blob: 6629e6046532f624ae7f14a8d05d32bd2b747db2 [file] [log] [blame]
//===-- llvm/CodeGen/LiveInterval.h - Interval representation ---*- C++ -*-===//
// 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 LiveRange and LiveInterval classes. Given some
// numbering of each the machine instructions an interval [i, j) is said to be a
// live range 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 ranges can have holes,
// i.e. a range might look like [1,20), [50,65), [1000,1001). Each
// individual segment is represented as an instance of LiveRange::Segment,
// and the whole range is represented as an instance of LiveRange.
#include "llvm/ADT/IntEqClasses.h"
#include "llvm/CodeGen/SlotIndexes.h"
#include "llvm/Support/AlignOf.h"
#include "llvm/Support/Allocator.h"
#include <cassert>
#include <climits>
namespace llvm {
class CoalescerPair;
class LiveIntervals;
class MachineInstr;
class MachineRegisterInfo;
class TargetRegisterInfo;
class raw_ostream;
template <typename T, unsigned Small> class SmallPtrSet;
/// VNInfo - Value Number Information.
/// This class holds information about a machine level values, including
/// definition and use points.
class VNInfo {
typedef BumpPtrAllocator Allocator;
/// The ID number of this value.
unsigned id;
/// The index of the defining instruction.
SlotIndex def;
/// VNInfo constructor.
VNInfo(unsigned i, SlotIndex d)
: id(i), def(d)
{ }
/// VNInfo construtor, copies values from orig, except for the value number.
VNInfo(unsigned i, const VNInfo &orig)
: id(i), def(orig.def)
{ }
/// Copy from the parameter into this VNInfo.
void copyFrom(VNInfo &src) {
def = src.def;
/// Returns true if this value is defined by a PHI instruction (or was,
/// PHI instructions may have been eliminated).
/// PHI-defs begin at a block boundary, all other defs begin at register or
/// EC slots.
bool isPHIDef() const { return def.isBlock(); }
/// Returns true if this value is unused.
bool isUnused() const { return !def.isValid(); }
/// Mark this value as unused.
void markUnused() { def = SlotIndex(); }
/// Result of a LiveRange query. This class hides the implementation details
/// of live ranges, and it should be used as the primary interface for
/// examining live ranges around instructions.
class LiveQueryResult {
VNInfo *const EarlyVal;
VNInfo *const LateVal;
const SlotIndex EndPoint;
const bool Kill;
LiveQueryResult(VNInfo *EarlyVal, VNInfo *LateVal, SlotIndex EndPoint,
bool Kill)
: EarlyVal(EarlyVal), LateVal(LateVal), EndPoint(EndPoint), Kill(Kill)
/// Return the value that is live-in to the instruction. This is the value
/// that will be read by the instruction's use operands. Return NULL if no
/// value is live-in.
VNInfo *valueIn() const {
return EarlyVal;
/// Return true if the live-in value is killed by this instruction. This
/// means that either the live range ends at the instruction, or it changes
/// value.
bool isKill() const {
return Kill;
/// Return true if this instruction has a dead def.
bool isDeadDef() const {
return EndPoint.isDead();
/// Return the value leaving the instruction, if any. This can be a
/// live-through value, or a live def. A dead def returns NULL.
VNInfo *valueOut() const {
return isDeadDef() ? nullptr : LateVal;
/// Return the value defined by this instruction, if any. This includes
/// dead defs, it is the value created by the instruction's def operands.
VNInfo *valueDefined() const {
return EarlyVal == LateVal ? nullptr : LateVal;
/// Return the end point of the last live range segment to interact with
/// the instruction, if any.
/// The end point is an invalid SlotIndex only if the live range doesn't
/// intersect the instruction at all.
/// The end point may be at or past the end of the instruction's basic
/// block. That means the value was live out of the block.
SlotIndex endPoint() const {
return EndPoint;
/// This class represents the liveness of a register, stack slot, etc.
/// It manages an ordered list of Segment objects.
/// The Segments are organized in a static single assignment form: At places
/// where a new value is defined or different values reach a CFG join a new
/// segment with a new value number is used.
class LiveRange {
/// This represents a simple continuous liveness interval for a value.
/// The start point is inclusive, the end point exclusive. These intervals
/// are rendered as [start,end).
struct Segment {
SlotIndex start; // Start point of the interval (inclusive)
SlotIndex end; // End point of the interval (exclusive)
VNInfo *valno; // identifier for the value contained in this segment.
