js-inlining-heuristic.cc

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// Copyright 2015 the V8 project authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
 
#include "src/compiler/js-inlining-heuristic.h"
 
#include "src/compiler/common-operator.h"
#include "src/compiler/compiler-source-position-table.h"
#include "src/compiler/js-heap-broker.h"
#include "src/compiler/node-matchers.h"
#include "src/compiler/simplified-operator.h"
#include "src/numbers/conversions.h"
 
namespace v8 {
namespace internal {
namespace compiler {
 
#define TRACE(...)                                \
  do {                                            \
    if (v8_flags.trace_turbo_inlining)            \
      StdoutStream{} << __VA_ARGS__ << std::endl; \
  } while (false)
 
namespace {
bool IsSmall(int const size) {
  return size <= v8_flags.max_inlined_bytecode_size_small;
}
 
bool CanConsiderForInlining(JSHeapBroker* broker,
                            FeedbackCellRef feedback_cell) {
  OptionalFeedbackVectorRef feedback_vector =
      feedback_cell.feedback_vector(broker);
  if (!feedback_vector.has_value()) {
    TRACE("Cannot consider " << feedback_cell
                             << " for inlining (no feedback vector)");
    return false;
  }
  SharedFunctionInfoRef shared = feedback_vector->shared_function_info(broker);
 
  if (!shared.HasBytecodeArray()) {
    TRACE("Cannot consider " << shared << " for inlining (no bytecode)");
    return false;
  }
  // Ensure we have a persistent handle to the bytecode in order to avoid
  // flushing it during the remaining compilation.
  shared.GetBytecodeArray(broker);
 
  // Read feedback vector again in case it got flushed before we were able to
  // prevent flushing above.
  OptionalFeedbackVectorRef feedback_vector_again =
      feedback_cell.feedback_vector(broker);
  if (!feedback_vector_again.has_value()) {
    TRACE("Cannot consider " << shared << " for inlining (no feedback vector)");
    return false;
  }
  if (!feedback_vector_again->equals(*feedback_vector)) {
    // The new feedback vector likely contains lots of uninitialized slots, so
    // it doesn't make much sense to inline this function now.
    TRACE("Not considering " << shared
                             << " for inlining (feedback vector changed)");
    return false;
  }
 
  SharedFunctionInfo::Inlineability inlineability =
      shared.GetInlineability(broker);
  if (inlineability != SharedFunctionInfo::kIsInlineable) {
    TRACE("Cannot consider "
          << shared << " for inlining (reason: " << inlineability << ")");
    return false;
  }
 
  TRACE("Considering " << shared << " for inlining with " << *feedback_vector);
  return true;
}
 
bool CanConsiderForInlining(JSHeapBroker* broker, JSFunctionRef function) {
  FeedbackCellRef feedback_cell = function.raw_feedback_cell(broker);
  bool const result = CanConsiderForInlining(broker, feedback_cell);
  if (result) {
    CHECK(function.shared(broker).equals(
        feedback_cell.shared_function_info(broker).value()));
  }
  return result;
}
 
}  // namespace
 
JSInliningHeuristic::Candidate JSInliningHeuristic::CollectFunctions(
    Node* node, int functions_size) {
  DCHECK_NE(0, functions_size);
  Node* callee = node->InputAt(0);
  Candidate out;
  out.node = node;
 
  HeapObjectMatcher m(callee);
  if (m.HasResolvedValue() && m.Ref(broker()).IsJSFunction()) {
    JSFunctionRef function = m.Ref(broker()).AsJSFunction();
    out.functions[0] = function;
    if (CanConsiderForInlining(broker(), function)) {
      out.bytecode[0] = function.shared(broker()).GetBytecodeArray(broker());
      out.num_functions = 1;
      return out;
    }
  }
  if (m.IsPhi()) {
    int const value_input_count = m.node()->op()->ValueInputCount();
    if (value_input_count > functions_size) {
      out.num_functions = 0;
      return out;
    }
    for (int n = 0; n < value_input_count; ++n) {
      HeapObjectMatcher m2(callee->InputAt(n));
      if (!m2.HasResolvedValue() || !m2.Ref(broker()).IsJSFunction()) {
        out.num_functions = 0;
        return out;
      }
 
