llvm/lib/CodeGen/InterferenceCache.cpp

   1 //===- InterferenceCache.cpp - Caching per-block interference -------------===//
   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 // InterferenceCache remembers per-block interference in LiveIntervalUnions.
  10 //
  11 //===----------------------------------------------------------------------===//
  12
  13 #include "InterferenceCache.h"
  14 #include "llvm/ADT/ArrayRef.h"
  15 #include "llvm/CodeGen/LiveIntervals.h"
  16 #include "llvm/CodeGen/MachineBasicBlock.h"
  17 #include "llvm/CodeGen/MachineFunction.h"
  18 #include "llvm/CodeGen/MachineOperand.h"
  19 #include "llvm/CodeGen/TargetRegisterInfo.h"
  20 #include "llvm/MC/MCRegisterInfo.h"
  21 #include "llvm/Support/ErrorHandling.h"
  22 #include <cassert>
  23 #include <cstdint>
  24 #include <tuple>
  25
  26 using namespace llvm;
  27
  28 #define DEBUG_TYPE "regalloc"
  29
  30 // Static member used for null interference cursors.
  31 const InterferenceCache::BlockInterference
  32     InterferenceCache::Cursor::NoInterference;
  33
  34 // Initializes PhysRegEntries (instead of a SmallVector, PhysRegEntries is a
  35 // buffer of size NumPhysRegs to speed up alloc/clear for targets with large
  36 // reg files). Calloced memory is used for good form, and quites tools like
  37 // Valgrind too, but zero initialized memory is not required by the algorithm:
  38 // this is because PhysRegEntries works like a SparseSet and its entries are
  39 // only valid when there is a corresponding CacheEntries assignment. There is
  40 // also support for when pass managers are reused for targets with different
  41 // numbers of PhysRegs: in this case PhysRegEntries is freed and reinitialized.
  42 void InterferenceCache::reinitPhysRegEntries() {
  43   if (PhysRegEntriesCount == TRI->getNumRegs()) return;
  44   free(PhysRegEntries);
  45   PhysRegEntriesCount = TRI->getNumRegs();
  46   PhysRegEntries = static_cast<unsigned char*>(
  47       safe_calloc(PhysRegEntriesCount, sizeof(unsigned char)));
  48 }
  49
  50 void InterferenceCache::init(MachineFunction *mf,
  51                              LiveIntervalUnion *liuarray,
  52                              SlotIndexes *indexes,
  53                              LiveIntervals *lis,
  54                              const TargetRegisterInfo *tri) {
  55   MF = mf;
  56   LIUArray = liuarray;
  57   TRI = tri;
  58   reinitPhysRegEntries();
  59   for (Entry &E : Entries)
  60     E.clear(mf, indexes, lis);
  61 }
  62
  63 InterferenceCache::Entry *InterferenceCache::get(MCRegister PhysReg) {
  64   unsigned char E = PhysRegEntries[PhysReg.id()];
  65   if (E < CacheEntries && Entries[E].getPhysReg() == PhysReg) {
  66     if (!Entries[E].valid(LIUArray, TRI))
  67       Entries[E].revalidate(LIUArray, TRI);
  68     return &Entries[E];
  69   }
  70   // No valid entry exists, pick the next round-robin entry.
  71   E = RoundRobin;
  72   if (++RoundRobin == CacheEntries)
  73     RoundRobin = 0;
  74   for (unsigned i = 0; i != CacheEntries; ++i) {
  75     // Skip entries that are in use.
  76     if (Entries[E].hasRefs()) {
  77       if (++E == CacheEntries)
  78         E = 0;
  79       continue;
  80     }
  81     Entries[E].reset(PhysReg, LIUArray, TRI, MF);
  82     PhysRegEntries[PhysReg] = E;
  83     return &Entries[E];
  84   }
  85   llvm_unreachable("Ran out of interference cache entries.");
  86 }
  87
  88 /// revalidate - LIU contents have changed, update tags.
