1 //===-- LiveIntervalUnion.cpp - Live interval union data structure --------===//
3 // The LLVM Compiler Infrastructure
5 // This file is distributed under the University of Illinois Open Source
6 // License. See LICENSE.TXT for details.
8 //===----------------------------------------------------------------------===//
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.
14 //===----------------------------------------------------------------------===//
16 #define DEBUG_TYPE "regalloc"
17 #include "LiveIntervalUnion.h"
18 #include "llvm/ADT/SparseBitVector.h"
19 #include "llvm/Support/Debug.h"
20 #include "llvm/Support/raw_ostream.h"
24 // Find the first segment in the range [segBegin,segments_.end()) that
25 // intersects with seg. If no intersection is found, return the first segI
26 // such that segI.start >= seg.end
28 // This logic is tied to the underlying LiveSegments data structure. For now, we
29 // use set::upper_bound to find the nearest starting position,
30 // then reverse iterate to find the first overlap.
32 // Upon entry we have segBegin.start < seg.end
37 // After set::upper_bound, we have segI.start >= seg.start:
42 // Assuming intervals are disjoint, if an intersection exists, it must be the
43 // segment found or the one immediately preceeding it. We continue reverse
44 // iterating to return the first overlapping segment.
45 LiveIntervalUnion::SegmentIter
46 LiveIntervalUnion::upperBound(SegmentIter segBegin,
47 const LiveSegment &seg) {
48 assert(seg.end > segBegin->start && "segment iterator precondition");
49 // get the next LIU segment such that segI->start is not less than seg.start
51 // FIXME: Once we have a B+tree, we can make good use of segBegin as a hint to
52 // upper_bound. For now, we're forced to search again from the root each time.
53 SegmentIter segI = segments_.upper_bound(seg);
54 while (segI != segBegin) {
56 if (seg.start >= segI->end)
62 // Merge a LiveInterval's segments. Guarantee no overlaps.
64 // Consider coalescing adjacent segments to save space, even though it makes
65 // extraction more complicated.
66 void LiveIntervalUnion::unify(LiveInterval &lvr) {
67 // Insert each of the virtual register's live segments into the map
68 SegmentIter segPos = segments_.begin();
69 for (LiveInterval::iterator lvrI = lvr.begin(), lvrEnd = lvr.end();
70 lvrI != lvrEnd; ++lvrI ) {
71 LiveSegment segment(lvrI->start, lvrI->end, &lvr);
72 segPos = segments_.insert(segPos, segment);
73 assert(*segPos == segment && "need equal val for equal key");
75 // check for overlap (inductively)
76 if (segPos != segments_.begin()) {
77 assert(prior(segPos)->end <= segment.start && "overlapping segments" );
79 SegmentIter nextPos = next(segPos);
80 if (nextPos != segments_.end())
81 assert(segment.end <= nextPos->start && "overlapping segments" );
86 // Remove a live virtual register's segments from this union.
87 void LiveIntervalUnion::extract(const LiveInterval &lvr) {
88 // Remove each of the virtual register's live segments from the map.
89 SegmentIter segPos = segments_.begin();
90 for (LiveInterval::const_iterator lvrI = lvr.begin(), lvrEnd = lvr.end();
91 lvrI != lvrEnd; ++lvrI) {
92 LiveSegment seg(lvrI->start, lvrI->end, const_cast<LiveInterval*>(&lvr));
93 segPos = upperBound(segPos, seg);
94 assert(segPos != segments_.end() && "missing lvr segment");
95 segments_.erase(segPos++);
99 raw_ostream& llvm::operator<<(raw_ostream& os, const LiveSegment &ls) {
100 return os << '[' << ls.start << ',' << ls.end << ':' <<
101 ls.liveVirtReg->reg << ")";
104 void LiveSegment::dump() const {
105 dbgs() << *this << "\n";
109 LiveIntervalUnion::print(raw_ostream &os,
110 const AbstractRegisterDescription *rdesc) const {
113 os << rdesc->getName(repReg_);
117 for (SegmentIter segI = segments_.begin(), segEnd = segments_.end();
118 segI != segEnd; ++segI) {
119 dbgs() << " " << *segI;
124 void LiveIntervalUnion::dump(const AbstractRegisterDescription *rdesc) const {
125 print(dbgs(), rdesc);
129 // Verify the live intervals in this union and add them to the visited set.