      out.functions[n] = m2.Ref(broker()).AsJSFunction();
      JSFunctionRef function = out.functions[n].value();
      if (CanConsiderForInlining(broker(), function)) {
        out.bytecode[n] = function.shared(broker()).GetBytecodeArray(broker());
      }
    }
    out.num_functions = value_input_count;
    return out;
  }
  if (m.IsCheckClosure()) {
    DCHECK(!out.functions[0].has_value());
    FeedbackCellRef feedback_cell = MakeRef(broker(), FeedbackCellOf(m.op()));
    if (CanConsiderForInlining(broker(), feedback_cell)) {
      out.shared_info = feedback_cell.shared_function_info(broker()).value();
      out.bytecode[0] = out.shared_info->GetBytecodeArray(broker());
    }
    out.num_functions = 1;
    return out;
  }
  if (m.IsJSCreateClosure()) {
    DCHECK(!out.functions[0].has_value());
    JSCreateClosureNode n(callee);
    FeedbackCellRef feedback_cell = n.GetFeedbackCellRefChecked(broker());
    if (CanConsiderForInlining(broker(), feedback_cell)) {
      out.shared_info = feedback_cell.shared_function_info(broker()).value();
      out.bytecode[0] = out.shared_info->GetBytecodeArray(broker());
      CHECK(out.shared_info->equals(n.Parameters().shared_info()));
    }
    out.num_functions = 1;
    return out;
  }
  out.num_functions = 0;
  return out;
}
 
Reduction JSInliningHeuristic::Reduce(Node* node) {
#if V8_ENABLE_WEBASSEMBLY
  if (mode() == kWasmWrappersOnly || mode() == kWasmFullInlining) {
    if (node->opcode() == IrOpcode::kJSWasmCall) {
      return inliner_.ReduceJSWasmCall(node);
    }
    return NoChange();
  }
#endif  // V8_ENABLE_WEBASSEMBLY
 
  DCHECK_EQ(mode(), kJSOnly);
  if (!IrOpcode::IsInlineeOpcode(node->opcode())) return NoChange();
 
  if (total_inlined_bytecode_size_ >= max_inlined_bytecode_size_absolute_) {
    return NoChange();
  }
 
  // Check if we already saw that {node} before, and if so, just skip it.
  if (seen_.find(node->id()) != seen_.end()) return NoChange();
 
  // Check if the {node} is an appropriate candidate for inlining.
  Candidate candidate = CollectFunctions(node, kMaxCallPolymorphism);
  if (candidate.num_functions == 0) {
    return NoChange();
  } else if (candidate.num_functions > 1 && !v8_flags.polymorphic_inlining) {
    TRACE("Not considering call site #"
          << node->id() << ":" << node->op()->mnemonic()
          << ", because polymorphic inlining is disabled");
    return NoChange();
  }
 
  bool can_inline_candidate = false, candidate_is_small = true;
  candidate.total_size = 0;
  FrameState frame_state{NodeProperties::GetFrameStateInput(node)};
  FrameStateInfo const& frame_info = frame_state.frame_state_info();
  Handle<SharedFunctionInfo> frame_shared_info;
  for (int i = 0; i < candidate.num_functions; ++i) {
    if (!candidate.bytecode[i].has_value()) {
      candidate.can_inline_function[i] = false;
      continue;
    }
 
    SharedFunctionInfoRef shared =
        candidate.functions[i].has_value()
            ? candidate.functions[i].value().shared(broker())
            : candidate.shared_info.value();
    candidate.can_inline_function[i] = candidate.bytecode[i].has_value();
    // Because of concurrent optimization, optimization of the inlining
    // candidate could have been disabled meanwhile.
    // JSInliner will check this again and not actually inline the function in
    // this case.
    CHECK_IMPLIES(candidate.can_inline_function[i],
                  shared.IsInlineable(broker()) ||
                      shared.GetInlineability(broker()) ==
                          SharedFunctionInfo::kHasOptimizationDisabled);
    // Do not allow direct recursion i.e. f() -> f(). We still allow indirect
    // recursion like f() -> g() -> f(). The indirect recursion is helpful in
    // cases where f() is a small dispatch function that calls the appropriate
    // function. In the case of direct recursion, we only have some static
    // information for the first level of inlining and it may not be that useful
    // to just inline one level in recursive calls. In some cases like tail
    // recursion we may benefit from recursive inlining, if we have additional
    // analysis that converts them to iterative implementations. Though it is
    // not obvious if such an analysis is needed.
    if (frame_info.shared_info().ToHandle(&frame_shared_info) &&
        frame_shared_info.equals(shared.object())) {
      TRACE("Not considering call site #" << node->id() << ":"
                                          << node->op()->mnemonic()
                                          << ", because of recursive inlining");
      candidate.can_inline_function[i] = false;
    }
    if (candidate.can_inline_function[i]) {
      can_inline_candidate = true;
      BytecodeArrayRef bytecode = candidate.bytecode[i].value();
      candidate.total_size += bytecode.length();
      unsigned inlined_bytecode_size = 0;
      if (OptionalJSFunctionRef function = candidate.functions[i]) {
        if (OptionalCodeRef code = function->code(broker())) {
          inlined_bytecode_size = code->GetInlinedBytecodeSize();
          candidate.total_size += inlined_bytecode_size;
        }
      }
      candidate_is_small = candidate_is_small &&
                           IsSmall(bytecode.length() + inlined_bytecode_size);
    }
  }
  if (!can_inline_candidate) return NoChange();
 
