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LiveIntervals.cpp
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//===- LiveIntervals.cpp - Live Interval Analysis -------------------------===//
//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See https://llvm.org/LICENSE.txt for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
//
//===----------------------------------------------------------------------===//
//
/// \file This file implements the LiveInterval analysis pass which is used
/// by the Linear Scan Register allocator. This pass linearizes the
/// basic blocks of the function in DFS order and computes live intervals for
/// each virtual and physical register.
//
//===----------------------------------------------------------------------===//
#include "llvm/CodeGen/LiveIntervals.h"
#include "llvm/ADT/ArrayRef.h"
#include "llvm/ADT/DepthFirstIterator.h"
#include "llvm/ADT/SmallPtrSet.h"
#include "llvm/ADT/SmallVector.h"
#include "llvm/ADT/iterator_range.h"
#include "llvm/Analysis/AliasAnalysis.h"
#include "llvm/CodeGen/LiveInterval.h"
#include "llvm/CodeGen/LiveIntervalCalc.h"
#include "llvm/CodeGen/LiveVariables.h"
#include "llvm/CodeGen/MachineBasicBlock.h"
#include "llvm/CodeGen/MachineBlockFrequencyInfo.h"
#include "llvm/CodeGen/MachineDominators.h"
#include "llvm/CodeGen/MachineFunction.h"
#include "llvm/CodeGen/MachineInstr.h"
#include "llvm/CodeGen/MachineInstrBundle.h"
#include "llvm/CodeGen/MachineOperand.h"
#include "llvm/CodeGen/MachineRegisterInfo.h"
#include "llvm/CodeGen/Passes.h"
#include "llvm/CodeGen/SlotIndexes.h"
#include "llvm/CodeGen/TargetRegisterInfo.h"
#include "llvm/CodeGen/TargetSubtargetInfo.h"
#include "llvm/CodeGen/VirtRegMap.h"
#include "llvm/Config/llvm-config.h"
#include "llvm/MC/LaneBitmask.h"
#include "llvm/MC/MCRegisterInfo.h"
#include "llvm/Pass.h"
#include "llvm/Support/BlockFrequency.h"
#include "llvm/Support/CommandLine.h"
#include "llvm/Support/Compiler.h"
#include "llvm/Support/Debug.h"
#include "llvm/Support/MathExtras.h"
#include "llvm/Support/raw_ostream.h"
#include <algorithm>
#include <cassert>
#include <cstdint>
#include <iterator>
#include <tuple>
#include <utility>
using namespace llvm;
#define DEBUG_TYPE "regalloc"
char LiveIntervals::ID = 0;
char &llvm::LiveIntervalsID = LiveIntervals::ID;
INITIALIZE_PASS_BEGIN(LiveIntervals, "liveintervals",
"Live Interval Analysis", false, false)
INITIALIZE_PASS_DEPENDENCY(AAResultsWrapperPass)
INITIALIZE_PASS_DEPENDENCY(MachineDominatorTree)
INITIALIZE_PASS_DEPENDENCY(SlotIndexes)
INITIALIZE_PASS_END(LiveIntervals, "liveintervals",
"Live Interval Analysis", false, false)
#ifndef NDEBUG
static cl::opt<bool> EnablePrecomputePhysRegs(
"precompute-phys-liveness", cl::Hidden,
cl::desc("Eagerly compute live intervals for all physreg units."));
#else
static bool EnablePrecomputePhysRegs = false;
#endif // NDEBUG
namespace llvm {
cl::opt<bool> UseSegmentSetForPhysRegs(
"use-segment-set-for-physregs", cl::Hidden, cl::init(true),
cl::desc(
"Use segment set for the computation of the live ranges of physregs."));
} // end namespace llvm
void LiveIntervals::getAnalysisUsage(AnalysisUsage &AU) const {
AU.setPreservesCFG();
AU.addRequired<AAResultsWrapperPass>();
AU.addPreserved<AAResultsWrapperPass>();
AU.addPreserved<LiveVariables>();
AU.addPreservedID(MachineLoopInfoID);
AU.addRequiredTransitiveID(MachineDominatorsID);
AU.addPreservedID(MachineDominatorsID);
AU.addPreserved<SlotIndexes>();
AU.addRequiredTransitive<SlotIndexes>();
MachineFunctionPass::getAnalysisUsage(AU);
}
LiveIntervals::LiveIntervals() : MachineFunctionPass(ID) {
initializeLiveIntervalsPass(*PassRegistry::getPassRegistry());
}
LiveIntervals::~LiveIntervals() { delete LICalc; }
void LiveIntervals::releaseMemory() {
// Free the live intervals themselves.
for (unsigned i = 0, e = VirtRegIntervals.size(); i != e; ++i)
delete VirtRegIntervals[Register::index2VirtReg(i)];
VirtRegIntervals.clear();
RegMaskSlots.clear();
RegMaskBits.clear();
RegMaskBlocks.clear();
for (LiveRange *LR : RegUnitRanges)
delete LR;
RegUnitRanges.clear();
// Release VNInfo memory regions, VNInfo objects don't need to be dtor'd.