Segment() : valno(nullptr) {}
Segment(SlotIndex S, SlotIndex E, VNInfo *V)
: start(S), end(E), valno(V) {
assert(S < E && "Cannot create empty or backwards segment");
/// Return true if the index is covered by this segment.
bool contains(SlotIndex I) const {
return start <= I && I < end;
/// Return true if the given interval, [S, E), is covered by this segment.
bool containsInterval(SlotIndex S, SlotIndex E) const {
assert((S < E) && "Backwards interval?");
return (start <= S && S < end) && (start < E && E <= end);
bool operator<(const Segment &Other) const {
return std::tie(start, end) < std::tie(Other.start, Other.end);
bool operator==(const Segment &Other) const {
return start == Other.start && end == Other.end;
void dump() const;
typedef SmallVector<Segment,4> Segments;
typedef SmallVector<VNInfo*,4> VNInfoList;
Segments segments; // the liveness segments
VNInfoList valnos; // value#'s
typedef Segments::iterator iterator;
iterator begin() { return segments.begin(); }
iterator end() { return segments.end(); }
typedef Segments::const_iterator const_iterator;
const_iterator begin() const { return segments.begin(); }
const_iterator end() const { return segments.end(); }
typedef VNInfoList::iterator vni_iterator;
vni_iterator vni_begin() { return valnos.begin(); }
vni_iterator vni_end() { return valnos.end(); }
typedef VNInfoList::const_iterator const_vni_iterator;
const_vni_iterator vni_begin() const { return valnos.begin(); }
const_vni_iterator vni_end() const { return valnos.end(); }
/// advanceTo - Advance the specified iterator to point to the Segment
/// containing the specified position, or end() if the position is past the
/// end of the range. If no Segment contains this position, but the
/// position is in a hole, this method returns an iterator pointing to the
/// Segment immediately after the hole.
iterator advanceTo(iterator I, SlotIndex Pos) {
assert(I != end());
if (Pos >= endIndex())
return end();
while (I->end <= Pos) ++I;
return I;
/// find - Return an iterator pointing to the first segment that ends after
/// Pos, or end(). This is the same as advanceTo(begin(), Pos), but faster
/// when searching large ranges.
/// If Pos is contained in a Segment, that segment is returned.
/// If Pos is in a hole, the following Segment is returned.
/// If Pos is beyond endIndex, end() is returned.
iterator find(SlotIndex Pos);
const_iterator find(SlotIndex Pos) const {
return const_cast<LiveRange*>(this)->find(Pos);
void clear() {
size_t size() const {
return segments.size();
bool hasAtLeastOneValue() const { return !valnos.empty(); }
bool containsOneValue() const { return valnos.size() == 1; }
unsigned getNumValNums() const { return (unsigned)valnos.size(); }
/// getValNumInfo - Returns pointer to the specified val#.
inline VNInfo *getValNumInfo(unsigned ValNo) {
return valnos[ValNo];
inline const VNInfo *getValNumInfo(unsigned ValNo) const {
return valnos[ValNo];
/// containsValue - Returns true if VNI belongs to this range.
bool containsValue(const VNInfo *VNI) const {
return VNI && VNI->id < getNumValNums() && VNI == getValNumInfo(VNI->id);
/// getNextValue - Create a new value number and return it. MIIdx specifies
/// the instruction that defines the value number.
VNInfo *getNextValue(SlotIndex def, VNInfo::Allocator &VNInfoAllocator) {
VNInfo *VNI =
new (VNInfoAllocator) VNInfo((unsigned)valnos.size(), def);
return VNI;
/// createDeadDef - Make sure the range has a value defined at Def.
/// If one already exists, return it. Otherwise allocate a new value and
/// add liveness for a dead def.
VNInfo *createDeadDef(SlotIndex Def, VNInfo::Allocator &VNInfoAllocator);
/// Create a copy of the given value. The new value will be identical except
/// for the Value number.
VNInfo *createValueCopy(const VNInfo *orig,
VNInfo::Allocator &VNInfoAllocator) {
VNInfo *VNI =
new (VNInfoAllocator) VNInfo((unsigned)valnos.size(), *orig);
return VNI;
/// RenumberValues - Renumber all values in order of appearance and remove
/// unused values.
void RenumberValues();
/// MergeValueNumberInto - This method is called when two value numbers
/// are found to be equivalent. This eliminates V1, replacing all
/// segments with the V1 value number with the V2 value number. This can
/// cause merging of V1/V2 values numbers and compaction of the value space.
