//
#include "llvm/CodeGen/RegisterPressure.h"
#include "llvm/CodeGen/LiveInterval.h"
#include "llvm/CodeGen/LiveIntervalAnalysis.h"
#include "llvm/CodeGen/MachineRegisterInfo.h"
#include "llvm/CodeGen/RegisterClassInfo.h"
#include "llvm/Support/Debug.h"
#include "llvm/Support/raw_ostream.h"
#include "llvm/Target/TargetMachine.h"
using namespace llvm;
/// Increase pressure for each pressure set provided by TargetRegisterInfo.
static void increaseSetPressure(std::vector<unsigned> &CurrSetPressure,
std::vector<unsigned> &MaxSetPressure,
const int *PSet, unsigned Weight) {
for (; *PSet != -1; ++PSet) {
CurrSetPressure[*PSet] += Weight;
if (&CurrSetPressure != &MaxSetPressure
&& CurrSetPressure[*PSet] > MaxSetPressure[*PSet]) {
MaxSetPressure[*PSet] = CurrSetPressure[*PSet];
}
}
}
/// Decrease pressure for each pressure set provided by TargetRegisterInfo.
static void decreaseSetPressure(std::vector<unsigned> &CurrSetPressure,
const int *PSet, unsigned Weight) {
for (; *PSet != -1; ++PSet) {
assert(CurrSetPressure[*PSet] >= Weight && "register pressure underflow");
CurrSetPressure[*PSet] -= Weight;
}
}
/// Directly increase pressure only within this RegisterPressure result.
void RegisterPressure::increase(unsigned Reg, const TargetRegisterInfo *TRI,
const MachineRegisterInfo *MRI) {
if (TargetRegisterInfo::isVirtualRegister(Reg)) {
const TargetRegisterClass *RC = MRI->getRegClass(Reg);
increaseSetPressure(MaxSetPressure, MaxSetPressure,
TRI->getRegClassPressureSets(RC),
TRI->getRegClassWeight(RC).RegWeight);
}
else {
increaseSetPressure(MaxSetPressure, MaxSetPressure,
TRI->getRegUnitPressureSets(Reg),
TRI->getRegUnitWeight(Reg));
}
}
/// Directly decrease pressure only within this RegisterPressure result.
void RegisterPressure::decrease(unsigned Reg, const TargetRegisterInfo *TRI,
const MachineRegisterInfo *MRI) {
if (TargetRegisterInfo::isVirtualRegister(Reg)) {
const TargetRegisterClass *RC = MRI->getRegClass(Reg);
decreaseSetPressure(MaxSetPressure, TRI->getRegClassPressureSets(RC),
TRI->getRegClassWeight(RC).RegWeight);
}
else {
decreaseSetPressure(MaxSetPressure, TRI->getRegUnitPressureSets(Reg),
TRI->getRegUnitWeight(Reg));
}
}
#if !defined(NDEBUG) || defined(LLVM_ENABLE_DUMP)
static void dumpSetPressure(const std::vector<unsigned> &SetPressure,
const TargetRegisterInfo *TRI) {
for (unsigned i = 0, e = SetPressure.size(); i < e; ++i) {
if (SetPressure[i] != 0)
dbgs() << TRI->getRegPressureSetName(i) << "=" << SetPressure[i] << '\n';
}
}
void RegisterPressure::dump(const TargetRegisterInfo *TRI) const {
dbgs() << "Max Pressure: ";
dumpSetPressure(MaxSetPressure, TRI);
dbgs() << "Live In: ";
for (unsigned i = 0, e = LiveInRegs.size(); i < e; ++i)
dbgs() << PrintReg(LiveInRegs[i], TRI) << " ";
dbgs() << '\n';
dbgs() << "Live Out: ";
for (unsigned i = 0, e = LiveOutRegs.size(); i < e; ++i)
dbgs() << PrintReg(LiveOutRegs[i], TRI) << " ";
dbgs() << '\n';
}
void RegPressureTracker::dump(const TargetRegisterInfo *TRI) const {
dbgs() << "Curr Pressure: ";
dumpSetPressure(CurrSetPressure, TRI);
P.dump(TRI);
}
#endif
/// Increase the current pressure as impacted by these registers and bump
/// the high water mark if needed.
