lib/CodeGen/LiveIntervalUnion.cpp

   1 //===- LiveIntervalUnion.cpp - Live interval union data structure ---------===//
   2 //
   3 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
   4 // See https://llvm.org/LICENSE.txt for license information.
   5 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
   6 //
   7 //===----------------------------------------------------------------------===//
   8 //
   9 // LiveIntervalUnion represents a coalesced set of live intervals. This may be
  10 // used during coalescing to represent a congruence class, or during register
  11 // allocation to model liveness of a physical register.
  12 //
  13 //===----------------------------------------------------------------------===//
  14
  15 #include "llvm/CodeGen/LiveIntervalUnion.h"
  16 #include "llvm/ADT/STLExtras.h"
  17 #include "llvm/ADT/SparseBitVector.h"
  18 #include "llvm/CodeGen/LiveInterval.h"
  19 #include "llvm/CodeGen/TargetRegisterInfo.h"
  20 #include "llvm/Support/raw_ostream.h"
  21 #include <cassert>
  22 #include <cstdlib>
  23
  24 using namespace llvm;
  25
  26 #define DEBUG_TYPE "regalloc"
  27
  28 // Merge a LiveInterval's segments. Guarantee no overlaps.
  29 void LiveIntervalUnion::unify(LiveInterval &VirtReg, const LiveRange &Range) {
  30   if (Range.empty())
  31     return;
  32   ++Tag;
  33
  34   // Insert each of the virtual register's live segments into the map.
  35   LiveRange::const_iterator RegPos = Range.begin();
  36   LiveRange::const_iterator RegEnd = Range.end();
  37   SegmentIter SegPos = Segments.find(RegPos->start);
  38
  39   while (SegPos.valid()) {
  40     SegPos.insert(RegPos->start, RegPos->end, &VirtReg);
  41     if (++RegPos == RegEnd)
  42       return;
  43     SegPos.advanceTo(RegPos->start);
  44   }
  45
  46   // We have reached the end of Segments, so it is no longer necessary to search
  47   // for the insertion position.
  48   // It is faster to insert the end first.
  49   --RegEnd;
  50   SegPos.insert(RegEnd->start, RegEnd->end, &VirtReg);
  51   for (; RegPos != RegEnd; ++RegPos, ++SegPos)
  52     SegPos.insert(RegPos->start, RegPos->end, &VirtReg);
  53 }
  54
  55 // Remove a live virtual register's segments from this union.
  56 void LiveIntervalUnion::extract(LiveInterval &VirtReg, const LiveRange &Range) {
  57   if (Range.empty())
  58     return;
  59   ++Tag;
  60
  61   // Remove each of the virtual register's live segments from the map.
  62   LiveRange::const_iterator RegPos = Range.begin();
  63   LiveRange::const_iterator RegEnd = Range.end();
  64   SegmentIter SegPos = Segments.find(RegPos->start);
  65
  66   while (true) {
  67     assert(SegPos.value() == &VirtReg && "Inconsistent LiveInterval");
  68     SegPos.erase();
  69     if (!SegPos.valid())
  70       return;
  71
  72     // Skip all segments that may have been coalesced.
  73     RegPos = Range.advanceTo(RegPos, SegPos.start());
  74     if (RegPos == RegEnd)
  75       return;
  76
  77     SegPos.advanceTo(RegPos->start);
  78   }
  79 }
  80
  81 void
  82 LiveIntervalUnion::print(raw_ostream &OS, const TargetRegisterInfo *TRI) const {
  83   if (empty()) {
  84     OS << " empty\n";
  85     return;
  86   }
  87   for (LiveSegments::const_iterator SI = Segments.begin(); SI.valid(); ++SI) {
  88     OS << " [" << SI.start() << ' ' << SI.stop() << "):"
  89        << printReg(SI.value()->reg, TRI);
  90   }
  91   OS << '\n';
  92 }
  93
  94 #ifndef NDEBUG
  95 // Verify the live intervals in this union and add them to the visited set.
  96 void LiveIntervalUnion::verify(LiveVirtRegBitSet& VisitedVRegs) {
  97   for (SegmentIter SI = Segments.begin(); SI.valid(); ++SI)
  98     VisitedVRegs.set(SI.value()->reg);
  99 }
 100 #endif //!NDEBUG
 101
 102 // Scan the vector of interfering virtual registers in this union. Assume it's
 103 // quite small.
