1 //===-- LiveIntervalUnion.h - Live interval union data struct --*- C++ -*--===//
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 is a union of live segments across multiple live virtual
11 // registers. This may be used during coalescing to represent a congruence
12 // class, or during register allocation to model liveness of a physical
15 //===----------------------------------------------------------------------===//
17 #ifndef LLVM_CODEGEN_LIVEINTERVALUNION
18 #define LLVM_CODEGEN_LIVEINTERVALUNION
20 #include "llvm/CodeGen/LiveInterval.h"
26 /// A LiveSegment is a copy of a LiveRange object used within
27 /// LiveIntervalUnion. LiveSegment additionally contains a pointer to its
28 /// original live virtual register (LiveInterval). This allows quick lookup of
29 /// the live virtual register as we iterate over live segments in a union. Note
30 /// that LiveRange is misnamed and actually represents only a single contiguous
31 /// interval within a virtual register's liveness. To limit confusion, in this
32 /// file we refer it as a live segment.
34 /// Note: This currently represents a half-open interval [start,end).
35 /// If LiveRange is modified to represent a closed interval, so should this.
39 LiveInterval *liveVirtReg;
41 LiveSegment(SlotIndex s, SlotIndex e, LiveInterval *lvr)
42 : start(s), end(e), liveVirtReg(lvr) {}
44 bool operator==(const LiveSegment &ls) const {
45 return start == ls.start && end == ls.end && liveVirtReg == ls.liveVirtReg;
48 bool operator!=(const LiveSegment &ls) const {
49 return !operator==(ls);
52 // Order segments by starting point only--we expect them to be disjoint.
53 bool operator<(const LiveSegment &ls) const { return start < ls.start; }
56 inline bool operator<(SlotIndex V, const LiveSegment &ls) {
60 inline bool operator<(const LiveSegment &ls, SlotIndex V) {
64 /// Compare a live virtual register segment to a LiveIntervalUnion segment.
65 inline bool overlap(const LiveRange &lvrSeg, const LiveSegment &liuSeg) {
66 return lvrSeg.start < liuSeg.end && liuSeg.start < lvrSeg.end;
69 /// Union of live intervals that are strong candidates for coalescing into a
70 /// single register (either physical or virtual depending on the context). We
71 /// expect the constituent live intervals to be disjoint, although we may
72 /// eventually make exceptions to handle value-based interference.
73 class LiveIntervalUnion {
74 // A set of live virtual register segments that supports fast insertion,
75 // intersection, and removal.
77 // FIXME: std::set is a placeholder until we decide how to
78 // efficiently represent it. Probably need to roll our own B-tree.
79 typedef std::set<LiveSegment> LiveSegments;
81 // A set of live virtual registers. Elements have type LiveInterval, where
82 // each element represents the liveness of a single live virtual register.
83 // This is traditionally known as a live range, but we refer is as a live
84 // virtual register to avoid confusing it with the misnamed LiveRange
86 typedef std::vector<LiveInterval*> LiveVirtRegs;
89 // SegmentIter can advance to the next segment ordered by starting position
90 // which may belong to a different live virtual register. We also must be able
91 // to reach the current segment's containing virtual register.
92 typedef LiveSegments::iterator SegmentIter;
94 class InterferenceResult;
98 unsigned repReg_; // representative register number
99 LiveSegments segments_; // union of virtual reg segements
102 // default ctor avoids placement new
103 LiveIntervalUnion() : repReg_(0) {}
105 // Initialize the union by associating it with a representative register
107 void init(unsigned repReg) { repReg_ = repReg; }
109 // Iterate over all segments in the union of live virtual registers ordered
110 // by their starting position.
111 SegmentIter begin() { return segments_.begin(); }
112 SegmentIter end() { return segments_.end(); }
114 // Return an iterator to the first segment after or including begin that
115 // intersects with lvrSeg.
116 SegmentIter upperBound(SegmentIter begin, const LiveSegment &seg);
118 // Add a live virtual register to this union and merge its segments.
119 // Holds a nonconst reference to the LVR for later maniplution.
120 void unify(LiveInterval &lvr);
122 // Remove a live virtual register's segments from this union.
123 void extract(const LiveInterval &lvr);
125 /// Cache a single interference test result in the form of two intersecting
126 /// segments. This allows efficiently iterating over the interferences. The
127 /// iteration logic is handled by LiveIntervalUnion::Query which may
128 /// filter interferences depending on the type of query.
129 class InterferenceResult {
132 LiveInterval::iterator lvrSegI_; // current position in _lvr
133 SegmentIter liuSegI_; // current position in _liu
136 InterferenceResult(LiveInterval::iterator lvrSegI, SegmentIter liuSegI)
137 : lvrSegI_(lvrSegI), liuSegI_(liuSegI) {}
140 // Public default ctor.
141 InterferenceResult(): lvrSegI_(), liuSegI_() {}
143 // Note: this interface provides raw access to the iterators because the
144 // result has no way to tell if it's valid to dereference them.
146 // Access the lvr segment.
147 const LiveInterval::iterator &lvrSegPos() const { return lvrSegI_; }
149 // Access the liu segment.
150 const SegmentIter &liuSegPos() const { return liuSegI_; }
152 bool operator==(const InterferenceResult &ir) const {
153 return lvrSegI_ == ir.lvrSegI_ && liuSegI_ == ir.liuSegI_;
155 bool operator!=(const InterferenceResult &ir) const {
156 return !operator==(ir);
160 /// Query interferences between a single live virtual register and a live
163 LiveIntervalUnion *liu_;
165 InterferenceResult firstInterference_;
166 // TBD: interfering vregs
169 Query(): liu_(), lvr_() {}
171 Query(LiveInterval *lvr, LiveIntervalUnion *liu): liu_(liu), lvr_(lvr) {}
176 firstInterference_ = InterferenceResult();
179 void init(LiveInterval *lvr, LiveIntervalUnion *liu) {
181 // We currently allow query objects to be reused acrossed live virtual
182 // registers, but always for the same live interval union.
183 assert(liu_ == liu && "inconsistent initialization");
184 // Retain cached results, e.g. firstInterference.
189 // Clear cached results.
190 firstInterference_ = InterferenceResult();
193 LiveInterval &lvr() const { assert(lvr_ && "uninitialized"); return *lvr_; }
195 bool isInterference(const InterferenceResult &ir) const {
196 if (ir.lvrSegI_ != lvr_->end()) {
197 assert(overlap(*ir.lvrSegI_, *ir.liuSegI_) &&
198 "invalid segment iterators");
204 // Does this live virtual register interfere with the union.
205 bool checkInterference() { return isInterference(firstInterference()); }
207 // Get the first pair of interfering segments, or a noninterfering result.
208 // This initializes the firstInterference_ cache.
209 InterferenceResult firstInterference();
211 // Treat the result as an iterator and advance to the next interfering pair
212 // of segments. Visiting each unique interfering pairs means that the same
213 // lvr or liu segment may be visited multiple times.
214 bool nextInterference(InterferenceResult &ir) const;
216 // TBD: bool collectInterferingVirtRegs(unsigned maxInterference)
219 // Private interface for queries
220 void findIntersection(InterferenceResult &ir) const;
224 } // end namespace llvm
226 #endif // !defined(LLVM_CODEGEN_LIVEINTERVALUNION)