VNInfoAllocator.Reset();
}
bool LiveIntervals::runOnMachineFunction(MachineFunction &fn) {
MF = &fn;
MRI = &MF->getRegInfo();
TRI = MF->getSubtarget().getRegisterInfo();
TII = MF->getSubtarget().getInstrInfo();
AA = &getAnalysis<AAResultsWrapperPass>().getAAResults();
Indexes = &getAnalysis<SlotIndexes>();
DomTree = &getAnalysis<MachineDominatorTree>();
if (!LICalc)
LICalc = new LiveIntervalCalc();
// Allocate space for all virtual registers.
VirtRegIntervals.resize(MRI->getNumVirtRegs());
computeVirtRegs();
computeRegMasks();
computeLiveInRegUnits();
if (EnablePrecomputePhysRegs) {
// For stress testing, precompute live ranges of all physical register
// units, including reserved registers.
for (unsigned i = 0, e = TRI->getNumRegUnits(); i != e; ++i)
getRegUnit(i);
}
LLVM_DEBUG(dump());
return true;
}
void LiveIntervals::print(raw_ostream &OS, const Module* ) const {
OS << "********** INTERVALS **********\n";
// Dump the regunits.
for (unsigned Unit = 0, UnitE = RegUnitRanges.size(); Unit != UnitE; ++Unit)
if (LiveRange *LR = RegUnitRanges[Unit])
OS << printRegUnit(Unit, TRI) << ' ' << *LR << '\n';
// Dump the virtregs.
for (unsigned i = 0, e = MRI->getNumVirtRegs(); i != e; ++i) {
Register Reg = Register::index2VirtReg(i);
if (hasInterval(Reg))
OS << getInterval(Reg) << '\n';
}
OS << "RegMasks:";
for (SlotIndex Idx : RegMaskSlots)
OS << ' ' << Idx;
OS << '\n';
printInstrs(OS);
}
void LiveIntervals::printInstrs(raw_ostream &OS) const {
OS << "********** MACHINEINSTRS **********\n";
MF->print(OS, Indexes);
}
#if !defined(NDEBUG) || defined(LLVM_ENABLE_DUMP)
LLVM_DUMP_METHOD void LiveIntervals::dumpInstrs() const {
printInstrs(dbgs());
}
#endif
LiveInterval *LiveIntervals::createInterval(Register reg) {
float Weight = Register::isPhysicalRegister(reg) ? huge_valf : 0.0F;
return new LiveInterval(reg, Weight);
}
/// Compute the live interval of a virtual register, based on defs and uses.
bool LiveIntervals::computeVirtRegInterval(LiveInterval &LI) {
assert(LICalc && "LICalc not initialized.");
assert(LI.empty() && "Should only compute empty intervals.");
LICalc->reset(MF, getSlotIndexes(), DomTree, &getVNInfoAllocator());
LICalc->calculate(LI, MRI->shouldTrackSubRegLiveness(LI.reg()));
return computeDeadValues(LI, nullptr);
}
void LiveIntervals::computeVirtRegs() {
for (unsigned i = 0, e = MRI->getNumVirtRegs(); i != e; ++i) {
Register Reg = Register::index2VirtReg(i);
if (MRI->reg_nodbg_empty(Reg))
continue;
LiveInterval &LI = createEmptyInterval(Reg);
bool NeedSplit = computeVirtRegInterval(LI);
if (NeedSplit) {
SmallVector<LiveInterval*, 8> SplitLIs;
splitSeparateComponents(LI, SplitLIs);
}
}
}
void LiveIntervals::computeRegMasks() {
RegMaskBlocks.resize(MF->getNumBlockIDs());
// Find all instructions with regmask operands.
for (const MachineBasicBlock &MBB : *MF) {
std::pair<unsigned, unsigned> &RMB = RegMaskBlocks[MBB.getNumber()];
RMB.first = RegMaskSlots.size();
// Some block starts, such as EH funclets, create masks.
if (const uint32_t *Mask = MBB.getBeginClobberMask(TRI)) {
RegMaskSlots.push_back(Indexes->getMBBStartIdx(&MBB));
RegMaskBits.push_back(Mask);
}
// Unwinders may clobber additional registers.
// FIXME: This functionality can possibly be merged into
// MachineBasicBlock::getBeginClobberMask().
if (MBB.isEHPad())
if (auto *Mask = TRI->getCustomEHPadPreservedMask(*MBB.getParent())) {
RegMaskSlots.push_back(Indexes->getMBBStartIdx(&MBB));
RegMaskBits.push_back(Mask);
}
for (const MachineInstr &MI : MBB) {
for (const MachineOperand &MO : MI.operands()) {
if (!MO.isRegMask())
continue;
RegMaskSlots.push_back(Indexes->getInstructionIndex(MI).getRegSlot());
RegMaskBits.push_back(MO.getRegMask());
}
}
// Some block ends, such as funclet returns, create masks. Put the mask on
// the last instruction of the block, because MBB slot index intervals are
// half-open.
if (const uint32_t *Mask = MBB.getEndClobberMask(TRI)) {
assert(!MBB.empty() && "empty return block?");
RegMaskSlots.push_back(
Indexes->getInstructionIndex(MBB.back()).getRegSlot());
RegMaskBits.push_back(Mask);
}
// Compute the number of register mask instructions in this block.