  // Gather feedback on how often this call site has been hit before.
  if (node->opcode() == IrOpcode::kJSCall) {
    CallParameters const p = CallParametersOf(node->op());
    candidate.frequency = p.frequency();
  } else {
    ConstructParameters const p = ConstructParametersOf(node->op());
    candidate.frequency = p.frequency();
  }
 
  // Don't consider a {candidate} whose frequency is below the
  // threshold, i.e. a call site that is only hit once every N
  // invocations of the caller.
  if (candidate.frequency.IsKnown() &&
      candidate.frequency.value() < v8_flags.min_inlining_frequency) {
    return NoChange();
  }
 
  // Found a candidate. Insert it into the set of seen nodes s.t. we don't
  // revisit in the future. Note this insertion happens here and not earlier in
  // order to make inlining decisions order-independent. A node may not be a
  // candidate when first seen, but later reductions may turn it into a valid
  // candidate. In that case, the node should be revisited by
  // JSInliningHeuristic.
  seen_.insert(node->id());
 
  // Forcibly inline small functions here. In the case of polymorphic inlining
  // candidate_is_small is set only when all functions are small.
  if (candidate_is_small) {
    TRACE("Inlining small function(s) at call site #"
          << node->id() << ":" << node->op()->mnemonic());
    return InlineCandidate(candidate, true);
  }
 
  // In the general case we remember the candidate for later.
  candidates_.insert(candidate);
  return NoChange();
}
 
void JSInliningHeuristic::Finalize() {
  if (candidates_.empty()) return;  // Nothing to do without candidates.
  if (v8_flags.trace_turbo_inlining) PrintCandidates();
 
  // We inline at most one candidate in every iteration of the fixpoint.
  // This is to ensure that we don't consume the full inlining budget
  // on things that aren't called very often.
  // TODO(bmeurer): Use std::priority_queue instead of std::set here.
  while (!candidates_.empty()) {
    auto i = candidates_.begin();
    Candidate candidate = *i;
    candidates_.erase(i);
 
    // Ignore this candidate if it's no longer valid.
    if (!IrOpcode::IsInlineeOpcode(candidate.node->opcode())) continue;
    if (candidate.node->IsDead()) continue;
 
    // Make sure we have some extra budget left, so that any small functions
    // exposed by this function would be given a chance to inline.
    double size_of_candidate =
        candidate.total_size * v8_flags.reserve_inline_budget_scale_factor;
    int total_size =
        total_inlined_bytecode_size_ + static_cast<int>(size_of_candidate);
    if (total_size > max_inlined_bytecode_size_cumulative_) {
      info_->set_could_not_inline_all_candidates();
      // Try if any smaller functions are available to inline.
      continue;
    }
 
    Reduction const reduction = InlineCandidate(candidate, false);
    if (reduction.Changed()) return;
  }
}
 
namespace {
 
struct NodeAndIndex {
  Node* node;
  int index;
};
 
bool CollectStateValuesOwnedUses(Node* node, Node* state_values,
                                 NodeAndIndex* uses_buffer, size_t* use_count,
                                 size_t max_uses) {
  // Only accumulate states that are not shared with other users.
  if (state_values->UseCount() > 1) return true;
  for (int i = 0; i < state_values->InputCount(); i++) {
    Node* input = state_values->InputAt(i);
    if (input->opcode() == IrOpcode::kStateValues) {
      if (!CollectStateValuesOwnedUses(node, input, uses_buffer, use_count,
                                       max_uses)) {
        return false;
      }
    } else if (input == node) {
      if (*use_count >= max_uses) return false;
      uses_buffer[*use_count] = {state_values, i};
      (*use_count)++;
    }
  }
  return true;
}
 