void RegPressureTracker::increaseRegPressure(ArrayRef<unsigned> Regs) {
for (unsigned I = 0, E = Regs.size(); I != E; ++I) {
if (TargetRegisterInfo::isVirtualRegister(Regs[I])) {
const TargetRegisterClass *RC = MRI->getRegClass(Regs[I]);
increaseSetPressure(CurrSetPressure, P.MaxSetPressure,
TRI->getRegClassPressureSets(RC),
TRI->getRegClassWeight(RC).RegWeight);
}
else {
increaseSetPressure(CurrSetPressure, P.MaxSetPressure,
TRI->getRegUnitPressureSets(Regs[I]),
TRI->getRegUnitWeight(Regs[I]));
}
}
}
/// Simply decrease the current pressure as impacted by these registers.
void RegPressureTracker::decreaseRegPressure(ArrayRef<unsigned> Regs) {
for (unsigned I = 0, E = Regs.size(); I != E; ++I) {
if (TargetRegisterInfo::isVirtualRegister(Regs[I])) {
const TargetRegisterClass *RC = MRI->getRegClass(Regs[I]);
decreaseSetPressure(CurrSetPressure,
TRI->getRegClassPressureSets(RC),
TRI->getRegClassWeight(RC).RegWeight);
}
else {
decreaseSetPressure(CurrSetPressure, TRI->getRegUnitPressureSets(Regs[I]),
TRI->getRegUnitWeight(Regs[I]));
}
}
}
/// Clear the result so it can be used for another round of pressure tracking.
void IntervalPressure::reset() {
TopIdx = BottomIdx = SlotIndex();
MaxSetPressure.clear();
LiveInRegs.clear();
LiveOutRegs.clear();
}
/// Clear the result so it can be used for another round of pressure tracking.
void RegionPressure::reset() {
TopPos = BottomPos = MachineBasicBlock::const_iterator();
MaxSetPressure.clear();
LiveInRegs.clear();
LiveOutRegs.clear();
}
/// If the current top is not less than or equal to the next index, open it.
/// We happen to need the SlotIndex for the next top for pressure update.
void IntervalPressure::openTop(SlotIndex NextTop) {
if (TopIdx <= NextTop)
return;
TopIdx = SlotIndex();
LiveInRegs.clear();
}
/// If the current top is the previous instruction (before receding), open it.
void RegionPressure::openTop(MachineBasicBlock::const_iterator PrevTop) {
if (TopPos != PrevTop)
return;
TopPos = MachineBasicBlock::const_iterator();
LiveInRegs.clear();
}
/// If the current bottom is not greater than the previous index, open it.
void IntervalPressure::openBottom(SlotIndex PrevBottom) {
if (BottomIdx > PrevBottom)
return;
BottomIdx = SlotIndex();
LiveInRegs.clear();
}
/// If the current bottom is the previous instr (before advancing), open it.
void RegionPressure::openBottom(MachineBasicBlock::const_iterator PrevBottom) {
if (BottomPos != PrevBottom)
return;
BottomPos = MachineBasicBlock::const_iterator();
LiveInRegs.clear();
}
const LiveInterval *RegPressureTracker::getInterval(unsigned Reg) const {
if (TargetRegisterInfo::isVirtualRegister(Reg))
return &LIS->getInterval(Reg);
return LIS->getCachedRegUnit(Reg);
}
/// Setup the RegPressureTracker.
///
/// TODO: Add support for pressure without LiveIntervals.
void RegPressureTracker::init(const MachineFunction *mf,
const RegisterClassInfo *rci,
const LiveIntervals *lis,
const MachineBasicBlock *mbb,
MachineBasicBlock::const_iterator pos)
{
MF = mf;
TRI = MF->getTarget().getRegisterInfo();
RCI = rci;
MRI = &MF->getRegInfo();
MBB = mbb;
if (RequireIntervals) {
assert(lis && "IntervalPressure requires LiveIntervals");
LIS = lis;
}
CurrPos = pos;
CurrSetPressure.assign(TRI->getNumRegPressureSets(), 0);
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());
}
/// Does this pressure result have a valid top position and live ins.
bool RegPressureTracker::isTopClosed() const {
if (RequireIntervals)
return static_cast<IntervalPressure&>(P).TopIdx.isValid();
return (static_cast<RegionPressure&>(P).TopPos ==
MachineBasicBlock::const_iterator());
}
/// Does this pressure result have a valid bottom position and live outs.
