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#define DEBUG_TYPE "regalloc"
17#include "LiveIntervalUnion.h"
18#include "llvm/ADT/SparseBitVector.h"
19#include "llvm/CodeGen/MachineLoopRanges.h"
20#include "llvm/Support/Debug.h"
21#include "llvm/Support/raw_ostream.h"
22#include "llvm/Target/TargetRegisterInfo.h"
23
24#include <algorithm>
25
26using namespace llvm;
27
28
29// Merge a LiveInterval's segments. Guarantee no overlaps.
30void LiveIntervalUnion::unify(LiveInterval &VirtReg) {
31  if (VirtReg.empty())
32    return;
33  ++Tag;
34
35  // Insert each of the virtual register's live segments into the map.
36  LiveInterval::iterator RegPos = VirtReg.begin();
37  LiveInterval::iterator RegEnd = VirtReg.end();
38  SegmentIter SegPos = Segments.find(RegPos->start);
39
40  while (SegPos.valid()) {
41    SegPos.insert(RegPos->start, RegPos->end, &VirtReg);
42    if (++RegPos == RegEnd)
43      return;
44    SegPos.advanceTo(RegPos->start);
45  }
46
47  // We have reached the end of Segments, so it is no longer necessary to search
48  // for the insertion position.
49  // It is faster to insert the end first.
50  --RegEnd;
51  SegPos.insert(RegEnd->start, RegEnd->end, &VirtReg);
52  for (; RegPos != RegEnd; ++RegPos, ++SegPos)
53    SegPos.insert(RegPos->start, RegPos->end, &VirtReg);
54}
55
56// Remove a live virtual register's segments from this union.
57void LiveIntervalUnion::extract(LiveInterval &VirtReg) {
58  if (VirtReg.empty())
59    return;
60  ++Tag;
61
62  // Remove each of the virtual register's live segments from the map.
63  LiveInterval::iterator RegPos = VirtReg.begin();
64  LiveInterval::iterator RegEnd = VirtReg.end();
65  SegmentIter SegPos = Segments.find(RegPos->start);
66
67  for (;;) {
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 = VirtReg.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
103// Scan the vector of interfering virtual registers in this union. Assume it's
104// quite small.
105bool LiveIntervalUnion::Query::isSeenInterference(LiveInterval *VirtReg) const {
106  SmallVectorImpl<LiveInterval*>::const_iterator I =
107    std::find(InterferingVRegs.begin(), InterferingVRegs.end(), VirtReg);
108  return I != InterferingVRegs.end();
109}
110
111// Collect virtual registers in this union that interfere with this
112// query's live virtual register.
113//
114// The query state is one of:
115//
116// 1. CheckedFirstInterference == false: Iterators are uninitialized.
117// 2. SeenAllInterferences == true: InterferingVRegs complete, iterators unused.
118// 3. Iterators left at the last seen intersection.
119//
120unsigned LiveIntervalUnion::Query::
121collectInterferingVRegs(unsigned MaxInterferingRegs) {
122  // Fast path return if we already have the desired information.
123  if (SeenAllInterferences || InterferingVRegs.size() >= MaxInterferingRegs)
124    return InterferingVRegs.size();
125
126  // Set up iterators on the first call.
127  if (!CheckedFirstInterference) {
128    CheckedFirstInterference = true;
129
130    // Quickly skip interference check for empty sets.
131    if (VirtReg->empty() || LiveUnion->empty()) {
132      SeenAllInterferences = true;
133      return 0;
134    }
135
136    // In most cases, the union will start before VirtReg.
137    VirtRegI = VirtReg->begin();
138    LiveUnionI.setMap(LiveUnion->getMap());
139    LiveUnionI.find(VirtRegI->start);
140  }
141
142  LiveInterval::iterator VirtRegEnd = VirtReg->end();
143  LiveInterval *RecentReg = 0;
144  while (LiveUnionI.valid()) {
145    assert(VirtRegI != VirtRegEnd && "Reached end of VirtReg");
146
147    // Check for overlapping interference.
148    while (VirtRegI->start < LiveUnionI.stop() &&
149           VirtRegI->end > LiveUnionI.start()) {
150      // This is an overlap, record the interfering register.
151      LiveInterval *VReg = LiveUnionI.value();
152      if (VReg != RecentReg && !isSeenInterference(VReg)) {
153        RecentReg = VReg;
154        InterferingVRegs.push_back(VReg);
155        if (InterferingVRegs.size() >= MaxInterferingRegs)
156          return InterferingVRegs.size();
157      }
158      // This LiveUnion segment is no longer interesting.
159      if (!(++LiveUnionI).valid()) {
160        SeenAllInterferences = true;
161        return InterferingVRegs.size();
162      }
163    }
164
165    // The iterators are now not overlapping, LiveUnionI has been advanced
166    // beyond VirtRegI.
167    assert(VirtRegI->end <= LiveUnionI.start() && "Expected non-overlap");
168
169    // Advance the iterator that ends first.
170    VirtRegI = VirtReg->advanceTo(VirtRegI, LiveUnionI.start());
171    if (VirtRegI == VirtRegEnd)
172      break;
173
174    // Detect overlap, handle above.
175    if (VirtRegI->start < LiveUnionI.stop())
176      continue;
177
178    // Still not overlapping. Catch up LiveUnionI.
179    LiveUnionI.advanceTo(VirtRegI->start);
180  }
181  SeenAllInterferences = true;
182  return InterferingVRegs.size();
183}
184
185bool LiveIntervalUnion::Query::checkLoopInterference(MachineLoopRange *Loop) {
186  // VirtReg is likely live throughout the loop, so start by checking LIU-Loop
187  // overlaps.
188  IntervalMapOverlaps<LiveIntervalUnion::Map, MachineLoopRange::Map>
189    Overlaps(LiveUnion->getMap(), Loop->getMap());
190  if (!Overlaps.valid())
191    return false;
192
193  // The loop is overlapping an LIU assignment. Check VirtReg as well.
194  LiveInterval::iterator VRI = VirtReg->find(Overlaps.start());
195
196  for (;;) {
197    if (VRI == VirtReg->end())
198      return false;
199    if (VRI->start < Overlaps.stop())
200      return true;
201
202    Overlaps.advanceTo(VRI->start);
203    if (!Overlaps.valid())
204      return false;
205    if (Overlaps.start() < VRI->end)
206      return true;
207
208    VRI = VirtReg->advanceTo(VRI, Overlaps.start());
209  }
210}
211
212void LiveIntervalUnion::Array::init(LiveIntervalUnion::Allocator &Alloc,
213                                    unsigned NSize) {
214  // Reuse existing allocation.
215  if (NSize == Size)
216    return;
217  clear();
218  Size = NSize;
219  LIUs = static_cast<LiveIntervalUnion*>(
220    malloc(sizeof(LiveIntervalUnion)*NSize));
221  for (unsigned i = 0; i != Size; ++i)
222    new(LIUs + i) LiveIntervalUnion(Alloc);
223}
224
225void LiveIntervalUnion::Array::clear() {
226  if (!LIUs)
227    return;
228  for (unsigned i = 0; i != Size; ++i)
229    LIUs[i].~LiveIntervalUnion();
230  free(LIUs);
231  Size =  0;
232  LIUs = 0;
233}
234