}  // namespace
 
Node* JSInliningHeuristic::DuplicateStateValuesAndRename(Node* state_values,
                                                         Node* from, Node* to,
                                                         StateCloneMode mode) {
  // Only rename in states that are not shared with other users. This needs to
  // be in sync with the condition in {CollectStateValuesOwnedUses}.
  if (state_values->UseCount() > 1) return state_values;
  Node* copy = mode == kChangeInPlace ? state_values : nullptr;
  for (int i = 0; i < state_values->InputCount(); i++) {
    Node* input = state_values->InputAt(i);
    Node* processed;
    if (input->opcode() == IrOpcode::kStateValues) {
      processed = DuplicateStateValuesAndRename(input, from, to, mode);
    } else if (input == from) {
      processed = to;
    } else {
      processed = input;
    }
    if (processed != input) {
      if (!copy) {
        copy = graph()->CloneNode(state_values);
      }
      copy->ReplaceInput(i, processed);
    }
  }
  return copy ? copy : state_values;
}
 
namespace {
 
bool CollectFrameStateUniqueUses(Node* node, FrameState frame_state,
                                 NodeAndIndex* uses_buffer, size_t* use_count,
                                 size_t max_uses) {
  // Only accumulate states that are not shared with other users.
  if (frame_state->UseCount() > 1) return true;
  if (frame_state.stack() == node) {
    if (*use_count >= max_uses) return false;
    uses_buffer[*use_count] = {frame_state, FrameState::kFrameStateStackInput};
    (*use_count)++;
  }
  if (!CollectStateValuesOwnedUses(node, frame_state.locals(), uses_buffer,
                                   use_count, max_uses)) {
    return false;
  }
  return true;
}
 
}  // namespace
 
FrameState JSInliningHeuristic::DuplicateFrameStateAndRename(
    FrameState frame_state, Node* from, Node* to, StateCloneMode mode) {
  // Only rename in states that are not shared with other users. This needs to
  // be in sync with the condition in {DuplicateFrameStateAndRename}.
  if (frame_state->UseCount() > 1) return frame_state;
  Node* copy =
      mode == kChangeInPlace ? static_cast<Node*>(frame_state) : nullptr;
  if (frame_state.stack() == from) {
    if (!copy) {
      copy = graph()->CloneNode(frame_state);
    }
    copy->ReplaceInput(FrameState::kFrameStateStackInput, to);
  }
  Node* locals = frame_state.locals();
  Node* new_locals = DuplicateStateValuesAndRename(locals, from, to, mode);
  if (new_locals != locals) {
    if (!copy) {
      copy = graph()->CloneNode(frame_state);
    }
    copy->ReplaceInput(FrameState::kFrameStateLocalsInput, new_locals);
  }
  return copy != nullptr ? FrameState{copy} : frame_state;
}
 
bool JSInliningHeuristic::TryReuseDispatch(Node* node, Node* callee,
                                           Node** if_successes, Node** calls,
                                           Node** inputs, int input_count,
                                           int* num_calls) {
  // We will try to reuse the control flow branch created for computing
  // the {callee} target of the call. We only reuse the branch if there
  // is no side-effect between the call and the branch, and if the callee is
  // only used as the target (and possibly also in the related frame states).
 