bool RegPressureTracker::isBottomClosed() const {
if (RequireIntervals)
return static_cast<IntervalPressure&>(P).BottomIdx.isValid();
return (static_cast<RegionPressure&>(P).BottomPos ==
MachineBasicBlock::const_iterator());
}
SlotIndex RegPressureTracker::getCurrSlot() const {
MachineBasicBlock::const_iterator IdxPos = CurrPos;
while (IdxPos != MBB->end() && IdxPos->isDebugValue())
++IdxPos;
if (IdxPos == MBB->end())
return LIS->getMBBEndIdx(MBB);
return LIS->getInstructionIndex(IdxPos).getRegSlot();
}
/// Set the boundary for the top of the region and summarize live ins.
void RegPressureTracker::closeTop() {
if (RequireIntervals)
static_cast<IntervalPressure&>(P).TopIdx = getCurrSlot();
else
static_cast<RegionPressure&>(P).TopPos = CurrPos;
assert(P.LiveInRegs.empty() && "inconsistent max pressure result");
P.LiveInRegs.reserve(LiveRegs.PhysRegs.size() + LiveRegs.VirtRegs.size());
P.LiveInRegs.append(LiveRegs.PhysRegs.begin(), LiveRegs.PhysRegs.end());
for (SparseSet<unsigned>::const_iterator I =
LiveRegs.VirtRegs.begin(), E = LiveRegs.VirtRegs.end(); I != E; ++I)
P.LiveInRegs.push_back(*I);
std::sort(P.LiveInRegs.begin(), P.LiveInRegs.end());
P.LiveInRegs.erase(std::unique(P.LiveInRegs.begin(), P.LiveInRegs.end()),
P.LiveInRegs.end());
}
/// Set the boundary for the bottom of the region and summarize live outs.
void RegPressureTracker::closeBottom() {
if (RequireIntervals)
static_cast<IntervalPressure&>(P).BottomIdx = getCurrSlot();
else
static_cast<RegionPressure&>(P).BottomPos = CurrPos;
assert(P.LiveOutRegs.empty() && "inconsistent max pressure result");
P.LiveOutRegs.reserve(LiveRegs.PhysRegs.size() + LiveRegs.VirtRegs.size());
P.LiveOutRegs.append(LiveRegs.PhysRegs.begin(), LiveRegs.PhysRegs.end());
for (SparseSet<unsigned>::const_iterator I =
LiveRegs.VirtRegs.begin(), E = LiveRegs.VirtRegs.end(); I != E; ++I)
P.LiveOutRegs.push_back(*I);
std::sort(P.LiveOutRegs.begin(), P.LiveOutRegs.end());
P.LiveOutRegs.erase(std::unique(P.LiveOutRegs.begin(), P.LiveOutRegs.end()),
P.LiveOutRegs.end());
}
/// Finalize the region boundaries and record live ins and live outs.
void RegPressureTracker::closeRegion() {
if (!isTopClosed() && !isBottomClosed()) {
assert(LiveRegs.PhysRegs.empty() && LiveRegs.VirtRegs.empty() &&
"no region boundary");
return;
}
if (!isBottomClosed())
closeBottom();
else if (!isTopClosed())
closeTop();
// If both top and bottom are closed, do nothing.
}
/// \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();
}
/// Collect this instruction's unique uses and defs into SmallVectors for
/// processing defs and uses in order.
class RegisterOperands {
const TargetRegisterInfo *TRI;
const MachineRegisterInfo *MRI;
public:
SmallVector<unsigned, 8> Uses;
SmallVector<unsigned, 8> Defs;
SmallVector<unsigned, 8> DeadDefs;
RegisterOperands(const TargetRegisterInfo *tri,
const MachineRegisterInfo *mri): TRI(tri), MRI(mri) {}
/// Push this operand's register onto the correct vector.
void collect(const MachineOperand &MO) {
if (!MO.isReg() || !MO.getReg())
return;
if (MO.readsReg())
pushRegUnits(MO.getReg(), Uses);
if (MO.isDef()) {
if (MO.isDead())
pushRegUnits(MO.getReg(), DeadDefs);
else
pushRegUnits(MO.getReg(), Defs);
}
}
protected:
void pushRegUnits(unsigned Reg, SmallVectorImpl<unsigned> &Regs) {
if (TargetRegisterInfo::isVirtualRegister(Reg)) {
if (containsReg(Regs, Reg))
return;
Regs.push_back(Reg);
}
else if (MRI->isAllocatable(Reg)) {
for (MCRegUnitIterator Units(Reg, TRI); Units.isValid(); ++Units) {
if (containsReg(Regs, *Units))
continue;
Regs.push_back(*Units);
}
}
}
};
/// Collect physical and virtual register operands.
