C++ OffsetSet类代码示例

OffsetSet instrSuccOffsets(Op* opc, const Unit* unit) {
  OffsetSet succBcOffs;
  Op* bcStart = (Op*)(unit->entry());

  if (!instrIsControlFlow(*opc)) {
    Offset succOff = opc + instrLen(opc) - bcStart;
    succBcOffs.insert(succOff);
    return succBcOffs;
  }

  if (instrAllowsFallThru(*opc)) {
    Offset succOff = opc + instrLen(opc) - bcStart;
    succBcOffs.insert(succOff);
  }

  if (isSwitch(*opc)) {
    foreachSwitchTarget(opc, [&](Offset& offset) {
        succBcOffs.insert(offset + opc - bcStart);
      });
  } else {
    Offset target = instrJumpTarget(bcStart, opc - bcStart);
    if (target != InvalidAbsoluteOffset) {
      succBcOffs.insert(target);
    }
  }
  return succBcOffs;
}

OffsetSet instrSuccOffsets(PC opc, const Unit* unit) {
  OffsetSet succBcOffs;
  auto const bcStart = unit->entry();
  auto const op = peek_op(opc);

  if (!instrIsControlFlow(op)) {
    Offset succOff = opc + instrLen(opc) - bcStart;
    succBcOffs.insert(succOff);
    return succBcOffs;
  }

  if (instrAllowsFallThru(op)) {
    Offset succOff = opc + instrLen(opc) - bcStart;
    succBcOffs.insert(succOff);
  }

  if (isSwitch(op)) {
    foreachSwitchTarget(opc, [&](Offset offset) {
      succBcOffs.insert(offset + opc - bcStart);
    });
  } else {
    Offset target = instrJumpTarget(bcStart, opc - bcStart);
    if (target != InvalidAbsoluteOffset) {
      succBcOffs.insert(target);
    }
  }
  return succBcOffs;
}

/*
 * 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.
//.........这里部分代码省略.........

RegionDescPtr selectHotTrace(TransID triggerId,
                             const ProfData* profData,
                             TransCFG& cfg,
                             TransIDSet& selectedSet,
                             TransIDVec* selectedVec) {
  auto region = std::make_shared<RegionDesc>();
  TransID tid    = triggerId;
  TransID prevId = kInvalidTransID;
  selectedSet.clear();
  if (selectedVec) selectedVec->clear();

  PostConditions accumPostConds;
  // Maps BlockIds to the set of BC offsets for its successor blocks.
  // Used to prevent multiple successors with the same SrcKey for now.
  // This can go away once task #4157613 is done.
  hphp_hash_map<RegionDesc::BlockId, SrcKeySet> succSKSet;

  // Maps from BlockIds to accumulated post conditions for that block.
  // Used to determine if we can add branch-over edges by checking the
  // pre-conditions of the successor block.
  hphp_hash_map<RegionDesc::BlockId, PostConditions> blockPostConds;

  while (!selectedSet.count(tid)) {

    RegionDescPtr blockRegion = profData->transRegion(tid);
    if (blockRegion == nullptr) break;

    // If the debugger is attached, only allow single-block regions.
    if (prevId != kInvalidTransID && isDebuggerAttachedProcess()) {
      FTRACE(2, "selectHotTrace: breaking region at Translation {} "
             "because of debugger is attached\n", tid);
      break;
    }

    // Break if block is not the first and requires reffiness checks.
    // Task #2589970: fix translateRegion to support mid-region reffiness checks
    if (prevId != kInvalidTransID) {
      auto nRefDeps = blockRegion->blocks[0]->reffinessPreds().size();
      if (nRefDeps > 0) {
        FTRACE(2, "selectHotTrace: breaking region because of refDeps ({}) at "
               "Translation {}\n", nRefDeps, tid);
        break;
      }
    }

    // Break if block is not the first and it corresponds to the main
    // function body entry.  This is to prevent creating multiple
    // large regions containing the function body (starting at various
    // DV funclets).
    if (prevId != kInvalidTransID) {
      const Func* func = profData->transFunc(tid);
      Offset  bcOffset = profData->transStartBcOff(tid);
      if (func->base() == bcOffset) {
        FTRACE(2, "selectHotTrace: breaking region because reached the main "
               "function body entry at Translation {} (BC offset {})\n",
               tid, bcOffset);
        break;
      }
    }

    if (prevId != kInvalidTransID) {
      auto sk = profData->transSrcKey(tid);
      if (profData->optimized(sk)) {
        FTRACE(2, "selectHotTrace: breaking region because next sk already "
               "optimized, for Translation {}\n", tid);
        break;
      }
    }