  // We are trying to match the following pattern:
  //
  //         C1     C2
  //          .     .
  //          |     |
  //         Merge(merge)  <-----------------+
  //           ^    ^                        |
  //  V1  V2   |    |         E1  E2         |
  //   .  .    |    +----+     .  .          |
  //   |  |    |         |     |  |          |
  //  Phi(callee)      EffectPhi(effect_phi) |
  //     ^                    ^              |
  //     |                    |              |
  //     +----+               |              |
  //     |    |               |              |
  //     |   StateValues      |              |
  //     |       ^            |              |
  //     +----+  |            |              |
  //     |    |  |            |              |
  //     |    FrameState      |              |
  //     |           ^        |              |
  //     |           |        |          +---+
  //     |           |        |          |   |
  //     +----+     Checkpoint(checkpoint)   |
  //     |    |           ^                  |
  //     |    StateValues |    +-------------+
  //     |        |       |    |
  //     +-----+  |       |    |
  //     |     |  |       |    |
  //     |     FrameState |    |
  //     |             ^  |    |
  //     +-----------+ |  |    |
  //                  Call(node)
  //                   |
  //                   |
  //                   .
  //
  // The {callee} here is a phi that merges the possible call targets, {node}
  // is the actual call that we will try to duplicate and connect to the
  // control that comes into {merge}. There can be a {checkpoint} between
  // the call and the calle phi.
  //
  // The idea is to get rid of the merge, effect phi and phi, then duplicate
  // the call (with all the frame states and such), and connect the duplicated
  // calls and states directly to the inputs of the ex-phi, ex-effect-phi and
  // ex-merge. The tricky part is to make sure that there is no interference
  // from the outside. In particular, there should not be any unaccounted uses
  // of the  phi, effect-phi and merge because we will remove them from
  // the graph.
  //
  //     V1              E1   C1  V2   E2               C2
  //     .                .    .  .    .                .
  //     |                |    |  |    |                |
  //     +----+           |    |  +----+                |
  //     |    |           |    |  |    |                |
  //     |   StateValues  |    |  |   StateValues       |
  //     |       ^        |    |  |       ^             |
  //     +----+  |        |    |  +----+  |             |
  //     |    |  |        |    |  |    |  |             |
  //     |    FrameState  |    |  |    FrameState       |
  //     |           ^    |    |  |           ^         |
  //     |           |    |    |  |           |         |
  //     |           |    |    |  |           |         |
  //     +----+     Checkpoint |  +----+     Checkpoint |
  //     |    |           ^    |  |    |           ^    |
  //     |    StateValues |    |  |    StateValues |    |
  //     |        |       |    |  |        |       |    |
  //     +-----+  |       |    |  +-----+  |       |    |
  //     |     |  |       |    |  |     |  |       |    |
  //     |     FrameState |    |  |     FrameState |    |
  //     |              ^ |    |  |              ^ |    |
  //     +-------------+| |    |  +-------------+| |    |
  //                   Call----+                Call----+
  //                     |                       |
  //                     +-------+  +------------+
  //                             |  |
  //                             Merge
  //                             EffectPhi
  //                             Phi
  //                              |
  //                             ...
 
  // Bailout if the call is not polymorphic anymore (other reducers might
  // have replaced the callee phi with a constant).
  if (callee->opcode() != IrOpcode::kPhi) return false;
 
  // If there is a control node between the callee computation
  // and the call, bail out.
  Node* merge = NodeProperties::GetControlInput(callee);
  if (NodeProperties::GetControlInput(node) != merge) return false;
 
  // If there is a non-checkpoint effect node between the callee computation
  // and the call, bail out. We will drop any checkpoint between the call and
  // the callee phi because the callee computation should have its own
  // checkpoint that the call can fall back to.
  Node* checkpoint = nullptr;
  Node* effect = NodeProperties::GetEffectInput(node);
  if (effect->opcode() == IrOpcode::kCheckpoint) {
    checkpoint = effect;
    if (NodeProperties::GetControlInput(checkpoint) != merge) return false;
    effect = NodeProperties::GetEffectInput(effect);
  }
  if (effect->opcode() != IrOpcode::kEffectPhi) return false;
  if (NodeProperties::GetControlInput(effect) != merge) return false;
  Node* effect_phi = effect;
 
  // The effect phi, the callee, the call and the checkpoint must be the only
  // users of the merge.
  for (Node* merge_use : merge->uses()) {
    if (merge_use != effect_phi && merge_use != callee && merge_use != node &&
        merge_use != checkpoint) {
      return false;
    }
  }
 
  // The effect phi must be only used by the checkpoint or the call.
  for (Node* effect_phi_use : effect_phi->uses()) {
    if (effect_phi_use != node && effect_phi_use != checkpoint) return false;
  }
 
  // We must replace the callee phi with the appropriate constant in
  // the entire subgraph reachable by inputs from the call (terminating
  // at phis and merges). Since we do not want to walk (and later duplicate)
  // the subgraph here, we limit the possible uses to this set:
  //
  // 1. In the call (as a target).
  // 2. The checkpoint between the call and the callee computation merge.
  // 3. The lazy deoptimization frame state.
  //
  // This corresponds to the most common pattern, where the function is
  // called with only local variables or constants as arguments.
  //
  // To check the uses, we first collect all the occurrences of callee in 1, 2
  // and 3, and then we check that all uses of callee are in the collected
  // occurrences. If there is an unaccounted use, we do not try to rewire
  // the control flow.
  //
  // Note: With CFG, this would be much easier and more robust - we would just
  // duplicate all the nodes between the merge and the call, replacing all
  // occurrences of the {callee} phi with the appropriate constant.
 
