Bring Time(Delta)::Min/Max() and related helpers to V8.

Copied as-is modulo compile tweaks from Chromium's base.

Copied tests highlighting existing overflow issues with V8's impl...

TimeDelta::Max() will initially be used in V8 to flag events that
never triggered in a TimedHistogram.

Also constexpr'ed a few things while I was in there, it's harmless
at worst and helps a little at best.
Ideally would constexpr all the Time*::From*() methods like in
Chromium but that has inlining implications and I don't know the
impact that could have on V8.

Bug: chromium:807606
Change-Id: If5aa92759d985be070e12af4dd20f0159169048b
Reviewed-on: https://chromium-review.googlesource.com/899342Reviewed-by: Hannes Payer <hpayer@chromium.org>
Commit-Queue: Gabriel Charette <gab@chromium.org>
Cr-Commit-Position: refs/heads/master@{#51073}

src/base/platform/time.cc

@@ -143,41 +143,83 @@ TimeDelta TimeDelta::FromNanoseconds(int64_t nanoseconds) {
 
 
 int TimeDelta::InDays() const {
+  if (IsMax()) {
+    // Preserve max to prevent overflow.
+    return std::numeric_limits<int>::max();
+  }
   return static_cast<int>(delta_ / Time::kMicrosecondsPerDay);
 }
 
-
 int TimeDelta::InHours() const {
+  if (IsMax()) {
+    // Preserve max to prevent overflow.
+    return std::numeric_limits<int>::max();
+  }
   return static_cast<int>(delta_ / Time::kMicrosecondsPerHour);
 }
 
-
 int TimeDelta::InMinutes() const {
+  if (IsMax()) {
+    // Preserve max to prevent overflow.
+    return std::numeric_limits<int>::max();
+  }
   return static_cast<int>(delta_ / Time::kMicrosecondsPerMinute);
 }
 
-
 double TimeDelta::InSecondsF() const {
+  if (IsMax()) {
+    // Preserve max to prevent overflow.
+    return std::numeric_limits<double>::infinity();
+  }
   return static_cast<double>(delta_) / Time::kMicrosecondsPerSecond;
 }
 
-
 int64_t TimeDelta::InSeconds() const {
+  if (IsMax()) {
+    // Preserve max to prevent overflow.
+    return std::numeric_limits<int64_t>::max();
+  }
   return delta_ / Time::kMicrosecondsPerSecond;
 }
 
-
 double TimeDelta::InMillisecondsF() const {
+  if (IsMax()) {
+    // Preserve max to prevent overflow.
+    return std::numeric_limits<double>::infinity();
+  }
   return static_cast<double>(delta_) / Time::kMicrosecondsPerMillisecond;
 }
 
-
 int64_t TimeDelta::InMilliseconds() const {
+  if (IsMax()) {
+    // Preserve max to prevent overflow.
+    return std::numeric_limits<int64_t>::max();
+  }
   return delta_ / Time::kMicrosecondsPerMillisecond;
 }
 
+int64_t TimeDelta::InMillisecondsRoundedUp() const {
+  if (IsMax()) {
+    // Preserve max to prevent overflow.
+    return std::numeric_limits<int64_t>::max();
+  }
+  return (delta_ + Time::kMicrosecondsPerMillisecond - 1) /
+         Time::kMicrosecondsPerMillisecond;
+}
+
+int64_t TimeDelta::InMicroseconds() const {
+  if (IsMax()) {
+    // Preserve max to prevent overflow.
+    return std::numeric_limits<int64_t>::max();
+  }
+  return delta_;
+}
 
 int64_t TimeDelta::InNanoseconds() const {
+  if (IsMax()) {
+    // Preserve max to prevent overflow.
+    return std::numeric_limits<int64_t>::max();
+  }
   return delta_ * Time::kNanosecondsPerMicrosecond;
 }
 

src/base/platform/time.h

@@ -47,7 +47,7 @@ class TimeBase;
 
 class V8_BASE_EXPORT TimeDelta final {
  public:
-  TimeDelta() : delta_(0) {}
+  constexpr TimeDelta() : delta_(0) {}
 
