[builtins] Migrate Math.clz32 to a TurboFan builtin.

src/compiler/js-builtin-reducer.cc

Index: src/compiler/js-builtin-reducer.cc
diff --git a/src/compiler/js-builtin-reducer.cc b/src/compiler/js-builtin-reducer.cc
index c7a2326254fcde55a150d552746b747c887152ef..b5caf9f1fe6ecc3824a487de3359f76bc038d6a4 100644
--- a/src/compiler/js-builtin-reducer.cc
+++ b/src/compiler/js-builtin-reducer.cc
@@ -129,7 +129,7 @@ Reduction JSBuiltinReducer::ReduceMathImul(Node* node) {
   return NoChange();
 }
 
-// ES6 draft 08-24-14, section 20.2.2.16.
+// ES6 section 20.2.2.10 Math.ceil ( x )
 Reduction JSBuiltinReducer::ReduceMathCeil(Node* node) {
   JSCallReduction r(node);
   if (r.InputsMatchOne(Type::Number())) {
@@ -140,6 +140,24 @@ Reduction JSBuiltinReducer::ReduceMathCeil(Node* node) {
   return NoChange();
 }
 
+// ES6 section 20.2.2.11 Math.clz32 ( x )
+Reduction JSBuiltinReducer::ReduceMathClz32(Node* node) {
+  JSCallReduction r(node);
+  if (r.InputsMatchOne(Type::Unsigned32())) {
+    // Math.clz32(a:unsigned32) -> NumberClz32(a)
+    Node* value = graph()->NewNode(simplified()->NumberClz32(), r.left());
+    return Replace(value);
+  }
+  if (r.InputsMatchOne(Type::Number())) {
+    // Math.clz32(a:number) -> NumberClz32(NumberToUint32(a))
+    Node* value = graph()->NewNode(
+        simplified()->NumberClz32(),
+        graph()->NewNode(simplified()->NumberToUint32(), r.left()));
+    return Replace(value);
+  }
+  return NoChange();
+}
+
 // ES6 draft 08-24-14, section 20.2.2.16.
 Reduction JSBuiltinReducer::ReduceMathFloor(Node* node) {
   JSCallReduction r(node);
@@ -209,6 +227,9 @@ Reduction JSBuiltinReducer::Reduce(Node* node) {
     case kMathImul:
       reduction = ReduceMathImul(node);
       break;
+    case kMathClz32:
+      reduction = ReduceMathClz32(node);
+      break;
     case kMathCeil:
       reduction = ReduceMathCeil(node);
       break;