  // First compute the set of uses that are only reachable from 2 and 3.
  const size_t kMaxUses = 8;
  NodeAndIndex replaceable_uses[kMaxUses];
  size_t replaceable_uses_count = 0;
 
  // Collect the uses to check case 2.
  Node* checkpoint_state = nullptr;
  if (checkpoint) {
    checkpoint_state = checkpoint->InputAt(0);
    if (!CollectFrameStateUniqueUses(callee, FrameState{checkpoint_state},
                                     replaceable_uses, &replaceable_uses_count,
                                     kMaxUses)) {
      return false;
    }
  }
 
  // Collect the uses to check case 3.
  FrameState frame_state{NodeProperties::GetFrameStateInput(node)};
  if (!CollectFrameStateUniqueUses(callee, frame_state, replaceable_uses,
                                   &replaceable_uses_count, kMaxUses)) {
    return false;
  }
 
  // Bail out if there is a use of {callee} that is not reachable from 1, 2
  // and 3.
  for (Edge edge : callee->use_edges()) {
    // Case 1 (use by the call as a target).
    if (edge.from() == node && edge.index() == 0) continue;
    // Case 2 and 3 - used in checkpoint and/or lazy deopt frame states.
    bool found = false;
    for (size_t i = 0; i < replaceable_uses_count; i++) {
      if (replaceable_uses[i].node == edge.from() &&
          replaceable_uses[i].index == edge.index()) {
        found = true;
        break;
      }
    }
    if (!found) return false;
  }
 
  *num_calls = callee->op()->ValueInputCount();
 
  // Clone the call and the framestate, including the uniquely reachable
  // state values, making sure that we replace the phi with the constant.
  for (int i = 0; i < *num_calls; ++i) {
    // Clone the calls for each branch.
    // We need to specialize the calls to the correct target, effect, and
    // control. We also need to duplicate the checkpoint and the lazy
    // frame state, and change all the uses of the callee to the constant
    // callee.
    Node* target = callee->InputAt(i);
    Node* effect_phi_effect = effect_phi->InputAt(i);
    Node* control = merge->InputAt(i);
 
    if (checkpoint) {
      // Duplicate the checkpoint.
      FrameState new_checkpoint_state = DuplicateFrameStateAndRename(
          FrameState{checkpoint_state}, callee, target,
          (i == *num_calls - 1) ? kChangeInPlace : kCloneState);
      effect_phi_effect = graph()->NewNode(
          checkpoint->op(), new_checkpoint_state, effect_phi_effect, control);
    }
 
    // Duplicate the call.
    FrameState new_lazy_frame_state = DuplicateFrameStateAndRename(
        frame_state, callee, target,
        (i == *num_calls - 1) ? kChangeInPlace : kCloneState);
    inputs[0] = target;
    inputs[input_count - 3] = new_lazy_frame_state;
    inputs[input_count - 2] = effect_phi_effect;
    inputs[input_count - 1] = control;
    calls[i] = if_successes[i] =
        graph()->NewNode(node->op(), input_count, inputs);
  }
 
  // Mark the control inputs dead, so that we can kill the merge.
  node->ReplaceInput(input_count - 1, jsgraph()->Dead());
  callee->ReplaceInput(*num_calls, jsgraph()->Dead());
  effect_phi->ReplaceInput(*num_calls, jsgraph()->Dead());
  if (checkpoint) {
    checkpoint->ReplaceInput(2, jsgraph()->Dead());
  }
 
  merge->Kill();
  return true;
}
 
void JSInliningHeuristic::CreateOrReuseDispatch(
    Node* node, Node* callee, Candidate const& candidate, Node** if_successes,
    Node** calls, Node** inputs, int input_count, int* num_calls) {
  SourcePositionTable::Scope position(
      source_positions_, source_positions_->GetSourcePosition(node));
  if (TryReuseDispatch(node, callee, if_successes, calls, inputs, input_count,
                       num_calls)) {
    return;
  }
 
  static_assert(JSCallOrConstructNode::kHaveIdenticalLayouts);
 