RMB.second = RegMaskSlots.size() - RMB.first;
}
}
//===----------------------------------------------------------------------===//
// Register Unit Liveness
//===----------------------------------------------------------------------===//
//
// Fixed interference typically comes from ABI boundaries: Function arguments
// and return values are passed in fixed registers, and so are exception
// pointers entering landing pads. Certain instructions require values to be
// present in specific registers. That is also represented through fixed
// interference.
//
/// Compute the live range of a register unit, based on the uses and defs of
/// aliasing registers. The range should be empty, or contain only dead
/// phi-defs from ABI blocks.
void LiveIntervals::computeRegUnitRange(LiveRange &LR, unsigned Unit) {
assert(LICalc && "LICalc not initialized.");
LICalc->reset(MF, getSlotIndexes(), DomTree, &getVNInfoAllocator());
// The physregs aliasing Unit are the roots and their super-registers.
// Create all values as dead defs before extending to uses. Note that roots
// may share super-registers. That's OK because createDeadDefs() is
// idempotent. It is very rare for a register unit to have multiple roots, so
// uniquing super-registers is probably not worthwhile.
bool IsReserved = false;
for (MCRegUnitRootIterator Root(Unit, TRI); Root.isValid(); ++Root) {
bool IsRootReserved = true;
for (MCSuperRegIterator Super(*Root, TRI, /*IncludeSelf=*/true);
Super.isValid(); ++Super) {
MCRegister Reg = *Super;
if (!MRI->reg_empty(Reg))
LICalc->createDeadDefs(LR, Reg);
// A register unit is considered reserved if all its roots and all their
// super registers are reserved.
if (!MRI->isReserved(Reg))
IsRootReserved = false;
}
IsReserved |= IsRootReserved;
}
assert(IsReserved == MRI->isReservedRegUnit(Unit) &&
"reserved computation mismatch");
// Now extend LR to reach all uses.
// Ignore uses of reserved registers. We only track defs of those.
if (!IsReserved) {
for (MCRegUnitRootIterator Root(Unit, TRI); Root.isValid(); ++Root) {
for (MCSuperRegIterator Super(*Root, TRI, /*IncludeSelf=*/true);
Super.isValid(); ++Super) {
MCRegister Reg = *Super;
if (!MRI->reg_empty(Reg))
LICalc->extendToUses(LR, Reg);
}
}
}
// Flush the segment set to the segment vector.
if (UseSegmentSetForPhysRegs)
LR.flushSegmentSet();
}
/// Precompute the live ranges of any register units that are live-in to an ABI
/// block somewhere. Register values can appear without a corresponding def when
/// entering the entry block or a landing pad.
void LiveIntervals::computeLiveInRegUnits() {
RegUnitRanges.resize(TRI->getNumRegUnits());
LLVM_DEBUG(dbgs() << "Computing live-in reg-units in ABI blocks.\n");
// Keep track of the live range sets allocated.
SmallVector<unsigned, 8> NewRanges;
// Check all basic blocks for live-ins.
for (const MachineBasicBlock &MBB : *MF) {
// We only care about ABI blocks: Entry + landing pads.
if ((&MBB != &MF->front() && !MBB.isEHPad()) || MBB.livein_empty())
continue;
// Create phi-defs at Begin for all live-in registers.
SlotIndex Begin = Indexes->getMBBStartIdx(&MBB);
LLVM_DEBUG(dbgs() << Begin << "\t" << printMBBReference(MBB));
for (const auto &LI : MBB.liveins()) {
for (MCRegUnitIterator Units(LI.PhysReg, TRI); Units.isValid(); ++Units) {
unsigned Unit = *Units;
LiveRange *LR = RegUnitRanges[Unit];
if (!LR) {
// Use segment set to speed-up initial computation of the live range.
