[turbofan] Introduce BranchMatcher and DiamondMatcher helpers.

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/js-graph.h"
@@ skipping 33 matching lines @@
 }
 
 
 Reduction CommonOperatorReducer::ReducePhi(Node* node) {
   DCHECK_EQ(IrOpcode::kPhi, node->opcode());
   int const input_count = node->InputCount();
   if (input_count == 3) {
     Node* vtrue = NodeProperties::GetValueInput(node, 0);
     Node* vfalse = NodeProperties::GetValueInput(node, 1);
     Node* merge = NodeProperties::GetControlInput(node);
-    Node* if_true = NodeProperties::GetControlInput(merge, 0);
-    Node* if_false = NodeProperties::GetControlInput(merge, 1);
-    if (if_true->opcode() != IrOpcode::kIfTrue) {
-      std::swap(if_true, if_false);
-      std::swap(vtrue, vfalse);
-    }
-    if (if_true->opcode() == IrOpcode::kIfTrue &&
-        if_false->opcode() == IrOpcode::kIfFalse &&
-        if_true->InputAt(0) == if_false->InputAt(0)) {
-      Node* branch = if_true->InputAt(0);
-      Node* cond = branch->InputAt(0);
+    DiamondMatcher matcher(merge);
+    if (matcher.Matched()) {
+      if (matcher.IfTrue() == merge->InputAt(1)) std::swap(vtrue, vfalse);
+      Node* cond = matcher.Branch()->InputAt(0);
       if (cond->opcode() == IrOpcode::kFloat64LessThan) {
         if (cond->InputAt(0) == vtrue && cond->InputAt(1) == vfalse &&
             machine()->HasFloat64Min()) {
           node->set_op(machine()->Float64Min());
           node->ReplaceInput(0, vtrue);
           node->ReplaceInput(1, vfalse);
           node->TrimInputCount(2);
           return Changed(node);
         } else if (cond->InputAt(0) == vfalse && cond->InputAt(1) == vtrue &&
                    machine()->HasFloat64Max()) {
@@ skipping 52 matching lines @@
 Graph* CommonOperatorReducer::graph() const { return jsgraph()->graph(); }
 
 
 MachineOperatorBuilder* CommonOperatorReducer::machine() const {
   return jsgraph()->machine();
 }
 
 }  // namespace compiler
 }  // namespace internal
 }  // namespace v8