C++ SmallVectorImpl::rbegin方法代码示例

// Instrumenting some of the accesses may be proven redundant.
// Currently handled:
//  - read-before-write (within same BB, no calls between)
//
// We do not handle some of the patterns that should not survive
// after the classic compiler optimizations.
// E.g. two reads from the same temp should be eliminated by CSE,
// two writes should be eliminated by DSE, etc.
//
// 'Local' is a vector of insns within the same BB (no calls between).
// 'All' is a vector of insns that will be instrumented.
void ThreadSanitizer::chooseInstructionsToInstrument(
    SmallVectorImpl<Instruction*> &Local,
    SmallVectorImpl<Instruction*> &All) {
  SmallSet<Value*, 8> WriteTargets;
  // Iterate from the end.
  for (SmallVectorImpl<Instruction*>::reverse_iterator It = Local.rbegin(),
       E = Local.rend(); It != E; ++It) {
    Instruction *I = *It;
    if (StoreInst *Store = dyn_cast<StoreInst>(I)) {
      WriteTargets.insert(Store->getPointerOperand());
    } else {
      LoadInst *Load = cast<LoadInst>(I);
      Value *Addr = Load->getPointerOperand();
      if (WriteTargets.count(Addr)) {
        // We will write to this temp, so no reason to analyze the read.
        NumOmittedReadsBeforeWrite++;
        continue;
      }
      if (addrPointsToConstantData(Addr)) {
        // Addr points to some constant data -- it can not race with any writes.
        continue;
      }
    }
    All.push_back(I);
  }
  Local.clear();
}

// Instrumenting some of the accesses may be proven redundant.
// Currently handled:
//  - read-before-write (within same BB, no calls between)
//  - not captured variables
//
// We do not handle some of the patterns that should not survive
// after the classic compiler optimizations.
// E.g. two reads from the same temp should be eliminated by CSE,
// two writes should be eliminated by DSE, etc.
//
// 'Local' is a vector of insns within the same BB (no calls between).
// 'All' is a vector of insns that will be instrumented.
void ThreadSanitizer::chooseInstructionsToInstrument(
    SmallVectorImpl<Instruction *> &Local, SmallVectorImpl<Instruction *> &All,
    const DataLayout &DL) {
  SmallSet<Value*, 8> WriteTargets;
  // Iterate from the end.
  for (SmallVectorImpl<Instruction*>::reverse_iterator It = Local.rbegin(),
       E = Local.rend(); It != E; ++It) {
    Instruction *I = *It;
    if (StoreInst *Store = dyn_cast<StoreInst>(I)) {
      Value *Addr = Store->getPointerOperand();
      if (!shouldInstrumentReadWriteFromAddress(Addr))
        continue;
      WriteTargets.insert(Addr);
    } else {
      LoadInst *Load = cast<LoadInst>(I);
      Value *Addr = Load->getPointerOperand();
      if (!shouldInstrumentReadWriteFromAddress(Addr))
        continue;
      if (WriteTargets.count(Addr)) {
        // We will write to this temp, so no reason to analyze the read.
        NumOmittedReadsBeforeWrite++;
        continue;
      }
      if (addrPointsToConstantData(Addr)) {
        // Addr points to some constant data -- it can not race with any writes.
        continue;
      }
    }
    Value *Addr = isa<StoreInst>(*I)
        ? cast<StoreInst>(I)->getPointerOperand()
        : cast<LoadInst>(I)->getPointerOperand();
    if (isa<AllocaInst>(GetUnderlyingObject(Addr, DL)) &&
        !PointerMayBeCaptured(Addr, true, true)) {
      // The variable is addressable but not captured, so it cannot be
      // referenced from a different thread and participate in a data race
      // (see llvm/Analysis/CaptureTracking.h for details).
      NumOmittedNonCaptured++;
      continue;
    }
    All.push_back(I);
  }
  Local.clear();
}

static void filterForDiscriminator(SmallVectorImpl<Result> &results,
                                   DebuggerClient *debugClient) {
  Identifier discriminator = debugClient->getPreferredPrivateDiscriminator();
  if (discriminator.empty())
    return;

  auto doesNotMatch = [discriminator](Result next) -> bool {
    return !matchesDiscriminator(discriminator, next);
  };

  auto lastMatchIter = std::find_if_not(results.rbegin(), results.rend(),
                                        doesNotMatch);
  if (lastMatchIter == results.rend())
    return;

  Result lastMatch = *lastMatchIter;

  auto newEnd = std::remove_if(results.begin(), lastMatchIter.base()-1,
                               doesNotMatch);
  results.erase(newEnd, results.end());
  results.push_back(lastMatch);
}

/// iterate - Repeatedly update the Hopfield nodes until stability or the
/// maximum number of iterations is reached.
/// @param Linked - Numbers of linked nodes that need updating.
void SpillPlacement::iterate(const SmallVectorImpl<unsigned> &Linked) {
  DEBUG(dbgs() << "Iterating over " << Linked.size() << " linked nodes:\n");
  if (Linked.empty())
    return;

  // Run up to 10 iterations. The edge bundle numbering is closely related to
  // basic block numbering, so there is a strong tendency towards chains of
  // linked nodes with sequential numbers. By scanning the linked nodes
  // backwards and forwards, we make it very likely that a single node can
  // affect the entire network in a single iteration. That means very fast
  // convergence, usually in a single iteration.
  for (unsigned iteration = 0; iteration != 10; ++iteration) {
    // Scan backwards, skipping the last node which was just updated.
    bool Changed = false;
    for (SmallVectorImpl<unsigned>::const_reverse_iterator I =
           llvm::next(Linked.rbegin()), E = Linked.rend(); I != E; ++I) {
      unsigned n = *I;
      bool C = nodes[n].update(nodes);
      Changed |= C;
      DEBUG(dbgs() << " \\EB#" << n << format(" = %+2.0f", nodes[n].Value)
                   << (C ? " *\n" : "\n"));
    }
    if (!Changed)
      return;

    // Scan forwards, skipping the first node which was just updated.
    Changed = false;
    for (SmallVectorImpl<unsigned>::const_iterator I =
           llvm::next(Linked.begin()), E = Linked.end(); I != E; ++I) {
      unsigned n = *I;
      bool C = nodes[n].update(nodes);
      Changed |= C;
      DEBUG(dbgs() << " /EB#" << n << format(" = %+2.0f", nodes[n].Value)
                   << (C ? " *\n" : "\n"));
    }
    if (!Changed)
      return;
  }
}