Пример #1
0
bool InliningDecider::shouldInline(SrcKey callerSk,
                                   const Func* callee,
                                   const RegionDesc& region,
                                   uint32_t maxTotalCost) {
  auto sk = region.empty() ? SrcKey() : region.start();
  assertx(callee);
  assertx(sk.func() == callee);

  // Tracing return lambdas.
  auto refuse = [&] (const char* why) {
    FTRACE(2, "shouldInline: rejecting callee region: {}", show(region));
    return traceRefusal(m_topFunc, callee, why);
  };

  auto accept = [&, this] (const char* kind) {
    FTRACE(2, "InliningDecider: inlining {}() <- {}()\t<reason: {}>\n",
           m_topFunc->fullName()->data(), callee->fullName()->data(), kind);
    return true;
  };

  if (m_stackDepth + callee->maxStackCells() >= kStackCheckLeafPadding) {
    return refuse("inlining stack depth limit exceeded");
  }

  // Even if the func contains NativeImpl we may have broken the trace before
  // we hit it.
  auto containsNativeImpl = [&] {
    for (auto block : region.blocks()) {
      if (!block->empty() && block->last().op() == OpNativeImpl) return true;
    }
    return false;
  };

  // Try to inline CPP builtin functions.
  // The NativeImpl opcode may appear later in the function because of Asserts
  // generated in hhbbc
  if (callee->isCPPBuiltin() && containsNativeImpl()) {
    if (isInlinableCPPBuiltin(callee)) {
      return accept("inlinable CPP builtin");
    }
    return refuse("non-inlinable CPP builtin");
  }

  // If the function may use a VarEnv (which is stored in the ActRec) or may be
  // variadic, we restrict inlined callees to certain whitelisted instructions
  // which we know won't actually require these features.
  const bool needsCheckVVSafe = callee->attrs() & AttrMayUseVV;

  bool hasRet = false;

  // Iterate through the region, checking its suitability for inlining.
  for (auto const& block : region.blocks()) {
    sk = block->start();

    for (auto i = 0, n = block->length(); i < n; ++i, sk.advance()) {
      auto op = sk.op();

      // We don't allow inlined functions in the region.  The client is
      // expected to disable inlining for the region it gives us to peek.
      if (sk.func() != callee) {
        return refuse("got region with inlined calls");
      }

      // Restrict to VV-safe opcodes if necessary.
      if (needsCheckVVSafe && !isInliningVVSafe(op)) {
        return refuse(folly::format("{} may use dynamic environment",
                                    opcodeToName(op)).str().c_str());
      }

      // Count the returns.
      if (isReturnish(op)) {
        hasRet = true;
      }

      // We can't inline FCallArray.  XXX: Why?
      if (op == Op::FCallArray) {
        return refuse("can't inline FCallArray");
      }
    }
  }

  if (!hasRet) {
    return refuse("region has no returns");
  }

  // Refuse if the cost exceeds our thresholds.
  // We measure the cost of inlining each callstack and stop when it exceeds a
  // certain threshold.  (Note that we do not measure the total cost of all the
  // inlined calls for a given caller---just the cost of each nested stack.)
  const int maxCost = maxTotalCost - m_cost;
  const int cost = computeTranslationCost(callerSk, region);
  if (cost > maxCost) {
    return refuse("too expensive");
  }

  return accept("small region with return");
}
Пример #2
0
/*
 * 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;
}
Пример #3
0
bool InliningDecider::shouldInline(const Func* callee,
                                   const RegionDesc& region) {
  auto sk = region.empty() ? SrcKey() : region.start();
  assertx(callee);
  assertx(sk.func() == callee);

  int cost = 0;

  // Tracing return lambdas.
  auto refuse = [&] (const char* why) {
    return traceRefusal(m_topFunc, callee, why);
  };

  auto accept = [&, this] (const char* kind) {
    FTRACE(1, "InliningDecider: inlining {}() <- {}()\t<reason: {}>\n",
           m_topFunc->fullName()->data(), callee->fullName()->data(), kind);