 104 bool LiveIntervalUnion::Query::isSeenInterference(LiveInterval *VirtReg) const {
 105   return is_contained(InterferingVRegs, VirtReg);
 106 }
 107
 108 // Collect virtual registers in this union that interfere with this
 109 // query's live virtual register.
 110 //
 111 // The query state is one of:
 112 //
 113 // 1. CheckedFirstInterference == false: Iterators are uninitialized.
 114 // 2. SeenAllInterferences == true: InterferingVRegs complete, iterators unused.
 115 // 3. Iterators left at the last seen intersection.
 116 //
 117 unsigned LiveIntervalUnion::Query::
 118 collectInterferingVRegs(unsigned MaxInterferingRegs) {
 119   // Fast path return if we already have the desired information.
 120   if (SeenAllInterferences || InterferingVRegs.size() >= MaxInterferingRegs)
 121     return InterferingVRegs.size();
 122
 123   // Set up iterators on the first call.
 124   if (!CheckedFirstInterference) {
 125     CheckedFirstInterference = true;
 126
 127     // Quickly skip interference check for empty sets.
 128     if (LR->empty() || LiveUnion->empty()) {
 129       SeenAllInterferences = true;
 130       return 0;
 131     }
 132
 133     // In most cases, the union will start before LR.
 134     LRI = LR->begin();
 135     LiveUnionI.setMap(LiveUnion->getMap());
 136     LiveUnionI.find(LRI->start);
 137   }
 138
 139   LiveRange::const_iterator LREnd = LR->end();
 140   LiveInterval *RecentReg = nullptr;
 141   while (LiveUnionI.valid()) {
 142     assert(LRI != LREnd && "Reached end of LR");
 143
 144     // Check for overlapping interference.
 145     while (LRI->start < LiveUnionI.stop() && LRI->end > LiveUnionI.start()) {
 146       // This is an overlap, record the interfering register.
 147       LiveInterval *VReg = LiveUnionI.value();
 148       if (VReg != RecentReg && !isSeenInterference(VReg)) {
 149         RecentReg = VReg;
 150         InterferingVRegs.push_back(VReg);
 151         if (InterferingVRegs.size() >= MaxInterferingRegs)
 152           return InterferingVRegs.size();
 153       }
 154       // This LiveUnion segment is no longer interesting.
 155       if (!(++LiveUnionI).valid()) {
 156         SeenAllInterferences = true;
 157         return InterferingVRegs.size();
 158       }
 159     }
 160
 161     // The iterators are now not overlapping, LiveUnionI has been advanced
 162     // beyond LRI.
 163     assert(LRI->end <= LiveUnionI.start() && "Expected non-overlap");
 164
 165     // Advance the iterator that ends first.
 166     LRI = LR->advanceTo(LRI, LiveUnionI.start());
 167     if (LRI == LREnd)
 168       break;
 169
 170     // Detect overlap, handle above.
 171     if (LRI->start < LiveUnionI.stop())
 172       continue;
 173
 174     // Still not overlapping. Catch up LiveUnionI.
 175     LiveUnionI.advanceTo(LRI->start);
 176   }
 177   SeenAllInterferences = true;
 178   return InterferingVRegs.size();
 179 }
 180
 181 void LiveIntervalUnion::Array::init(LiveIntervalUnion::Allocator &Alloc,
 182                                     unsigned NSize) {
 183   // Reuse existing allocation.
 184   if (NSize == Size)
 185     return;
 186   clear();
 187   Size = NSize;
 188   LIUs = static_cast<LiveIntervalUnion*>(
 189       safe_malloc(sizeof(LiveIntervalUnion)*NSize));
 190   for (unsigned i = 0; i != Size; ++i)
 191     new(LIUs + i) LiveIntervalUnion(Alloc);
 192 }
 193
 194 void LiveIntervalUnion::Array::clear() {
 195   if (!LIUs)
 196     return;
 197   for (unsigned i = 0; i != Size; ++i)
 198     LIUs[i].~LiveIntervalUnion();
 199   free(LIUs);
 200   Size =  0;
 201   LIUs = nullptr;
 202 }