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"
27 // forward declaration
28 template <unsigned Element> class SparseBitVector;
29 typedef SparseBitVector<128> LvrBitSet;
32 /// A LiveSegment is a copy of a LiveRange object used within
33 /// LiveIntervalUnion. LiveSegment additionally contains a pointer to its
34 /// original live virtual register (LiveInterval). This allows quick lookup of
35 /// the live virtual register as we iterate over live segments in a union. Note
36 /// that LiveRange is misnamed and actually represents only a single contiguous
37 /// interval within a virtual register's liveness. To limit confusion, in this
38 /// file we refer it as a live segment.
40 /// Note: This currently represents a half-open interval [start,end).
41 /// If LiveRange is modified to represent a closed interval, so should this.
45 LiveInterval *liveVirtReg;
47 LiveSegment(SlotIndex s, SlotIndex e, LiveInterval *lvr)
48 : start(s), end(e), liveVirtReg(lvr) {}
50 bool operator==(const LiveSegment &ls) const {
51 return start == ls.start && end == ls.end && liveVirtReg == ls.liveVirtReg;
54 bool operator!=(const LiveSegment &ls) const {
55 return !operator==(ls);
58 // Order segments by starting point only--we expect them to be disjoint.
59 bool operator<(const LiveSegment &ls) const { return start < ls.start; }
62 void print(raw_ostream &os) const;
65 inline bool operator<(SlotIndex V, const LiveSegment &ls) {
69 inline bool operator<(const LiveSegment &ls, SlotIndex V) {
73 /// Compare a live virtual register segment to a LiveIntervalUnion segment.
74 inline bool overlap(const LiveRange &lvrSeg, const LiveSegment &liuSeg) {
75 return lvrSeg.start < liuSeg.end && liuSeg.start < lvrSeg.end;
78 template <> struct isPodLike<LiveSegment> { static const bool value = true; };
80 raw_ostream& operator<<(raw_ostream& os, const LiveSegment &ls);
82 /// Abstraction to provide info for the representative register.
83 class AbstractRegisterDescription {
85 virtual const char *getName(unsigned reg) const = 0;
88 /// Union of live intervals that are strong candidates for coalescing into a
89 /// single register (either physical or virtual depending on the context). We
90 /// expect the constituent live intervals to be disjoint, although we may
91 /// eventually make exceptions to handle value-based interference.
92 class LiveIntervalUnion {
93 // A set of live virtual register segments that supports fast insertion,
94 // intersection, and removal.
96 // FIXME: std::set is a placeholder until we decide how to
97 // efficiently represent it. Probably need to roll our own B-tree.
98 typedef std::set<LiveSegment> LiveSegments;
100 // A set of live virtual registers. Elements have type LiveInterval, where
101 // each element represents the liveness of a single live virtual register.
102 // This is traditionally known as a live range, but we refer is as a live
103 // virtual register to avoid confusing it with the misnamed LiveRange
105 typedef std::vector<LiveInterval*> LiveVirtRegs;
108 // SegmentIter can advance to the next segment ordered by starting position
109 // which may belong to a different live virtual register. We also must be able
110 // to reach the current segment's containing virtual register.
111 typedef LiveSegments::iterator SegmentIter;
113 class InterferenceResult;
117 unsigned repReg_; // representative register number
118 LiveSegments segments_; // union of virtual reg segements
121 // default ctor avoids placement new
122 LiveIntervalUnion() : repReg_(0) {}
124 // Initialize the union by associating it with a representative register
126 void init(unsigned repReg) { repReg_ = repReg; }
128 // Iterate over all segments in the union of live virtual registers ordered
129 // by their starting position.
130 SegmentIter begin() { return segments_.begin(); }
131 SegmentIter end() { return segments_.end(); }
133 // Return an iterator to the first segment after or including begin that
134 // intersects with lvrSeg.
135 SegmentIter upperBound(SegmentIter begin, const LiveSegment &seg);
137 // Add a live virtual register to this union and merge its segments.
138 // Holds a nonconst reference to the LVR for later maniplution.
139 void unify(LiveInterval &lvr);
141 // Remove a live virtual register's segments from this union.
142 void extract(const LiveInterval &lvr);
144 void dump(const AbstractRegisterDescription *regInfo) const;
146 // If tri != NULL, use it to decode repReg_
147 void print(raw_ostream &os, const AbstractRegisterDescription *rdesc) const;
150 // Verify the live intervals in this union and add them to the visited set.
151 void verify(LvrBitSet& visitedVRegs);
154 /// Cache a single interference test result in the form of two intersecting
155 /// segments. This allows efficiently iterating over the interferences. The
156 /// iteration logic is handled by LiveIntervalUnion::Query which may
157 /// filter interferences depending on the type of query.
158 class InterferenceResult {
161 LiveInterval::iterator lvrSegI_; // current position in _lvr
162 SegmentIter liuSegI_; // current position in _liu
165 InterferenceResult(LiveInterval::iterator lvrSegI, SegmentIter liuSegI)
166 : lvrSegI_(lvrSegI), liuSegI_(liuSegI) {}
169 // Public default ctor.
170 InterferenceResult(): lvrSegI_(), liuSegI_() {}
172 // Note: this interface provides raw access to the iterators because the
173 // result has no way to tell if it's valid to dereference them.
175 // Access the lvr segment.
176 const LiveInterval::iterator &lvrSegPos() const { return lvrSegI_; }
178 // Access the liu segment.
179 const SegmentIter &liuSegPos() const { return liuSegI_; }
181 bool operator==(const InterferenceResult &ir) const {
182 return lvrSegI_ == ir.lvrSegI_ && liuSegI_ == ir.liuSegI_;
184 bool operator!=(const InterferenceResult &ir) const {
185 return !operator==(ir);
189 /// Query interferences between a single live virtual register and a live
192 LiveIntervalUnion *liu_;
194 InterferenceResult firstInterference_;
195 // TBD: interfering vregs
198 Query(): liu_(), lvr_() {}
200 Query(LiveInterval *lvr, LiveIntervalUnion *liu): liu_(liu), lvr_(lvr) {}
205 firstInterference_ = InterferenceResult();
208 void init(LiveInterval *lvr, LiveIntervalUnion *liu) {
210 // We currently allow query objects to be reused acrossed live virtual
211 // registers, but always for the same live interval union.
212 assert(liu_ == liu && "inconsistent initialization");
213 // Retain cached results, e.g. firstInterference.
218 // Clear cached results.
219 firstInterference_ = InterferenceResult();
222 LiveInterval &lvr() const { assert(lvr_ && "uninitialized"); return *lvr_; }
224 bool isInterference(const InterferenceResult &ir) const {
225 if (ir.lvrSegI_ != lvr_->end()) {
226 assert(overlap(*ir.lvrSegI_, *ir.liuSegI_) &&
227 "invalid segment iterators");
233 // Does this live virtual register interfere with the union.
234 bool checkInterference() { return isInterference(firstInterference()); }
236 // Get the first pair of interfering segments, or a noninterfering result.
237 // This initializes the firstInterference_ cache.
238 InterferenceResult firstInterference();
240 // Treat the result as an iterator and advance to the next interfering pair
241 // of segments. Visiting each unique interfering pairs means that the same
242 // lvr or liu segment may be visited multiple times.
243 bool nextInterference(InterferenceResult &ir) const;
245 // TBD: bool collectInterferingVirtRegs(unsigned maxInterference)
248 // Private interface for queries
249 void findIntersection(InterferenceResult &ir) const;
253 } // end namespace llvm
255 #endif // !defined(LLVM_CODEGEN_LIVEINTERVALUNION)