   // Converts units of time to TimeDeltas.
   static TimeDelta FromDays(int days);
@@ -60,6 +60,27 @@ class V8_BASE_EXPORT TimeDelta final {
   }
   static TimeDelta FromNanoseconds(int64_t nanoseconds);
 
+  // Returns the maximum time delta, which should be greater than any reasonable
+  // time delta we might compare it to. Adding or subtracting the maximum time
+  // delta to a time or another time delta has an undefined result.
+  static constexpr TimeDelta Max();
+
+  // Returns the minimum time delta, which should be less than than any
+  // reasonable time delta we might compare it to. Adding or subtracting the
+  // minimum time delta to a time or another time delta has an undefined result.
+  static constexpr TimeDelta Min();
+
+  // Returns true if the time delta is zero.
+  constexpr bool IsZero() const { return delta_ == 0; }
+
+  // Returns true if the time delta is the maximum/minimum time delta.
+  constexpr bool IsMax() const {
+    return delta_ == std::numeric_limits<int64_t>::max();
+  }
+  constexpr bool IsMin() const {
+    return delta_ == std::numeric_limits<int64_t>::min();
+  }
+
   // Returns the time delta in some unit. The F versions return a floating
   // point value, the "regular" versions return a rounded-down value.
   //
@@ -73,7 +94,7 @@ class V8_BASE_EXPORT TimeDelta final {
   double InMillisecondsF() const;
   int64_t InMilliseconds() const;
   int64_t InMillisecondsRoundedUp() const;
-  int64_t InMicroseconds() const { return delta_; }
+  int64_t InMicroseconds() const;
   int64_t InNanoseconds() const;
 
   // Converts to/from Mach time specs.
@@ -105,9 +126,7 @@ class V8_BASE_EXPORT TimeDelta final {
     delta_ -= other.delta_;
     return *this;
   }
-  TimeDelta operator-() const {
-    return TimeDelta(-delta_);
-  }
+  constexpr TimeDelta operator-() const { return TimeDelta(-delta_); }
 
   double TimesOf(const TimeDelta& other) const {
     return static_cast<double>(delta_) / static_cast<double>(other.delta_);
@@ -137,22 +156,22 @@ class V8_BASE_EXPORT TimeDelta final {
   }
 
   // Comparison operators.
-  bool operator==(const TimeDelta& other) const {
+  constexpr bool operator==(const TimeDelta& other) const {
     return delta_ == other.delta_;
   }
-  bool operator!=(const TimeDelta& other) const {
+  constexpr bool operator!=(const TimeDelta& other) const {
     return delta_ != other.delta_;
   }
-  bool operator<(const TimeDelta& other) const {
+  constexpr bool operator<(const TimeDelta& other) const {
     return delta_ < other.delta_;
   }
-  bool operator<=(const TimeDelta& other) const {
+  constexpr bool operator<=(const TimeDelta& other) const {
     return delta_ <= other.delta_;
   }
-  bool operator>(const TimeDelta& other) const {
+  constexpr bool operator>(const TimeDelta& other) const {
     return delta_ > other.delta_;
   }
-  bool operator>=(const TimeDelta& other) const {
+  constexpr bool operator>=(const TimeDelta& other) const {
     return delta_ >= other.delta_;
   }
 
@@ -161,12 +180,21 @@ class V8_BASE_EXPORT TimeDelta final {
   // Constructs a delta given the duration in microseconds. This is private
   // to avoid confusion by callers with an integer constructor. Use
   // FromSeconds, FromMilliseconds, etc. instead.
-  explicit TimeDelta(int64_t delta) : delta_(delta) {}
+  explicit constexpr TimeDelta(int64_t delta) : delta_(delta) {}
 
   // Delta in microseconds.
   int64_t delta_;
 };
 
