[turbofan] NodeMarker in ControlReducer.
R=mstarzinger@chromium.org BUG= Review URL: https://codereview.chromium.org/767743003 Cr-Commit-Position: refs/heads/master@{#25583}
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@ -15,9 +15,32 @@ namespace internal {
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namespace compiler {
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enum VisitState { kUnvisited = 0, kOnStack = 1, kRevisit = 2, kVisited = 3 };
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enum Reachability { kFromStart = 8 };
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enum Decision { kFalse, kUnknown, kTrue };
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class ReachabilityMarker : public NodeMarker<uint8_t> {
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public:
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explicit ReachabilityMarker(Graph* graph) : NodeMarker<uint8_t>(graph, 8) {}
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bool SetReachableFromEnd(Node* node) {
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uint8_t before = Get(node);
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Set(node, before | kFromEnd);
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return before & kFromEnd;
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}
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bool IsReachableFromEnd(Node* node) { return Get(node) & kFromEnd; }
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bool SetReachableFromStart(Node* node) {
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uint8_t before = Get(node);
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Set(node, before | kFromStart);
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return before & kFromStart;
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}
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bool IsReachableFromStart(Node* node) { return Get(node) & kFromStart; }
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void Push(Node* node) { Set(node, Get(node) | kFwStack); }
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void Pop(Node* node) { Set(node, Get(node) & ~kFwStack); }
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bool IsOnStack(Node* node) { return Get(node) & kFwStack; }
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private:
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enum Bit { kFromEnd = 1, kFromStart = 2, kFwStack = 4 };
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};
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#define TRACE(x) \
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if (FLAG_trace_turbo_reduction) PrintF x
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@ -72,15 +95,15 @@ class ControlReducerImpl {
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// we have to be careful about proper loop detection during reduction.
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// Gather all nodes backwards-reachable from end (through inputs).
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state_.assign(graph()->NodeCount(), kUnvisited);
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ReachabilityMarker marked(graph());
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NodeVector nodes(zone_);
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AddNodesReachableFromEnd(nodes);
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AddNodesReachableFromEnd(marked, nodes);
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// Walk forward through control nodes, looking for back edges to nodes
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// that are not connected to end. Those are non-terminating loops (NTLs).
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Node* start = graph()->start();
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ZoneVector<byte> fw_reachability(graph()->NodeCount(), 0, zone_);
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fw_reachability[start->id()] = kFromStart | kOnStack;
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marked.Push(start);
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marked.SetReachableFromStart(start);
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// We use a stack of (Node, UseIter) pairs to avoid O(n^2) traversal.
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typedef std::pair<Node*, UseIter> FwIter;
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@ -93,20 +116,23 @@ class ControlReducerImpl {
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bool pop = true;
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while (fw_stack.back().second != node->uses().end()) {
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Node* succ = *(fw_stack.back().second);
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byte reach = fw_reachability[succ->id()];
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if ((reach & kOnStack) != 0 && state_[succ->id()] != kVisited) {
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if (marked.IsOnStack(succ) && !marked.IsReachableFromEnd(succ)) {
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// {succ} is on stack and not reachable from end.
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ConnectNTL(nodes, succ);
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fw_reachability.resize(graph()->NodeCount(), 0);
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Node* added = ConnectNTL(succ);
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nodes.push_back(added);
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marked.SetReachableFromEnd(added);
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AddBackwardsReachableNodes(marked, nodes, nodes.size() - 1);
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// The use list of {succ} might have changed.
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fw_stack[fw_stack.size() - 1] = FwIter(succ, succ->uses().begin());
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pop = false; // restart traversing successors of this node.
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break;
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}
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if ((reach & kFromStart) == 0 &&
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IrOpcode::IsControlOpcode(succ->opcode())) {
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if (IrOpcode::IsControlOpcode(succ->opcode()) &&
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!marked.IsReachableFromStart(succ)) {
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// {succ} is a control node and not yet reached from start.
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fw_reachability[succ->id()] |= kFromStart | kOnStack;
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marked.Push(succ);
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marked.SetReachableFromStart(succ);
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fw_stack.push_back(FwIter(succ, succ->uses().begin()));
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pop = false; // "recurse" into successor control node.
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break;
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@ -114,21 +140,20 @@ class ControlReducerImpl {
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++fw_stack.back().second;
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}
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if (pop) {
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fw_reachability[node->id()] &= ~kOnStack;
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marked.Pop(node);
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fw_stack.pop_back();
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}
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}
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// Trim references from dead nodes to live nodes first.
