lib/CodeGen/LiveIntervalUnion.cpp

   1 //===- LiveIntervalUnion.cpp - Live interval union data structure ---------===//
   2 //
   3 //                     The LLVM Compiler Infrastructure
   4 //
   5 // This file is distributed under the University of Illinois Open Source
   6 // License. See LICENSE.TXT for details.
   7 //
   8 //===----------------------------------------------------------------------===//
   9 //
  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.
  13 //
  14 //===----------------------------------------------------------------------===//
  15
  16 #include "llvm/CodeGen/LiveIntervalUnion.h"
  17 #include "llvm/ADT/STLExtras.h"
  18 #include "llvm/ADT/SparseBitVector.h"
  19 #include "llvm/CodeGen/LiveInterval.h"
  20 #include "llvm/CodeGen/TargetRegisterInfo.h"
  21 #include "llvm/Support/raw_ostream.h"
  22 #include <cassert>
  23 #include <cstdlib>
  24
  25 using namespace llvm;
  26
  27 #define DEBUG_TYPE "regalloc"
  28
  29 // Merge a LiveInterval's segments. Guarantee no overlaps.
  30 void LiveIntervalUnion::unify(LiveInterval &VirtReg, const LiveRange &Range) {
  31   if (Range.empty())
  32     return;
  33   ++Tag;
  34
  35   // Insert each of the virtual register's live segments into the map.
  36   LiveRange::const_iterator RegPos = Range.begin();
  37   LiveRange::const_iterator RegEnd = Range.end();
  38   SegmentIter SegPos = Segments.find(RegPos->start);
  39
  40   while (SegPos.valid()) {
  41     SegPos.insert(RegPos->start, RegPos->end, &VirtReg);
  42     if (++RegPos == RegEnd)
  43       return;
  44     SegPos.advanceTo(RegPos->start);
  45   }
  46
  47   // We have reached the end of Segments, so it is no longer necessary to search
  48   // for the insertion position.
  49   // It is faster to insert the end first.
  50   --RegEnd;
  51   SegPos.insert(RegEnd->start, RegEnd->end, &VirtReg);
  52   for (; RegPos != RegEnd; ++RegPos, ++SegPos)
  53     SegPos.insert(RegPos->start, RegPos->end, &VirtReg);
  54 }
  55
  56 // Remove a live virtual register's segments from this union.
  57 void LiveIntervalUnion::extract(LiveInterval &VirtReg, const LiveRange &Range) {
  58   if (Range.empty())
  59     return;
  60   ++Tag;
  61
  62   // Remove each of the virtual register's live segments from the map.
  63   LiveRange::const_iterator RegPos = Range.begin();
  64   LiveRange::const_iterator RegEnd = Range.end();
  65   SegmentIter SegPos = Segments.find(RegPos->start);
  66
  67   while (true) {
  68     assert(SegPos.value() == &VirtReg && "Inconsistent LiveInterval");
  69     SegPos.erase();
  70     if (!SegPos.valid())
  71       return;
  72
  73     // Skip all segments that may have been coalesced.
  74     RegPos = Range.advanceTo(RegPos, SegPos.start());
  75     if (RegPos == RegEnd)
  76       return;
  77
  78     SegPos.advanceTo(RegPos->start);
  79   }
  80 }
  81
  82 void
  83 LiveIntervalUnion::print(raw_ostream &OS, const TargetRegisterInfo *TRI) const {
  84   if (empty()) {
  85     OS << " empty\n";
  86     return;
  87   }
  88   for (LiveSegments::const_iterator SI = Segments.begin(); SI.valid(); ++SI) {
  89     OS << " [" << SI.start() << ' ' << SI.stop() << "):"
  90        << printReg(SI.value()->reg, TRI);
  91   }
  92   OS << '\n';
  93 }
  94
  95 #ifndef NDEBUG
  96 // Verify the live intervals in this union and add them to the visited set.
  97 void LiveIntervalUnion::verify(LiveVirtRegBitSet& VisitedVRegs) {
  98   for (SegmentIter SI = Segments.begin(); SI.valid(); ++SI)
  99     VisitedVRegs.set(SI.value()->reg);
 100 }
 101 #endif //!NDEBUG
 102
 103 // Scan the vector of interfering virtual registers in this union. Assume it's
 104 // quite small.
