LiveIntervals.h

Go to the documentation of this file.

//===- LiveIntervals.h - Live Interval Analysis -----------------*- C++ -*-===//
//
// 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.  Given some
/// numbering of each the machine instructions (in this implemention depth-first
/// order) an interval [i, j) is said to be a live interval for register v if
/// there is no instruction with number j' > j such that v is live at j' and
/// there is no instruction with number i' < i such that v is live at i'. In
/// this implementation intervals can have holes, i.e. an interval might look
/// like [1,20), [50,65), [1000,1001).
//
//===----------------------------------------------------------------------===//
 
#ifndef LLVM_CODEGEN_LIVEINTERVALS_H
#define LLVM_CODEGEN_LIVEINTERVALS_H
 
#include "llvm/ADT/ArrayRef.h"
#include "llvm/ADT/IndexedMap.h"
#include "llvm/ADT/SmallVector.h"
#include "llvm/CodeGen/LiveInterval.h"
#include "llvm/CodeGen/LiveIntervalCalc.h"
#include "llvm/CodeGen/MachineBasicBlock.h"
#include "llvm/CodeGen/MachineFunctionPass.h"
#include "llvm/CodeGen/MachinePassManager.h"
#include "llvm/CodeGen/SlotIndexes.h"
#include "llvm/CodeGen/TargetRegisterInfo.h"
#include "llvm/MC/LaneBitmask.h"
#include "llvm/Support/CommandLine.h"
#include "llvm/Support/Compiler.h"
#include "llvm/Support/ErrorHandling.h"
#include <cassert>
#include <cstdint>
#include <utility>
 
namespace llvm {
 
extern cl::opt<bool> UseSegmentSetForPhysRegs;
 
class BitVector;
class MachineBlockFrequencyInfo;
class MachineDominatorTree;
class MachineFunction;
class MachineInstr;
class MachineRegisterInfo;
class ProfileSummaryInfo;
class raw_ostream;
class TargetInstrInfo;
class VirtRegMap;
 
class LiveIntervals {
  friend class LiveIntervalsAnalysis;
  friend class LiveIntervalsWrapperPass;
 
  MachineFunction *MF = nullptr;
  MachineRegisterInfo *MRI = nullptr;
  const TargetRegisterInfo *TRI = nullptr;
  const TargetInstrInfo *TII = nullptr;
  SlotIndexes *Indexes = nullptr;
  MachineDominatorTree *DomTree = nullptr;
  std::unique_ptr<LiveIntervalCalc> LICalc;
 
  /// Special pool allocator for VNInfo's (LiveInterval val#).
  VNInfo::Allocator VNInfoAllocator;
 
  /// Live interval pointers for all the virtual registers.
  IndexedMap<LiveInterval *, VirtReg2IndexFunctor> VirtRegIntervals;
 
  /// Sorted list of instructions with register mask operands. Always use the
  /// 'r' slot, RegMasks are normal clobbers, not early clobbers.
  SmallVector<SlotIndex, 8> RegMaskSlots;
 
  /// This vector is parallel to RegMaskSlots, it holds a pointer to the
  /// corresponding register mask.  This pointer can be recomputed as:
  ///
  ///   MI = Indexes->getInstructionFromIndex(RegMaskSlot[N]);
  ///   unsigned OpNum = findRegMaskOperand(MI);
  ///   RegMaskBits[N] = MI->getOperand(OpNum).getRegMask();
  ///
  /// This is kept in a separate vector partly because some standard
  /// libraries don't support lower_bound() with mixed objects, partly to
  /// improve locality when searching in RegMaskSlots.
  /// Also see the comment in LiveInterval::find().
  SmallVector<const uint32_t *, 8> RegMaskBits;
 
  /// For each basic block number, keep (begin, size) pairs indexing into the
  /// RegMaskSlots and RegMaskBits arrays.
  /// Note that basic block numbers may not be layout contiguous, that's why
  /// we can't just keep track of the first register mask in each basic
  /// block.
  SmallVector<std::pair<unsigned, unsigned>, 8> RegMaskBlocks;
 