130 void LiveIntervalUnion::verify(LvrBitSet& visitedVRegs) {
131 SegmentIter segI = segments_.begin();
132 SegmentIter segEnd = segments_.end();
133 if (segI == segEnd) return;
134 visitedVRegs.set(segI->liveVirtReg->reg);
135 for (++segI; segI != segEnd; ++segI) {
136 visitedVRegs.set(segI->liveVirtReg->reg);
137 assert(prior(segI)->end <= segI->start && "overlapping segments" );
142 // Private interface accessed by Query.
144 // Find a pair of segments that intersect, one in the live virtual register
145 // (LiveInterval), and the other in this LiveIntervalUnion. The caller (Query)
146 // is responsible for advancing the LiveIntervalUnion segments to find a
147 // "notable" intersection, which requires query-specific logic.
149 // This design assumes only a fast mechanism for intersecting a single live
150 // virtual register segment with a set of LiveIntervalUnion segments. This may
151 // be ok since most LVRs have very few segments. If we had a data
152 // structure that optimizd MxN intersection of segments, then we would bypass
153 // the loop that advances within the LiveInterval.
155 // If no intersection exists, set lvrI = lvrEnd, and set segI to the first
156 // segment whose start point is greater than LiveInterval's end point.
158 // Assumes that segments are sorted by start position in both
159 // LiveInterval and LiveSegments.
160 void LiveIntervalUnion::Query::findIntersection(InterferenceResult &ir) const {
161 LiveInterval::iterator lvrEnd = lvr_->end();
162 SegmentIter liuEnd = liu_->end();
163 while (ir.liuSegI_ != liuEnd) {
164 // Slowly advance the live virtual reg iterator until we surpass the next
165 // segment in this union. If this is ever used for coalescing of fixed
166 // registers and we have a LiveInterval with thousands of segments, then use
167 // upper bound instead.
168 while (ir.lvrSegI_ != lvrEnd && ir.lvrSegI_->end <= ir.liuSegI_->start)
170 if (ir.lvrSegI_ == lvrEnd)
172 // lvrSegI_ may have advanced far beyond liuSegI_,
173 // do a fast intersection test to "catch up"
174 LiveSegment seg(ir.lvrSegI_->start, ir.lvrSegI_->end, lvr_);
175 ir.liuSegI_ = liu_->upperBound(ir.liuSegI_, seg);
176 // Check if no liuSegI_ exists with lvrSegI_->start < liuSegI_.end
177 if (ir.liuSegI_ == liuEnd)
179 if (ir.liuSegI_->start < ir.lvrSegI_->end) {
180 assert(overlap(*ir.lvrSegI_, *ir.liuSegI_) && "upperBound postcondition");
184 if (ir.liuSegI_ == liuEnd)
185 ir.lvrSegI_ = lvrEnd;
188 // Find the first intersection, and cache interference info
189 // (retain segment iterators into both lvr_ and liu_).
190 LiveIntervalUnion::InterferenceResult
191 LiveIntervalUnion::Query::firstInterference() {
192 if (firstInterference_ != LiveIntervalUnion::InterferenceResult()) {
193 return firstInterference_;
195 firstInterference_ = InterferenceResult(lvr_->begin(), liu_->begin());
196 findIntersection(firstInterference_);
197 return firstInterference_;
200 // Treat the result as an iterator and advance to the next interfering pair
201 // of segments. This is a plain iterator with no filter.
202 bool LiveIntervalUnion::Query::nextInterference(InterferenceResult &ir) const {
203 assert(isInterference(ir) && "iteration past end of interferences");
204 // Advance either the lvr or liu segment to ensure that we visit all unique
205 // overlapping pairs.
206 if (ir.lvrSegI_->end < ir.liuSegI_->end) {
207 if (++ir.lvrSegI_ == lvr_->end())
211 if (++ir.liuSegI_ == liu_->end()) {
212 ir.lvrSegI_ = lvr_->end();
216 if (overlap(*ir.lvrSegI_, *ir.liuSegI_))
218 // find the next intersection
219 findIntersection(ir);
220 return isInterference(ir);