Tagged most functions in absl/time/time.h as ABSL_ATTRIBUTE_CONST_FUNCTION or ABSL_ATTRIBUTE_PURE_FUNCTION

However, both absl_attributes are now unimplemented to avoid breaking existing users.

PiperOrigin-RevId: 496769399
Change-Id: I9c00cb60b885526300d744f9ea7c0f2178f092bb

2 files changed, 261 insertions, 161 deletions

diff --git a/absl/time/time.h b/absl/time/time.h
index 11796b4f..cc390082 100644
--- a/absl/time/time.h
+++ b/absl/time/time.h
@@ -78,6 +78,7 @@ struct timeval;
 #include <cmath>
 #include <cstdint>
 #include <ctime>
+#include <limits>
 #include <ostream>
 #include <string>
 #include <type_traits>
@@ -97,19 +98,24 @@ class TimeZone;  // Defined below
 
 namespace time_internal {
 int64_t IDivDuration(bool satq, Duration num, Duration den, Duration* rem);
-constexpr Time FromUnixDuration(Duration d);
-constexpr Duration ToUnixDuration(Time t);
-constexpr int64_t GetRepHi(Duration d);
-constexpr uint32_t GetRepLo(Duration d);
-constexpr Duration MakeDuration(int64_t hi, uint32_t lo);
-constexpr Duration MakeDuration(int64_t hi, int64_t lo);
-inline Duration MakePosDoubleDuration(double n);
+ABSL_ATTRIBUTE_CONST_FUNCTION constexpr Time FromUnixDuration(Duration d);
+ABSL_ATTRIBUTE_CONST_FUNCTION constexpr Duration ToUnixDuration(Time t);
+ABSL_ATTRIBUTE_CONST_FUNCTION constexpr int64_t GetRepHi(Duration d);
+ABSL_ATTRIBUTE_CONST_FUNCTION constexpr uint32_t GetRepLo(Duration d);
+ABSL_ATTRIBUTE_CONST_FUNCTION constexpr Duration MakeDuration(int64_t hi,
+                                                              uint32_t lo);
+ABSL_ATTRIBUTE_CONST_FUNCTION constexpr Duration MakeDuration(int64_t hi,
+                                                              int64_t lo);
+ABSL_ATTRIBUTE_CONST_FUNCTION inline Duration MakePosDoubleDuration(double n);
 constexpr int64_t kTicksPerNanosecond = 4;
 constexpr int64_t kTicksPerSecond = 1000 * 1000 * 1000 * kTicksPerNanosecond;
 template <std::intmax_t N>
-constexpr Duration FromInt64(int64_t v, std::ratio<1, N>);
-constexpr Duration FromInt64(int64_t v, std::ratio<60>);
-constexpr Duration FromInt64(int64_t v, std::ratio<3600>);
+ABSL_ATTRIBUTE_CONST_FUNCTION constexpr Duration FromInt64(int64_t v,
+                                                           std::ratio<1, N>);
+ABSL_ATTRIBUTE_CONST_FUNCTION constexpr Duration FromInt64(int64_t v,
+                                                           std::ratio<60>);
+ABSL_ATTRIBUTE_CONST_FUNCTION constexpr Duration FromInt64(int64_t v,
+                                                           std::ratio<3600>);
 template <typename T>
 using EnableIfIntegral = typename std::enable_if<
     std::is_integral<T>::value || std::is_enum<T>::value, int>::type;
@@ -222,37 +228,61 @@ class Duration {
 };
 
