[turbofan] Add support for pushing returns into merges.

src/compiler/common-operator-reducer.cc

 // Copyright 2014 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/common-operator-reducer.h"
 
 #include <algorithm>
 
 #include "src/compiler/common-operator.h"
 #include "src/compiler/graph.h"
 #include "src/compiler/machine-operator.h"
 #include "src/compiler/node.h"
 #include "src/compiler/node-matchers.h"
+#include "src/compiler/node-properties.h"
 
 namespace v8 {
 namespace internal {
 namespace compiler {
 
 namespace {
 
 enum class Decision { kUnknown, kTrue, kFalse };
 
 Decision DecideCondition(Node* const cond) {
@@ skipping 12 matching lines @@
                                                     : Decision::kFalse;
     }
     default:
       return Decision::kUnknown;
   }
 }
 
 }  // namespace
 
 
+CommonOperatorReducer::CommonOperatorReducer(Editor* editor, Graph* graph,
+                                             CommonOperatorBuilder* common,
+                                             MachineOperatorBuilder* machine)
+    : AdvancedReducer(editor),
+      graph_(graph),
+      common_(common),
+      machine_(machine),
+      dead_(graph->NewNode(common->Dead())) {}
+
+
 Reduction CommonOperatorReducer::Reduce(Node* node) {
   switch (node->opcode()) {
     case IrOpcode::kBranch:
       return ReduceBranch(node);
     case IrOpcode::kMerge:
       return ReduceMerge(node);
     case IrOpcode::kEffectPhi:
       return ReduceEffectPhi(node);
     case IrOpcode::kPhi:
       return ReducePhi(node);
+    case IrOpcode::kReturn:
+      return ReduceReturn(node);
     case IrOpcode::kSelect:
       return ReduceSelect(node);
     default:
       break;
   }
   return NoChange();
 }
 
 
 Reduction CommonOperatorReducer::ReduceBranch(Node* node) {
@@ skipping 18 matching lines @@
     }
     // Update the condition of {branch}. No need to mark the uses for revisit,
     // since we tell the graph reducer that the {branch} was changed and the
     // graph reduction logic will ensure that the uses are revisited properly.
     node->ReplaceInput(0, cond->InputAt(0));
     return Changed(node);
   }
   Decision const decision = DecideCondition(cond);
   if (decision == Decision::kUnknown) return NoChange();
   Node* const control = node->InputAt(1);
-  if (!dead_.is_set()) dead_.set(graph()->NewNode(common()->Dead()));
   for (Node* const use : node->uses()) {
     switch (use->opcode()) {
       case IrOpcode::kIfTrue:
-        Replace(use, (decision == Decision::kTrue) ? control : dead_.get());
+        Replace(use, (decision == Decision::kTrue) ? control : dead());
         break;
       case IrOpcode::kIfFalse:
-        Replace(use, (decision == Decision::kFalse) ? control : dead_.get());
+        Replace(use, (decision == Decision::kFalse) ? control : dead());
         break;
       default:
         UNREACHABLE();
     }
   }
-  return Replace(dead_.get());
+  return Replace(dead());
 }
 
 
 Reduction CommonOperatorReducer::ReduceMerge(Node* node) {
   DCHECK_EQ(IrOpcode::kMerge, node->opcode());
   //
   // Check if this is a merge that belongs to an unused diamond, which means
   // that:
   //
   //  a) the {Merge} has no {Phi} or {EffectPhi} uses, and
@@ skipping 128 matching lines @@
       continue;
     }
     if (input != value) return NoChange();
   }
   // We might now be able to further reduce the {merge} node.
   Revisit(merge);
   return Replace(value);
 }
 
 
+Reduction CommonOperatorReducer::ReduceReturn(Node* node) {
+  DCHECK_EQ(IrOpcode::kReturn, node->opcode());
+  Node* const value = node->InputAt(0);
+  Node* const effect = node->InputAt(1);
+  Node* const control = node->InputAt(2);
+  if (value->opcode() == IrOpcode::kPhi &&
+      NodeProperties::GetControlInput(value) == control &&
+      effect->opcode() == IrOpcode::kEffectPhi &&
+      NodeProperties::GetControlInput(effect) == control &&
+      control->opcode() == IrOpcode::kMerge) {
+    int const control_input_count = control->InputCount();
+    DCHECK_NE(0, control_input_count);
+    DCHECK_EQ(control_input_count, value->InputCount() - 1);
+    DCHECK_EQ(control_input_count, effect->InputCount() - 1);
+    Node* const end = graph()->end();
+    DCHECK_EQ(IrOpcode::kEnd, end->opcode());
+    DCHECK_NE(0, end->InputCount());
+    for (int i = 0; i < control_input_count; ++i) {
+      // Create a new {Return} and connect it to {end}. We don't need to mark
+      // {end} as revisit, because we mark {node} as {Dead} below, which was
+      // previously connected to {end}, so we know for sure that at some point
+      // the reducer logic will visit {end} again.
+      Node* ret = graph()->NewNode(common()->Return(), value->InputAt(i),
+                                   effect->InputAt(i), control->InputAt(i));
+      end->set_op(common()->End(end->InputCount() + 1));
+      end->AppendInput(graph()->zone(), ret);
+    }
+    // Mark the merge {control} and return {node} as {dead}.
+    Replace(control, dead());
+    return Replace(dead());
+  }
+  return NoChange();
+}
+
+
 Reduction CommonOperatorReducer::ReduceSelect(Node* node) {
   DCHECK_EQ(IrOpcode::kSelect, node->opcode());
   Node* const cond = node->InputAt(0);
   Node* const vtrue = node->InputAt(1);
   Node* const vfalse = node->InputAt(2);
   if (vtrue == vfalse) return Replace(vtrue);
   switch (DecideCondition(cond)) {
     case Decision::kTrue:
       return Replace(vtrue);
     case Decision::kFalse:
@@ skipping 59 matching lines @@
   node->set_op(op);
   node->ReplaceInput(0, a);
   node->ReplaceInput(1, b);
   node->TrimInputCount(2);
   return Changed(node);
 }
 
 }  // namespace compiler
 }  // namespace internal
 }  // namespace v8