  Node* fallthrough_control = NodeProperties::GetControlInput(node);
  *num_calls = candidate.num_functions;
 
  // Create the appropriate control flow to dispatch to the cloned calls.
  for (int i = 0; i < *num_calls; ++i) {
    // TODO(2206): Make comparison be based on underlying SharedFunctionInfo
    // instead of the target JSFunction reference directly.
    Node* target =
        jsgraph()->ConstantNoHole(candidate.functions[i].value(), broker());
    if (i != (*num_calls - 1)) {
      Node* check =
          graph()->NewNode(simplified()->ReferenceEqual(), callee, target);
      Node* branch =
          graph()->NewNode(common()->Branch(), check, fallthrough_control);
      fallthrough_control = graph()->NewNode(common()->IfFalse(), branch);
      if_successes[i] = graph()->NewNode(common()->IfTrue(), branch);
    } else {
      if_successes[i] = fallthrough_control;
    }
 
    // Clone the calls for each branch.
    // The first input to the call is the actual target (which we specialize
    // to the known {target}); the last input is the control dependency.
    // We also specialize the new.target of JSConstruct {node}s if it refers
    // to the same node as the {node}'s target input, so that we can later
    // properly inline the JSCreate operations.
    if (node->opcode() == IrOpcode::kJSConstruct) {
      // TODO(jgruber, v8:10675): This branch seems unreachable.
      JSConstructNode n(node);
      if (inputs[n.TargetIndex()] == inputs[n.NewTargetIndex()]) {
        inputs[n.NewTargetIndex()] = target;
      }
    }
    inputs[JSCallOrConstructNode::TargetIndex()] = target;
    inputs[input_count - 1] = if_successes[i];
    calls[i] = if_successes[i] =
        graph()->NewNode(node->op(), input_count, inputs);
  }
}
 
Reduction JSInliningHeuristic::InlineCandidate(Candidate const& candidate,
                                               bool small_function) {
  int num_calls = candidate.num_functions;
  Node* const node = candidate.node;
#if V8_ENABLE_WEBASSEMBLY
  DCHECK_NE(node->opcode(), IrOpcode::kJSWasmCall);
#endif  // V8_ENABLE_WEBASSEMBLY
  if (num_calls == 1) {
    Reduction const reduction = inliner_.ReduceJSCall(node);
    if (reduction.Changed()) {
      total_inlined_bytecode_size_ += candidate.bytecode[0].value().length();
    }
    return reduction;
  }
 
  // Expand the JSCall/JSConstruct node to a subgraph first if
  // we have multiple known target functions.
  DCHECK_LT(1, num_calls);
  Node* calls[kMaxCallPolymorphism + 1];
  Node* if_successes[kMaxCallPolymorphism];
  Node* callee = NodeProperties::GetValueInput(node, 0);
 
  // Setup the inputs for the cloned call nodes.
  int const input_count = node->InputCount();
  Node** inputs = graph()->zone()->AllocateArray<Node*>(input_count);
  for (int i = 0; i < input_count; ++i) {
    inputs[i] = node->InputAt(i);
  }
 
  // Create the appropriate control flow to dispatch to the cloned calls.
  CreateOrReuseDispatch(node, callee, candidate, if_successes, calls, inputs,
                        input_count, &num_calls);
 
  // Check if we have an exception projection for the call {node}.
  Node* if_exception = nullptr;
  if (NodeProperties::IsExceptionalCall(node, &if_exception)) {
    Node* if_exceptions[kMaxCallPolymorphism + 1];
    for (int i = 0; i < num_calls; ++i) {
      if_successes[i] = graph()->NewNode(common()->IfSuccess(), calls[i]);
      if_exceptions[i] =
          graph()->NewNode(common()->IfException(), calls[i], calls[i]);
    }
 
    // Morph the {if_exception} projection into a join.
    Node* exception_control =
        graph()->NewNode(common()->Merge(num_calls), num_calls, if_exceptions);
    if_exceptions[num_calls] = exception_control;
    Node* exception_effect = graph()->NewNode(common()->EffectPhi(num_calls),
                                              num_calls + 1, if_exceptions);
    Node* exception_value = graph()->NewNode(
        common()->Phi(MachineRepresentation::kTagged, num_calls), num_calls + 1,
        if_exceptions);
    ReplaceWithValue(if_exception, exception_value, exception_effect,
                     exception_control);
  }
 
