LiveIntervalUnion.cpp revision d04a8d4b33ff316ca4cf961e06c9e312eff8e64f 
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 "llvm/CodeGen/LiveIntervalUnion.h"
18#include "llvm/ADT/SparseBitVector.h"
19#include "llvm/Support/Debug.h"
20#include "llvm/Support/raw_ostream.h"
21#include "llvm/Target/TargetRegisterInfo.h"
22#include <algorithm>
23
24using namespace llvm;
25
26
27// Merge a LiveInterval's segments. Guarantee no overlaps.
28void LiveIntervalUnion::unify(LiveInterval &VirtReg) {
29  if (VirtReg.empty())
30    return;
31  ++Tag;
32
33  // Insert each of the virtual register's live segments into the map.
34  LiveInterval::iterator RegPos = VirtReg.begin();
35  LiveInterval::iterator RegEnd = VirtReg.end();
36  SegmentIter SegPos = Segments.find(RegPos->start);
37
38  while (SegPos.valid()) {
39    SegPos.insert(RegPos->start, RegPos->end, &VirtReg);
40    if (++RegPos == RegEnd)
41      return;
42    SegPos.advanceTo(RegPos->start);
43  }
44
45  // We have reached the end of Segments, so it is no longer necessary to search
46  // for the insertion position.
47  // It is faster to insert the end first.
48  --RegEnd;
49  SegPos.insert(RegEnd->start, RegEnd->end, &VirtReg);
50  for (; RegPos != RegEnd; ++RegPos, ++SegPos)
51    SegPos.insert(RegPos->start, RegPos->end, &VirtReg);
52}
53
54// Remove a live virtual register's segments from this union.
55void LiveIntervalUnion::extract(LiveInterval &VirtReg) {
56  if (VirtReg.empty())
57    return;
58  ++Tag;
59
60  // Remove each of the virtual register's live segments from the map.
61  LiveInterval::iterator RegPos = VirtReg.begin();
62  LiveInterval::iterator RegEnd = VirtReg.end();
63  SegmentIter SegPos = Segments.find(RegPos->start);
64
65  for (;;) {
66    assert(SegPos.value() == &VirtReg && "Inconsistent LiveInterval");
67    SegPos.erase();
68    if (!SegPos.valid())
69      return;
70
71    // Skip all segments that may have been coalesced.
72    RegPos = VirtReg.advanceTo(RegPos, SegPos.start());
73    if (RegPos == RegEnd)
74      return;
75
76    SegPos.advanceTo(RegPos->start);
77  }
78}
79
80void
81LiveIntervalUnion::print(raw_ostream &OS, const TargetRegisterInfo *TRI) const {
82  if (empty()) {
83    OS << " empty\n";
84    return;
85  }
86  for (LiveSegments::const_iterator SI = Segments.begin(); SI.valid(); ++SI) {
87    OS << " [" << SI.start() << ' ' << SI.stop() << "):"
88       << PrintReg(SI.value()->reg, TRI);
89  }
90  OS << '\n';
91}
92
93#ifndef NDEBUG
94// Verify the live intervals in this union and add them to the visited set.
95void LiveIntervalUnion::verify(LiveVirtRegBitSet& VisitedVRegs) {
96  for (SegmentIter SI = Segments.begin(); SI.valid(); ++SI)
97    VisitedVRegs.set(SI.value()->reg);
98}
99#endif //!NDEBUG
100
101// Scan the vector of interfering virtual registers in this union. Assume it's
102// quite small.
103bool LiveIntervalUnion::Query::isSeenInterference(LiveInterval *VirtReg) const {
104  SmallVectorImpl<LiveInterval*>::const_iterator I =
105    std::find(InterferingVRegs.begin(), InterferingVRegs.end(), VirtReg);
106  return I != InterferingVRegs.end();
107}
108
109// Collect virtual registers in this union that interfere with this
110// query's live virtual register.
111//
112// The query state is one of:
113//
114// 1. CheckedFirstInterference == false: Iterators are uninitialized.
115// 2. SeenAllInterferences == true: InterferingVRegs complete, iterators unused.
116// 3. Iterators left at the last seen intersection.
117//
118unsigned LiveIntervalUnion::Query::
119collectInterferingVRegs(unsigned MaxInterferingRegs) {
120  // Fast path return if we already have the desired information.
121  if (SeenAllInterferences || InterferingVRegs.size() >= MaxInterferingRegs)
122    return InterferingVRegs.size();
123
124  // Set up iterators on the first call.
125  if (!CheckedFirstInterference) {
126    CheckedFirstInterference = true;
127
128    // Quickly skip interference check for empty sets.
129    if (VirtReg->empty() || LiveUnion->empty()) {
130      SeenAllInterferences = true;
131      return 0;
132    }
133
134    // In most cases, the union will start before VirtReg.
135    VirtRegI = VirtReg->begin();
136    LiveUnionI.setMap(LiveUnion->getMap());
137    LiveUnionI.find(VirtRegI->start);
138  }
139
140  LiveInterval::iterator VirtRegEnd = VirtReg->end();
141  LiveInterval *RecentReg = 0;
142  while (LiveUnionI.valid()) {
143    assert(VirtRegI != VirtRegEnd && "Reached end of VirtReg");
144
145    // Check for overlapping interference.
146    while (VirtRegI->start < LiveUnionI.stop() &&
147           VirtRegI->end > LiveUnionI.start()) {
148      // This is an overlap, record the interfering register.
149      LiveInterval *VReg = LiveUnionI.value();
150      if (VReg != RecentReg && !isSeenInterference(VReg)) {
151        RecentReg = VReg;
152        InterferingVRegs.push_back(VReg);
153        if (InterferingVRegs.size() >= MaxInterferingRegs)
154          return InterferingVRegs.size();
155      }
156      // This LiveUnion segment is no longer interesting.
157      if (!(++LiveUnionI).valid()) {
158        SeenAllInterferences = true;
159        return InterferingVRegs.size();
160      }
161    }
162
163    // The iterators are now not overlapping, LiveUnionI has been advanced
164    // beyond VirtRegI.
165    assert(VirtRegI->end <= LiveUnionI.start() && "Expected non-overlap");
166
167    // Advance the iterator that ends first.
168    VirtRegI = VirtReg->advanceTo(VirtRegI, LiveUnionI.start());
169    if (VirtRegI == VirtRegEnd)
170      break;
171
172    // Detect overlap, handle above.
173    if (VirtRegI->start < LiveUnionI.stop())
174      continue;
175
176    // Still not overlapping. Catch up LiveUnionI.
177    LiveUnionI.advanceTo(VirtRegI->start);
178  }
179  SeenAllInterferences = true;
180  return InterferingVRegs.size();
181}
182
183void LiveIntervalUnion::Array::init(LiveIntervalUnion::Allocator &Alloc,
184                                    unsigned NSize) {
185  // Reuse existing allocation.
186  if (NSize == Size)
187    return;
188  clear();
189  Size = NSize;
190  LIUs = static_cast<LiveIntervalUnion*>(
191    malloc(sizeof(LiveIntervalUnion)*NSize));
192  for (unsigned i = 0; i != Size; ++i)
193    new(LIUs + i) LiveIntervalUnion(Alloc);
194}
195
196void LiveIntervalUnion::Array::clear() {
197  if (!LIUs)
198    return;
199  for (unsigned i = 0; i != Size; ++i)
200    LIUs[i].~LiveIntervalUnion();
201  free(LIUs);
202  Size =  0;
203  LIUs = 0;
204}
205