LR = RegUnitRanges[Unit] = new LiveRange(UseSegmentSetForPhysRegs);
NewRanges.push_back(Unit);
}
VNInfo *VNI = LR->createDeadDef(Begin, getVNInfoAllocator());
(void)VNI;
LLVM_DEBUG(dbgs() << ' ' << printRegUnit(Unit, TRI) << '#' << VNI->id);
}
}
LLVM_DEBUG(dbgs() << '\n');
}
LLVM_DEBUG(dbgs() << "Created " << NewRanges.size() << " new intervals.\n");
// Compute the 'normal' part of the ranges.
for (unsigned Unit : NewRanges)
computeRegUnitRange(*RegUnitRanges[Unit], Unit);
}
static void createSegmentsForValues(LiveRange &LR,
iterator_range<LiveInterval::vni_iterator> VNIs) {
for (VNInfo *VNI : VNIs) {
if (VNI->isUnused())
continue;
SlotIndex Def = VNI->def;
LR.addSegment(LiveRange::Segment(Def, Def.getDeadSlot(), VNI));
}
}
void LiveIntervals::extendSegmentsToUses(LiveRange &Segments,
ShrinkToUsesWorkList &WorkList,
Register Reg, LaneBitmask LaneMask) {
// Keep track of the PHIs that are in use.
SmallPtrSet<VNInfo*, 8> UsedPHIs;
// Blocks that have already been added to WorkList as live-out.
SmallPtrSet<const MachineBasicBlock*, 16> LiveOut;
auto getSubRange = [](const LiveInterval &I, LaneBitmask M)
-> const LiveRange& {
if (M.none())
return I;
for (const LiveInterval::SubRange &SR : I.subranges()) {
if ((SR.LaneMask & M).any()) {
assert(SR.LaneMask == M && "Expecting lane masks to match exactly");
return SR;
}
}
llvm_unreachable("Subrange for mask not found");
};
const LiveInterval &LI = getInterval(Reg);
const LiveRange &OldRange = getSubRange(LI, LaneMask);
// Extend intervals to reach all uses in WorkList.
while (!WorkList.empty()) {
SlotIndex Idx = WorkList.back().first;
VNInfo *VNI = WorkList.back().second;
WorkList.pop_back();
const MachineBasicBlock *MBB = Indexes->getMBBFromIndex(Idx.getPrevSlot());
SlotIndex BlockStart = Indexes->getMBBStartIdx(MBB);
// Extend the live range for VNI to be live at Idx.
if (VNInfo *ExtVNI = Segments.extendInBlock(BlockStart, Idx)) {
assert(ExtVNI == VNI && "Unexpected existing value number");
(void)ExtVNI;
// Is this a PHIDef we haven't seen before?
if (!VNI->isPHIDef() || VNI->def != BlockStart ||
!UsedPHIs.insert(VNI).second)
continue;
// The PHI is live, make sure the predecessors are live-out.
for (const MachineBasicBlock *Pred : MBB->predecessors()) {
if (!LiveOut.insert(Pred).second)
continue;
SlotIndex Stop = Indexes->getMBBEndIdx(Pred);
// A predecessor is not required to have a live-out value for a PHI.
if (VNInfo *PVNI = OldRange.getVNInfoBefore(Stop))
WorkList.push_back(std::make_pair(Stop, PVNI));
}
continue;
}
// VNI is live-in to MBB.
LLVM_DEBUG(dbgs() << " live-in at " << BlockStart << '\n');
Segments.addSegment(LiveRange::Segment(BlockStart, Idx, VNI));
// Make sure VNI is live-out from the predecessors.
for (const MachineBasicBlock *Pred : MBB->predecessors()) {
if (!LiveOut.insert(Pred).second)
continue;
SlotIndex Stop = Indexes->getMBBEndIdx(Pred);
if (VNInfo *OldVNI = OldRange.getVNInfoBefore(Stop)) {
assert(OldVNI == VNI && "Wrong value out of predecessor");
(void)OldVNI;
WorkList.push_back(std::make_pair(Stop, VNI));
} else {
#ifndef NDEBUG
// There was no old VNI. Verify that Stop is jointly dominated
// by <undef>s for this live range.
assert(LaneMask.any() &&
"Missing value out of predecessor for main range");
SmallVector<SlotIndex,8> Undefs;
LI.computeSubRangeUndefs(Undefs, LaneMask, *MRI, *Indexes);
assert(LiveRangeCalc::isJointlyDominated(Pred, Undefs, *Indexes) &&
"Missing value out of predecessor for subrange");
#endif
}
}
}
}
bool LiveIntervals::shrinkToUses(LiveInterval *li,
SmallVectorImpl<MachineInstr*> *dead) {
LLVM_DEBUG(dbgs() << "Shrink: " << *li << '\n');
assert(Register::isVirtualRegister(li->reg()) &&
"Can only shrink virtual registers");
// Shrink subregister live ranges.
bool NeedsCleanup = false;
for (LiveInterval::SubRange &S : li->subranges()) {
shrinkToUses(S, li->reg());
if (S.empty())
NeedsCleanup = true;
}
if (NeedsCleanup)
li->removeEmptySubRanges();
// Find all the values used, including PHI kills.
ShrinkToUsesWorkList WorkList;
// Visit all instructions reading li->reg().
