[turbofan] Infer proper type for calls to Date.now.

Recognize Date.now() calls in the Typer and assign the proper integer
type to them.

See Node issue https://github.com/nodejs/node/issues/9729 for more
information.

R=yangguo@chromium.org
BUG=v8:5267

Review-Url: https://codereview.chromium.org/2528853003
Cr-Commit-Position: refs/heads/master@{#41242}

src/compiler/type-cache.h

@@ -97,6 +97,11 @@ class TypeCache final {
   // [0, String::kMaxLength].
   Type* const kStringLengthType = CreateRange(0.0, String::kMaxLength);
 
+  // A time value always contains a tagged number in the range
+  // [-kMaxTimeInMs, kMaxTimeInMs].
+  Type* const kTimeValueType =
+      CreateRange(-DateCache::kMaxTimeInMs, DateCache::kMaxTimeInMs);
+
   // The JSDate::day property always contains a tagged number in the range
   // [1, 31] or NaN.
   Type* const kJSDateDayType =
@@ -123,9 +128,8 @@ class TypeCache final {
 
   // The JSDate::value property always contains a tagged number in the range
   // [-kMaxTimeInMs, kMaxTimeInMs] or NaN.
-  Type* const kJSDateValueType = Type::Union(
-      CreateRange(-DateCache::kMaxTimeInMs, DateCache::kMaxTimeInMs),
-      Type::NaN(), zone());
+  Type* const kJSDateValueType =
+      Type::Union(kTimeValueType, Type::NaN(), zone());
 
   // The JSDate::weekday property always contains a tagged number in the range
   // [0, 6] or NaN.

src/compiler/typer.cc

@@ -1348,6 +1348,8 @@ Type* Typer::Visitor::JSCallFunctionTyper(Type* fun, Typer* t) {
         case kMathClz32:
           return t->cache_.kZeroToThirtyTwo;
         // Date functions.
+        case kDateNow:
+          return t->cache_.kTimeValueType;
         case kDateGetDate:
           return t->cache_.kJSDateDayType;
         case kDateGetDay:

src/objects.h

@@ -7237,6 +7237,7 @@ class Script: public Struct {
   V(Array.prototype, push, ArrayPush)                       \
   V(Array.prototype, pop, ArrayPop)                         \
   V(Array.prototype, shift, ArrayShift)                     \
+  V(Date, now, DateNow)                                     \
   V(Date.prototype, getDate, DateGetDate)                   \
   V(Date.prototype, getDay, DateGetDay)                     \
   V(Date.prototype, getFullYear, DateGetFullYear)           \