1//===-- LiveIntervalUnion.cpp - Live interval union data structure --------===//
2//
3//                     The LLVM Compiler Infrastructure
4//
5// This file is distributed under the University of Illinois Open Source
6// License. See LICENSE.TXT for details.
7//
8//===----------------------------------------------------------------------===//
9//
10// LiveIntervalUnion represents a coalesced set of live intervals. This may be
11// used during coalescing to represent a congruence class, or during register
12// allocation to model liveness of a physical register.
13//
14//===----------------------------------------------------------------------===//
15
16#include "llvm/CodeGen/LiveIntervalUnion.h"
17#include "llvm/ADT/SparseBitVector.h"
18#include "llvm/Support/Debug.h"
19#include "llvm/Support/raw_ostream.h"
20#include "llvm/Target/TargetRegisterInfo.h"
21#include <algorithm>
22
23using namespace llvm;
24
25#define DEBUG_TYPE "regalloc"
26
27
28// Merge a LiveInterval's segments. Guarantee no overlaps.
29void LiveIntervalUnion::unify(LiveInterval &VirtReg) {
30  if (VirtReg.empty())
31    return;
32  ++Tag;
33
34  // Insert each of the virtual register's live segments into the map.
35  LiveInterval::iterator RegPos = VirtReg.begin();
36  LiveInterval::iterator RegEnd = VirtReg.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) {
57  if (VirtReg.empty())
58    return;
59  ++Tag;
60
61  // Remove each of the virtual register's live segments from the map.
62  LiveInterval::iterator RegPos = VirtReg.begin();
63  LiveInterval::iterator RegEnd = VirtReg.end();
64  SegmentIter SegPos = Segments.find(RegPos->start);
65
66  for (;;) {
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 = VirtReg.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  SmallVectorImpl<LiveInterval*>::const_iterator I =
106    std::find(InterferingVRegs.begin(), InterferingVRegs.end(), VirtReg);
107  return I != InterferingVRegs.end();
108}
109
110// Collect virtual registers in this union that interfere with this
111// query's live virtual register.
112//
113// The query state is one of:
114//
115// 1. CheckedFirstInterference == false: Iterators are uninitialized.
116// 2. SeenAllInterferences == true: InterferingVRegs complete, iterators unused.
117// 3. Iterators left at the last seen intersection.
118//
119unsigned LiveIntervalUnion::Query::
120collectInterferingVRegs(unsigned MaxInterferingRegs) {
121  // Fast path return if we already have the desired information.
122  if (SeenAllInterferences || InterferingVRegs.size() >= MaxInterferingRegs)
123    return InterferingVRegs.size();
124
125  // Set up iterators on the first call.
126  if (!CheckedFirstInterference) {
127    CheckedFirstInterference = true;
128
129    // Quickly skip interference check for empty sets.
130    if (VirtReg->empty() || LiveUnion->empty()) {
131      SeenAllInterferences = true;
132      return 0;
133    }
134
135    // In most cases, the union will start before VirtReg.
136    VirtRegI = VirtReg->begin();
137    LiveUnionI.setMap(LiveUnion->getMap());
138    LiveUnionI.find(VirtRegI->start);
139  }
140
141  LiveInterval::iterator VirtRegEnd = VirtReg->end();
142  LiveInterval *RecentReg = nullptr;
143  while (LiveUnionI.valid()) {
144    assert(VirtRegI != VirtRegEnd && "Reached end of VirtReg");
145
146    // Check for overlapping interference.
147    while (VirtRegI->start < LiveUnionI.stop() &&
148           VirtRegI->end > LiveUnionI.start()) {
149      // This is an overlap, record the interfering register.
150      LiveInterval *VReg = LiveUnionI.value();
151      if (VReg != RecentReg && !isSeenInterference(VReg)) {
152        RecentReg = VReg;
153        InterferingVRegs.push_back(VReg);
154        if (InterferingVRegs.size() >= MaxInterferingRegs)
155          return InterferingVRegs.size();
156      }
157      // This LiveUnion segment is no longer interesting.
158      if (!(++LiveUnionI).valid()) {
159        SeenAllInterferences = true;
160        return InterferingVRegs.size();
161      }
162    }
163
164    // The iterators are now not overlapping, LiveUnionI has been advanced
165    // beyond VirtRegI.
166    assert(VirtRegI->end <= LiveUnionI.start() && "Expected non-overlap");
167
168    // Advance the iterator that ends first.
169    VirtRegI = VirtReg->advanceTo(VirtRegI, LiveUnionI.start());
170    if (VirtRegI == VirtRegEnd)
171      break;
172
173    // Detect overlap, handle above.
174    if (VirtRegI->start < LiveUnionI.stop())
175      continue;
176
177    // Still not overlapping. Catch up LiveUnionI.
178    LiveUnionI.advanceTo(VirtRegI->start);
179  }
180  SeenAllInterferences = true;
181  return InterferingVRegs.size();
182}
183
184void LiveIntervalUnion::Array::init(LiveIntervalUnion::Allocator &Alloc,
185                                    unsigned NSize) {
186  // Reuse existing allocation.
187  if (NSize == Size)
188    return;
189  clear();
190  Size = NSize;
191  LIUs = static_cast<LiveIntervalUnion*>(
192    malloc(sizeof(LiveIntervalUnion)*NSize));
193  for (unsigned i = 0; i != Size; ++i)
194    new(LIUs + i) LiveIntervalUnion(Alloc);
195}
196
197void LiveIntervalUnion::Array::clear() {
198  if (!LIUs)
199    return;
200  for (unsigned i = 0; i != Size; ++i)
201    LIUs[i].~LiveIntervalUnion();
202  free(LIUs);
203  Size =  0;
204  LIUs = nullptr;
205}
206