Register Reg = li->reg();
for (MachineInstr &UseMI : MRI->reg_instructions(Reg)) {
if (UseMI.isDebugValue() || !UseMI.readsVirtualRegister(Reg))
continue;
SlotIndex Idx = getInstructionIndex(UseMI).getRegSlot();
LiveQueryResult LRQ = li->Query(Idx);
VNInfo *VNI = LRQ.valueIn();
if (!VNI) {
// This shouldn't happen: readsVirtualRegister returns true, but there is
// no live value. It is likely caused by a target getting <undef> flags
// wrong.
LLVM_DEBUG(
dbgs() << Idx << '\t' << UseMI
<< "Warning: Instr claims to read non-existent value in "
<< *li << '\n');
continue;
}
// Special case: An early-clobber tied operand reads and writes the
// register one slot early.
if (VNInfo *DefVNI = LRQ.valueDefined())
Idx = DefVNI->def;
WorkList.push_back(std::make_pair(Idx, VNI));
}
// Create new live ranges with only minimal live segments per def.
LiveRange NewLR;
createSegmentsForValues(NewLR, make_range(li->vni_begin(), li->vni_end()));
extendSegmentsToUses(NewLR, WorkList, Reg, LaneBitmask::getNone());
// Move the trimmed segments back.
li->segments.swap(NewLR.segments);
// Handle dead values.
bool CanSeparate = computeDeadValues(*li, dead);
LLVM_DEBUG(dbgs() << "Shrunk: " << *li << '\n');
return CanSeparate;
}
bool LiveIntervals::computeDeadValues(LiveInterval &LI,
SmallVectorImpl<MachineInstr*> *dead) {
bool MayHaveSplitComponents = false;
bool HaveDeadDef = false;
for (VNInfo *VNI : LI.valnos) {
if (VNI->isUnused())
continue;
SlotIndex Def = VNI->def;
LiveRange::iterator I = LI.FindSegmentContaining(Def);
assert(I != LI.end() && "Missing segment for VNI");
// Is the register live before? Otherwise we may have to add a read-undef
// flag for subregister defs.
Register VReg = LI.reg();
if (MRI->shouldTrackSubRegLiveness(VReg)) {
if ((I == LI.begin() || std::prev(I)->end < Def) && !VNI->isPHIDef()) {
MachineInstr *MI = getInstructionFromIndex(Def);
MI->setRegisterDefReadUndef(VReg);
}
}
if (I->end != Def.getDeadSlot())
continue;
if (VNI->isPHIDef()) {
// This is a dead PHI. Remove it.
VNI->markUnused();
LI.removeSegment(I);
LLVM_DEBUG(dbgs() << "Dead PHI at " << Def << " may separate interval\n");
MayHaveSplitComponents = true;
} else {
// This is a dead def. Make sure the instruction knows.
MachineInstr *MI = getInstructionFromIndex(Def);
assert(MI && "No instruction defining live value");
MI->addRegisterDead(LI.reg(), TRI);
if (HaveDeadDef)
MayHaveSplitComponents = true;
HaveDeadDef = true;
if (dead && MI->allDefsAreDead()) {
LLVM_DEBUG(dbgs() << "All defs dead: " << Def << '\t' << *MI);
dead->push_back(MI);
}
}
}
return MayHaveSplitComponents;
}
void LiveIntervals::shrinkToUses(LiveInterval::SubRange &SR, Register Reg) {
LLVM_DEBUG(dbgs() << "Shrink: " << SR << '\n');
assert(Register::isVirtualRegister(Reg) &&
"Can only shrink virtual registers");
// Find all the values used, including PHI kills.
ShrinkToUsesWorkList WorkList;
// Visit all instructions reading Reg.
SlotIndex LastIdx;
for (MachineOperand &MO : MRI->use_nodbg_operands(Reg)) {
// Skip "undef" uses.
if (!MO.readsReg())
continue;
// Maybe the operand is for a subregister we don't care about.
unsigned SubReg = MO.getSubReg();
if (SubReg != 0) {
LaneBitmask LaneMask = TRI->getSubRegIndexLaneMask(SubReg);
if ((LaneMask & SR.LaneMask).none())
continue;
}
// We only need to visit each instruction once.
MachineInstr *UseMI = MO.getParent();
SlotIndex Idx = getInstructionIndex(*UseMI).getRegSlot();
if (Idx == LastIdx)
continue;
LastIdx = Idx;
LiveQueryResult LRQ = SR.Query(Idx);
VNInfo *VNI = LRQ.valueIn();
// For Subranges it is possible that only undef values are left in that
// part of the subregister, so there is no real liverange at the use
if (!VNI)
continue;
// Special case: An early-clobber tied operand reads and writes the
// register one slot early.
if (VNInfo *DefVNI = LRQ.valueDefined())
Idx = DefVNI->def;
WorkList.push_back(std::make_pair(Idx, VNI));
}
// Create a new live ranges with only minimal live segments per def.
LiveRange NewLR;
createSegmentsForValues(NewLR, make_range(SR.vni_begin(), SR.vni_end()));
extendSegmentsToUses(NewLR, WorkList, Reg, SR.LaneMask);
// Move the trimmed ranges back.
