1//===- LiveIntervalUnion.cpp - Live interval union data structure ---------===//
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 represents a coalesced set of live intervals. This may be
10// used during coalescing to represent a congruence class, or during register
11// allocation to model liveness of a physical register.
12//
13//===----------------------------------------------------------------------===//
14
15#include "llvm/CodeGen/LiveIntervalUnion.h"
16#include "llvm/ADT/STLExtras.h"
17#include "llvm/ADT/SparseBitVector.h"
18#include "llvm/CodeGen/LiveInterval.h"
19#include "llvm/CodeGen/TargetRegisterInfo.h"
20#include "llvm/Support/raw_ostream.h"
21#include <cassert>
22#include <cstdlib>
23
24using namespace llvm;
25
26#define DEBUG_TYPE "regalloc"
27
28// Merge a LiveInterval's segments. Guarantee no overlaps.
29void LiveIntervalUnion::unify(LiveInterval &VirtReg, const LiveRange &Range) {
30  if (Range.empty())
31    return;
32  ++Tag;
33
34  // Insert each of the virtual register's live segments into the map.
35  LiveRange::const_iterator RegPos = Range.begin();
36  LiveRange::const_iterator RegEnd = Range.end();
37  SegmentIter SegPos = Segments.find(RegPos->start);
38
39  while (SegPos.valid()) {
40    SegPos.insert(RegPos->start, RegPos->end, &VirtReg);
41    if (++RegPos == RegEnd)
42      return;
43    SegPos.advanceTo(RegPos->start);
44  }
45
46  // We have reached the end of Segments, so it is no longer necessary to search
47  // for the insertion position.
48  // It is faster to insert the end first.
49  --RegEnd;
50  SegPos.insert(RegEnd->start, RegEnd->end, &VirtReg);
51  for (; RegPos != RegEnd; ++RegPos, ++SegPos)
52    SegPos.insert(RegPos->start, RegPos->end, &VirtReg);
53}
54
55// Remove a live virtual register's segments from this union.
56void LiveIntervalUnion::extract(LiveInterval &VirtReg, const LiveRange &Range) {
57  if (Range.empty())
58    return;
59  ++Tag;
60
61  // Remove each of the virtual register's live segments from the map.
62  LiveRange::const_iterator RegPos = Range.begin();
63  LiveRange::const_iterator RegEnd = Range.end();
64  SegmentIter SegPos = Segments.find(RegPos->start);
65
66  while (true) {
67    assert(SegPos.value() == &VirtReg && "Inconsistent LiveInterval");
68    SegPos.erase();
69    if (!SegPos.valid())
70      return;
71
72    // Skip all segments that may have been coalesced.
73    RegPos = Range.advanceTo(RegPos, SegPos.start());
74    if (RegPos == RegEnd)
75      return;
76
77    SegPos.advanceTo(RegPos->start);
78  }
79}
80
81void
82LiveIntervalUnion::print(raw_ostream &OS, const TargetRegisterInfo *TRI) const {
83  if (empty()) {
84    OS << " empty\n";
85    return;
86  }
87  for (LiveSegments::const_iterator SI = Segments.begin(); SI.valid(); ++SI) {
88    OS << " [" << SI.start() << ' ' << SI.stop() << "):"
89       << printReg(SI.value()->reg, TRI);
90  }
91  OS << '\n';
92}
93
94#ifndef NDEBUG
95// Verify the live intervals in this union and add them to the visited set.
96void LiveIntervalUnion::verify(LiveVirtRegBitSet& VisitedVRegs) {
97  for (SegmentIter SI = Segments.begin(); SI.valid(); ++SI)
98    VisitedVRegs.set(SI.value()->reg);
99}
100#endif //!NDEBUG
101
102// Scan the vector of interfering virtual registers in this union. Assume it's
103// quite small.
104bool LiveIntervalUnion::Query::isSeenInterference(LiveInterval *VirtReg) const {
105  return is_contained(InterferingVRegs, VirtReg);
106}
107
108// Collect virtual registers in this union that interfere with this
109// query's live virtual register.
110//
111// The query state is one of:
112//
113// 1. CheckedFirstInterference == false: Iterators are uninitialized.
114// 2. SeenAllInterferences == true: InterferingVRegs complete, iterators unused.
115// 3. Iterators left at the last seen intersection.
116//
117unsigned LiveIntervalUnion::Query::
118collectInterferingVRegs(unsigned MaxInterferingRegs) {
119  // Fast path return if we already have the desired information.
120  if (SeenAllInterferences || InterferingVRegs.size() >= MaxInterferingRegs)
121    return InterferingVRegs.size();
122
123  // Set up iterators on the first call.
124  if (!CheckedFirstInterference) {
125    CheckedFirstInterference = true;
126
127    // Quickly skip interference check for empty sets.
128    if (LR->empty() || LiveUnion->empty()) {
129      SeenAllInterferences = true;
130      return 0;
131    }
132
133    // In most cases, the union will start before LR.
134    LRI = LR->begin();
135    LiveUnionI.setMap(LiveUnion->getMap());
136    LiveUnionI.find(LRI->start);
137  }
138
139  LiveRange::const_iterator LREnd = LR->end();
140  LiveInterval *RecentReg = nullptr;
141  while (LiveUnionI.valid()) {
142    assert(LRI != LREnd && "Reached end of LR");
143
144    // Check for overlapping interference.
145    while (LRI->start < LiveUnionI.stop() && LRI->end > LiveUnionI.start()) {
146      // This is an overlap, record the interfering register.
147      LiveInterval *VReg = LiveUnionI.value();
148      if (VReg != RecentReg && !isSeenInterference(VReg)) {
149        RecentReg = VReg;
150        InterferingVRegs.push_back(VReg);
151        if (InterferingVRegs.size() >= MaxInterferingRegs)
152          return InterferingVRegs.size();
153      }
154      // This LiveUnion segment is no longer interesting.
155      if (!(++LiveUnionI).valid()) {
156        SeenAllInterferences = true;
157        return InterferingVRegs.size();
158      }
159    }
160
161    // The iterators are now not overlapping, LiveUnionI has been advanced
162    // beyond LRI.
163    assert(LRI->end <= LiveUnionI.start() && "Expected non-overlap");
164
165    // Advance the iterator that ends first.
166    LRI = LR->advanceTo(LRI, LiveUnionI.start());
167    if (LRI == LREnd)
168      break;
169
170    // Detect overlap, handle above.
171    if (LRI->start < LiveUnionI.stop())
172      continue;
173
174    // Still not overlapping. Catch up LiveUnionI.
175    LiveUnionI.advanceTo(LRI->start);
176  }
177  SeenAllInterferences = true;
178  return InterferingVRegs.size();
179}
180
181void LiveIntervalUnion::Array::init(LiveIntervalUnion::Allocator &Alloc,
182                                    unsigned NSize) {
183  // Reuse existing allocation.
184  if (NSize == Size)
185    return;
186  clear();
187  Size = NSize;
188  LIUs = static_cast<LiveIntervalUnion*>(
189      safe_malloc(sizeof(LiveIntervalUnion)*NSize));
190  for (unsigned i = 0; i != Size; ++i)
191    new(LIUs + i) LiveIntervalUnion(Alloc);
192}
193
194void LiveIntervalUnion::Array::clear() {
195  if (!LIUs)
196    return;
197  for (unsigned i = 0; i != Size; ++i)
198    LIUs[i].~LiveIntervalUnion();
199  free(LIUs);
200  Size =  0;
201  LIUs = nullptr;
202}
203