LiveIntervalUnion.h revision 360784 
1//===- LiveIntervalUnion.h - Live interval union data struct ---*- C++ -*--===//
2//
3// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
4// See https://llvm.org/LICENSE.txt for license information.
5// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
6//
7//===----------------------------------------------------------------------===//
8//
9// LiveIntervalUnion is a union of live segments across multiple live virtual
10// registers. This may be used during coalescing to represent a congruence
11// class, or during register allocation to model liveness of a physical
12// register.
13//
14//===----------------------------------------------------------------------===//
15
16#ifndef LLVM_CODEGEN_LIVEINTERVALUNION_H
17#define LLVM_CODEGEN_LIVEINTERVALUNION_H
18
19#include "llvm/ADT/IntervalMap.h"
20#include "llvm/ADT/SmallVector.h"
21#include "llvm/CodeGen/LiveInterval.h"
22#include "llvm/CodeGen/SlotIndexes.h"
23#include <cassert>
24#include <limits>
25
26namespace llvm {
27
28class raw_ostream;
29class TargetRegisterInfo;
30
31#ifndef NDEBUG
32// forward declaration
33template <unsigned Element> class SparseBitVector;
34
35using LiveVirtRegBitSet = SparseBitVector<128>;
36#endif
37
38/// Union of live intervals that are strong candidates for coalescing into a
39/// single register (either physical or virtual depending on the context).  We
40/// expect the constituent live intervals to be disjoint, although we may
41/// eventually make exceptions to handle value-based interference.
42class LiveIntervalUnion {
43  // A set of live virtual register segments that supports fast insertion,
44  // intersection, and removal.
45  // Mapping SlotIndex intervals to virtual register numbers.
46  using LiveSegments = IntervalMap<SlotIndex, LiveInterval*>;
47
48public:
49  // SegmentIter can advance to the next segment ordered by starting position
50  // which may belong to a different live virtual register. We also must be able
51  // to reach the current segment's containing virtual register.
52  using SegmentIter = LiveSegments::iterator;
53
54  /// Const version of SegmentIter.
55  using ConstSegmentIter = LiveSegments::const_iterator;
56
57  // LiveIntervalUnions share an external allocator.
58  using Allocator = LiveSegments::Allocator;
59
60private:
61  unsigned Tag = 0;       // unique tag for current contents.
62  LiveSegments Segments;  // union of virtual reg segments
63
64public:
65  explicit LiveIntervalUnion(Allocator &a) : Segments(a) {}
66
67  // Iterate over all segments in the union of live virtual registers ordered
68  // by their starting position.
69  SegmentIter begin() { return Segments.begin(); }
70  SegmentIter end() { return Segments.end(); }
71  SegmentIter find(SlotIndex x) { return Segments.find(x); }
72  ConstSegmentIter begin() const { return Segments.begin(); }
73  ConstSegmentIter end() const { return Segments.end(); }
74  ConstSegmentIter find(SlotIndex x) const { return Segments.find(x); }
75
76  bool empty() const { return Segments.empty(); }
77  SlotIndex startIndex() const { return Segments.start(); }
78  SlotIndex endIndex() const { return Segments.stop(); }
79
80  // Provide public access to the underlying map to allow overlap iteration.
81  using Map = LiveSegments;
82  const Map &getMap() const { return Segments; }
83
84  /// getTag - Return an opaque tag representing the current state of the union.
85  unsigned getTag() const { return Tag; }
86
87  /// changedSince - Return true if the union change since getTag returned tag.
88  bool changedSince(unsigned tag) const { return tag != Tag; }
89
90  // Add a live virtual register to this union and merge its segments.
91  void unify(LiveInterval &VirtReg, const LiveRange &Range);
92
93  // Remove a live virtual register's segments from this union.
94  void extract(LiveInterval &VirtReg, const LiveRange &Range);
95
96  // Remove all inserted virtual registers.