+// static
+constexpr TimeDelta TimeDelta::Max() {
+  return TimeDelta(std::numeric_limits<int64_t>::max());
+}
+
+// static
+constexpr TimeDelta TimeDelta::Min() {
+  return TimeDelta(std::numeric_limits<int64_t>::min());
+}
 
 namespace time_internal {
 
@@ -207,12 +235,24 @@ class TimeBase {
   // Warning: Be careful when writing code that performs math on time values,
   // since it's possible to produce a valid "zero" result that should not be
   // interpreted as a "null" value.
-  bool IsNull() const {
-    return us_ == 0;
+  constexpr bool IsNull() const { return us_ == 0; }
+
+  // Returns the maximum/minimum times, which should be greater/less than any
+  // reasonable time with which we might compare it.
+  static TimeClass Max() {
+    return TimeClass(std::numeric_limits<int64_t>::max());
+  }
+  static TimeClass Min() {
+    return TimeClass(std::numeric_limits<int64_t>::min());
   }
 
-  // Returns true if this object represents the maximum time.
-  bool IsMax() const { return us_ == std::numeric_limits<int64_t>::max(); }
+  // Returns true if this object represents the maximum/minimum time.
+  constexpr bool IsMax() const {
+    return us_ == std::numeric_limits<int64_t>::max();
+  }
+  constexpr bool IsMin() const {
+    return us_ == std::numeric_limits<int64_t>::min();
+  }
 
   // For serializing only. Use FromInternalValue() to reconstitute. Please don't
   // use this and do arithmetic on it, as it is more error prone than using the
@@ -272,7 +312,7 @@ class TimeBase {
   static TimeClass FromInternalValue(int64_t us) { return TimeClass(us); }
 
  protected:
-  explicit TimeBase(int64_t us) : us_(us) {}
+  explicit constexpr TimeBase(int64_t us) : us_(us) {}
 
   // Time value in a microsecond timebase.
   int64_t us_;
@@ -290,7 +330,7 @@ class TimeBase {
 class V8_BASE_EXPORT Time final : public time_internal::TimeBase<Time> {
  public:
   // Contains the nullptr time. Use Time::Now() to get the current time.
-  Time() : TimeBase(0) {}
+  constexpr Time() : TimeBase(0) {}
 
   // Returns the current time. Watch out, the system might adjust its clock
   // in which case time will actually go backwards. We don't guarantee that
@@ -306,10 +346,6 @@ class V8_BASE_EXPORT Time final : public time_internal::TimeBase<Time> {
   // Returns the time for epoch in Unix-like system (Jan 1, 1970).
   static Time UnixEpoch() { return Time(0); }
 
-  // Returns the maximum time, which should be greater than any reasonable time
-  // with which we might compare it.
-  static Time Max() { return Time(std::numeric_limits<int64_t>::max()); }
-
   // Converts to/from POSIX time specs.
   static Time FromTimespec(struct timespec ts);
   struct timespec ToTimespec() const;
@@ -329,7 +365,7 @@ class V8_BASE_EXPORT Time final : public time_internal::TimeBase<Time> {
 
  private:
   friend class time_internal::TimeBase<Time>;
-  explicit Time(int64_t us) : TimeBase(us) {}
+  explicit constexpr Time(int64_t us) : TimeBase(us) {}
 };
 
 V8_BASE_EXPORT std::ostream& operator<<(std::ostream&, const Time&);
@@ -352,7 +388,7 @@ inline Time operator+(const TimeDelta& delta, const Time& time) {
 class V8_BASE_EXPORT TimeTicks final
     : public time_internal::TimeBase<TimeTicks> {
  public:
-  TimeTicks() : TimeBase(0) {}
+  constexpr TimeTicks() : TimeBase(0) {}
 
   // Platform-dependent tick count representing "right now." When
   // IsHighResolution() returns false, the resolution of the clock could be as
@@ -374,7 +410,7 @@ class V8_BASE_EXPORT TimeTicks final
 
   // Please use Now() to create a new object. This is for internal use
   // and testing. Ticks are in microseconds.
-  explicit TimeTicks(int64_t ticks) : TimeBase(ticks) {}
+  explicit constexpr TimeTicks(int64_t ticks) : TimeBase(ticks) {}
 };
 
 inline TimeTicks operator+(const TimeDelta& delta, const TimeTicks& ticks) {
@@ -389,7 +425,7 @@ inline TimeTicks operator+(const TimeDelta& delta, const TimeTicks& ticks) {
 class V8_BASE_EXPORT ThreadTicks final
     : public time_internal::TimeBase<ThreadTicks> {
  public:
-  ThreadTicks() : TimeBase(0) {}
+  constexpr ThreadTicks() : TimeBase(0) {}
 
