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/Support/Debug.h"
19 #include "llvm/Support/raw_ostream.h"
23 // Merge a LiveInterval's segments. Guarantee no overlaps.
24 void LiveIntervalUnion::unify(LiveInterval &lvr) {
25 // Add this live virtual register to the union
26 LiveVirtRegs::iterator pos = std::upper_bound(lvrs_.begin(), lvrs_.end(),
27 &lvr, less_ptr<LiveInterval>());
28 assert((pos == lvrs_.end() || *pos != &lvr) && "duplicate LVR insertion");
29 lvrs_.insert(pos, &lvr);
30 // Insert each of the virtual register's live segments into the map
31 SegmentIter segPos = segments_.begin();
32 for (LiveInterval::iterator lvrI = lvr.begin(), lvrEnd = lvr.end();
33 lvrI != lvrEnd; ++lvrI ) {
34 LiveSegment segment(lvrI->start, lvrI->end, lvr);
35 segPos = segments_.insert(segPos, segment);
36 assert(*segPos == segment && "need equal val for equal key");
42 // Keep LVRs sorted for fast membership test and extraction.
44 : public std::binary_function<LiveInterval*, LiveInterval*, bool> {
45 bool operator()(const LiveInterval *left, const LiveInterval *right) const {
46 return left->reg < right->reg;
50 // Low-level helper to find the first segment in the range [segI,segEnd) that
51 // intersects with a live virtual register segment, or segI.start >= lvr.end
53 // This logic is tied to the underlying LiveSegments data structure. For now, we
54 // use a binary search within the vector to find the nearest starting position,
55 // then reverse iterate to find the first overlap.
57 // Upon entry we have segI.start < lvrSeg.end
62 // After binary search, we have segI.start >= lvrSeg.start:
67 // Assuming intervals are disjoint, if an intersection exists, it must be the
68 // segment found or immediately behind it. We continue reverse iterating to
69 // return the first overlap.
71 // FIXME: support extract(), handle tombstones of extracted lvrs.
72 typedef LiveIntervalUnion::SegmentIter SegmentIter;
73 SegmentIter upperBound(SegmentIter segBegin,
75 const LiveRange &lvrSeg) {
76 assert(lvrSeg.end > segBegin->start && "segment iterator precondition");
77 // get the next LIU segment such that setg.start is not less than
79 SegmentIter segI = std::upper_bound(segBegin, segEnd, lvrSeg.start);
80 while (segI != segBegin) {
82 if (lvrSeg.start >= segI->end)
87 } // end anonymous namespace
89 // Private interface accessed by Query.
91 // Find a pair of segments that intersect, one in the live virtual register
92 // (LiveInterval), and the other in this LiveIntervalUnion. The caller (Query)
93 // is responsible for advancing the LiveIntervalUnion segments to find a
94 // "notable" intersection, which requires query-specific logic.
96 // This design assumes only a fast mechanism for intersecting a single live
97 // virtual register segment with a set of LiveIntervalUnion segments. This may
98 // be ok since most LVRs have very few segments. If we had a data
99 // structure that optimizd MxN intersection of segments, then we would bypass
100 // the loop that advances within the LiveInterval.
102 // If no intersection exists, set lvrI = lvrEnd, and set segI to the first
103 // segment whose start point is greater than LiveInterval's end point.
105 // Assumes that segments are sorted by start position in both
106 // LiveInterval and LiveSegments.
107 void LiveIntervalUnion::Query::findIntersection(InterferenceResult &ir) const {
108 LiveInterval::iterator lvrEnd = lvr_.end();
109 SegmentIter liuEnd = liu_.end();
110 while (ir.liuSegI_ != liuEnd) {
111 // Slowly advance the live virtual reg iterator until we surpass the next
112 // segment in this union. If this is ever used for coalescing of fixed
113 // registers and we have a LiveInterval with thousands of segments, then use
114 // upper bound instead.
115 while (ir.lvrSegI_ != lvrEnd && ir.lvrSegI_->end <= ir.liuSegI_->start)
117 if (ir.lvrSegI_ == lvrEnd)
119 // lvrSegI_ may have advanced far beyond liuSegI_,
120 // do a fast intersection test to "catch up"
121 ir.liuSegI_ = upperBound(ir.liuSegI_, liuEnd, *ir.lvrSegI_);
122 // Check if no liuSegI_ exists with lvrSegI_->start < liuSegI_.end
123 if (ir.liuSegI_ == liuEnd)
125 if (ir.liuSegI_->start < ir.lvrSegI_->end) {
126 assert(overlap(*ir.lvrSegI_, *ir.liuSegI_) && "upperBound postcondition");
130 if (ir.liuSegI_ == liuEnd)
131 ir.lvrSegI_ = lvrEnd;
134 // Find the first intersection, and cache interference info
135 // (retain segment iterators into both lvr_ and liu_).
136 LiveIntervalUnion::InterferenceResult
137 LiveIntervalUnion::Query::firstInterference() {
138 if (firstInterference_ != LiveIntervalUnion::InterferenceResult()) {
139 return firstInterference_;
141 firstInterference_ = InterferenceResult(lvr_.begin(), liu_.begin());
142 findIntersection(firstInterference_);
143 return firstInterference_;
146 // Treat the result as an iterator and advance to the next interfering pair
147 // of segments. This is a plain iterator with no filter.
148 bool LiveIntervalUnion::Query::nextInterference(InterferenceResult &ir) const {
149 assert(isInterference(ir) && "iteration past end of interferences");
150 // Advance either the lvr or liu segment to ensure that we visit all unique
151 // overlapping pairs.
152 if (ir.lvrSegI_->end < ir.liuSegI_->end) {
153 if (++ir.lvrSegI_ == lvr_.end())
157 if (++ir.liuSegI_ == liu_.end()) {
158 ir.lvrSegI_ = lvr_.end();
162 if (overlap(*ir.lvrSegI_, *ir.liuSegI_))
164 // find the next intersection
165 findIntersection(ir);
166 return isInterference(ir);