[turbofan] Optimize ReferenceEqual based on input types.

We can constant-fold ReferenceEqual(a,b) to false, if the intersection
of the types of a and b is empty. This also repairs a regression in the
RestParameter performance test.

R=petermarshall@chromium.org
BUG=chromium:686668

Review-Url: https://codereview.chromium.org/2666543002
Cr-Commit-Position: refs/heads/master@{#42775}

src/compiler/typed-optimization.cc

@@ -92,6 +92,8 @@ Reduction TypedOptimization::Reduce(Node* node) {
       return ReduceNumberToUint8Clamped(node);
     case IrOpcode::kPhi:
       return ReducePhi(node);
+    case IrOpcode::kReferenceEqual:
+      return ReduceReferenceEqual(node);
     case IrOpcode::kSelect:
       return ReduceSelect(node);
     default:
@@ -258,6 +260,18 @@ Reduction TypedOptimization::ReducePhi(Node* node) {
   return NoChange();
 }
 
+Reduction TypedOptimization::ReduceReferenceEqual(Node* node) {
+  DCHECK_EQ(IrOpcode::kReferenceEqual, node->opcode());
+  Node* const lhs = NodeProperties::GetValueInput(node, 0);
+  Node* const rhs = NodeProperties::GetValueInput(node, 1);
+  Type* const lhs_type = NodeProperties::GetType(lhs);
+  Type* const rhs_type = NodeProperties::GetType(rhs);
+  if (!lhs_type->Maybe(rhs_type)) {
+    return Replace(jsgraph()->FalseConstant());
+  }
+  return NoChange();
+}
+
 Reduction TypedOptimization::ReduceSelect(Node* node) {
   DCHECK_EQ(IrOpcode::kSelect, node->opcode());
   Node* const condition = NodeProperties::GetValueInput(node, 0);

src/compiler/typed-optimization.h

@@ -50,6 +50,7 @@ class V8_EXPORT_PRIVATE TypedOptimization final
   Reduction ReduceNumberRoundop(Node* node);
   Reduction ReduceNumberToUint8Clamped(Node* node);
   Reduction ReducePhi(Node* node);
+  Reduction ReduceReferenceEqual(Node* node);
   Reduction ReduceSelect(Node* node);
 
   CompilationDependencies* dependencies() const { return dependencies_; }