   // Returns true if ThreadTicks::Now() is supported on this system.
   static bool IsSupported();
@@ -424,7 +460,7 @@ class V8_BASE_EXPORT ThreadTicks final
 
   // Please use Now() or GetForThread() to create a new object. This is for
   // internal use and testing. Ticks are in microseconds.
-  explicit ThreadTicks(int64_t ticks) : TimeBase(ticks) {}
+  explicit constexpr ThreadTicks(int64_t ticks) : TimeBase(ticks) {}
 
 #if V8_OS_WIN
   // Returns the frequency of the TSC in ticks per second, or 0 if it hasn't

test/unittests/base/platform/time-unittest.cc

@@ -24,6 +24,163 @@
 namespace v8 {
 namespace base {
 
+TEST(TimeDelta, ZeroMinMax) {
+  constexpr TimeDelta kZero;
+  static_assert(kZero.IsZero(), "");
+
+  constexpr TimeDelta kMax = TimeDelta::Max();
+  static_assert(kMax.IsMax(), "");
+  static_assert(kMax == TimeDelta::Max(), "");
+  EXPECT_GT(kMax, TimeDelta::FromDays(100 * 365));
+  static_assert(kMax > kZero, "");
+
+  constexpr TimeDelta kMin = TimeDelta::Min();
+  static_assert(kMin.IsMin(), "");
+  static_assert(kMin == TimeDelta::Min(), "");
+  EXPECT_LT(kMin, TimeDelta::FromDays(-100 * 365));
+  static_assert(kMin < kZero, "");
+}
+
+TEST(TimeDelta, MaxConversions) {
+  // static_assert also confirms constexpr works as intended.
+  constexpr TimeDelta kMax = TimeDelta::Max();
+  EXPECT_EQ(kMax.InDays(), std::numeric_limits<int>::max());
+  EXPECT_EQ(kMax.InHours(), std::numeric_limits<int>::max());
+  EXPECT_EQ(kMax.InMinutes(), std::numeric_limits<int>::max());
+  EXPECT_EQ(kMax.InSecondsF(), std::numeric_limits<double>::infinity());
+  EXPECT_EQ(kMax.InSeconds(), std::numeric_limits<int64_t>::max());
+  EXPECT_EQ(kMax.InMillisecondsF(), std::numeric_limits<double>::infinity());
+  EXPECT_EQ(kMax.InMilliseconds(), std::numeric_limits<int64_t>::max());
+  EXPECT_EQ(kMax.InMillisecondsRoundedUp(),
+            std::numeric_limits<int64_t>::max());
+
+  // TODO(v8-team): Import overflow support from Chromium's base.
+
+  // EXPECT_TRUE(TimeDelta::FromDays(std::numeric_limits<int>::max()).IsMax());
+
+  // EXPECT_TRUE(
+  //     TimeDelta::FromHours(std::numeric_limits<int>::max()).IsMax());
+
+  // EXPECT_TRUE(
+  //     TimeDelta::FromMinutes(std::numeric_limits<int>::max()).IsMax());
+
+  // constexpr int64_t max_int = std::numeric_limits<int64_t>::max();
+  // constexpr int64_t min_int = std::numeric_limits<int64_t>::min();
+
+  // EXPECT_TRUE(
+  //     TimeDelta::FromSeconds(max_int / Time::kMicrosecondsPerSecond + 1)
+  //         .IsMax());
+
+  // EXPECT_TRUE(TimeDelta::FromMilliseconds(
+  //                 max_int / Time::kMillisecondsPerSecond + 1)
+  //                 .IsMax());
+
+  // EXPECT_TRUE(TimeDelta::FromMicroseconds(max_int).IsMax());
+
+  // EXPECT_TRUE(
+  //     TimeDelta::FromSeconds(min_int / Time::kMicrosecondsPerSecond - 1)
+  //         .IsMin());
+
+  // EXPECT_TRUE(TimeDelta::FromMilliseconds(
+  //                 min_int / Time::kMillisecondsPerSecond - 1)
+  //                 .IsMin());
+
+  // EXPECT_TRUE(TimeDelta::FromMicroseconds(min_int).IsMin());
+
+  // EXPECT_TRUE(
+  //     TimeDelta::FromMicroseconds(std::numeric_limits<int64_t>::min())
+  //         .IsMin());
+}
+
+TEST(TimeDelta, NumericOperators) {
+  constexpr int i = 2;
+  EXPECT_EQ(TimeDelta::FromMilliseconds(2000),
+            (TimeDelta::FromMilliseconds(1000) * i));
+  EXPECT_EQ(TimeDelta::FromMilliseconds(500),
+            (TimeDelta::FromMilliseconds(1000) / i));
