[turbofan] Introduce BranchMatcher and DiamondMatcher helpers.

src/compiler/node-matchers.cc

Index: src/compiler/node-matchers.cc
diff --git a/src/compiler/node-matchers.cc b/src/compiler/node-matchers.cc
index c6ae39000c025ae98f6f1b8a0ad67faf148c185e..e7b5d1b97fedc801d88987b6d748f52796be4ea7 100644
--- a/src/compiler/node-matchers.cc
+++ b/src/compiler/node-matchers.cc
@@ -12,6 +12,50 @@ bool NodeMatcher::IsComparison() const {
   return IrOpcode::IsComparisonOpcode(opcode());
 }
 
+
+BranchMatcher::BranchMatcher(Node* branch)
+    : NodeMatcher(branch), if_true_(nullptr), if_false_(nullptr) {
+  if (branch->opcode() != IrOpcode::kBranch) return;
+  for (Node* use : branch->uses()) {
+    if (use->opcode() == IrOpcode::kIfTrue) {
+      DCHECK_NULL(if_true_);
+      if_true_ = use;
+    } else if (use->opcode() == IrOpcode::kIfFalse) {
+      DCHECK_NULL(if_false_);
+      if_false_ = use;
+    }
+  }
+}
+
+
+DiamondMatcher::DiamondMatcher(Node* merge)
+    : NodeMatcher(merge),
+      branch_(nullptr),
+      if_true_(nullptr),
+      if_false_(nullptr) {
+  if (merge->InputCount() != 2) return;
+  if (merge->opcode() != IrOpcode::kMerge) return;
+  Node* input0 = merge->InputAt(0);
+  if (input0->InputCount() != 1) return;
+  Node* input1 = merge->InputAt(1);
+  if (input1->InputCount() != 1) return;
+  Node* branch = input0->InputAt(0);
+  if (branch != input1->InputAt(0)) return;
+  if (branch->opcode() != IrOpcode::kBranch) return;
+  if (input0->opcode() == IrOpcode::kIfTrue &&
+      input1->opcode() == IrOpcode::kIfFalse) {
+    branch_ = branch;
+    if_true_ = input0;
+    if_false_ = input1;
+  }
+  if (input0->opcode() == IrOpcode::kIfFalse &&

[Benedikt Meurer, 2015/04/07 07:19:01]

Nit: Use else if.

[titzer, 2015/04/07 08:41:00]

Done.

+      input1->opcode() == IrOpcode::kIfTrue) {
+    branch_ = branch;
+    if_true_ = input1;
+    if_false_ = input0;
+  }
+}
+
 }  // namespace compiler
 }  // namespace internal
 }  // namespace v8