C++ IRGenFunction::getActiveDominancePoint方法代码示例

/// Emit a dynamic alloca call to allocate enough memory to hold an object of
/// type 'T' and an optional llvm.stackrestore point if 'isInEntryBlock' is
/// false.
DynamicAlloca irgen::emitDynamicAlloca(IRGenFunction &IGF, SILType T,
                                       bool isInEntryBlock) {
  llvm::Value *stackRestorePoint = nullptr;

  // Save the stack pointer if we are not in the entry block (we could be
  // executed more than once).
  if (!isInEntryBlock) {
    auto *stackSaveFn = llvm::Intrinsic::getDeclaration(
        &IGF.IGM.Module, llvm::Intrinsic::ID::stacksave);

    stackRestorePoint =  IGF.Builder.CreateCall(stackSaveFn, {}, "spsave");
  }

  // Emit the dynamic alloca.
  llvm::Value *size = emitLoadOfSize(IGF, T);
  auto *alloca = IGF.Builder.CreateAlloca(IGF.IGM.Int8Ty, size, "alloca");
  alloca->setAlignment(16);
  assert(!isInEntryBlock ||
         IGF.getActiveDominancePoint().isUniversal() &&
             "Must be in entry block if we insert dynamic alloca's without "
             "stackrestores");
  return {alloca, stackRestorePoint};
}

void LocalTypeDataCache::
addAbstractForFulfillments(IRGenFunction &IGF, FulfillmentMap &&fulfillments,
                           llvm::function_ref<AbstractSource()> createSource) {
  // Add the source lazily.
  Optional<unsigned> sourceIndex;
  auto getSourceIndex = [&]() -> unsigned {
    if (!sourceIndex) {
      AbstractSources.emplace_back(createSource());
      sourceIndex = AbstractSources.size() - 1;
    }
    return *sourceIndex;
  };

  for (auto &fulfillment : fulfillments) {
    CanType type = CanType(fulfillment.first.first);
    LocalTypeDataKind localDataKind;

    // For now, ignore witness-table fulfillments when they're not for
    // archetypes.
    if (ProtocolDecl *protocol = fulfillment.first.second) {
      if (auto archetype = dyn_cast<ArchetypeType>(type)) {
        auto conformsTo = archetype->getConformsTo();
        auto it = std::find(conformsTo.begin(), conformsTo.end(), protocol);
        if (it == conformsTo.end()) continue;
        localDataKind = LocalTypeDataKind::forAbstractProtocolWitnessTable(*it);
      } else {
        continue;
      }

    } else {
      // Ignore type metadata fulfillments for non-dependent types that
      // we can produce very cheaply.  We don't want to end up emitting
      // the type metadata for Int by chasing through N layers of metadata
      // just because that path happens to be in the cache.
      if (!type->hasArchetype() &&
          isTypeMetadataAccessTrivial(IGF.IGM, type)) {
        continue;
      }

      localDataKind = LocalTypeDataKind::forTypeMetadata();
    }

    // Find the chain for the key.
    auto key = getKey(type, localDataKind);
    auto &chain = Map[key];

    // Check whether there's already an entry that's at least as good as the
    // fulfillment.
    Optional<unsigned> fulfillmentCost;
    auto getFulfillmentCost = [&]() -> unsigned {
      if (!fulfillmentCost)
        fulfillmentCost = fulfillment.second.Path.cost();
      return *fulfillmentCost;
    };

    bool isConditional = IGF.isConditionalDominancePoint();

    bool foundBetter = false;
    for (CacheEntry *cur = chain.Root, *last = nullptr; cur;
         last = cur, cur = cur->getNext()) {
      // Ensure the entry is acceptable.
      if (!IGF.isActiveDominancePointDominatedBy(cur->DefinitionPoint))
        continue;

      // Ensure that the entry isn't better than the fulfillment.
      auto curCost = cur->cost();
      if (curCost == 0 || curCost <= getFulfillmentCost()) {
        foundBetter = true;
        break;
      }

      // If the entry is defined at the current point, (1) we know there
      // won't be a better entry and (2) we should remove it.
      if (cur->DefinitionPoint == IGF.getActiveDominancePoint() &&
          !isConditional) {
        // Splice it out of the chain.
        assert(!cur->isConditional());
        chain.eraseEntry(last, cur);
        break;
      }
    }
    if (foundBetter) continue;

    // Okay, make a new entry.

    // Register with the conditional dominance scope if necessary.
    if (isConditional) {
      IGF.registerConditionalLocalTypeDataKey(key);
    }

    // Allocate the new entry.
    auto newEntry = new AbstractCacheEntry(IGF.getActiveDominancePoint(),
                                           isConditional,
                                           getSourceIndex(),
                                           std::move(fulfillment.second.Path));

    // Add it to the front of the chain.
    chain.push_front(newEntry);
  }
}

MetadataResponse
LocalTypeDataCache::tryGet(IRGenFunction &IGF, LocalTypeDataKey key,
                           bool allowAbstract, DynamicMetadataRequest request) {
  // Use the caching key.
  key = key.getCachingKey();

  auto it = Map.find(key);
  if (it == Map.end()) return MetadataResponse();
  auto &chain = it->second;

  CacheEntry *best = nullptr;
  Optional<OperationCost> bestCost;

  CacheEntry *next = chain.Root;
  while (next) {
    CacheEntry *cur = next;
    next = cur->getNext();

    // Ignore abstract entries if so requested.
    if (!allowAbstract && !isa<ConcreteCacheEntry>(cur))
      continue;

    // Ignore unacceptable entries.
    if (!IGF.isActiveDominancePointDominatedBy(cur->DefinitionPoint))
      continue;

    // If there's a collision, compare by cost, ignoring higher-cost entries.
    if (best) {
      // Compute the cost of the best entry if we haven't done so already.
      // If that's zero, go ahead and short-circuit out.
      if (!bestCost) {
        bestCost = best->costForRequest(key, request);
        if (*bestCost == OperationCost::Free) break;
      }

      auto curCost = cur->costForRequest(key, request);
      if (curCost >= *bestCost) continue;

      // Replace the best cost and fall through.
      bestCost = curCost;
    }
    best = cur;
  }

  // If we didn't find anything, we're done.
  if (!best) return MetadataResponse();

  // Okay, we've found the best entry available.
  switch (best->getKind()) {

  // For concrete caches, this is easy.
  case CacheEntry::Kind::Concrete: {
    auto entry = cast<ConcreteCacheEntry>(best);

    if (entry->immediatelySatisfies(key, request))
      return entry->Value;

    assert(key.Kind.isAnyTypeMetadata());

    // Emit a dynamic check that the type metadata matches the request.
    // TODO: we could potentially end up calling this redundantly with a
    //   dynamic request.  Fortunately, those are used only in very narrow
    //   circumstances.
    auto response = emitCheckTypeMetadataState(IGF, request, entry->Value);

    // Add a concrete entry for the checked result.
    IGF.setScopedLocalTypeData(key, response);

    return response;
  }

  // For abstract caches, we need to follow a path.
  case CacheEntry::Kind::Abstract: {
    auto entry = cast<AbstractCacheEntry>(best);

    // Follow the path.
    auto &source = AbstractSources[entry->SourceIndex];
    auto response = entry->follow(IGF, source, request);

    // Following the path automatically caches at every point along it,
    // including the end.
    assert(chain.Root->DefinitionPoint == IGF.getActiveDominancePoint());
    assert(isa<ConcreteCacheEntry>(chain.Root));

    return response;
  }

  }
  llvm_unreachable("bad cache entry kind");
}