  89 void InterferenceCache::Entry::revalidate(LiveIntervalUnion *LIUArray,
  90                                           const TargetRegisterInfo *TRI) {
  91   // Invalidate all block entries.
  92   ++Tag;
  93   // Invalidate all iterators.
  94   PrevPos = SlotIndex();
  95   unsigned i = 0;
  96   for (MCRegUnit Unit : TRI->regunits(PhysReg))
  97     RegUnits[i++].VirtTag = LIUArray[Unit].getTag();
  98 }
  99
 100 void InterferenceCache::Entry::reset(MCRegister physReg,
 101                                      LiveIntervalUnion *LIUArray,
 102                                      const TargetRegisterInfo *TRI,
 103                                      const MachineFunction *MF) {
 104   assert(!hasRefs() && "Cannot reset cache entry with references");
 105   // LIU's changed, invalidate cache.
 106   ++Tag;
 107   PhysReg = physReg;
 108   Blocks.resize(MF->getNumBlockIDs());
 109
 110   // Reset iterators.
 111   PrevPos = SlotIndex();
 112   RegUnits.clear();
 113   for (MCRegUnit Unit : TRI->regunits(PhysReg)) {
 114     RegUnits.push_back(LIUArray[Unit]);
 115     RegUnits.back().Fixed = &LIS->getRegUnit(Unit);
 116   }
 117 }
 118
 119 bool InterferenceCache::Entry::valid(LiveIntervalUnion *LIUArray,
 120                                      const TargetRegisterInfo *TRI) {
 121   unsigned i = 0, e = RegUnits.size();
 122   for (MCRegUnit Unit : TRI->regunits(PhysReg)) {
 123     if (i == e)
 124       return false;
 125     if (LIUArray[Unit].changedSince(RegUnits[i].VirtTag))
 126       return false;
 127     ++i;
 128   }
 129   return i == e;
 130 }
 131
 132 void InterferenceCache::Entry::update(unsigned MBBNum) {
 133   SlotIndex Start, Stop;
 134   std::tie(Start, Stop) = Indexes->getMBBRange(MBBNum);
 135
 136   // Use advanceTo only when possible.
 137   if (PrevPos != Start) {
 138     if (!PrevPos.isValid() || Start < PrevPos) {
 139       for (unsigned i = 0, e = RegUnits.size(); i != e; ++i) {
 140         RegUnitInfo &RUI = RegUnits[i];
 141         RUI.VirtI.find(Start);
 142         RUI.FixedI = RUI.Fixed->find(Start);
 143       }
 144     } else {
 145       for (unsigned i = 0, e = RegUnits.size(); i != e; ++i) {
 146         RegUnitInfo &RUI = RegUnits[i];
 147         RUI.VirtI.advanceTo(Start);
 148         if (RUI.FixedI != RUI.Fixed->end())
 149           RUI.FixedI = RUI.Fixed->advanceTo(RUI.FixedI, Start);
 150       }
 151     }
 152     PrevPos = Start;
 153   }
 154
 155   MachineFunction::const_iterator MFI =
 156       MF->getBlockNumbered(MBBNum)->getIterator();
 157   BlockInterference *BI = &Blocks[MBBNum];
 158   ArrayRef<SlotIndex> RegMaskSlots;
 159   ArrayRef<const uint32_t*> RegMaskBits;
 160   while (true) {
 161     BI->Tag = Tag;
 162     BI->First = BI->Last = SlotIndex();
 163
 164     // Check for first interference from virtregs.
 165     for (unsigned i = 0, e = RegUnits.size(); i != e; ++i) {
 166       LiveIntervalUnion::SegmentIter &I = RegUnits[i].VirtI;
 167       if (!I.valid())
 168         continue;
 169       SlotIndex StartI = I.start();
 170       if (StartI >= Stop)
 171         continue;
 172       if (!BI->First.isValid() || StartI < BI->First)
 173         BI->First = StartI;
 174     }
 175
 176     // Same thing for fixed interference.
