/*
 * Perform a DFS starting at block `bid', storing the post-order in
 * `outVec'.
 */
void RegionDesc::postOrderSort(RegionDesc::BlockId     bid,
                               RegionDesc::BlockIdSet& visited,
                               RegionDesc::BlockIdVec& outVec) {
  if (visited.count(bid)) return;
  visited.insert(bid);

  if (auto nextRetr = nextRetrans(bid)) {
    postOrderSort(nextRetr.value(), visited, outVec);
  }
  for (auto succ : succs(bid)) {
    postOrderSort(succ, visited, outVec);
  }
  outVec.push_back(bid);
}
Example #2
0
/**
 * Sort the m_blocks vector in reverse post order.  This enforces that
 * m_blocks will be a topological order in case the region is acyclic.
 * All region arcs are taken into account, including retranslation arcs.
 */
void RegionDesc::sortBlocks() {
  RegionDesc::BlockIdSet visited;
  RegionDesc::BlockIdVec reverse;

  postOrderSort(entry()->id(), visited, reverse);
  assertx(m_blocks.size() >= reverse.size());

  // Remove unreachable blocks from `m_data'.
  for (auto it = m_blocks.begin(); it != m_blocks.end();) {
    auto bid = (*it)->id();
    if (visited.count(bid) == 0) {
      it = deleteBlock(it);
    } else {
      it++;
    }
  }

  // Update `m_blocks' vector.
  m_blocks.clear();
  auto size = reverse.size();
  for (size_t i = 0; i < size; i++) {
    m_blocks.push_back(block(reverse[size - i - 1]));
  }
}
/*
 * Checks if the given region is well-formed, which entails the
 * following properties:
 *
 *   1) The region has at least one block.
 *
 *   2) Each block in the region has a different id.
 *
 *   3) All arcs involve blocks within the region.
 *
 *   4) For each arc, the bytecode offset of the dst block must
 *      possibly follow the execution of the src block.
 *
 *   5) Each block contains at most one successor corresponding to a
 *      given SrcKey.
 *
 *   6) The region doesn't contain any loops, unless JitLoops is
 *      enabled.
 *
 *   7) All blocks are reachable from the entry block.
 *
 *   8) For each block, there must be a path from the entry to it that
 *      includes only earlier blocks in the region.
 *
 *   9) The region is topologically sorted unless loops are enabled.
 *
 *  10) The block-retranslation chains cannot have cycles.
 *
 */
bool check(const RegionDesc& region, std::string& error) {

  auto bad = [&](const std::string& errorMsg) {
    error = errorMsg;
    return false;
  };

  // 1) The region has at least one block.
  if (region.empty()) return bad("empty region");

  RegionDesc::BlockIdSet blockSet;
  for (auto b : region.blocks()) {
    auto bid = b->id();
    // 2) Each block in the region has a different id.
    if (blockSet.count(bid)) {
      return bad(folly::sformat("many blocks with id {}", bid));
    }
    blockSet.insert(bid);
  }

  for (auto b : region.blocks()) {
    auto bid = b->id();
    SrcKey    lastSk = region.block(bid)->last();
    OffsetSet validSuccOffsets = lastSk.succOffsets();
    OffsetSet succOffsets;

    for (auto succ : region.succs(bid)) {
      SrcKey succSk = region.block(succ)->start();
      Offset succOffset = succSk.offset();

      // 3) All arcs involve blocks within the region.
      if (blockSet.count(succ) == 0) {
        return bad(folly::sformat("arc with dst not in the region: {} -> {}",
                                  bid, succ));
      }

      // Checks 4) and 5) below don't make sense for arcs corresponding
      // to inlined calls and returns, so skip them in such cases.
      // This won't be possible once task #4076399 is done.
      if (lastSk.func() != succSk.func()) continue;

      // 4) For each arc, the bytecode offset of the dst block must
      //    possibly follow the execution of the src block.
      if (validSuccOffsets.count(succOffset) == 0) {
        return bad(folly::sformat("arc with impossible control flow: {} -> {}",
                                  bid, succ));
      }

      // 5) Each block contains at most one successor corresponding to a
      //    given SrcKey.
      if (succOffsets.count(succOffset) > 0) {
        return bad(folly::sformat("block {} has multiple successors with SK {}",
                                  bid, show(succSk)));
      }
      succOffsets.insert(succOffset);
    }
    for (auto pred : region.preds(bid)) {
      if (blockSet.count(pred) == 0) {
        return bad(folly::sformat("arc with src not in the region: {} -> {}",
                                  pred, bid));
      }
    }
  }

  // 6) is checked by dfsCheck.
  DFSChecker dfsCheck(region);
  if (!dfsCheck.check(region.entry()->id())) {
    return bad("region is cyclic");
  }

  // 7) All blocks are reachable from the entry (first) block.
  if (dfsCheck.numVisited() != blockSet.size()) {
    return bad("region has unreachable blocks");
  }

  // 8) and 9) are checked below.
  RegionDesc::BlockIdSet visited;
  auto& blocks = region.blocks();
  for (unsigned i = 0; i < blocks.size(); i++) {
    auto bid = blocks[i]->id();
    unsigned nVisited = 0;
    for (auto pred : region.preds(bid)) {
      nVisited += visited.count(pred);
    }
    // 8) For each block, there must be a path from the entry to it that
    //    includes only earlier blocks in the region.
    if (nVisited == 0 && i != 0) {
      return bad(folly::sformat("block {} appears before all its predecessors",
                                bid));
    }
    // 9) The region is topologically sorted unless loops are enabled.
    if (!RuntimeOption::EvalJitLoops && nVisited != region.preds(bid).size()) {
      return bad(folly::sformat("non-topological order (bid: {})", bid));
    }
    visited.insert(bid);
  }

  // 10) The block-retranslation chains cannot have cycles.
  for (auto b : blocks) {
    auto bid = b->id();
    RegionDesc::BlockIdSet chainSet;
    chainSet.insert(bid);
    while (auto next = region.nextRetrans(bid)) {
      auto nextId = next.value();
      if (chainSet.count(nextId)) {
        return bad(folly::sformat("cyclic retranslation chain for block {}",
                                  bid));
      }
      chainSet.insert(nextId);
      bid = nextId;
    }
  }

  return true;
}