[turbofan] Optimize BooleanNot conditions to Branch nodes.

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"
@@ skipping 47 matching lines @@
     default:
       break;
   }
   return NoChange();
 }
 
 
 Reduction CommonOperatorReducer::ReduceBranch(Node* node) {
   DCHECK_EQ(IrOpcode::kBranch, node->opcode());
   Node* const cond = node->InputAt(0);
+  // Swap IfTrue/IfFalse on {branch} if {cond} is a BooleanNot and use the input
+  // to BooleanNot as new condition for {branch}. Note we assume that {cond} was
+  // already properly optimized before we get here (as guaranteed by the graph
+  // reduction logic).
+  if (cond->opcode() == IrOpcode::kBooleanNot) {
+    for (Node* const use : node->uses()) {
+      switch (use->opcode()) {
+        case IrOpcode::kIfTrue:
+          use->set_op(common()->IfFalse());
+          break;
+        case IrOpcode::kIfFalse:
+          use->set_op(common()->IfTrue());
+          break;
+        default:
+          UNREACHABLE();
+      }
+    }
+    // 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());
         break;
       case IrOpcode::kIfFalse:
@@ skipping 224 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