  /// Keeps a live range set for each register unit to track fixed physreg
  /// interference.
  SmallVector<LiveRange *, 0> RegUnitRanges;
 
  // Can only be created from pass manager.
  LiveIntervals() = default;
  LiveIntervals(MachineFunction &MF, SlotIndexes &SI, MachineDominatorTree &DT)
      : Indexes(&SI), DomTree(&DT) {
    analyze(MF);
  }
 
  void analyze(MachineFunction &MF);
 
  void clear();
 
public:
  LiveIntervals(LiveIntervals &&) = default;
  ~LiveIntervals();
 
  bool invalidate(MachineFunction &MF, const PreservedAnalyses &PA,
                  MachineFunctionAnalysisManager::Invalidator &Inv);
 
  /// Calculate the spill weight to assign to a single instruction.
  /// If \p PSI is provided the calculation is altered for optsize functions.
  static float getSpillWeight(bool isDef, bool isUse,
                              const MachineBlockFrequencyInfo *MBFI,
                              const MachineInstr &MI,
                              ProfileSummaryInfo *PSI = nullptr);
 
  /// Calculate the spill weight to assign to a single instruction.
  /// If \p PSI is provided the calculation is altered for optsize functions.
  static float getSpillWeight(bool isDef, bool isUse,
                              const MachineBlockFrequencyInfo *MBFI,
                              const MachineBasicBlock *MBB,
                              ProfileSummaryInfo *PSI = nullptr);
 
  LiveInterval &getInterval(Register Reg) {
    if (hasInterval(Reg))
      return *VirtRegIntervals[Reg.id()];
 
    return createAndComputeVirtRegInterval(Reg);
  }
 
  const LiveInterval &getInterval(Register Reg) const {
    return const_cast<LiveIntervals *>(this)->getInterval(Reg);
  }
 
  bool hasInterval(Register Reg) const {
    return VirtRegIntervals.inBounds(Reg.id()) && VirtRegIntervals[Reg.id()];
  }
 
  /// Interval creation.
  LiveInterval &createEmptyInterval(Register Reg) {
    assert(!hasInterval(Reg) && "Interval already exists!");
    VirtRegIntervals.grow(Reg.id());
    auto &Interval = VirtRegIntervals[Reg.id()];
    Interval = createInterval(Reg);
    return *Interval;
  }
 
  LiveInterval &createAndComputeVirtRegInterval(Register Reg) {
    LiveInterval &LI = createEmptyInterval(Reg);
    computeVirtRegInterval(LI);
    return LI;
  }
 
  /// Return an existing interval for \p Reg.
  /// If \p Reg has no interval then this creates a new empty one instead.
  /// Note: does not trigger interval computation.
  LiveInterval &getOrCreateEmptyInterval(Register Reg) {
    return hasInterval(Reg) ? getInterval(Reg) : createEmptyInterval(Reg);
  }
 
  /// Interval removal.
  void removeInterval(Register Reg) {
    auto &Interval = VirtRegIntervals[Reg];
    delete Interval;
    Interval = nullptr;
  }
 
  /// Given a register and an instruction, adds a live segment from that
  /// instruction to the end of its MBB.
  LiveInterval::Segment addSegmentToEndOfBlock(Register Reg,
                                               MachineInstr &startInst);
 
  /// After removing some uses of a register, shrink its live range to just
  /// the remaining uses. This method does not compute reaching defs for new
  /// uses, and it doesn't remove dead defs.
  /// Dead PHIDef values are marked as unused. New dead machine instructions
  /// are added to the dead vector. Returns true if the interval may have been
  /// separated into multiple connected components.
  bool shrinkToUses(LiveInterval *li,
                    SmallVectorImpl<MachineInstr *> *dead = nullptr);
 