SR.segments.swap(NewLR.segments);
// Remove dead PHI value numbers
for (VNInfo *VNI : SR.valnos) {
if (VNI->isUnused())
continue;
const LiveRange::Segment *Segment = SR.getSegmentContaining(VNI->def);
assert(Segment != nullptr && "Missing segment for VNI");
if (Segment->end != VNI->def.getDeadSlot())
continue;
if (VNI->isPHIDef()) {
// This is a dead PHI. Remove it.
LLVM_DEBUG(dbgs() << "Dead PHI at " << VNI->def
<< " may separate interval\n");
VNI->markUnused();
SR.removeSegment(*Segment);
}
}
LLVM_DEBUG(dbgs() << "Shrunk: " << SR << '\n');
}
void LiveIntervals::extendToIndices(LiveRange &LR,
ArrayRef<SlotIndex> Indices,
ArrayRef<SlotIndex> Undefs) {
assert(LICalc && "LICalc not initialized.");
LICalc->reset(MF, getSlotIndexes(), DomTree, &getVNInfoAllocator());
for (SlotIndex Idx : Indices)
LICalc->extend(LR, Idx, /*PhysReg=*/0, Undefs);
}
void LiveIntervals::pruneValue(LiveRange &LR, SlotIndex Kill,
SmallVectorImpl<SlotIndex> *EndPoints) {
LiveQueryResult LRQ = LR.Query(Kill);
VNInfo *VNI = LRQ.valueOutOrDead();
if (!VNI)
return;
MachineBasicBlock *KillMBB = Indexes->getMBBFromIndex(Kill);
SlotIndex MBBEnd = Indexes->getMBBEndIdx(KillMBB);
// If VNI isn't live out from KillMBB, the value is trivially pruned.
if (LRQ.endPoint() < MBBEnd) {
LR.removeSegment(Kill, LRQ.endPoint());
if (EndPoints) EndPoints->push_back(LRQ.endPoint());
return;
}
// VNI is live out of KillMBB.
LR.removeSegment(Kill, MBBEnd);
if (EndPoints) EndPoints->push_back(MBBEnd);
// Find all blocks that are reachable from KillMBB without leaving VNI's live
// range. It is possible that KillMBB itself is reachable, so start a DFS
// from each successor.
using VisitedTy = df_iterator_default_set<MachineBasicBlock*,9>;
VisitedTy Visited;
for (MachineBasicBlock *Succ : KillMBB->successors()) {
for (df_ext_iterator<MachineBasicBlock*, VisitedTy>
I = df_ext_begin(Succ, Visited), E = df_ext_end(Succ, Visited);
I != E;) {
MachineBasicBlock *MBB = *I;
// Check if VNI is live in to MBB.
SlotIndex MBBStart, MBBEnd;
std::tie(MBBStart, MBBEnd) = Indexes->getMBBRange(MBB);
LiveQueryResult LRQ = LR.Query(MBBStart);
if (LRQ.valueIn() != VNI) {
// This block isn't part of the VNI segment. Prune the search.
I.skipChildren();
continue;
}
// Prune the search if VNI is killed in MBB.
if (LRQ.endPoint() < MBBEnd) {
LR.removeSegment(MBBStart, LRQ.endPoint());
if (EndPoints) EndPoints->push_back(LRQ.endPoint());
I.skipChildren();
continue;
}
// VNI is live through MBB.
LR.removeSegment(MBBStart, MBBEnd);
if (EndPoints) EndPoints->push_back(MBBEnd);
++I;
}
}
}
//===----------------------------------------------------------------------===//
// Register allocator hooks.
//
void LiveIntervals::addKillFlags(const VirtRegMap *VRM) {
// Keep track of regunit ranges.
SmallVector<std::pair<const LiveRange*, LiveRange::const_iterator>, 8> RU;
// Keep track of subregister ranges.
SmallVector<std::pair<const LiveInterval::SubRange*,
LiveRange::const_iterator>, 4> SRs;
for (unsigned i = 0, e = MRI->getNumVirtRegs(); i != e; ++i) {
Register Reg = Register::index2VirtReg(i);
if (MRI->reg_nodbg_empty(Reg))
continue;
const LiveInterval &LI = getInterval(Reg);
if (LI.empty())
continue;
// Find the regunit intervals for the assigned register. They may overlap
// the virtual register live range, cancelling any kills.
RU.clear();
for (MCRegUnitIterator Unit(VRM->getPhys(Reg), TRI); Unit.isValid();
++Unit) {
const LiveRange &RURange = getRegUnit(*Unit);
if (RURange.empty())
continue;
RU.push_back(std::make_pair(&RURange, RURange.find(LI.begin()->end)));
}
if (MRI->subRegLivenessEnabled()) {
SRs.clear();
for (const LiveInterval::SubRange &SR : LI.subranges()) {
SRs.push_back(std::make_pair(&SR, SR.find(LI.begin()->end)));
}
}
// Every instruction that kills Reg corresponds to a segment range end
// point.
for (LiveInterval::const_iterator RI = LI.begin(), RE = LI.end(); RI != RE;
++RI) {
// A block index indicates an MBB edge.
if (RI->end.isBlock())
continue;
MachineInstr *MI = getInstructionFromIndex(RI->end);
if (!MI)
continue;
// Check if any of the regunits are live beyond the end of RI. That could
// happen when a physreg is defined as a copy of a virtreg:
//
// %eax = COPY %5
// FOO %5 <--- MI, cancel kill because %eax is live.