static void collectOperands(const MachineInstr *MI,
RegisterOperands &RegOpers) {
for(ConstMIBundleOperands OperI(MI); OperI.isValid(); ++OperI)
RegOpers.collect(*OperI);
// Remove redundant physreg dead defs.
for (unsigned i = RegOpers.DeadDefs.size(); i > 0; --i) {
unsigned Reg = RegOpers.DeadDefs[i-1];
if (containsReg(RegOpers.Defs, Reg))
RegOpers.DeadDefs.erase(&RegOpers.DeadDefs[i-1]);
}
}
/// Force liveness of registers.
void RegPressureTracker::addLiveRegs(ArrayRef<unsigned> Regs) {
for (unsigned i = 0, e = Regs.size(); i != e; ++i) {
if (LiveRegs.insert(Regs[i]))
increaseRegPressure(Regs[i]);
}
}
/// Add Reg to the live in set and increase max pressure.
void RegPressureTracker::discoverLiveIn(unsigned Reg) {
assert(!LiveRegs.contains(Reg) && "avoid bumping max pressure twice");
if (containsReg(P.LiveInRegs, Reg))
return;
// At live in discovery, unconditionally increase the high water mark.
P.LiveInRegs.push_back(Reg);
P.increase(Reg, TRI, MRI);
}
/// Add Reg to the live out set and increase max pressure.
void RegPressureTracker::discoverLiveOut(unsigned Reg) {
assert(!LiveRegs.contains(Reg) && "avoid bumping max pressure twice");
if (containsReg(P.LiveOutRegs, Reg))
return;
// At live out discovery, unconditionally increase the high water mark.
P.LiveOutRegs.push_back(Reg);
P.increase(Reg, TRI, MRI);
}
/// Recede across the previous instruction.
bool RegPressureTracker::recede() {
// Check for the top of the analyzable region.
if (CurrPos == MBB->begin()) {
closeRegion();
return false;
}
if (!isBottomClosed())
closeBottom();
// Open the top of the region using block iterators.
if (!RequireIntervals && isTopClosed())
static_cast<RegionPressure&>(P).openTop(CurrPos);
// Find the previous instruction.
do
--CurrPos;
while (CurrPos != MBB->begin() && CurrPos->isDebugValue());
if (CurrPos->isDebugValue()) {
closeRegion();
return false;
}
SlotIndex SlotIdx;
if (RequireIntervals)
SlotIdx = LIS->getInstructionIndex(CurrPos).getRegSlot();
// Open the top of the region using slot indexes.
if (RequireIntervals && isTopClosed())
static_cast<IntervalPressure&>(P).openTop(SlotIdx);
RegisterOperands RegOpers(TRI, MRI);
collectOperands(CurrPos, RegOpers);
// Boost pressure for all dead defs together.
increaseRegPressure(RegOpers.DeadDefs);
decreaseRegPressure(RegOpers.DeadDefs);
// Kill liveness at live defs.
// TODO: consider earlyclobbers?
for (unsigned i = 0, e = RegOpers.Defs.size(); i < e; ++i) {
unsigned Reg = RegOpers.Defs[i];
if (LiveRegs.erase(Reg))
decreaseRegPressure(Reg);
else
discoverLiveOut(Reg);
}
// Generate liveness for uses.
for (unsigned i = 0, e = RegOpers.Uses.size(); i < e; ++i) {
unsigned Reg = RegOpers.Uses[i];
if (!LiveRegs.contains(Reg)) {
// Adjust liveouts if LiveIntervals are available.
if (RequireIntervals) {
const LiveInterval *LI = getInterval(Reg);
if (LI && !LI->killedAt(SlotIdx))
discoverLiveOut(Reg);
}
increaseRegPressure(Reg);
LiveRegs.insert(Reg);
}
}
return true;
}
/// Advance across the current instruction.
bool RegPressureTracker::advance() {
// Check for the bottom of the analyzable region.