VNInfo* MergeValueNumberInto(VNInfo *V1, VNInfo *V2);
/// Merge all of the live segments of a specific val# in RHS into this live
/// range as the specified value number. The segments in RHS are allowed
/// to overlap with segments in the current range, it will replace the
/// value numbers of the overlaped live segments with the specified value
/// number.
void MergeSegmentsInAsValue(const LiveRange &RHS, VNInfo *LHSValNo);
/// MergeValueInAsValue - Merge all of the segments of a specific val#
/// in RHS into this live range as the specified value number.
/// The segments in RHS are allowed to overlap with segments in the
/// current range, but only if the overlapping segments have the
/// specified value number.
void MergeValueInAsValue(const LiveRange &RHS,
const VNInfo *RHSValNo, VNInfo *LHSValNo);
bool empty() const { return segments.empty(); }
/// beginIndex - Return the lowest numbered slot covered.
SlotIndex beginIndex() const {
assert(!empty() && "Call to beginIndex() on empty range.");
return segments.front().start;
/// endNumber - return the maximum point of the range of the whole,
/// exclusive.
SlotIndex endIndex() const {
assert(!empty() && "Call to endIndex() on empty range.");
return segments.back().end;
bool expiredAt(SlotIndex index) const {
return index >= endIndex();
bool liveAt(SlotIndex index) const {
const_iterator r = find(index);
return r != end() && r->start <= index;
/// Return the segment that contains the specified index, or null if there
/// is none.
const Segment *getSegmentContaining(SlotIndex Idx) const {
const_iterator I = FindSegmentContaining(Idx);
return I == end() ? nullptr : &*I;
/// Return the live segment that contains the specified index, or null if
/// there is none.
Segment *getSegmentContaining(SlotIndex Idx) {
iterator I = FindSegmentContaining(Idx);
return I == end() ? nullptr : &*I;
/// getVNInfoAt - Return the VNInfo that is live at Idx, or NULL.
VNInfo *getVNInfoAt(SlotIndex Idx) const {
const_iterator I = FindSegmentContaining(Idx);
return I == end() ? nullptr : I->valno;
/// getVNInfoBefore - Return the VNInfo that is live up to but not
/// necessarilly including Idx, or NULL. Use this to find the reaching def
/// used by an instruction at this SlotIndex position.
VNInfo *getVNInfoBefore(SlotIndex Idx) const {
const_iterator I = FindSegmentContaining(Idx.getPrevSlot());
return I == end() ? nullptr : I->valno;
/// Return an iterator to the segment that contains the specified index, or
/// end() if there is none.
iterator FindSegmentContaining(SlotIndex Idx) {
iterator I = find(Idx);
return I != end() && I->start <= Idx ? I : end();
const_iterator FindSegmentContaining(SlotIndex Idx) const {
const_iterator I = find(Idx);
return I != end() && I->start <= Idx ? I : end();
/// overlaps - Return true if the intersection of the two live ranges is
/// not empty.
bool overlaps(const LiveRange &other) const {
if (other.empty())
return false;
return overlapsFrom(other, other.begin());
/// overlaps - Return true if the two ranges have overlapping segments
/// that are not coalescable according to CP.
/// Overlapping segments where one range is defined by a coalescable
/// copy are allowed.
bool overlaps(const LiveRange &Other, const CoalescerPair &CP,
const SlotIndexes&) const;
/// overlaps - Return true if the live range overlaps an interval specified
/// by [Start, End).
bool overlaps(SlotIndex Start, SlotIndex End) const;
/// overlapsFrom - Return true if the intersection of the two live ranges
/// is not empty. The specified iterator is a hint that we can begin
/// scanning the Other range starting at I.
bool overlapsFrom(const LiveRange &Other, const_iterator I) const;
/// Add the specified Segment to this range, merging segments as
/// appropriate. This returns an iterator to the inserted segment (which
/// may have grown since it was inserted).
iterator addSegment(Segment S) {
return addSegmentFrom(S, segments.begin());
/// extendInBlock - If this range is live before Kill in the basic block
/// that starts at StartIdx, extend it to be live up to Kill, and return
/// the value. If there is no segment before Kill, return NULL.