// BAR killed %eax
//
// There should be no kill flag on FOO when %5 is rewritten as %eax.
for (auto &RUP : RU) {
const LiveRange &RURange = *RUP.first;
LiveRange::const_iterator &I = RUP.second;
if (I == RURange.end())
continue;
I = RURange.advanceTo(I, RI->end);
if (I == RURange.end() || I->start >= RI->end)
continue;
// I is overlapping RI.
goto CancelKill;
}
if (MRI->subRegLivenessEnabled()) {
// When reading a partial undefined value we must not add a kill flag.
// The regalloc might have used the undef lane for something else.
// Example:
// %1 = ... ; R32: %1
// %2:high16 = ... ; R64: %2
// = read killed %2 ; R64: %2
// = read %1 ; R32: %1
// The <kill> flag is correct for %2, but the register allocator may
// assign R0L to %1, and R0 to %2 because the low 32bits of R0
// are actually never written by %2. After assignment the <kill>
// flag at the read instruction is invalid.
LaneBitmask DefinedLanesMask;
if (!SRs.empty()) {
// Compute a mask of lanes that are defined.
DefinedLanesMask = LaneBitmask::getNone();
for (auto &SRP : SRs) {
const LiveInterval::SubRange &SR = *SRP.first;
LiveRange::const_iterator &I = SRP.second;
if (I == SR.end())
continue;
I = SR.advanceTo(I, RI->end);
if (I == SR.end() || I->start >= RI->end)
continue;
// I is overlapping RI
DefinedLanesMask |= SR.LaneMask;
}
} else
DefinedLanesMask = LaneBitmask::getAll();
bool IsFullWrite = false;
for (const MachineOperand &MO : MI->operands()) {
if (!MO.isReg() || MO.getReg() != Reg)
continue;
if (MO.isUse()) {
// Reading any undefined lanes?
LaneBitmask UseMask = TRI->getSubRegIndexLaneMask(MO.getSubReg());
if ((UseMask & ~DefinedLanesMask).any())
goto CancelKill;
} else if (MO.getSubReg() == 0) {
// Writing to the full register?
assert(MO.isDef());
IsFullWrite = true;
}
}
// If an instruction writes to a subregister, a new segment starts in
// the LiveInterval. But as this is only overriding part of the register
// adding kill-flags is not correct here after registers have been
// assigned.
if (!IsFullWrite) {
// Next segment has to be adjacent in the subregister write case.
LiveRange::const_iterator N = std::next(RI);
if (N != LI.end() && N->start == RI->end)
goto CancelKill;
}
}
MI->addRegisterKilled(Reg, nullptr);
continue;
CancelKill:
MI->clearRegisterKills(Reg, nullptr);
}
}
}
MachineBasicBlock*
LiveIntervals::intervalIsInOneMBB(const LiveInterval &LI) const {
// A local live range must be fully contained inside the block, meaning it is
// defined and killed at instructions, not at block boundaries. It is not
// live in or out of any block.
//
// It is technically possible to have a PHI-defined live range identical to a
// single block, but we are going to return false in that case.
SlotIndex Start = LI.beginIndex();
if (Start.isBlock())
return nullptr;
SlotIndex Stop = LI.endIndex();
if (Stop.isBlock())
return nullptr;
// getMBBFromIndex doesn't need to search the MBB table when both indexes
// belong to proper instructions.
MachineBasicBlock *MBB1 = Indexes->getMBBFromIndex(Start);
MachineBasicBlock *MBB2 = Indexes->getMBBFromIndex(Stop);
return MBB1 == MBB2 ? MBB1 : nullptr;
}
bool
LiveIntervals::hasPHIKill(const LiveInterval &LI, const VNInfo *VNI) const {
for (const VNInfo *PHI : LI.valnos) {
if (PHI->isUnused() || !PHI->isPHIDef())
continue;
const MachineBasicBlock *PHIMBB = getMBBFromIndex(PHI->def);
// Conservatively return true instead of scanning huge predecessor lists.