  // Morph the original call site into a join of the dispatched call sites.
  Node* control =
      graph()->NewNode(common()->Merge(num_calls), num_calls, if_successes);
  calls[num_calls] = control;
  Node* effect =
      graph()->NewNode(common()->EffectPhi(num_calls), num_calls + 1, calls);
  Node* value =
      graph()->NewNode(common()->Phi(MachineRepresentation::kTagged, num_calls),
                       num_calls + 1, calls);
  ReplaceWithValue(node, value, effect, control);
 
  // Inline the individual, cloned call sites.
  for (int i = 0; i < num_calls && total_inlined_bytecode_size_ <
                                       max_inlined_bytecode_size_absolute_;
       ++i) {
    if (candidate.can_inline_function[i] &&
        (small_function || total_inlined_bytecode_size_ <
                               max_inlined_bytecode_size_cumulative_)) {
      Node* call = calls[i];
      Reduction const reduction = inliner_.ReduceJSCall(call);
      if (reduction.Changed()) {
        total_inlined_bytecode_size_ += candidate.bytecode[i]->length();
        // Killing the call node is not strictly necessary, but it is safer to
        // make sure we do not resurrect the node.
        call->Kill();
      }
    }
  }
 
  return Replace(value);
}
 
bool JSInliningHeuristic::CandidateCompare::operator()(
    const Candidate& left, const Candidate& right) const {
  constexpr bool kInlineLeftFirst = true, kInlineRightFirst = false;
  if (right.frequency.IsUnknown()) {
    if (left.frequency.IsUnknown()) {
      // If left and right are both unknown then the ordering is indeterminate,
      // which breaks strict weak ordering requirements, so we fall back to the
      // node id as a tie breaker.
      if (left.total_size < right.total_size) {
        return kInlineLeftFirst;
      } else if (left.total_size > right.total_size) {
        return kInlineRightFirst;
      } else {
        return left.node->id() > right.node->id();
      }
    } else {
      return kInlineLeftFirst;
    }
  } else if (left.frequency.IsUnknown()) {
    return kInlineRightFirst;
  }
 
  float left_score = left.frequency.value() / left.total_size;
  float right_score = right.frequency.value() / right.total_size;
 
  if (left_score > right_score) {
    return kInlineLeftFirst;
  } else if (left_score < right_score) {
    return kInlineRightFirst;
  } else {
    return left.node->id() > right.node->id();
  }
}
 
void JSInliningHeuristic::PrintCandidates() {
  StdoutStream os;
  os << candidates_.size() << " candidate(s) for inlining:" << std::endl;
  for (const Candidate& candidate : candidates_) {
    os << "- candidate: " << candidate.node->op()->mnemonic() << " node #"
       << candidate.node->id() << " with frequency " << candidate.frequency
       << ", " << candidate.num_functions << " target(s):" << std::endl;
    for (int i = 0; i < candidate.num_functions; ++i) {
      SharedFunctionInfoRef shared =
          candidate.functions[i].has_value()
              ? candidate.functions[i]->shared(broker())
              : candidate.shared_info.value();
      os << "  - target: " << shared;
      if (candidate.bytecode[i].has_value()) {
        os << ", bytecode size: " << candidate.bytecode[i]->length();
        if (OptionalJSFunctionRef function = candidate.functions[i]) {
          if (OptionalCodeRef code = function->code(broker())) {
            unsigned inlined_bytecode_size = code->GetInlinedBytecodeSize();
            if (inlined_bytecode_size > 0) {
              os << ", existing opt code's inlined bytecode size: "
                 << inlined_bytecode_size;
            }
          }
        }
      } else {
        os << ", no bytecode";
      }
      os << std::endl;
    }
  }
}
 
TFGraph* JSInliningHeuristic::graph() const { return jsgraph()->graph(); }
 
CompilationDependencies* JSInliningHeuristic::dependencies() const {
  return broker()->dependencies();
}
 
CommonOperatorBuilder* JSInliningHeuristic::common() const {
  return jsgraph()->common();
}
 
SimplifiedOperatorBuilder* JSInliningHeuristic::simplified() const {
  return jsgraph()->simplified();
}
 
#undef TRACE
 
}  // namespace compiler
}  // namespace internal
}  // namespace v8