    // Update our context.
    m_costStack.push_back(cost);
    m_cost += cost;
    m_callDepth += 1;
    m_stackDepth += callee->maxStackCells();

    return true;
  };

  // Check inlining depths.
  if (m_callDepth + 1 >= RuntimeOption::EvalHHIRInliningMaxDepth) {
    return refuse("inlining call depth limit exceeded");
  }
  if (m_stackDepth + callee->maxStackCells() >= kStackCheckLeafPadding) {
    return refuse("inlining stack depth limit exceeded");
  }

  // Even if the func contains NativeImpl we may have broken the trace before
  // we hit it.
  auto containsNativeImpl = [&] {
    for (auto block : region.blocks()) {
      if (!block->empty() && block->last().op() == OpNativeImpl) return true;
    }
    return false;
  };

  // Try to inline CPP builtin functions.
  // The NativeImpl opcode may appear later in the function because of Asserts
  // generated in hhbbc
  if (callee->isCPPBuiltin() && containsNativeImpl()) {
    if (isInlinableCPPBuiltin(callee)) {
      return accept("inlinable CPP builtin");
    }
    return refuse("non-inlinable CPP builtin");
  }

  // If the function may use a VarEnv (which is stored in the ActRec) or may be
  // variadic, we restrict inlined callees to certain whitelisted instructions
  // which we know won't actually require these features.
  const bool needsCheckVVSafe = callee->attrs() & AttrMayUseVV;

  // We measure the cost of inlining each callstack and stop when it exceeds a
  // certain threshold.  (Note that we do not measure the total cost of all the
  // inlined calls for a given caller---just the cost of each nested stack.)
  const int maxCost = RuntimeOption::EvalHHIRInliningMaxCost - m_cost;

  // We only inline callee regions that have exactly one return.
  //
  // NOTE: Currently, the tracelet selector uses the first Ret in the child's
  // region to determine when to stop inlining.  However, the safety of this
  // behavior should not be considered guaranteed by InliningDecider; the
  // "right" way to decide when inlining ends is to inline all of `region'.
  int numRets = 0;

  // Iterate through the region, checking its suitability for inlining.
  for (auto const& block : region.blocks()) {
    sk = block->start();

    for (auto i = 0, n = block->length(); i < n; ++i, sk.advance()) {
      auto op = sk.op();

      // We don't allow inlined functions in the region.  The client is
      // expected to disable inlining for the region it gives us to peek.
      if (sk.func() != callee) {
        return refuse("got region with inlined calls");
      }

      // Restrict to VV-safe opcodes if necessary.
      if (needsCheckVVSafe && !isInliningVVSafe(op)) {
        return refuse(folly::format("{} may use dynamic environment",
                                    opcodeToName(op)).str().c_str());
      }

      // Count the returns.
      if (isRet(op) || op == Op::NativeImpl) {
        if (++numRets > 1) {
          return refuse("region has too many returns");
        }
        continue;
      }

      // We can't inline FCallArray.  XXX: Why?
      if (op == Op::FCallArray) {
        return refuse("can't inline FCallArray");
      }

      // Assert opcodes don't contribute to the inlining cost.
      if (op == Op::AssertRATL || op == Op::AssertRATStk) continue;

      cost += 1;

      // Add the size of immediate vectors to the cost.
      auto const pc = reinterpret_cast<const Op*>(sk.pc());
      if (hasMVector(op)) {
        cost += getMVector(pc).size();
      } else if (hasImmVector(op)) {
        cost += getImmVector(pc).size();
      }

      // Refuse if the cost exceeds our thresholds.
      if (cost > maxCost) {
        return refuse("too expensive");
      }
    }
  }

  if (numRets != 1) {
    return refuse("region has no returns");
  }
  return accept("small region with single return");
}