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jsgraph_->GetCachedNodes(&nodes);
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TrimNodes(nodes);
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TrimNodes(marked, nodes);
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// Any control nodes not reachable from start are dead, even loops.
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for (size_t i = 0; i < nodes.size(); i++) {
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Node* node = nodes[i];
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byte reach = fw_reachability[node->id()];
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if ((reach & kFromStart) == 0 &&
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IrOpcode::IsControlOpcode(node->opcode())) {
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if (IrOpcode::IsControlOpcode(node->opcode()) &&
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!marked.IsReachableFromStart(node)) {
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ReplaceNode(node, dead()); // uses will be added to revisit queue.
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}
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}
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@ -136,7 +161,7 @@ class ControlReducerImpl {
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}
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// Connect {loop}, the header of a non-terminating loop, to the end node.
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void ConnectNTL(NodeVector& nodes, Node* loop) {
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Node* ConnectNTL(Node* loop) {
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TRACE(("ConnectNTL: #%d:%s\n", loop->id(), loop->op()->mnemonic()));
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if (loop->opcode() != IrOpcode::kTerminate) {
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@ -173,27 +198,24 @@ class ControlReducerImpl {
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merge->AppendInput(graph()->zone(), loop);
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merge->set_op(common_->Merge(merge->InputCount()));
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}
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nodes.push_back(to_add);
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state_.resize(graph()->NodeCount(), kUnvisited);
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state_[to_add->id()] = kVisited;
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AddBackwardsReachableNodes(nodes, nodes.size() - 1);
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return to_add;
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}
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void AddNodesReachableFromEnd(NodeVector& nodes) {
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void AddNodesReachableFromEnd(ReachabilityMarker& marked, NodeVector& nodes) {
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Node* end = graph()->end();
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state_[end->id()] = kVisited;
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marked.SetReachableFromEnd(end);
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if (!end->IsDead()) {
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nodes.push_back(end);
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AddBackwardsReachableNodes(nodes, nodes.size() - 1);
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AddBackwardsReachableNodes(marked, nodes, nodes.size() - 1);
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}
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}
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void AddBackwardsReachableNodes(NodeVector& nodes, size_t cursor) {
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void AddBackwardsReachableNodes(ReachabilityMarker& marked, NodeVector& nodes,
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size_t cursor) {
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while (cursor < nodes.size()) {
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Node* node = nodes[cursor++];
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for (Node* const input : node->inputs()) {
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if (state_[input->id()] != kVisited) {
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state_[input->id()] = kVisited;
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if (!marked.SetReachableFromEnd(input)) {
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nodes.push_back(input);
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}
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}
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@ -202,22 +224,21 @@ class ControlReducerImpl {
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void Trim() {
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// Gather all nodes backwards-reachable from end through inputs.
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state_.assign(graph()->NodeCount(), kUnvisited);
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ReachabilityMarker marked(graph());
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NodeVector nodes(zone_);
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AddNodesReachableFromEnd(nodes);
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AddNodesReachableFromEnd(marked, nodes);
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// Process cached nodes in the JSGraph too.
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jsgraph_->GetCachedNodes(&nodes);
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TrimNodes(nodes);
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TrimNodes(marked, nodes);
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}
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void TrimNodes(NodeVector& nodes) {
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void TrimNodes(ReachabilityMarker& marked, NodeVector& nodes) {
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// Remove dead->live edges.
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for (size_t j = 0; j < nodes.size(); j++) {
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Node* node = nodes[j];
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for (UseIter i = node->uses().begin(); i != node->uses().end();) {
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size_t id = static_cast<size_t>((*i)->id());
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if (state_[id] != kVisited) {
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if (!marked.IsReachableFromEnd(*i)) {
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TRACE(("DeadLink: #%d:%s(%d) -> #%d:%s\n", (*i)->id(),
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(*i)->op()->mnemonic(), i.index(), node->id(),
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node->op()->mnemonic()));
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@ -235,8 +256,7 @@ class ControlReducerImpl {
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CHECK_NE(NULL, input);
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}
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for (Node* const use : node->uses()) {
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size_t id = static_cast<size_t>(use->id());
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CHECK_EQ(kVisited, state_[id]);
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CHECK(marked.IsReachableFromEnd(use));
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}
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}
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#endif
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@ -519,7 +539,6 @@ void ControlReducer::ReduceGraph(Zone* zone, JSGraph* jsgraph,
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CommonOperatorBuilder* common) {
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ControlReducerImpl impl(zone, jsgraph, common);
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impl.Reduce();
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impl.Trim();
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}
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