  /// Specialized version of
  /// shrinkToUses(LiveInterval *li, SmallVectorImpl<MachineInstr*> *dead)
  /// that works on a subregister live range and only looks at uses matching
  /// the lane mask of the subregister range.
  /// This may leave the subrange empty which needs to be cleaned up with
  /// LiveInterval::removeEmptySubranges() afterwards.
  void shrinkToUses(LiveInterval::SubRange &SR, Register Reg);
 
  /// Extend the live range \p LR to reach all points in \p Indices. The
  /// points in the \p Indices array must be jointly dominated by the union
  /// of the existing defs in \p LR and points in \p Undefs.
  ///
  /// PHI-defs are added as needed to maintain SSA form.
  ///
  /// If a SlotIndex in \p Indices is the end index of a basic block, \p LR
  /// will be extended to be live out of the basic block.
  /// If a SlotIndex in \p Indices is jointy dominated only by points in
  /// \p Undefs, the live range will not be extended to that point.
  ///
  /// See also LiveRangeCalc::extend().
  void extendToIndices(LiveRange &LR, ArrayRef<SlotIndex> Indices,
                       ArrayRef<SlotIndex> Undefs);
 
  void extendToIndices(LiveRange &LR, ArrayRef<SlotIndex> Indices) {
    extendToIndices(LR, Indices, /*Undefs=*/{});
  }
 
  /// If \p LR has a live value at \p Kill, prune its live range by removing
  /// any liveness reachable from Kill. Add live range end points to
  /// EndPoints such that extendToIndices(LI, EndPoints) will reconstruct the
  /// value's live range.
  ///
  /// Calling pruneValue() and extendToIndices() can be used to reconstruct
  /// SSA form after adding defs to a virtual register.
  void pruneValue(LiveRange &LR, SlotIndex Kill,
                  SmallVectorImpl<SlotIndex> *EndPoints);
 
  /// This function should not be used. Its intent is to tell you that you are
  /// doing something wrong if you call pruneValue directly on a
  /// LiveInterval. Indeed, you are supposed to call pruneValue on the main
  /// LiveRange and all the LiveRanges of the subranges if any.
  LLVM_ATTRIBUTE_UNUSED void pruneValue(LiveInterval &, SlotIndex,
                                        SmallVectorImpl<SlotIndex> *) {
    llvm_unreachable(
        "Use pruneValue on the main LiveRange and on each subrange");
  }
 
  SlotIndexes *getSlotIndexes() const { return Indexes; }
 
  /// Returns true if the specified machine instr has been removed or was
  /// never entered in the map.
  bool isNotInMIMap(const MachineInstr &Instr) const {
    return !Indexes->hasIndex(Instr);
  }
 
  /// Returns the base index of the given instruction.
  SlotIndex getInstructionIndex(const MachineInstr &Instr) const {
    return Indexes->getInstructionIndex(Instr);
  }
 
  /// Returns the instruction associated with the given index.
  MachineInstr *getInstructionFromIndex(SlotIndex index) const {
    return Indexes->getInstructionFromIndex(index);
  }
 
  /// Return the first index in the given basic block.
  SlotIndex getMBBStartIdx(const MachineBasicBlock *mbb) const {
    return Indexes->getMBBStartIdx(mbb);
  }
 
  /// Return the last index in the given basic block.
  SlotIndex getMBBEndIdx(const MachineBasicBlock *mbb) const {
    return Indexes->getMBBEndIdx(mbb);
  }
 
  bool isLiveInToMBB(const LiveRange &LR, const MachineBasicBlock *mbb) const {
    return LR.liveAt(getMBBStartIdx(mbb));
  }
 
  bool isLiveOutOfMBB(const LiveRange &LR, const MachineBasicBlock *mbb) const {
    return LR.liveAt(getMBBEndIdx(mbb).getPrevSlot());
  }
 