+  EXPECT_EQ(TimeDelta::FromMilliseconds(2000),
+            (TimeDelta::FromMilliseconds(1000) *= i));
+  EXPECT_EQ(TimeDelta::FromMilliseconds(500),
+            (TimeDelta::FromMilliseconds(1000) /= i));
+
+  constexpr int64_t i64 = 2;
+  EXPECT_EQ(TimeDelta::FromMilliseconds(2000),
+            (TimeDelta::FromMilliseconds(1000) * i64));
+  EXPECT_EQ(TimeDelta::FromMilliseconds(500),
+            (TimeDelta::FromMilliseconds(1000) / i64));
+  EXPECT_EQ(TimeDelta::FromMilliseconds(2000),
+            (TimeDelta::FromMilliseconds(1000) *= i64));
+  EXPECT_EQ(TimeDelta::FromMilliseconds(500),
+            (TimeDelta::FromMilliseconds(1000) /= i64));
+
+  EXPECT_EQ(TimeDelta::FromMilliseconds(2000),
+            (TimeDelta::FromMilliseconds(1000) * 2));
+  EXPECT_EQ(TimeDelta::FromMilliseconds(500),
+            (TimeDelta::FromMilliseconds(1000) / 2));
+  EXPECT_EQ(TimeDelta::FromMilliseconds(2000),
+            (TimeDelta::FromMilliseconds(1000) *= 2));
+  EXPECT_EQ(TimeDelta::FromMilliseconds(500),
+            (TimeDelta::FromMilliseconds(1000) /= 2));
+}
+
+// TODO(v8-team): Import support for overflow from Chromium's base.
+TEST(TimeDelta, DISABLED_Overflows) {
+  // Some sanity checks. static_assert's used were possible to verify constexpr
+  // evaluation at the same time.
+  static_assert(TimeDelta::Max().IsMax(), "");
+  static_assert(-TimeDelta::Max() < TimeDelta(), "");
+  static_assert(-TimeDelta::Max() > TimeDelta::Min(), "");
+  static_assert(TimeDelta() > -TimeDelta::Max(), "");
+
+  TimeDelta large_delta = TimeDelta::Max() - TimeDelta::FromMilliseconds(1);
+  TimeDelta large_negative = -large_delta;
+  EXPECT_GT(TimeDelta(), large_negative);
+  EXPECT_FALSE(large_delta.IsMax());
+  EXPECT_FALSE((-large_negative).IsMin());
+  const TimeDelta kOneSecond = TimeDelta::FromSeconds(1);
+
+  // Test +, -, * and / operators.
+  EXPECT_TRUE((large_delta + kOneSecond).IsMax());
+  EXPECT_TRUE((large_negative + (-kOneSecond)).IsMin());
+  EXPECT_TRUE((large_negative - kOneSecond).IsMin());
+  EXPECT_TRUE((large_delta - (-kOneSecond)).IsMax());
+  EXPECT_TRUE((large_delta * 2).IsMax());
+  EXPECT_TRUE((large_delta * -2).IsMin());
+
+  // Test +=, -=, *= and /= operators.
+  TimeDelta delta = large_delta;
+  delta += kOneSecond;
+  EXPECT_TRUE(delta.IsMax());
+  delta = large_negative;
+  delta += -kOneSecond;
+  EXPECT_TRUE((delta).IsMin());
+
+  delta = large_negative;
+  delta -= kOneSecond;
+  EXPECT_TRUE((delta).IsMin());
+  delta = large_delta;
+  delta -= -kOneSecond;
+  EXPECT_TRUE(delta.IsMax());
+
+  delta = large_delta;
+  delta *= 2;
+  EXPECT_TRUE(delta.IsMax());
+
+  // Test operations with Time and TimeTicks.
+  EXPECT_TRUE((large_delta + Time::Now()).IsMax());
+  EXPECT_TRUE((large_delta + TimeTicks::Now()).IsMax());
+  EXPECT_TRUE((Time::Now() + large_delta).IsMax());
+  EXPECT_TRUE((TimeTicks::Now() + large_delta).IsMax());
+
+  Time time_now = Time::Now();
+  EXPECT_EQ(kOneSecond, (time_now + kOneSecond) - time_now);
+  EXPECT_EQ(-kOneSecond, (time_now - kOneSecond) - time_now);
+
+  TimeTicks ticks_now = TimeTicks::Now();
+  EXPECT_EQ(-kOneSecond, (ticks_now - kOneSecond) - ticks_now);
+  EXPECT_EQ(kOneSecond, (ticks_now + kOneSecond) - ticks_now);
+}
+
 TEST(TimeDelta, FromAndIn) {
   EXPECT_EQ(TimeDelta::FromDays(2), TimeDelta::FromHours(48));
   EXPECT_EQ(TimeDelta::FromHours(3), TimeDelta::FromMinutes(180));
@@ -54,6 +211,47 @@ TEST(TimeDelta, MachTimespec) {
 }
 #endif
 
