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 template <> struct isPodLike<LiveSegment> { static const bool value = true; };
71 raw_ostream& operator<<(raw_ostream& os, const LiveSegment &ls);
73 /// Abstraction to provide info for the representative register.
74 class AbstractRegisterDescription {
76 virtual const char *getName(unsigned reg) const = 0;
77 virtual ~AbstractRegisterDescription() { }
80 /// Union of live intervals that are strong candidates for coalescing into a
81 /// single register (either physical or virtual depending on the context). We
82 /// expect the constituent live intervals to be disjoint, although we may
83 /// eventually make exceptions to handle value-based interference.
84 class LiveIntervalUnion {
85 // A set of live virtual register segments that supports fast insertion,
86 // intersection, and removal.
88 // FIXME: std::set is a placeholder until we decide how to
89 // efficiently represent it. Probably need to roll our own B-tree.
90 typedef std::set<LiveSegment> LiveSegments;
92 // A set of live virtual registers. Elements have type LiveInterval, where
93 // each element represents the liveness of a single live virtual register.
94 // This is traditionally known as a live range, but we refer is as a live
95 // virtual register to avoid confusing it with the misnamed LiveRange
97 typedef std::vector<LiveInterval*> LiveVirtRegs;
100 // SegmentIter can advance to the next segment ordered by starting position
101 // which may belong to a different live virtual register. We also must be able
102 // to reach the current segment's containing virtual register.
103 typedef LiveSegments::iterator SegmentIter;
105 class InterferenceResult;
109 unsigned repReg_; // representative register number
110 LiveSegments segments_; // union of virtual reg segements
113 // default ctor avoids placement new
114 LiveIntervalUnion() : repReg_(0) {}
116 // Initialize the union by associating it with a representative register
118 void init(unsigned repReg) { repReg_ = repReg; }
120 // Iterate over all segments in the union of live virtual registers ordered
121 // by their starting position.
122 SegmentIter begin() { return segments_.begin(); }
123 SegmentIter end() { return segments_.end(); }
125 // Return an iterator to the first segment after or including begin that
126 // intersects with lvrSeg.
127 SegmentIter upperBound(SegmentIter begin, const LiveSegment &seg);
129 // Add a live virtual register to this union and merge its segments.
130 // Holds a nonconst reference to the LVR for later maniplution.
131 void unify(LiveInterval &lvr);
133 // Remove a live virtual register's segments from this union.
134 void extract(const LiveInterval &lvr);
136 /// Cache a single interference test result in the form of two intersecting
137 /// segments. This allows efficiently iterating over the interferences. The
138 /// iteration logic is handled by LiveIntervalUnion::Query which may
139 /// filter interferences depending on the type of query.
140 class InterferenceResult {
143 LiveInterval::iterator lvrSegI_; // current position in _lvr
144 SegmentIter liuSegI_; // current position in _liu
147 InterferenceResult(LiveInterval::iterator lvrSegI, SegmentIter liuSegI)
148 : lvrSegI_(lvrSegI), liuSegI_(liuSegI) {}
151 // Public default ctor.
152 InterferenceResult(): lvrSegI_(), liuSegI_() {}
154 // Note: this interface provides raw access to the iterators because the
155 // result has no way to tell if it's valid to dereference them.
157 // Access the lvr segment.
158 const LiveInterval::iterator &lvrSegPos() const { return lvrSegI_; }
160 // Access the liu segment.
161 const SegmentIter &liuSegPos() const { return liuSegI_; }
163 bool operator==(const InterferenceResult &ir) const {
164 return lvrSegI_ == ir.lvrSegI_ && liuSegI_ == ir.liuSegI_;
166 bool operator!=(const InterferenceResult &ir) const {
167 return !operator==(ir);
171 /// Query interferences between a single live virtual register and a live
174 LiveIntervalUnion *liu_;
176 InterferenceResult firstInterference_;
177 // TBD: interfering vregs
180 Query(): liu_(), lvr_() {}
182 Query(LiveInterval *lvr, LiveIntervalUnion *liu): liu_(liu), lvr_(lvr) {}
187 firstInterference_ = InterferenceResult();
190 void init(LiveInterval *lvr, LiveIntervalUnion *liu) {
192 // We currently allow query objects to be reused acrossed live virtual
193 // registers, but always for the same live interval union.
194 assert(liu_ == liu && "inconsistent initialization");
195 // Retain cached results, e.g. firstInterference.
200 // Clear cached results.
201 firstInterference_ = InterferenceResult();
204 LiveInterval &lvr() const { assert(lvr_ && "uninitialized"); return *lvr_; }
206 bool isInterference(const InterferenceResult &ir) const {
207 if (ir.lvrSegI_ != lvr_->end()) {
208 assert(overlap(*ir.lvrSegI_, *ir.liuSegI_) &&
209 "invalid segment iterators");
215 // Does this live virtual register interfere with the union.
216 bool checkInterference() { return isInterference(firstInterference()); }
218 // Get the first pair of interfering segments, or a noninterfering result.
219 // This initializes the firstInterference_ cache.
220 InterferenceResult firstInterference();
222 // Treat the result as an iterator and advance to the next interfering pair
223 // of segments. Visiting each unique interfering pairs means that the same
224 // lvr or liu segment may be visited multiple times.
225 bool nextInterference(InterferenceResult &ir) const;
227 // TBD: bool collectInterferingVirtRegs(unsigned maxInterference)
230 // Private interface for queries
231 void findIntersection(InterferenceResult &ir) const;
235 } // end namespace llvm
237 #endif // !defined(LLVM_CODEGEN_LIVEINTERVALUNION)