[turbofan] Introduce NumberFloor simplified operator.

src/compiler/js-builtin-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/js-builtin-reducer.h"
 #include "src/compiler/js-graph.h"
 #include "src/compiler/node-matchers.h"
 #include "src/compiler/node-properties.h"
 #include "src/compiler/simplified-operator.h"
 #include "src/objects-inl.h"
@@ skipping 114 matching lines @@
     // Math.imul(a:int32, b:int32) -> Int32Mul(a, b)
     Node* value = graph()->NewNode(machine()->Int32Mul(), r.left(), r.right());
     return Replace(value);
   }
   return NoChange();
 }
 
 // ES6 draft 08-24-14, section 20.2.2.16.
 Reduction JSBuiltinReducer::ReduceMathFloor(Node* node) {
   JSCallReduction r(node);
-  if (r.InputsMatchOne(Type::Number()) &&
-      machine()->Float64RoundDown().IsSupported()) {
-    // Math.floor(a:number) -> Float64RoundDown(a)
-    Node* value =
-        graph()->NewNode(machine()->Float64RoundDown().op(), r.left());
+  if (r.InputsMatchOne(Type::Number())) {
+    // Math.floor(a:number) -> NumberFloor(a)
+    Node* value = graph()->NewNode(simplified()->NumberFloor(), r.left());
     return Replace(value);
   }
   return NoChange();
 }
 
 // ES6 draft 08-24-14, section 20.2.2.17.
 Reduction JSBuiltinReducer::ReduceMathFround(Node* node) {
   JSCallReduction r(node);
   if (r.InputsMatchOne(Type::Number())) {
     // Math.fround(a:number) -> TruncateFloat64ToFloat32(a)
@@ skipping 94 matching lines @@
 }
 
 
 SimplifiedOperatorBuilder* JSBuiltinReducer::simplified() const {
   return jsgraph()->simplified();
 }
 
 }  // namespace compiler
 }  // namespace internal
 }  // namespace v8