  MachineBasicBlock *getMBBFromIndex(SlotIndex index) const {
    return Indexes->getMBBFromIndex(index);
  }
 
  void insertMBBInMaps(MachineBasicBlock *MBB) {
    Indexes->insertMBBInMaps(MBB);
    assert(unsigned(MBB->getNumber()) == RegMaskBlocks.size() &&
           "Blocks must be added in order.");
    RegMaskBlocks.push_back(std::make_pair(RegMaskSlots.size(), 0));
  }
 
  SlotIndex InsertMachineInstrInMaps(MachineInstr &MI) {
    return Indexes->insertMachineInstrInMaps(MI);
  }
 
  void InsertMachineInstrRangeInMaps(MachineBasicBlock::iterator B,
                                     MachineBasicBlock::iterator E) {
    for (MachineBasicBlock::iterator I = B; I != E; ++I)
      Indexes->insertMachineInstrInMaps(*I);
  }
 
  void RemoveMachineInstrFromMaps(MachineInstr &MI) {
    Indexes->removeMachineInstrFromMaps(MI);
  }
 
  SlotIndex ReplaceMachineInstrInMaps(MachineInstr &MI, MachineInstr &NewMI) {
    return Indexes->replaceMachineInstrInMaps(MI, NewMI);
  }
 
  VNInfo::Allocator &getVNInfoAllocator() { return VNInfoAllocator; }
 
  /// Implement the dump method.
  void print(raw_ostream &O) const;
  void dump() const;
 
  // For legacy pass to recompute liveness.
  void reanalyze(MachineFunction &MF) {
    clear();
    analyze(MF);
  }
 
  MachineDominatorTree &getDomTree() { return *DomTree; }
 
  /// If LI is confined to a single basic block, return a pointer to that
  /// block.  If LI is live in to or out of any block, return NULL.
  MachineBasicBlock *intervalIsInOneMBB(const LiveInterval &LI) const;
 
  /// Returns true if VNI is killed by any PHI-def values in LI.
  /// This may conservatively return true to avoid expensive computations.
  bool hasPHIKill(const LiveInterval &LI, const VNInfo *VNI) const;
 
  /// Add kill flags to any instruction that kills a virtual register.
  void addKillFlags(const VirtRegMap *);
 
  /// Call this method to notify LiveIntervals that instruction \p MI has been
  /// moved within a basic block. This will update the live intervals for all
  /// operands of \p MI. Moves between basic blocks are not supported.
  ///
  /// \param UpdateFlags Update live intervals for nonallocatable physregs.
  void handleMove(MachineInstr &MI, bool UpdateFlags = false);
 
  /// Update intervals of operands of all instructions in the newly
  /// created bundle specified by \p BundleStart.
  ///
  /// \param UpdateFlags Update live intervals for nonallocatable physregs.
  ///
  /// Assumes existing liveness is accurate.
  /// \pre BundleStart should be the first instruction in the Bundle.
  /// \pre BundleStart should not have a have SlotIndex as one will be assigned.
  void handleMoveIntoNewBundle(MachineInstr &BundleStart,
                               bool UpdateFlags = false);
 
  /// Update live intervals for instructions in a range of iterators. It is
  /// intended for use after target hooks that may insert or remove
  /// instructions, and is only efficient for a small number of instructions.
  ///
  /// OrigRegs is a vector of registers that were originally used by the
  /// instructions in the range between the two iterators.
  ///
  /// Currently, the only changes that are supported are simple removal
  /// and addition of uses.
  void repairIntervalsInRange(MachineBasicBlock *MBB,
                              MachineBasicBlock::iterator Begin,
                              MachineBasicBlock::iterator End,
                              ArrayRef<Register> OrigRegs);
 
  // Register mask functions.
  //
  // Machine instructions may use a register mask operand to indicate that a
  // large number of registers are clobbered by the instruction.  This is
  // typically used for calls.
  //
  // For compile time performance reasons, these clobbers are not recorded in
  // the live intervals for individual physical registers.  Instead,
  // LiveIntervalAnalysis maintains a sorted list of instructions with
  // register mask operands.
 