 // Relational Operators
-constexpr bool operator<(Duration lhs, Duration rhs);
-constexpr bool operator>(Duration lhs, Duration rhs) { return rhs < lhs; }
-constexpr bool operator>=(Duration lhs, Duration rhs) { return !(lhs < rhs); }
-constexpr bool operator<=(Duration lhs, Duration rhs) { return !(rhs < lhs); }
-constexpr bool operator==(Duration lhs, Duration rhs);
-constexpr bool operator!=(Duration lhs, Duration rhs) { return !(lhs == rhs); }
+ABSL_ATTRIBUTE_CONST_FUNCTION constexpr bool operator<(Duration lhs,
+                                                       Duration rhs);
+ABSL_ATTRIBUTE_CONST_FUNCTION constexpr bool operator>(Duration lhs,
+                                                       Duration rhs) {
+  return rhs < lhs;
+}
+ABSL_ATTRIBUTE_CONST_FUNCTION constexpr bool operator>=(Duration lhs,
+                                                        Duration rhs) {
+  return !(lhs < rhs);
+}
+ABSL_ATTRIBUTE_CONST_FUNCTION constexpr bool operator<=(Duration lhs,
+                                                        Duration rhs) {
+  return !(rhs < lhs);
+}
+ABSL_ATTRIBUTE_CONST_FUNCTION constexpr bool operator==(Duration lhs,
+                                                        Duration rhs);
+ABSL_ATTRIBUTE_CONST_FUNCTION constexpr bool operator!=(Duration lhs,
+                                                        Duration rhs) {
+  return !(lhs == rhs);
+}
 
 // Additive Operators
-constexpr Duration operator-(Duration d);
-inline Duration operator+(Duration lhs, Duration rhs) { return lhs += rhs; }
-inline Duration operator-(Duration lhs, Duration rhs) { return lhs -= rhs; }
+ABSL_ATTRIBUTE_CONST_FUNCTION constexpr Duration operator-(Duration d);
+ABSL_ATTRIBUTE_CONST_FUNCTION inline Duration operator+(Duration lhs,
+                                                        Duration rhs) {
+  return lhs += rhs;
+}
+ABSL_ATTRIBUTE_CONST_FUNCTION inline Duration operator-(Duration lhs,
+                                                        Duration rhs) {
+  return lhs -= rhs;
+}
 
 // Multiplicative Operators
 // Integer operands must be representable as int64_t.
 template <typename T>
-Duration operator*(Duration lhs, T rhs) {
+ABSL_ATTRIBUTE_CONST_FUNCTION Duration operator*(Duration lhs, T rhs) {
   return lhs *= rhs;
 }
 template <typename T>
-Duration operator*(T lhs, Duration rhs) {
+ABSL_ATTRIBUTE_CONST_FUNCTION Duration operator*(T lhs, Duration rhs) {
   return rhs *= lhs;
 }
 template <typename T>
-Duration operator/(Duration lhs, T rhs) {
+ABSL_ATTRIBUTE_CONST_FUNCTION Duration operator/(Duration lhs, T rhs) {
   return lhs /= rhs;
 }
-inline int64_t operator/(Duration lhs, Duration rhs) {
+ABSL_ATTRIBUTE_CONST_FUNCTION inline int64_t operator/(Duration lhs,
+                                                       Duration rhs) {
   return time_internal::IDivDuration(true, lhs, rhs,
                                      &lhs);  // trunc towards zero
 }
-inline Duration operator%(Duration lhs, Duration rhs) { return lhs %= rhs; }
+ABSL_ATTRIBUTE_CONST_FUNCTION inline Duration operator%(Duration lhs,
+                                                        Duration rhs) {
+  return lhs %= rhs;
+}
 
 // IDivDuration()
 //
@@ -299,18 +329,20 @@ inline int64_t IDivDuration(Duration num, Duration den, Duration* rem) {
 //
 //   double d = absl::FDivDuration(absl::Milliseconds(1500), absl::Seconds(1));
 //   // d == 1.5
-double FDivDuration(Duration num, Duration den);
+ABSL_ATTRIBUTE_CONST_FUNCTION double FDivDuration(Duration num, Duration den);
 
 // ZeroDuration()
 //
 // Returns a zero-length duration. This function behaves just like the default
 // constructor, but the name helps make the semantics clear at call sites.
-constexpr Duration ZeroDuration() { return Duration(); }
+ABSL_ATTRIBUTE_CONST_FUNCTION constexpr Duration ZeroDuration() {
+  return Duration();
+}
 
 // AbsDuration()
 //
 // Returns the absolute value of a duration.
-inline Duration AbsDuration(Duration d) {
+ABSL_ATTRIBUTE_CONST_FUNCTION inline Duration AbsDuration(Duration d) {
   return (d < ZeroDuration()) ? -d : d;
 }
 
