[builtins] Introduce proper Float64Exp operator.

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 363ad9db4e8ed946858ce5b89c70338c9b9bdf67..84c07dc9d5926473ec657e84e3ebeba2be79dd66 100644
--- a/src/compiler/js-builtin-reducer.cc
+++ b/src/compiler/js-builtin-reducer.cc
@@ -142,6 +142,18 @@ Reduction JSBuiltinReducer::ReduceMathClz32(Node* node) {
   return NoChange();
 }
 
+// ES6 section 20.2.2.14 Math.exp ( x )
+Reduction JSBuiltinReducer::ReduceMathExp(Node* node) {
+  JSCallReduction r(node);
+  if (r.InputsMatchOne(Type::PlainPrimitive())) {
+    // Math.exp(a:plain-primitive) -> NumberExp(ToNumber(a))
+    Node* input = ToNumber(r.GetJSCallInput(0));
+    Node* value = graph()->NewNode(simplified()->NumberExp(), input);
+    return Replace(value);
+  }
+  return NoChange();
+}
+
 // ES6 section 20.2.2.16 Math.floor ( x )
 Reduction JSBuiltinReducer::ReduceMathFloor(Node* node) {
   JSCallReduction r(node);
@@ -348,6 +360,9 @@ Reduction JSBuiltinReducer::Reduce(Node* node) {
     case kMathCeil:
       reduction = ReduceMathCeil(node);
       break;
+    case kMathExp:
+      reduction = ReduceMathExp(node);
+      break;
     case kMathFloor:
       reduction = ReduceMathFloor(node);
       break;