VNInfo *extendInBlock(SlotIndex StartIdx, SlotIndex Kill);
/// join - Join two live ranges (this, and other) together. This applies
/// mappings to the value numbers in the LHS/RHS ranges as specified. If
/// the ranges are not joinable, this aborts.
void join(LiveRange &Other,
const int *ValNoAssignments,
const int *RHSValNoAssignments,
SmallVectorImpl<VNInfo *> &NewVNInfo);
/// True iff this segment is a single segment that lies between the
/// specified boundaries, exclusively. Vregs live across a backedge are not
/// considered local. The boundaries are expected to lie within an extended
/// basic block, so vregs that are not live out should contain no holes.
bool isLocal(SlotIndex Start, SlotIndex End) const {
return beginIndex() > Start.getBaseIndex() &&
endIndex() < End.getBoundaryIndex();
/// Remove the specified segment from this range. Note that the segment
/// must be a single Segment in its entirety.
void removeSegment(SlotIndex Start, SlotIndex End,
bool RemoveDeadValNo = false);
void removeSegment(Segment S, bool RemoveDeadValNo = false) {
removeSegment(S.start, S.end, RemoveDeadValNo);
/// Query Liveness at Idx.
/// The sub-instruction slot of Idx doesn't matter, only the instruction
/// it refers to is considered.
LiveQueryResult Query(SlotIndex Idx) const {
// Find the segment that enters the instruction.
const_iterator I = find(Idx.getBaseIndex());
const_iterator E = end();
if (I == E)
return LiveQueryResult(nullptr, nullptr, SlotIndex(), false);
// Is this an instruction live-in segment?
// If Idx is the start index of a basic block, include live-in segments
// that start at Idx.getBaseIndex().
VNInfo *EarlyVal = nullptr;
VNInfo *LateVal = nullptr;
SlotIndex EndPoint;
bool Kill = false;
if (I->start <= Idx.getBaseIndex()) {
EarlyVal = I->valno;
EndPoint = I->end;
// Move to the potentially live-out segment.
if (SlotIndex::isSameInstr(Idx, I->end)) {
Kill = true;
if (++I == E)
return LiveQueryResult(EarlyVal, LateVal, EndPoint, Kill);
// Special case: A PHIDef value can have its def in the middle of a
// segment if the value happens to be live out of the layout
// predecessor.
// Such a value is not live-in.
if (EarlyVal->def == Idx.getBaseIndex())
EarlyVal = nullptr;
// I now points to the segment that may be live-through, or defined by
// this instr. Ignore segments starting after the current instr.
if (!SlotIndex::isEarlierInstr(Idx, I->start)) {
LateVal = I->valno;
EndPoint = I->end;
return LiveQueryResult(EarlyVal, LateVal, EndPoint, Kill);
/// removeValNo - Remove all the segments defined by the specified value#.
/// Also remove the value# from value# list.
void removeValNo(VNInfo *ValNo);
/// Returns true if the live range is zero length, i.e. no live segments
/// span instructions. It doesn't pay to spill such a range.
bool isZeroLength(SlotIndexes *Indexes) const {
for (const_iterator i = begin(), e = end(); i != e; ++i)
if (Indexes->getNextNonNullIndex(i->start).getBaseIndex() <
return false;
return true;
bool operator<(const LiveRange& other) const {
const SlotIndex &thisIndex = beginIndex();
const SlotIndex &otherIndex = other.beginIndex();
return thisIndex < otherIndex;
void print(raw_ostream &OS) const;
void dump() const;
/// \brief Walk the range and assert if any invariants fail to hold.
/// Note that this is a no-op when asserts are disabled.
#ifdef NDEBUG
void verify() const {}
void verify() const;
iterator addSegmentFrom(Segment S, iterator From);
void extendSegmentEndTo(iterator I, SlotIndex NewEnd);
iterator extendSegmentStartTo(iterator I, SlotIndex NewStr);
void markValNoForDeletion(VNInfo *V);
inline raw_ostream &operator<<(raw_ostream &OS, const LiveRange &LR) {
return OS;
/// LiveInterval - This class represents the liveness of a register,
/// or stack slot.
class LiveInterval : public LiveRange {
typedef LiveRange super;
const unsigned reg; // the register or stack slot of this interval.
float weight; // weight of this interval
LiveInterval(unsigned Reg, float Weight)
: reg(Reg), weight(Weight) {}
/// getSize - Returns the sum of sizes of all the LiveRange's.
