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/CodeGen/LiveInterval.h"
18#include "llvm/CodeGen/TargetRegisterInfo.h"
19#include "llvm/Support/raw_ostream.h"
20#include <cassert>
21#include <cstdlib>
22
23using namespace llvm;
24
25#define DEBUG_TYPE "regalloc"
26
27// Merge a LiveInterval's segments. Guarantee no overlaps.
28void LiveIntervalUnion::unify(const LiveInterval &VirtReg,
29                              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(const LiveInterval &VirtReg,
57                                const LiveRange &Range) {
58  if (Range.empty())
59    return;
60  ++Tag;
61
62  // Remove each of the virtual register's live segments from the map.
63  LiveRange::const_iterator RegPos = Range.begin();
64  LiveRange::const_iterator RegEnd = Range.end();
65  SegmentIter SegPos = Segments.find(RegPos->start);
66
67  while (true) {
68    assert(SegPos.value() == &VirtReg && "Inconsistent LiveInterval");
69    SegPos.erase();
70    if (!SegPos.valid())
71      return;
72
73    // Skip all segments that may have been coalesced.
74    RegPos = Range.advanceTo(RegPos, SegPos.start());
75    if (RegPos == RegEnd)
76      return;
77
78    SegPos.advanceTo(RegPos->start);
79  }
80}
81
82void
83LiveIntervalUnion::print(raw_ostream &OS, const TargetRegisterInfo *TRI) const {
84  if (empty()) {
85    OS << " empty\n";
86    return;
87  }
88  for (LiveSegments::const_iterator SI = Segments.begin(); SI.valid(); ++SI) {
89    OS << " [" << SI.start() << ' ' << SI.stop()
90       << "):" << printReg(SI.value()->reg(), TRI);
91  }
92  OS << '\n';
93}
94
95#ifndef NDEBUG
96// Verify the live intervals in this union and add them to the visited set.
97void LiveIntervalUnion::verify(LiveVirtRegBitSet& VisitedVRegs) {
98  for (SegmentIter SI = Segments.begin(); SI.valid(); ++SI)
99    VisitedVRegs.set(SI.value()->reg());
100}
101#endif //!NDEBUG
102
103const LiveInterval *LiveIntervalUnion::getOneVReg() const {
104  if (empty())
105    return nullptr;
106  for (LiveSegments::const_iterator SI = Segments.begin(); SI.valid(); ++SI) {
107    // return the first valid live interval
108    return SI.value();
109  }
110  return nullptr;
111}
112
113// Scan the vector of interfering virtual registers in this union. Assume it's
114// quite small.
115bool LiveIntervalUnion::Query::isSeenInterference(
116    const LiveInterval *VirtReg) const {
117  return is_contained(InterferingVRegs, VirtReg);
118}
119
120// Collect virtual registers in this union that interfere with this
121// query's live virtual register.
122//
123// The query state is one of:
124//
125// 1. CheckedFirstInterference == false: Iterators are uninitialized.
126// 2. SeenAllInterferences == true: InterferingVRegs complete, iterators unused.
127// 3. Iterators left at the last seen intersection.
128//
129unsigned
130LiveIntervalUnion::Query::collectInterferingVRegs(unsigned MaxInterferingRegs) {
131  // Fast path return if we already have the desired information.
132  if (SeenAllInterferences || InterferingVRegs.size() >= MaxInterferingRegs)
133    return InterferingVRegs.size();
134
135  // Set up iterators on the first call.
136  if (!CheckedFirstInterference) {
137    CheckedFirstInterference = true;
138
139    // Quickly skip interference check for empty sets.
140    if (LR->empty() || LiveUnion->empty()) {
141      SeenAllInterferences = true;
142      return 0;
143    }
144
145    // In most cases, the union will start before LR.
146    LRI = LR->begin();
147    LiveUnionI.setMap(LiveUnion->getMap());
148    LiveUnionI.find(LRI->start);
149  }
150
151  LiveRange::const_iterator LREnd = LR->end();
152  const LiveInterval *RecentReg = nullptr;
153  while (LiveUnionI.valid()) {
154    assert(LRI != LREnd && "Reached end of LR");
155
156    // Check for overlapping interference.
157    while (LRI->start < LiveUnionI.stop() && LRI->end > LiveUnionI.start()) {
158      // This is an overlap, record the interfering register.
159      const LiveInterval *VReg = LiveUnionI.value();
160      if (VReg != RecentReg && !isSeenInterference(VReg)) {
161        RecentReg = VReg;
162        InterferingVRegs.push_back(VReg);
163        if (InterferingVRegs.size() >= MaxInterferingRegs)
164          return InterferingVRegs.size();
165      }
166      // This LiveUnion segment is no longer interesting.
167      if (!(++LiveUnionI).valid()) {
168        SeenAllInterferences = true;
169        return InterferingVRegs.size();
170      }
171    }
172
173    // The iterators are now not overlapping, LiveUnionI has been advanced
174    // beyond LRI.
175    assert(LRI->end <= LiveUnionI.start() && "Expected non-overlap");
176
177    // Advance the iterator that ends first.
178    LRI = LR->advanceTo(LRI, LiveUnionI.start());
179    if (LRI == LREnd)
180      break;
181
182    // Detect overlap, handle above.
183    if (LRI->start < LiveUnionI.stop())
184      continue;
185
186    // Still not overlapping. Catch up LiveUnionI.
187    LiveUnionI.advanceTo(LRI->start);
188  }
189  SeenAllInterferences = true;
190  return InterferingVRegs.size();
191}
192
193void LiveIntervalUnion::Array::init(LiveIntervalUnion::Allocator &Alloc,
194                                    unsigned NSize) {
195  // Reuse existing allocation.
196  if (NSize == Size)
197    return;
198  clear();
199  Size = NSize;
200  LIUs = static_cast<LiveIntervalUnion*>(
201      safe_malloc(sizeof(LiveIntervalUnion)*NSize));
202  for (unsigned i = 0; i != Size; ++i)
203    new(LIUs + i) LiveIntervalUnion(Alloc);
204}
205
206void LiveIntervalUnion::Array::clear() {
207  if (!LIUs)
208    return;
209  for (unsigned i = 0; i != Size; ++i)
210    LIUs[i].~LiveIntervalUnion();
211  free(LIUs);
212  Size =  0;
213  LIUs = nullptr;
214}
215