  /// Returns a sorted array of slot indices of all instructions with
  /// register mask operands.
  ArrayRef<SlotIndex> getRegMaskSlots() const { return RegMaskSlots; }
 
  /// Returns a sorted array of slot indices of all instructions with register
  /// mask operands in the basic block numbered \p MBBNum.
  ArrayRef<SlotIndex> getRegMaskSlotsInBlock(unsigned MBBNum) const {
    std::pair<unsigned, unsigned> P = RegMaskBlocks[MBBNum];
    return getRegMaskSlots().slice(P.first, P.second);
  }
 
  /// Returns an array of register mask pointers corresponding to
  /// getRegMaskSlots().
  ArrayRef<const uint32_t *> getRegMaskBits() const { return RegMaskBits; }
 
  /// Returns an array of mask pointers corresponding to
  /// getRegMaskSlotsInBlock(MBBNum).
  ArrayRef<const uint32_t *> getRegMaskBitsInBlock(unsigned MBBNum) const {
    std::pair<unsigned, unsigned> P = RegMaskBlocks[MBBNum];
    return getRegMaskBits().slice(P.first, P.second);
  }
 
  /// Test if \p LI is live across any register mask instructions, and
  /// compute a bit mask of physical registers that are not clobbered by any
  /// of them.
  ///
  /// Returns false if \p LI doesn't cross any register mask instructions. In
  /// that case, the bit vector is not filled in.
  bool checkRegMaskInterference(const LiveInterval &LI, BitVector &UsableRegs);
 
  // Register unit functions.
  //
  // Fixed interference occurs when MachineInstrs use physregs directly
  // instead of virtual registers. This typically happens when passing
  // arguments to a function call, or when instructions require operands in
  // fixed registers.
  //
  // Each physreg has one or more register units, see MCRegisterInfo. We
  // track liveness per register unit to handle aliasing registers more
  // efficiently.
 
  /// Return the live range for register unit \p Unit. It will be computed if
  /// it doesn't exist.
  LiveRange &getRegUnit(unsigned Unit) {
    LiveRange *LR = RegUnitRanges[Unit];
    if (!LR) {
      // Compute missing ranges on demand.
      // Use segment set to speed-up initial computation of the live range.
      RegUnitRanges[Unit] = LR = new LiveRange(UseSegmentSetForPhysRegs);
      computeRegUnitRange(*LR, Unit);
    }
    return *LR;
  }
 
  /// Return the live range for register unit \p Unit if it has already been
  /// computed, or nullptr if it hasn't been computed yet.
  LiveRange *getCachedRegUnit(unsigned Unit) { return RegUnitRanges[Unit]; }
 
  const LiveRange *getCachedRegUnit(unsigned Unit) const {
    return RegUnitRanges[Unit];
  }
 
  /// Remove computed live range for register unit \p Unit. Subsequent uses
  /// should rely on on-demand recomputation.
  void removeRegUnit(unsigned Unit) {
    delete RegUnitRanges[Unit];
    RegUnitRanges[Unit] = nullptr;
  }
 
  /// Remove associated live ranges for the register units associated with \p
  /// Reg. Subsequent uses should rely on on-demand recomputation.  \note This
  /// method can result in inconsistent liveness tracking if multiple phyical
  /// registers share a regunit, and should be used cautiously.
  void removeAllRegUnitsForPhysReg(MCRegister Reg) {
    for (MCRegUnit Unit : TRI->regunits(Reg))
      removeRegUnit(Unit);
  }
 
  /// Remove value numbers and related live segments starting at position
  /// \p Pos that are part of any liverange of physical register \p Reg or one
  /// of its subregisters.
  void removePhysRegDefAt(MCRegister Reg, SlotIndex Pos);
 