unsigned getSize() const;
/// isSpillable - Can this interval be spilled?
bool isSpillable() const {
return weight != llvm::huge_valf;
/// markNotSpillable - Mark interval as not spillable
void markNotSpillable() {
weight = llvm::huge_valf;
bool operator<(const LiveInterval& other) const {
const SlotIndex &thisIndex = beginIndex();
const SlotIndex &otherIndex = other.beginIndex();
return std::tie(thisIndex, reg) < std::tie(otherIndex, other.reg);
void print(raw_ostream &OS) const;
void dump() const;
LiveInterval& operator=(const LiveInterval& rhs) LLVM_DELETED_FUNCTION;
inline raw_ostream &operator<<(raw_ostream &OS, const LiveInterval &LI) {
return OS;
raw_ostream &operator<<(raw_ostream &OS, const LiveRange::Segment &S);
inline bool operator<(SlotIndex V, const LiveRange::Segment &S) {
return V < S.start;
inline bool operator<(const LiveRange::Segment &S, SlotIndex V) {
return S.start < V;
/// Helper class for performant LiveRange bulk updates.
/// Calling LiveRange::addSegment() repeatedly can be expensive on large
/// live ranges because segments after the insertion point may need to be
/// shifted. The LiveRangeUpdater class can defer the shifting when adding
/// many segments in order.
/// The LiveRange will be in an invalid state until flush() is called.
class LiveRangeUpdater {
LiveRange *LR;
SlotIndex LastStart;
LiveRange::iterator WriteI;
LiveRange::iterator ReadI;
SmallVector<LiveRange::Segment, 16> Spills;
void mergeSpills();
/// Create a LiveRangeUpdater for adding segments to LR.
/// LR will temporarily be in an invalid state until flush() is called.
LiveRangeUpdater(LiveRange *lr = nullptr) : LR(lr) {}
~LiveRangeUpdater() { flush(); }
/// Add a segment to LR and coalesce when possible, just like
/// LR.addSegment(). Segments should be added in increasing start order for
/// best performance.
void add(LiveRange::Segment);
void add(SlotIndex Start, SlotIndex End, VNInfo *VNI) {
add(LiveRange::Segment(Start, End, VNI));
/// Return true if the LR is currently in an invalid state, and flush()
/// needs to be called.
bool isDirty() const { return LastStart.isValid(); }
/// Flush the updater state to LR so it is valid and contains all added
/// segments.
void flush();
/// Select a different destination live range.
void setDest(LiveRange *lr) {
if (LR != lr && isDirty())
LR = lr;
/// Get the current destination live range.
LiveRange *getDest() const { return LR; }
void dump() const;
void print(raw_ostream&) const;
inline raw_ostream &operator<<(raw_ostream &OS, const LiveRangeUpdater &X) {
return OS;
/// ConnectedVNInfoEqClasses - Helper class that can divide VNInfos in a
/// LiveInterval into equivalence clases of connected components. A
/// LiveInterval that has multiple connected components can be broken into
/// multiple LiveIntervals.
/// Given a LiveInterval that may have multiple connected components, run:
/// unsigned numComps = ConEQ.Classify(LI);
/// if (numComps > 1) {
/// // allocate numComps-1 new LiveIntervals into LIS[1..]
/// ConEQ.Distribute(LIS);
/// }
class ConnectedVNInfoEqClasses {
LiveIntervals &LIS;
IntEqClasses EqClass;
// Note that values a and b are connected.
void Connect(unsigned a, unsigned b);
unsigned Renumber();
explicit ConnectedVNInfoEqClasses(LiveIntervals &lis) : LIS(lis) {}
/// Classify - Classify the values in LI into connected components.
/// Return the number of connected components.
unsigned Classify(const LiveInterval *LI);
/// getEqClass - Classify creates equivalence classes numbered 0..N. Return
/// the equivalence class assigned the VNI.
unsigned getEqClass(const VNInfo *VNI) const { return EqClass[VNI->id]; }
/// Distribute - Distribute values in LIV[0] into a separate LiveInterval
/// for each connected component. LIV must have a LiveInterval for each
/// connected component. The LiveIntervals in Liv[1..] must be empty.
/// Instructions using LIV[0] are rewritten.
void Distribute(LiveInterval *LIV[], MachineRegisterInfo &MRI);