 177     for (unsigned i = 0, e = RegUnits.size(); i != e; ++i) {
 178       LiveInterval::const_iterator I = RegUnits[i].FixedI;
 179       LiveInterval::const_iterator E = RegUnits[i].Fixed->end();
 180       if (I == E)
 181         continue;
 182       SlotIndex StartI = I->start;
 183       if (StartI >= Stop)
 184         continue;
 185       if (!BI->First.isValid() || StartI < BI->First)
 186         BI->First = StartI;
 187     }
 188
 189     // Also check for register mask interference.
 190     RegMaskSlots = LIS->getRegMaskSlotsInBlock(MBBNum);
 191     RegMaskBits = LIS->getRegMaskBitsInBlock(MBBNum);
 192     SlotIndex Limit = BI->First.isValid() ? BI->First : Stop;
 193     for (unsigned i = 0, e = RegMaskSlots.size();
 194          i != e && RegMaskSlots[i] < Limit; ++i)
 195       if (MachineOperand::clobbersPhysReg(RegMaskBits[i], PhysReg)) {
 196         // Register mask i clobbers PhysReg before the LIU interference.
 197         BI->First = RegMaskSlots[i];
 198         break;
 199       }
 200
 201     PrevPos = Stop;
 202     if (BI->First.isValid())
 203       break;
 204
 205     // No interference in this block? Go ahead and precompute the next block.
 206     if (++MFI == MF->end())
 207       return;
 208     MBBNum = MFI->getNumber();
 209     BI = &Blocks[MBBNum];
 210     if (BI->Tag == Tag)
 211       return;
 212     std::tie(Start, Stop) = Indexes->getMBBRange(MBBNum);
 213   }
 214
 215   // Check for last interference in block.
 216   for (unsigned i = 0, e = RegUnits.size(); i != e; ++i) {
 217     LiveIntervalUnion::SegmentIter &I = RegUnits[i].VirtI;
 218     if (!I.valid() || I.start() >= Stop)
 219       continue;
 220     I.advanceTo(Stop);
 221     bool Backup = !I.valid() || I.start() >= Stop;
 222     if (Backup)
 223       --I;
 224     SlotIndex StopI = I.stop();
 225     if (!BI->Last.isValid() || StopI > BI->Last)
 226       BI->Last = StopI;
 227     if (Backup)
 228       ++I;
 229   }
 230
 231   // Fixed interference.
 232   for (unsigned i = 0, e = RegUnits.size(); i != e; ++i) {
 233     LiveInterval::iterator &I = RegUnits[i].FixedI;
 234     LiveRange *LR = RegUnits[i].Fixed;
 235     if (I == LR->end() || I->start >= Stop)
 236       continue;
 237     I = LR->advanceTo(I, Stop);
 238     bool Backup = I == LR->end() || I->start >= Stop;
 239     if (Backup)
 240       --I;
 241     SlotIndex StopI = I->end;
 242     if (!BI->Last.isValid() || StopI > BI->Last)
 243       BI->Last = StopI;
 244     if (Backup)
 245       ++I;
 246   }
 247
 248   // Also check for register mask interference.
 249   SlotIndex Limit = BI->Last.isValid() ? BI->Last : Start;
 250   for (unsigned i = RegMaskSlots.size();
 251        i && RegMaskSlots[i-1].getDeadSlot() > Limit; --i)
 252     if (MachineOperand::clobbersPhysReg(RegMaskBits[i-1], PhysReg)) {
 253       // Register mask i-1 clobbers PhysReg after the LIU interference.
 254       // Model the regmask clobber as a dead def.
 255       BI->Last = RegMaskSlots[i-1].getDeadSlot();
 256       break;
 257     }
 258 }