if (PHIMBB->pred_size() > 100)
return true;
for (const MachineBasicBlock *Pred : PHIMBB->predecessors())
if (VNI == LI.getVNInfoBefore(Indexes->getMBBEndIdx(Pred)))
return true;
}
return false;
}
float LiveIntervals::getSpillWeight(bool isDef, bool isUse,
const MachineBlockFrequencyInfo *MBFI,
const MachineInstr &MI) {
return getSpillWeight(isDef, isUse, MBFI, MI.getParent());
}
float LiveIntervals::getSpillWeight(bool isDef, bool isUse,
const MachineBlockFrequencyInfo *MBFI,
const MachineBasicBlock *MBB) {
return (isDef + isUse) * MBFI->getBlockFreqRelativeToEntryBlock(MBB);
}
LiveRange::Segment
LiveIntervals::addSegmentToEndOfBlock(Register Reg, MachineInstr &startInst) {
LiveInterval &Interval = createEmptyInterval(Reg);
VNInfo *VN = Interval.getNextValue(
SlotIndex(getInstructionIndex(startInst).getRegSlot()),
getVNInfoAllocator());
LiveRange::Segment S(SlotIndex(getInstructionIndex(startInst).getRegSlot()),
getMBBEndIdx(startInst.getParent()), VN);
Interval.addSegment(S);
return S;
}
//===----------------------------------------------------------------------===//
// Register mask functions
//===----------------------------------------------------------------------===//
bool LiveIntervals::checkRegMaskInterference(LiveInterval &LI,
BitVector &UsableRegs) {
if (LI.empty())
return false;
LiveInterval::iterator LiveI = LI.begin(), LiveE = LI.end();
// Use a smaller arrays for local live ranges.
ArrayRef<SlotIndex> Slots;
ArrayRef<const uint32_t*> Bits;
if (MachineBasicBlock *MBB = intervalIsInOneMBB(LI)) {
Slots = getRegMaskSlotsInBlock(MBB->getNumber());
Bits = getRegMaskBitsInBlock(MBB->getNumber());
} else {
Slots = getRegMaskSlots();
Bits = getRegMaskBits();
}
// We are going to enumerate all the register mask slots contained in LI.
// Start with a binary search of RegMaskSlots to find a starting point.
ArrayRef<SlotIndex>::iterator SlotI = llvm::lower_bound(Slots, LiveI->start);
ArrayRef<SlotIndex>::iterator SlotE = Slots.end();
// No slots in range, LI begins after the last call.
if (SlotI == SlotE)
return false;
bool Found = false;
while (true) {
assert(*SlotI >= LiveI->start);
// Loop over all slots overlapping this segment.
while (*SlotI < LiveI->end) {
// *SlotI overlaps LI. Collect mask bits.
if (!Found) {
// This is the first overlap. Initialize UsableRegs to all ones.
UsableRegs.clear();
UsableRegs.resize(TRI->getNumRegs(), true);
Found = true;
}
// Remove usable registers clobbered by this mask.
UsableRegs.clearBitsNotInMask(Bits[SlotI-Slots.begin()]);
if (++SlotI == SlotE)
return Found;
}
// *SlotI is beyond the current LI segment.
LiveI = LI.advanceTo(LiveI, *SlotI);
if (LiveI == LiveE)
return Found;
// Advance SlotI until it overlaps.
while (*SlotI < LiveI->start)
if (++SlotI == SlotE)
return Found;
}
}
//===----------------------------------------------------------------------===//
// IntervalUpdate class.
//===----------------------------------------------------------------------===//
/// Toolkit used by handleMove to trim or extend live intervals.
class LiveIntervals::HMEditor {
private:
LiveIntervals& LIS;
const MachineRegisterInfo& MRI;
const TargetRegisterInfo& TRI;
SlotIndex OldIdx;
SlotIndex NewIdx;
SmallPtrSet<LiveRange*, 8> Updated;
bool UpdateFlags;
public:
HMEditor(LiveIntervals& LIS, const MachineRegisterInfo& MRI,
const TargetRegisterInfo& TRI,
SlotIndex OldIdx, SlotIndex NewIdx, bool UpdateFlags)
: LIS(LIS), MRI(MRI), TRI(TRI), OldIdx(OldIdx), NewIdx(NewIdx),
UpdateFlags(UpdateFlags) {}
// FIXME: UpdateFlags is a workaround that creates live intervals for all
// physregs, even those that aren't needed for regalloc, in order to update
// kill flags. This is wasteful. Eventually, LiveVariables will strip all kill
// flags, and postRA passes will use a live register utility instead.
LiveRange *getRegUnitLI(unsigned Unit) {
if (UpdateFlags && !MRI.isReservedRegUnit(Unit))
return &LIS.getRegUnit(Unit);
return LIS.getCachedRegUnit(Unit);
}
/// Update all live ranges touched by MI, assuming a move from OldIdx to
/// NewIdx.
void updateAllRanges(MachineInstr *MI) {
LLVM_DEBUG(dbgs() << "handleMove " << OldIdx << " -> " << NewIdx << ": "
<< *MI);
bool hasRegMask = false;
for (MachineOperand &MO : MI->operands()) {
if (MO.isRegMask())
hasRegMask = true;
if (!MO.isReg())
continue;
if (MO.isUse()) {
if (!MO.readsReg())
continue;
// Aggressively clear all kill flags.