 105 bool LiveIntervalUnion::Query::isSeenInterference(LiveInterval *VirtReg) const {
 106   return is_contained(InterferingVRegs, VirtReg);
 107 }
 108
 109 // Collect virtual registers in this union that interfere with this
 110 // query's live virtual register.
 111 //
 112 // The query state is one of:
 113 //
 114 // 1. CheckedFirstInterference == false: Iterators are uninitialized.
 115 // 2. SeenAllInterferences == true: InterferingVRegs complete, iterators unused.
 116 // 3. Iterators left at the last seen intersection.
 117 //
 118 unsigned LiveIntervalUnion::Query::
 119 collectInterferingVRegs(unsigned MaxInterferingRegs) {
 120   // Fast path return if we already have the desired information.
 121   if (SeenAllInterferences || InterferingVRegs.size() >= MaxInterferingRegs)
 122     return InterferingVRegs.size();
 123
 124   // Set up iterators on the first call.
 125   if (!CheckedFirstInterference) {
 126     CheckedFirstInterference = true;
 127
 128     // Quickly skip interference check for empty sets.
 129     if (LR->empty() || LiveUnion->empty()) {
 130       SeenAllInterferences = true;
 131       return 0;
 132     }
 133
 134     // In most cases, the union will start before LR.
 135     LRI = LR->begin();
 136     LiveUnionI.setMap(LiveUnion->getMap());
 137     LiveUnionI.find(LRI->start);
 138   }
 139
 140   LiveRange::const_iterator LREnd = LR->end();
 141   LiveInterval *RecentReg = nullptr;
 142   while (LiveUnionI.valid()) {
 143     assert(LRI != LREnd && "Reached end of LR");
 144
 145     // Check for overlapping interference.
 146     while (LRI->start < LiveUnionI.stop() && LRI->end > LiveUnionI.start()) {
 147       // This is an overlap, record the interfering register.
 148       LiveInterval *VReg = LiveUnionI.value();
 149       if (VReg != RecentReg && !isSeenInterference(VReg)) {
 150         RecentReg = VReg;
 151         InterferingVRegs.push_back(VReg);
 152         if (InterferingVRegs.size() >= MaxInterferingRegs)
 153           return InterferingVRegs.size();
 154       }
 155       // This LiveUnion segment is no longer interesting.
 156       if (!(++LiveUnionI).valid()) {
 157         SeenAllInterferences = true;
 158         return InterferingVRegs.size();
 159       }
 160     }
 161
 162     // The iterators are now not overlapping, LiveUnionI has been advanced
 163     // beyond LRI.
 164     assert(LRI->end <= LiveUnionI.start() && "Expected non-overlap");
 165
 166     // Advance the iterator that ends first.
 167     LRI = LR->advanceTo(LRI, LiveUnionI.start());
 168     if (LRI == LREnd)
 169       break;
 170
 171     // Detect overlap, handle above.
 172     if (LRI->start < LiveUnionI.stop())
 173       continue;
 174
 175     // Still not overlapping. Catch up LiveUnionI.
 176     LiveUnionI.advanceTo(LRI->start);
 177   }
 178   SeenAllInterferences = true;
 179   return InterferingVRegs.size();
 180 }
 181
 182 void LiveIntervalUnion::Array::init(LiveIntervalUnion::Allocator &Alloc,
 183                                     unsigned NSize) {
 184   // Reuse existing allocation.
 185   if (NSize == Size)
 186     return;
 187   clear();
 188   Size = NSize;
 189   LIUs = static_cast<LiveIntervalUnion*>(
 190       safe_malloc(sizeof(LiveIntervalUnion)*NSize));
 191   for (unsigned i = 0; i != Size; ++i)
 192     new(LIUs + i) LiveIntervalUnion(Alloc);
 193 }
 194
 195 void LiveIntervalUnion::Array::clear() {
 196   if (!LIUs)
 197     return;
 198   for (unsigned i = 0; i != Size; ++i)
 199     LIUs[i].~LiveIntervalUnion();
 200   free(LIUs);
 201   Size =  0;
 202   LIUs = nullptr;
 203 }