[turbofan] Finish support for holey double elements backing stores.

src/compiler/js-typed-lowering.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/code-factory.h"
 #include "src/compilation-dependencies.h"
 #include "src/compiler/access-builder.h"
 #include "src/compiler/js-graph.h"
 #include "src/compiler/js-typed-lowering.h"
 #include "src/compiler/linkage.h"
@@ skipping 729 matching lines @@
 }
 
 
 Reduction JSTypedLowering::ReduceJSToNumberInput(Node* input) {
   if (input->opcode() == IrOpcode::kJSToNumber) {
     // Recursively try to reduce the input first.
     Reduction result = ReduceJSToNumber(input);
     if (result.Changed()) return result;
     return Changed(input);  // JSToNumber(JSToNumber(x)) => JSToNumber(x)
   }
+  // Check for ToNumber truncation of signaling NaN to undefined mapping.
+  if (input->opcode() == IrOpcode::kSelect) {
+    Node* check = NodeProperties::GetValueInput(input, 0);
+    Node* vtrue = NodeProperties::GetValueInput(input, 1);
+    Type* vtrue_type = NodeProperties::GetType(vtrue);
+    Node* vfalse = NodeProperties::GetValueInput(input, 2);
+    Type* vfalse_type = NodeProperties::GetType(vfalse);
+    if (vtrue_type->Is(Type::Undefined()) && vfalse_type->Is(Type::Number())) {
+      if (check->opcode() == IrOpcode::kNumberIsHoleNaN &&
+          check->InputAt(0) == vfalse) {
+        // JSToNumber(Select(NumberIsHoleNaN(x), y:undefined, x:number)) => x
+        return Replace(vfalse);
+      }
+    }
+  }
   // Check if we have a cached conversion.
   Type* input_type = NodeProperties::GetType(input);
   if (input_type->Is(Type::Number())) {
     // JSToNumber(x:number) => x
     return Changed(input);
   }
   if (input_type->Is(Type::Undefined())) {
     // JSToNumber(undefined) => #NaN
     return Replace(jsgraph()->NaNConstant());
   }
@@ skipping 1608 matching lines @@
 }
 
 
 CompilationDependencies* JSTypedLowering::dependencies() const {
   return dependencies_;
 }
 
 }  // namespace compiler
 }  // namespace internal
 }  // namespace v8