+TEST(Time, Max) {
+  Time max = Time::Max();
+  EXPECT_TRUE(max.IsMax());
+  EXPECT_EQ(max, Time::Max());
+  EXPECT_GT(max, Time::Now());
+  EXPECT_GT(max, Time());
+}
+
+TEST(Time, MaxConversions) {
+  Time t = Time::Max();
+  EXPECT_EQ(std::numeric_limits<int64_t>::max(), t.ToInternalValue());
+
+// TODO(v8-team): Time::FromJsTime() overflows with infinity. Import support
+// from Chromium's base.
+// t = Time::FromJsTime(std::numeric_limits<double>::infinity());
+// EXPECT_TRUE(t.IsMax());
+// EXPECT_EQ(std::numeric_limits<double>::infinity(), t.ToJsTime());
+
+#if defined(OS_POSIX)
+  struct timeval tval;
+  tval.tv_sec = std::numeric_limits<time_t>::max();
+  tval.tv_usec = static_cast<suseconds_t>(Time::kMicrosecondsPerSecond) - 1;
+  t = Time::FromTimeVal(tval);
+  EXPECT_TRUE(t.IsMax());
+  tval = t.ToTimeVal();
+  EXPECT_EQ(std::numeric_limits<time_t>::max(), tval.tv_sec);
+  EXPECT_EQ(static_cast<suseconds_t>(Time::kMicrosecondsPerSecond) - 1,
+            tval.tv_usec);
+#endif
+
+#if defined(OS_WIN)
+  FILETIME ftime;
+  ftime.dwHighDateTime = std::numeric_limits<DWORD>::max();
+  ftime.dwLowDateTime = std::numeric_limits<DWORD>::max();
+  t = Time::FromFileTime(ftime);
+  EXPECT_TRUE(t.IsMax());
+  ftime = t.ToFileTime();
+  EXPECT_EQ(std::numeric_limits<DWORD>::max(), ftime.dwHighDateTime);
+  EXPECT_EQ(std::numeric_limits<DWORD>::max(), ftime.dwLowDateTime);
+#endif
+}
 
 TEST(Time, JsTime) {
   Time t = Time::FromJsTime(700000.3);