    // Break trace if translation tid cannot follow the execution of
    // the entire translation prevId.  This can only happen if the
    // execution of prevId takes a side exit that leads to the
    // execution of tid.
    if (prevId != kInvalidTransID) {
      Op* lastInstr = profData->transLastInstr(prevId);
      const Unit* unit = profData->transFunc(prevId)->unit();
      OffsetSet succOffs = findSuccOffsets(lastInstr, unit);
      if (!succOffs.count(profData->transSrcKey(tid).offset())) {
        if (HPHP::Trace::moduleEnabled(HPHP::Trace::pgo, 2)) {
          FTRACE(2, "selectHotTrace: WARNING: Breaking region @: {}\n",
                 show(*region));
          FTRACE(2, "selectHotTrace: next translation selected: tid = {}\n{}\n",
                 tid, show(*blockRegion));
          FTRACE(2, "\nsuccOffs = {}\n", folly::join(", ", succOffs));
        }
        break;
      }
    }
    if (region->blocks.size() > 0) {
      auto& newBlock   = blockRegion->blocks.front();
      auto newBlockId  = newBlock->id();
      auto predBlockId = region->blocks.back().get()->id();
      if (!RuntimeOption::EvalHHIRBytecodeControlFlow) {
        region->addArc(predBlockId, newBlockId);
      } else {
      // With bytecode control-flow, we add all forward arcs in the TransCFG
      // that are induced by the blocks in the region, as a simple way
      // to expose control-flow for now.
      // This can go away once Task #4075822 is done.
        auto newBlockSrcKey = blockRegion->blocks.front().get()->start();
//.........这里部分代码省略.........

RegionDescPtr selectHotTrace(TransID triggerId,
                             const ProfData* profData,
                             TransCFG& cfg,
                             TransIDSet& selectedSet,
                             TransIDVec* selectedVec) {
  auto region = std::make_shared<RegionDesc>();
  TransID tid    = triggerId;
  TransID prevId = InvalidID;
  selectedSet.clear();
  if (selectedVec) selectedVec->clear();

  PostConditions accumPostConds;

  while (!selectedSet.count(tid)) {

    RegionDescPtr blockRegion = profData->transRegion(tid);
    if (blockRegion == nullptr) break;

    // If the debugger is attached, only allow single-block regions.
    if (prevId != InvalidID && isDebuggerAttachedProcess()) {
      FTRACE(2, "selectHotTrace: breaking region at Translation {} "
             "because of debugger is attached\n", tid);
      break;
    }

    // Break if block is not the first and requires reffiness checks.
    // Task #2589970: fix translateRegion to support mid-region reffiness checks
    if (prevId != InvalidID) {
      auto nRefDeps = blockRegion->blocks[0]->reffinessPreds().size();
      if (nRefDeps > 0) {
        FTRACE(2, "selectHotTrace: breaking region because of refDeps ({}) at "
               "Translation {}\n", nRefDeps, tid);
        break;
      }
    }

    // Break if block is not the first and it corresponds to the main
    // function body entry.  This is to prevent creating multiple
    // large regions containing the function body (starting at various
    // DV funclets).
    if (prevId != InvalidID) {
      const Func* func = profData->transFunc(tid);
      Offset  bcOffset = profData->transStartBcOff(tid);
      if (func->base() == bcOffset) {
        FTRACE(2, "selectHotTrace: breaking region because reached the main "
               "function body entry at Translation {} (BC offset {})\n",
               tid, bcOffset);
        break;
      }
    }

    if (prevId != InvalidID) {
      auto sk = profData->transSrcKey(tid);
      if (profData->optimized(sk)) {
        FTRACE(2, "selectHotTrace: breaking region because next sk already "
               "optimized, for Translation {}\n", tid);
        break;
      }
    }

    // Break trace if translation tid cannot follow the execution of
    // the entire translation prevId.  This can only happen if the
    // execution of prevId takes a side exit that leads to the
    // execution of tid.
    if (prevId != InvalidID) {
      Op* lastInstr = profData->transLastInstr(prevId);
      const Unit* unit = profData->transFunc(prevId)->unit();
      OffsetSet succOffs = findSuccOffsets(lastInstr, unit);
      if (!succOffs.count(profData->transSrcKey(tid).offset())) {
        if (HPHP::Trace::moduleEnabled(HPHP::Trace::pgo, 2)) {
          FTRACE(2, "selectHotTrace: WARNING: Breaking region @: {}\n",
                 JIT::show(*region));
          FTRACE(2, "selectHotTrace: next translation selected: tid = {}\n{}\n",
                 tid, JIT::show(*blockRegion));
          FTRACE(2, "\nsuccOffs = {}\n", folly::join(", ", succOffs));
        }
        break;
      }
    }
    region->blocks.insert(region->blocks.end(), blockRegion->blocks.begin(),
                          blockRegion->blocks.end());
    selectedSet.insert(tid);
    if (selectedVec) selectedVec->push_back(tid);

    Op lastOp = *(profData->transLastInstr(tid));
    if (breaksRegion(lastOp)) {
      FTRACE(2, "selectHotTrace: breaking region because of last instruction "
             "in Translation {}: {}\n", tid, opcodeToName(lastOp));
      break;
    }

    auto outArcs = cfg.outArcs(tid);
    if (outArcs.size() == 0) {
      FTRACE(2, "selectHotTrace: breaking region because there's no successor "
             "for Translation {}\n", tid);
      break;
    }

    auto lastNewBlock = blockRegion->blocks.back();
    discardPoppedTypes(accumPostConds,
//.........这里部分代码省略.........