  /// Remove value number and related live segments of \p LI and its subranges
  /// that start at position \p Pos.
  void removeVRegDefAt(LiveInterval &LI, SlotIndex Pos);
 
  /// Split separate components in LiveInterval \p LI into separate intervals.
  void splitSeparateComponents(LiveInterval &LI,
                               SmallVectorImpl<LiveInterval *> &SplitLIs);
 
  /// For live interval \p LI with correct SubRanges construct matching
  /// information for the main live range. Expects the main live range to not
  /// have any segments or value numbers.
  void constructMainRangeFromSubranges(LiveInterval &LI);
 
private:
  /// Compute live intervals for all virtual registers.
  void computeVirtRegs();
 
  /// Compute RegMaskSlots and RegMaskBits.
  void computeRegMasks();
 
  /// Walk the values in \p LI and check for dead values:
  /// - Dead PHIDef values are marked as unused.
  /// - Dead operands are marked as such.
  /// - Completely dead machine instructions are added to the \p dead vector
  ///   if it is not nullptr.
  /// Returns true if any PHI value numbers have been removed which may
  /// have separated the interval into multiple connected components.
  bool computeDeadValues(LiveInterval &LI,
                         SmallVectorImpl<MachineInstr *> *dead);
 
  static LiveInterval *createInterval(Register Reg);
 
  void printInstrs(raw_ostream &O) const;
  void dumpInstrs() const;
 
  void computeLiveInRegUnits();
  void computeRegUnitRange(LiveRange &, unsigned Unit);
  bool computeVirtRegInterval(LiveInterval &);
 
  using ShrinkToUsesWorkList = SmallVector<std::pair<SlotIndex, VNInfo *>, 16>;
  void extendSegmentsToUses(LiveRange &Segments, ShrinkToUsesWorkList &WorkList,
                            Register Reg, LaneBitmask LaneMask);
 
  /// Helper function for repairIntervalsInRange(), walks backwards and
  /// creates/modifies live segments in \p LR to match the operands found.
  /// Only full operands or operands with subregisters matching \p LaneMask
  /// are considered.
  void repairOldRegInRange(MachineBasicBlock::iterator Begin,
                           MachineBasicBlock::iterator End,
                           const SlotIndex endIdx, LiveRange &LR, Register Reg,
                           LaneBitmask LaneMask = LaneBitmask::getAll());
 
  class HMEditor;
};
 
class LiveIntervalsAnalysis : public AnalysisInfoMixin<LiveIntervalsAnalysis> {
  friend AnalysisInfoMixin<LiveIntervalsAnalysis>;
  static AnalysisKey Key;
 
public:
  using Result = LiveIntervals;
  Result run(MachineFunction &MF, MachineFunctionAnalysisManager &MFAM);
};
 
class LiveIntervalsPrinterPass
    : public PassInfoMixin<LiveIntervalsPrinterPass> {
  raw_ostream &OS;
 
public:
  explicit LiveIntervalsPrinterPass(raw_ostream &OS) : OS(OS) {}
  PreservedAnalyses run(MachineFunction &MF,
                        MachineFunctionAnalysisManager &MFAM);
  static bool isRequired() { return true; }
};
 
class LiveIntervalsWrapperPass : public MachineFunctionPass {
  LiveIntervals LIS;
 
public:
  static char ID;
 
  LiveIntervalsWrapperPass();
 
  void getAnalysisUsage(AnalysisUsage &AU) const override;
  void releaseMemory() override { LIS.clear(); }
 
  /// Pass entry point; Calculates LiveIntervals.
  bool runOnMachineFunction(MachineFunction &) override;
 
  /// Implement the dump method.
  void print(raw_ostream &O, const Module * = nullptr) const override {
    LIS.print(O);
  }
 
  LiveIntervals &getLIS() { return LIS; }
};
 
} // end namespace llvm
 
#endif