97  void clear() { Segments.clear(); ++Tag; }
98
99  // Print union, using TRI to translate register names
100  void print(raw_ostream &OS, const TargetRegisterInfo *TRI) const;
101
102#ifndef NDEBUG
103  // Verify the live intervals in this union and add them to the visited set.
104  void verify(LiveVirtRegBitSet& VisitedVRegs);
105#endif
106
107  /// Query interferences between a single live virtual register and a live
108  /// interval union.
109  class Query {
110    const LiveIntervalUnion *LiveUnion = nullptr;
111    const LiveRange *LR = nullptr;
112    LiveRange::const_iterator LRI;  ///< current position in LR
113    ConstSegmentIter LiveUnionI;    ///< current position in LiveUnion
114    SmallVector<LiveInterval*,4> InterferingVRegs;
115    bool CheckedFirstInterference = false;
116    bool SeenAllInterferences = false;
117    unsigned Tag = 0;
118    unsigned UserTag = 0;
119
120    void reset(unsigned NewUserTag, const LiveRange &NewLR,
121               const LiveIntervalUnion &NewLiveUnion) {
122      LiveUnion = &NewLiveUnion;
123      LR = &NewLR;
124      InterferingVRegs.clear();
125      CheckedFirstInterference = false;
126      SeenAllInterferences = false;
127      Tag = NewLiveUnion.getTag();
128      UserTag = NewUserTag;
129    }
130
131  public:
132    Query() = default;
133    Query(const LiveRange &LR, const LiveIntervalUnion &LIU):
134      LiveUnion(&LIU), LR(&LR) {}
135    Query(const Query &) = delete;
136    Query &operator=(const Query &) = delete;
137
138    void init(unsigned NewUserTag, const LiveRange &NewLR,
139              const LiveIntervalUnion &NewLiveUnion) {
140      if (UserTag == NewUserTag && LR == &NewLR && LiveUnion == &NewLiveUnion &&
141          !NewLiveUnion.changedSince(Tag)) {
142        // Retain cached results, e.g. firstInterference.
143        return;
144      }
145      reset(NewUserTag, NewLR, NewLiveUnion);
146    }
147
148    // Does this live virtual register interfere with the union?
149    bool checkInterference() { return collectInterferingVRegs(1); }
150
151    // Count the virtual registers in this union that interfere with this
152    // query's live virtual register, up to maxInterferingRegs.
153    unsigned collectInterferingVRegs(
154        unsigned MaxInterferingRegs = std::numeric_limits<unsigned>::max());
155
156    // Was this virtual register visited during collectInterferingVRegs?
157    bool isSeenInterference(LiveInterval *VirtReg) const;
158
159    // Did collectInterferingVRegs collect all interferences?
160    bool seenAllInterferences() const { return SeenAllInterferences; }
161
162    // Vector generated by collectInterferingVRegs.
163    const SmallVectorImpl<LiveInterval*> &interferingVRegs() const {
164      return InterferingVRegs;
165    }
166  };
167
168  // Array of LiveIntervalUnions.
169  class Array {
170    unsigned Size = 0;
171    LiveIntervalUnion *LIUs = nullptr;
172
173  public:
174    Array() = default;
175    ~Array() { clear(); }
176
177    // Initialize the array to have Size entries.
178    // Reuse an existing allocation if the size matches.
179    void init(LiveIntervalUnion::Allocator&, unsigned Size);
180
181    unsigned size() const { return Size; }
182
183    void clear();
184
185    LiveIntervalUnion& operator[](unsigned idx) {
186      assert(idx <  Size && "idx out of bounds");
187      return LIUs[idx];
188    }
189
190    const LiveIntervalUnion& operator[](unsigned Idx) const {
191      assert(Idx < Size && "Idx out of bounds");
192      return LIUs[Idx];
193    }
194  };
195};
196
197} // end namespace llvm
198
199#endif // LLVM_CODEGEN_LIVEINTERVALUNION_H
200