@@ -322,7 +354,7 @@ inline Duration AbsDuration(Duration d) {
 //
 //   absl::Duration d = absl::Nanoseconds(123456789);
 //   absl::Duration a = absl::Trunc(d, absl::Microseconds(1));  // 123456us
-Duration Trunc(Duration d, Duration unit);
+ABSL_ATTRIBUTE_CONST_FUNCTION Duration Trunc(Duration d, Duration unit);
 
 // Floor()
 //
@@ -333,7 +365,7 @@ Duration Trunc(Duration d, Duration unit);
 //
 //   absl::Duration d = absl::Nanoseconds(123456789);
 //   absl::Duration b = absl::Floor(d, absl::Microseconds(1));  // 123456us
-Duration Floor(Duration d, Duration unit);
+ABSL_ATTRIBUTE_CONST_FUNCTION Duration Floor(Duration d, Duration unit);
 
 // Ceil()
 //
@@ -344,7 +376,7 @@ Duration Floor(Duration d, Duration unit);
 //
 //   absl::Duration d = absl::Nanoseconds(123456789);
 //   absl::Duration c = absl::Ceil(d, absl::Microseconds(1));   // 123457us
-Duration Ceil(Duration d, Duration unit);
+ABSL_ATTRIBUTE_CONST_FUNCTION Duration Ceil(Duration d, Duration unit);
 
 // InfiniteDuration()
 //
@@ -380,7 +412,7 @@ Duration Ceil(Duration d, Duration unit);
 //
 // The examples involving the `/` operator above also apply to `IDivDuration()`
 // and `FDivDuration()`.
-constexpr Duration InfiniteDuration();
+ABSL_ATTRIBUTE_CONST_FUNCTION constexpr Duration InfiniteDuration();
 
 // Nanoseconds()
 // Microseconds()
@@ -404,27 +436,27 @@ constexpr Duration InfiniteDuration();
 //   absl::Duration a = absl::Seconds(60);
 //   absl::Duration b = absl::Minutes(1);  // b == a
 template <typename T, time_internal::EnableIfIntegral<T> = 0>
-constexpr Duration Nanoseconds(T n) {
+ABSL_ATTRIBUTE_CONST_FUNCTION constexpr Duration Nanoseconds(T n) {
   return time_internal::FromInt64(n, std::nano{});
 }
 template <typename T, time_internal::EnableIfIntegral<T> = 0>
-constexpr Duration Microseconds(T n) {
+ABSL_ATTRIBUTE_CONST_FUNCTION constexpr Duration Microseconds(T n) {
   return time_internal::FromInt64(n, std::micro{});
 }
 template <typename T, time_internal::EnableIfIntegral<T> = 0>
-constexpr Duration Milliseconds(T n) {
+ABSL_ATTRIBUTE_CONST_FUNCTION constexpr Duration Milliseconds(T n) {
   return time_internal::FromInt64(n, std::milli{});
 }
 template <typename T, time_internal::EnableIfIntegral<T> = 0>
-constexpr Duration Seconds(T n) {
+ABSL_ATTRIBUTE_CONST_FUNCTION constexpr Duration Seconds(T n) {
   return time_internal::FromInt64(n, std::ratio<1>{});
 }
 template <typename T, time_internal::EnableIfIntegral<T> = 0>
-constexpr Duration Minutes(T n) {
+ABSL_ATTRIBUTE_CONST_FUNCTION constexpr Duration Minutes(T n) {
   return time_internal::FromInt64(n, std::ratio<60>{});
 }
 template <typename T, time_internal::EnableIfIntegral<T> = 0>
-constexpr Duration Hours(T n) {
+ABSL_ATTRIBUTE_CONST_FUNCTION constexpr Duration Hours(T n) {
   return time_internal::FromInt64(n, std::ratio<3600>{});
 }
 