if (CurrPos == MBB->end()) {
closeRegion();
return false;
}
if (!isTopClosed())
closeTop();
SlotIndex SlotIdx;
if (RequireIntervals)
SlotIdx = getCurrSlot();
// Open the bottom of the region using slot indexes.
if (isBottomClosed()) {
if (RequireIntervals)
static_cast<IntervalPressure&>(P).openBottom(SlotIdx);
else
static_cast<RegionPressure&>(P).openBottom(CurrPos);
}
RegisterOperands RegOpers(TRI, MRI);
collectOperands(CurrPos, RegOpers);
for (unsigned i = 0, e = RegOpers.Uses.size(); i < e; ++i) {
unsigned Reg = RegOpers.Uses[i];
// Discover live-ins.
bool isLive = LiveRegs.contains(Reg);
if (!isLive)
discoverLiveIn(Reg);
// Kill liveness at last uses.
bool lastUse = false;
if (RequireIntervals) {
const LiveInterval *LI = getInterval(Reg);
lastUse = LI && LI->killedAt(SlotIdx);
}
else {
// Allocatable physregs are always single-use before register rewriting.
lastUse = !TargetRegisterInfo::isVirtualRegister(Reg);
}
if (lastUse && isLive) {
LiveRegs.erase(Reg);
decreaseRegPressure(Reg);
}
else if (!lastUse && !isLive)
increaseRegPressure(Reg);
}
// Generate liveness for defs.
for (unsigned i = 0, e = RegOpers.Defs.size(); i < e; ++i) {
unsigned Reg = RegOpers.Defs[i];
if (LiveRegs.insert(Reg))
increaseRegPressure(Reg);
}
// Boost pressure for all dead defs together.
increaseRegPressure(RegOpers.DeadDefs);
decreaseRegPressure(RegOpers.DeadDefs);
// Find the next instruction.
do
++CurrPos;
while (CurrPos != MBB->end() && CurrPos->isDebugValue());
return true;
}
/// Find the max change in excess pressure across all sets.
static void computeExcessPressureDelta(ArrayRef<unsigned> OldPressureVec,
ArrayRef<unsigned> NewPressureVec,
RegPressureDelta &Delta,
const TargetRegisterInfo *TRI) {
int ExcessUnits = 0;
unsigned PSetID = ~0U;
for (unsigned i = 0, e = OldPressureVec.size(); i < e; ++i) {
unsigned POld = OldPressureVec[i];
unsigned PNew = NewPressureVec[i];
int PDiff = (int)PNew - (int)POld;
if (!PDiff) // No change in this set in the common case.
continue;
// Only consider change beyond the limit.
unsigned Limit = TRI->getRegPressureSetLimit(i);
if (Limit > POld) {
if (Limit > PNew)
PDiff = 0; // Under the limit
else
PDiff = PNew - Limit; // Just exceeded limit.
}
else if (Limit > PNew)
PDiff = Limit - POld; // Just obeyed limit.
if (std::abs(PDiff) > std::abs(ExcessUnits)) {
ExcessUnits = PDiff;
PSetID = i;
}
}
Delta.Excess.PSetID = PSetID;
Delta.Excess.UnitIncrease = ExcessUnits;
}
/// Find the max change in max pressure that either surpasses a critical PSet
/// limit or exceeds the current MaxPressureLimit.
///
/// FIXME: comparing each element of the old and new MaxPressure vectors here is
/// silly. It's done now to demonstrate the concept but will go away with a
/// RegPressureTracker API change to work with pressure differences.
static void computeMaxPressureDelta(ArrayRef<unsigned> OldMaxPressureVec,
ArrayRef<unsigned> NewMaxPressureVec,
ArrayRef<PressureElement> CriticalPSets,
ArrayRef<unsigned> MaxPressureLimit,
RegPressureDelta &Delta) {
Delta.CriticalMax = PressureElement();
Delta.CurrentMax = PressureElement();
unsigned CritIdx = 0, CritEnd = CriticalPSets.size();
for (unsigned i = 0, e = OldMaxPressureVec.size(); i < e; ++i) {
unsigned POld = OldMaxPressureVec[i];
unsigned PNew = NewMaxPressureVec[i];
if (PNew == POld) // No change in this set in the common case.
continue;
while (CritIdx != CritEnd && CriticalPSets[CritIdx].PSetID < i)
++CritIdx;
if (CritIdx != CritEnd && CriticalPSets[CritIdx].PSetID == i) {
int PDiff = (int)PNew - (int)CriticalPSets[CritIdx].UnitIncrease;
if (PDiff > Delta.CriticalMax.UnitIncrease) {
Delta.CriticalMax.PSetID = i;
Delta.CriticalMax.UnitIncrease = PDiff;
}
}
// Find the greatest increase above MaxPressureLimit.
