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;
86 virtual ~AbstractRegisterDescription() {}
89 /// Union of live intervals that are strong candidates for coalescing into a
90 /// single register (either physical or virtual depending on the context). We
91 /// expect the constituent live intervals to be disjoint, although we may
92 /// eventually make exceptions to handle value-based interference.
93 class LiveIntervalUnion {
94 // A set of live virtual register segments that supports fast insertion,
95 // intersection, and removal.
97 // FIXME: std::set is a placeholder until we decide how to
98 // efficiently represent it. Probably need to roll our own B-tree.
99 typedef std::set<LiveSegment> LiveSegments;
101 // A set of live virtual registers. Elements have type LiveInterval, where
102 // each element represents the liveness of a single live virtual register.
103 // This is traditionally known as a live range, but we refer is as a live
104 // virtual register to avoid confusing it with the misnamed LiveRange
106 typedef std::vector<LiveInterval*> LiveVirtRegs;
109 // SegmentIter can advance to the next segment ordered by starting position
110 // which may belong to a different live virtual register. We also must be able
111 // to reach the current segment's containing virtual register.
112 typedef LiveSegments::iterator SegmentIter;
114 class InterferenceResult;
118 unsigned repReg_; // representative register number
119 LiveSegments segments_; // union of virtual reg segements
122 // default ctor avoids placement new
123 LiveIntervalUnion() : repReg_(0) {}
125 // Initialize the union by associating it with a representative register
127 void init(unsigned repReg) { repReg_ = repReg; }
129 // Iterate over all segments in the union of live virtual registers ordered
130 // by their starting position.
131 SegmentIter begin() { return segments_.begin(); }
132 SegmentIter end() { return segments_.end(); }
134 // Return an iterator to the first segment after or including begin that
135 // intersects with lvrSeg.
136 SegmentIter upperBound(SegmentIter begin, const LiveSegment &seg);
138 // Add a live virtual register to this union and merge its segments.
139 // Holds a nonconst reference to the LVR for later maniplution.
140 void unify(LiveInterval &lvr);
142 // Remove a live virtual register's segments from this union.
143 void extract(const LiveInterval &lvr);
145 void dump(const AbstractRegisterDescription *regInfo) const;
147 // If tri != NULL, use it to decode repReg_
148 void print(raw_ostream &os, const AbstractRegisterDescription *rdesc) const;
151 // Verify the live intervals in this union and add them to the visited set.
152 void verify(LvrBitSet& visitedVRegs);
155 /// Cache a single interference test result in the form of two intersecting
156 /// segments. This allows efficiently iterating over the interferences. The
157 /// iteration logic is handled by LiveIntervalUnion::Query which may
158 /// filter interferences depending on the type of query.
159 class InterferenceResult {
162 LiveInterval::iterator lvrSegI_; // current position in _lvr
163 SegmentIter liuSegI_; // current position in _liu
166 InterferenceResult(LiveInterval::iterator lvrSegI, SegmentIter liuSegI)
167 : lvrSegI_(lvrSegI), liuSegI_(liuSegI) {}
170 // Public default ctor.
171 InterferenceResult(): lvrSegI_(), liuSegI_() {}
173 // Note: this interface provides raw access to the iterators because the
174 // result has no way to tell if it's valid to dereference them.
176 // Access the lvr segment.
177 LiveInterval::iterator lvrSegPos() const { return lvrSegI_; }
179 // Access the liu segment.
180 SegmentIter liuSegPos() const { return liuSegI_; }
182 bool operator==(const InterferenceResult &ir) const {
183 return lvrSegI_ == ir.lvrSegI_ && liuSegI_ == ir.liuSegI_;
185 bool operator!=(const InterferenceResult &ir) const {
186 return !operator==(ir);
190 /// Query interferences between a single live virtual register and a live
193 LiveIntervalUnion *liu_;
195 InterferenceResult firstInterference_;
196 SmallVector<LiveInterval*,4> interferingVRegs_;
197 bool seenUnspillableVReg_;
200 Query(): liu_(), lvr_() {}
202 Query(LiveInterval *lvr, LiveIntervalUnion *liu):
203 liu_(liu), lvr_(lvr), seenUnspillableVReg_(false) {}
208 firstInterference_ = InterferenceResult();
209 interferingVRegs_.clear();
210 seenUnspillableVReg_ = false;
213 void init(LiveInterval *lvr, LiveIntervalUnion *liu) {
215 // We currently allow query objects to be reused acrossed live virtual
216 // registers, but always for the same live interval union.
217 assert(liu_ == liu && "inconsistent initialization");
218 // Retain cached results, e.g. firstInterference.
223 // Clear cached results.
224 firstInterference_ = InterferenceResult();
225 interferingVRegs_.clear();
226 seenUnspillableVReg_ = false;
229 LiveInterval &lvr() const { assert(lvr_ && "uninitialized"); return *lvr_; }
231 bool isInterference(const InterferenceResult &ir) const {
232 if (ir.lvrSegI_ != lvr_->end()) {
233 assert(overlap(*ir.lvrSegI_, *ir.liuSegI_) &&
234 "invalid segment iterators");
240 // Does this live virtual register interfere with the union.
241 bool checkInterference() { return isInterference(firstInterference()); }
243 // Get the first pair of interfering segments, or a noninterfering result.
244 // This initializes the firstInterference_ cache.
245 InterferenceResult firstInterference();
247 // Treat the result as an iterator and advance to the next interfering pair
248 // of segments. Visiting each unique interfering pairs means that the same
249 // lvr or liu segment may be visited multiple times.
250 bool nextInterference(InterferenceResult &ir) const;
252 // Count the virtual registers in this union that interfere with this
253 // query's live virtual register, up to maxInterferingRegs.
254 unsigned collectInterferingVRegs(unsigned maxInterferingRegs = UINT_MAX);
256 // Was this virtual register visited during collectInterferingVRegs?
257 bool isSeenInterference(LiveInterval *lvr) const;
259 // Did collectInterferingVRegs encounter an unspillable vreg?
260 bool seenUnspillableVReg() const {
261 return seenUnspillableVReg_;
264 // Vector generated by collectInterferingVRegs.
265 const SmallVectorImpl<LiveInterval*> &interferingVRegs() const {
266 return interferingVRegs_;
270 Query(const Query&); // DO NOT IMPLEMENT
271 void operator=(const Query&); // DO NOT IMPLEMENT
273 // Private interface for queries
274 void findIntersection(InterferenceResult &ir) const;
278 } // end namespace llvm
280 #endif // !defined(LLVM_CODEGEN_LIVEINTERVALUNION)