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//===- LiveIntervals.h - Live Interval Analysis -----------------*- C++ -*-===//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See 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).
#include "llvm/ADT/ArrayRef.h"
#include "llvm/ADT/IndexedMap.h"
#include "llvm/ADT/SmallVector.h"
#include "llvm/Analysis/AliasAnalysis.h"
#include "llvm/CodeGen/LiveInterval.h"
#include "llvm/CodeGen/MachineBasicBlock.h"
#include "llvm/CodeGen/MachineFunctionPass.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 LiveRangeCalc;
class MachineBlockFrequencyInfo;
class MachineDominatorTree;
class MachineFunction;
class MachineInstr;
class MachineRegisterInfo;
class raw_ostream;
class TargetInstrInfo;
class VirtRegMap;
class LiveIntervals : public MachineFunctionPass {
MachineFunction* MF;
MachineRegisterInfo* MRI;
const TargetRegisterInfo* TRI;
const TargetInstrInfo* TII;
AliasAnalysis *AA;
SlotIndexes* Indexes;
MachineDominatorTree *DomTree = nullptr;
LiveRangeCalc *LRCalc = nullptr;
/// 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;
static char ID;
~LiveIntervals() override;
/// Calculate the spill weight to assign to a single instruction.
static float getSpillWeight(bool isDef, bool isUse,
const MachineBlockFrequencyInfo *MBFI,
const MachineInstr &MI);
/// Calculate the spill weight to assign to a single instruction.
static float getSpillWeight(bool isDef, bool isUse,
const MachineBlockFrequencyInfo *MBFI,
const MachineBasicBlock *MBB);
LiveInterval &getInterval(unsigned Reg) {
if (hasInterval(Reg))
return *VirtRegIntervals[Reg];
return createAndComputeVirtRegInterval(Reg);
const LiveInterval &getInterval(unsigned Reg) const {
return const_cast<LiveIntervals*>(this)->getInterval(Reg);
bool hasInterval(unsigned Reg) const {
return VirtRegIntervals.inBounds(Reg) && VirtRegIntervals[Reg];
/// Interval creation.
LiveInterval &createEmptyInterval(unsigned Reg) {
assert(!hasInterval(Reg) && "Interval already exists!");
VirtRegIntervals[Reg] = createInterval(Reg);
return *VirtRegIntervals[Reg];
LiveInterval &createAndComputeVirtRegInterval(unsigned Reg) {
LiveInterval &LI = createEmptyInterval(Reg);
return LI;
/// Interval removal.
void removeInterval(unsigned Reg) {
delete VirtRegIntervals[Reg];
VirtRegIntervals[Reg] = nullptr;
/// Given a register and an instruction, adds a live segment from that
/// instruction to the end of its MBB.
LiveInterval::Segment addSegmentToEndOfBlock(unsigned 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, unsigned 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> *) {
"Use pruneValue on the main LiveRange and on each subrange");
SlotIndexes *getSlotIndexes() const {
return Indexes;
AliasAnalysis *getAliasAnalysis() const {
return AA;
/// 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) {
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)
void RemoveMachineInstrFromMaps(MachineInstr &MI) {
SlotIndex ReplaceMachineInstrInMaps(MachineInstr &MI, MachineInstr &NewMI) {
return Indexes->replaceMachineInstrInMaps(MI, NewMI);
VNInfo::Allocator& getVNInfoAllocator() { return VNInfoAllocator; }
void getAnalysisUsage(AnalysisUsage &AU) const override;
void releaseMemory() override;
/// Pass entry point; Calculates LiveIntervals.
bool runOnMachineFunction(MachineFunction&) override;
/// Implement the dump method.
void print(raw_ostream &O, const Module* = nullptr) const override;
/// 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 for operands of \p MI so that they begin/end on the
/// SlotIndex for \p BundleStart.
/// \param UpdateFlags Update live intervals for nonallocatable physregs.
/// Requires MI and BundleStart to have SlotIndexes, and assumes
/// existing liveness is accurate. BundleStart should be the first
/// instruction in the Bundle.
void handleMoveIntoBundle(MachineInstr &MI, 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 only changes that are supported are simple removal
/// and addition of uses.
void repairIntervalsInRange(MachineBasicBlock *MBB,
MachineBasicBlock::iterator Begin,
MachineBasicBlock::iterator End,
ArrayRef<unsigned> 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(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(unsigned Reg) {
for (MCRegUnitIterator Units(Reg, TRI); Units.isValid(); ++Units)
/// 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(unsigned 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);
/// 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(unsigned Reg);
void printInstrs(raw_ostream &O) const;
void dumpInstrs() const;
void computeLiveInRegUnits();
void computeRegUnitRange(LiveRange&, unsigned Unit);
void computeVirtRegInterval(LiveInterval&);
using ShrinkToUsesWorkList = SmallVector<std::pair<SlotIndex, VNInfo*>, 16>;
void extendSegmentsToUses(LiveRange &Segments,
ShrinkToUsesWorkList &WorkList, unsigned 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,
unsigned Reg,
LaneBitmask LaneMask = LaneBitmask::getAll());
class HMEditor;
} // end namespace llvm