// (Ignores negative MDiff).
int MDiff = (int)PNew - (int)MaxPressureLimit[i];
if (MDiff > Delta.CurrentMax.UnitIncrease) {
Delta.CurrentMax.PSetID = i;
Delta.CurrentMax.UnitIncrease = PNew;
}
}
}
/// Record the upward impact of a single instruction on current register
/// pressure. Unlike the advance/recede pressure tracking interface, this does
/// not discover live in/outs.
///
/// This is intended for speculative queries. It leaves pressure inconsistent
/// with the current position, so must be restored by the caller.
void RegPressureTracker::bumpUpwardPressure(const MachineInstr *MI) {
assert(!MI->isDebugValue() && "Expect a nondebug instruction.");
// Account for register pressure similar to RegPressureTracker::recede().
RegisterOperands RegOpers(TRI, MRI);
collectOperands(MI, RegOpers);
// Boost max pressure for all dead defs together.
// Since CurrSetPressure and MaxSetPressure
increaseRegPressure(RegOpers.DeadDefs);
decreaseRegPressure(RegOpers.DeadDefs);
// Kill liveness at live defs.
for (unsigned i = 0, e = RegOpers.Defs.size(); i < e; ++i) {
unsigned Reg = RegOpers.Defs[i];
if (!containsReg(RegOpers.Uses, Reg))
decreaseRegPressure(Reg);
}
// Generate liveness for uses.
for (unsigned i = 0, e = RegOpers.Uses.size(); i < e; ++i) {
unsigned Reg = RegOpers.Uses[i];
if (!LiveRegs.contains(Reg))
increaseRegPressure(Reg);
}
}
/// Consider the pressure increase caused by traversing this instruction
/// bottom-up. Find the pressure set with the most change beyond its pressure
/// limit based on the tracker's current pressure, and return the change in
/// number of register units of that pressure set introduced by this
/// instruction.
///
/// This assumes that the current LiveOut set is sufficient.
///
/// FIXME: This is expensive for an on-the-fly query. We need to cache the
/// result per-SUnit with enough information to adjust for the current
/// scheduling position. But this works as a proof of concept.
void RegPressureTracker::
getMaxUpwardPressureDelta(const MachineInstr *MI, RegPressureDelta &Delta,
ArrayRef<PressureElement> CriticalPSets,
ArrayRef<unsigned> MaxPressureLimit) {
// Snapshot Pressure.
// FIXME: The snapshot heap space should persist. But I'm planning to
// summarize the pressure effect so we don't need to snapshot at all.
std::vector<unsigned> SavedPressure = CurrSetPressure;
std::vector<unsigned> SavedMaxPressure = P.MaxSetPressure;
bumpUpwardPressure(MI);
computeExcessPressureDelta(SavedPressure, CurrSetPressure, Delta, TRI);
computeMaxPressureDelta(SavedMaxPressure, P.MaxSetPressure, CriticalPSets,
MaxPressureLimit, Delta);
assert(Delta.CriticalMax.UnitIncrease >= 0 &&
Delta.CurrentMax.UnitIncrease >= 0 && "cannot decrease max pressure");
// Restore the tracker's state.
P.MaxSetPressure.swap(SavedMaxPressure);
CurrSetPressure.swap(SavedPressure);
}
/// Helper to find a vreg use between two indices [PriorUseIdx, NextUseIdx).
static bool findUseBetween(unsigned Reg,
SlotIndex PriorUseIdx, SlotIndex NextUseIdx,
const MachineRegisterInfo *MRI,
const LiveIntervals *LIS) {
for (MachineRegisterInfo::use_nodbg_iterator
UI = MRI->use_nodbg_begin(Reg), UE = MRI->use_nodbg_end();
UI != UE; UI.skipInstruction()) {
const MachineInstr* MI = &*UI;
if (MI->isDebugValue())
continue;
SlotIndex InstSlot = LIS->getInstructionIndex(MI).getRegSlot();
if (InstSlot >= PriorUseIdx && InstSlot < NextUseIdx)
return true;
}
return false;
}
/// Record the downward impact of a single instruction on current register
/// pressure. Unlike the advance/recede pressure tracking interface, this does
/// not discover live in/outs.
