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//===- LiveIntervalUnion.h - Live interval union data struct ---*- 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
// LiveIntervalUnion is a union of live segments across multiple live virtual
// registers. This may be used during coalescing to represent a congruence
// class, or during register allocation to model liveness of a physical
// register.
#include "llvm/ADT/IntervalMap.h"
#include "llvm/ADT/SmallVector.h"
#include "llvm/CodeGen/LiveInterval.h"
#include "llvm/CodeGen/SlotIndexes.h"
#include <cassert>
#include <limits>
namespace llvm {
class raw_ostream;
class TargetRegisterInfo;
#ifndef NDEBUG
// forward declaration
template <unsigned Element> class SparseBitVector;
using LiveVirtRegBitSet = SparseBitVector<128>;
/// Union of live intervals that are strong candidates for coalescing into a
/// single register (either physical or virtual depending on the context). We
/// expect the constituent live intervals to be disjoint, although we may
/// eventually make exceptions to handle value-based interference.
class LiveIntervalUnion {
// A set of live virtual register segments that supports fast insertion,
// intersection, and removal.
// Mapping SlotIndex intervals to virtual register numbers.
using LiveSegments = IntervalMap<SlotIndex, LiveInterval*>;
// SegmentIter can advance to the next segment ordered by starting position
// which may belong to a different live virtual register. We also must be able
// to reach the current segment's containing virtual register.
using SegmentIter = LiveSegments::iterator;
/// Const version of SegmentIter.
using ConstSegmentIter = LiveSegments::const_iterator;
// LiveIntervalUnions share an external allocator.
using Allocator = LiveSegments::Allocator;
unsigned Tag = 0; // unique tag for current contents.
LiveSegments Segments; // union of virtual reg segments
explicit LiveIntervalUnion(Allocator &a) : Segments(a) {}
// Iterate over all segments in the union of live virtual registers ordered
// by their starting position.
SegmentIter begin() { return Segments.begin(); }
SegmentIter end() { return Segments.end(); }
SegmentIter find(SlotIndex x) { return Segments.find(x); }
ConstSegmentIter begin() const { return Segments.begin(); }
ConstSegmentIter end() const { return Segments.end(); }
ConstSegmentIter find(SlotIndex x) const { return Segments.find(x); }
bool empty() const { return Segments.empty(); }
SlotIndex startIndex() const { return Segments.start(); }
// Provide public access to the underlying map to allow overlap iteration.
using Map = LiveSegments;
const Map &getMap() const { return Segments; }
/// getTag - Return an opaque tag representing the current state of the union.
unsigned getTag() const { return Tag; }
/// changedSince - Return true if the union change since getTag returned tag.
bool changedSince(unsigned tag) const { return tag != Tag; }
// Add a live virtual register to this union and merge its segments.
void unify(LiveInterval &VirtReg, const LiveRange &Range);
// Remove a live virtual register's segments from this union.
void extract(LiveInterval &VirtReg, const LiveRange &Range);
// Remove all inserted virtual registers.
void clear() { Segments.clear(); ++Tag; }
// Print union, using TRI to translate register names
void print(raw_ostream &OS, const TargetRegisterInfo *TRI) const;
#ifndef NDEBUG
// Verify the live intervals in this union and add them to the visited set.
void verify(LiveVirtRegBitSet& VisitedVRegs);
/// Query interferences between a single live virtual register and a live
/// interval union.
class Query {
const LiveIntervalUnion *LiveUnion = nullptr;
const LiveRange *LR = nullptr;
LiveRange::const_iterator LRI; ///< current position in LR
ConstSegmentIter LiveUnionI; ///< current position in LiveUnion
SmallVector<LiveInterval*,4> InterferingVRegs;
bool CheckedFirstInterference = false;
bool SeenAllInterferences = false;
unsigned Tag = 0;
unsigned UserTag = 0;
void reset(unsigned NewUserTag, const LiveRange &NewLR,
const LiveIntervalUnion &NewLiveUnion) {
LiveUnion = &NewLiveUnion;
LR = &NewLR;
CheckedFirstInterference = false;
SeenAllInterferences = false;
Tag = NewLiveUnion.getTag();
UserTag = NewUserTag;
Query() = default;
Query(const LiveRange &LR, const LiveIntervalUnion &LIU):
LiveUnion(&LIU), LR(&LR) {}
Query(const Query &) = delete;
Query &operator=(const Query &) = delete;
void init(unsigned NewUserTag, const LiveRange &NewLR,
const LiveIntervalUnion &NewLiveUnion) {
if (UserTag == NewUserTag && LR == &NewLR && LiveUnion == &NewLiveUnion &&
!NewLiveUnion.changedSince(Tag)) {
// Retain cached results, e.g. firstInterference.
reset(NewUserTag, NewLR, NewLiveUnion);
// Does this live virtual register interfere with the union?
bool checkInterference() { return collectInterferingVRegs(1); }
// Count the virtual registers in this union that interfere with this
// query's live virtual register, up to maxInterferingRegs.
unsigned collectInterferingVRegs(
unsigned MaxInterferingRegs = std::numeric_limits<unsigned>::max());
// Was this virtual register visited during collectInterferingVRegs?
bool isSeenInterference(LiveInterval *VirtReg) const;
// Did collectInterferingVRegs collect all interferences?
bool seenAllInterferences() const { return SeenAllInterferences; }
// Vector generated by collectInterferingVRegs.
const SmallVectorImpl<LiveInterval*> &interferingVRegs() const {
return InterferingVRegs;
// Array of LiveIntervalUnions.
class Array {
unsigned Size = 0;
LiveIntervalUnion *LIUs = nullptr;
Array() = default;
~Array() { clear(); }
// Initialize the array to have Size entries.
// Reuse an existing allocation if the size matches.
void init(LiveIntervalUnion::Allocator&, unsigned Size);
unsigned size() const { return Size; }
void clear();
LiveIntervalUnion& operator[](unsigned idx) {
assert(idx < Size && "idx out of bounds");
return LIUs[idx];
const LiveIntervalUnion& operator[](unsigned Idx) const {
assert(Idx < Size && "Idx out of bounds");
return LIUs[Idx];
} // end namespace llvm