///
/// This is intended for speculative queries. It leaves pressure inconsistent
/// with the current position, so must be restored by the caller.
void RegPressureTracker::bumpDownwardPressure(const MachineInstr *MI) {
assert(!MI->isDebugValue() && "Expect a nondebug instruction.");
// Account for register pressure similar to RegPressureTracker::recede().
RegisterOperands RegOpers(TRI, MRI);
collectOperands(MI, RegOpers);
// Kill liveness at last uses. Assume allocatable physregs are single-use
// rather than checking LiveIntervals.
SlotIndex SlotIdx;
if (RequireIntervals)
SlotIdx = LIS->getInstructionIndex(MI).getRegSlot();
for (unsigned i = 0, e = RegOpers.Uses.size(); i < e; ++i) {
unsigned Reg = RegOpers.Uses[i];
if (RequireIntervals) {
// FIXME: allow the caller to pass in the list of vreg uses that remain
// to be bottom-scheduled to avoid searching uses at each query.
SlotIndex CurrIdx = getCurrSlot();
const LiveInterval *LI = getInterval(Reg);
if (LI && LI->killedAt(SlotIdx)
&& !findUseBetween(Reg, CurrIdx, SlotIdx, MRI, LIS)) {
decreaseRegPressure(Reg);
}
}
else if (!TargetRegisterInfo::isVirtualRegister(Reg)) {
// Allocatable physregs are always single-use before register rewriting.
decreaseRegPressure(Reg);
}
}
// Generate liveness for defs.
increaseRegPressure(RegOpers.Defs);
// Boost pressure for all dead defs together.
increaseRegPressure(RegOpers.DeadDefs);
decreaseRegPressure(RegOpers.DeadDefs);
}
/// Consider the pressure increase caused by traversing this instruction
/// top-down. Find the register class with the most change in its pressure limit
/// based on the tracker's current pressure, and return the number of excess
/// register units of that pressure set introduced by this instruction.
///
/// This assumes that the current LiveIn set is sufficient.
void RegPressureTracker::
getMaxDownwardPressureDelta(const MachineInstr *MI, RegPressureDelta &Delta,
ArrayRef<PressureElement> CriticalPSets,
ArrayRef<unsigned> MaxPressureLimit) {
// Snapshot Pressure.
std::vector<unsigned> SavedPressure = CurrSetPressure;
std::vector<unsigned> SavedMaxPressure = P.MaxSetPressure;
bumpDownwardPressure(MI);
computeExcessPressureDelta(SavedPressure, CurrSetPressure, Delta, TRI);
computeMaxPressureDelta(SavedMaxPressure, P.MaxSetPressure, CriticalPSets,
MaxPressureLimit, Delta);
assert(Delta.CriticalMax.UnitIncrease >= 0 &&
Delta.CurrentMax.UnitIncrease >= 0 && "cannot decrease max pressure");
// Restore the tracker's state.
P.MaxSetPressure.swap(SavedMaxPressure);
CurrSetPressure.swap(SavedPressure);
}
/// Get the pressure of each PSet after traversing this instruction bottom-up.
void RegPressureTracker::
getUpwardPressure(const MachineInstr *MI,
std::vector<unsigned> &PressureResult,
std::vector<unsigned> &MaxPressureResult) {
// Snapshot pressure.
PressureResult = CurrSetPressure;
MaxPressureResult = P.MaxSetPressure;
bumpUpwardPressure(MI);
// Current pressure becomes the result. Restore current pressure.
P.MaxSetPressure.swap(MaxPressureResult);
CurrSetPressure.swap(PressureResult);
}
/// Get the pressure of each PSet after traversing this instruction top-down.
void RegPressureTracker::
getDownwardPressure(const MachineInstr *MI,
std::vector<unsigned> &PressureResult,
std::vector<unsigned> &MaxPressureResult) {
// Snapshot pressure.
PressureResult = CurrSetPressure;
MaxPressureResult = P.MaxSetPressure;
bumpDownwardPressure(MI);
// Current pressure becomes the result. Restore current pressure.
P.MaxSetPressure.swap(MaxPressureResult);
CurrSetPressure.swap(PressureResult);
}
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