@@ -438,19 +470,19 @@ constexpr Duration Hours(T n) {
 //   auto a = absl::Seconds(1.5);        // OK
 //   auto b = absl::Milliseconds(1500);  // BETTER
 template <typename T, time_internal::EnableIfFloat<T> = 0>
-Duration Nanoseconds(T n) {
+ABSL_ATTRIBUTE_CONST_FUNCTION Duration Nanoseconds(T n) {
   return n * Nanoseconds(1);
 }
 template <typename T, time_internal::EnableIfFloat<T> = 0>
-Duration Microseconds(T n) {
+ABSL_ATTRIBUTE_CONST_FUNCTION Duration Microseconds(T n) {
   return n * Microseconds(1);
 }
 template <typename T, time_internal::EnableIfFloat<T> = 0>
-Duration Milliseconds(T n) {
+ABSL_ATTRIBUTE_CONST_FUNCTION Duration Milliseconds(T n) {
   return n * Milliseconds(1);
 }
 template <typename T, time_internal::EnableIfFloat<T> = 0>
-Duration Seconds(T n) {
+ABSL_ATTRIBUTE_CONST_FUNCTION Duration Seconds(T n) {
   if (n >= 0) {  // Note: `NaN >= 0` is false.
     if (n >= static_cast<T>((std::numeric_limits<int64_t>::max)())) {
       return InfiniteDuration();
@@ -464,11 +496,11 @@ Duration Seconds(T n) {
   }
 }
 template <typename T, time_internal::EnableIfFloat<T> = 0>
-Duration Minutes(T n) {
+ABSL_ATTRIBUTE_CONST_FUNCTION Duration Minutes(T n) {
   return n * Minutes(1);
 }
 template <typename T, time_internal::EnableIfFloat<T> = 0>
-Duration Hours(T n) {
+ABSL_ATTRIBUTE_CONST_FUNCTION Duration Hours(T n) {
   return n * Hours(1);
 }
 
@@ -488,12 +520,12 @@ Duration Hours(T n) {
 //
 //   absl::Duration d = absl::Milliseconds(1500);
 //   int64_t isec = absl::ToInt64Seconds(d);  // isec == 1
-ABSL_ATTRIBUTE_PURE_FUNCTION int64_t ToInt64Nanoseconds(Duration d);
-ABSL_ATTRIBUTE_PURE_FUNCTION int64_t ToInt64Microseconds(Duration d);
-ABSL_ATTRIBUTE_PURE_FUNCTION int64_t ToInt64Milliseconds(Duration d);
-ABSL_ATTRIBUTE_PURE_FUNCTION int64_t ToInt64Seconds(Duration d);
-ABSL_ATTRIBUTE_PURE_FUNCTION int64_t ToInt64Minutes(Duration d);
-ABSL_ATTRIBUTE_PURE_FUNCTION int64_t ToInt64Hours(Duration d);
+ABSL_ATTRIBUTE_CONST_FUNCTION int64_t ToInt64Nanoseconds(Duration d);
+ABSL_ATTRIBUTE_CONST_FUNCTION int64_t ToInt64Microseconds(Duration d);
+ABSL_ATTRIBUTE_CONST_FUNCTION int64_t ToInt64Milliseconds(Duration d);
+ABSL_ATTRIBUTE_CONST_FUNCTION int64_t ToInt64Seconds(Duration d);
+ABSL_ATTRIBUTE_CONST_FUNCTION int64_t ToInt64Minutes(Duration d);
+ABSL_ATTRIBUTE_CONST_FUNCTION int64_t ToInt64Hours(Duration d);
 
 // ToDoubleNanoseconds()
 // ToDoubleMicroseconds()
@@ -510,12 +542,12 @@ ABSL_ATTRIBUTE_PURE_FUNCTION int64_t ToInt64Hours(Duration d);
 //
 //   absl::Duration d = absl::Milliseconds(1500);
 //   double dsec = absl::ToDoubleSeconds(d);  // dsec == 1.5
-ABSL_ATTRIBUTE_PURE_FUNCTION double ToDoubleNanoseconds(Duration d);
-ABSL_ATTRIBUTE_PURE_FUNCTION double ToDoubleMicroseconds(Duration d);
-ABSL_ATTRIBUTE_PURE_FUNCTION double ToDoubleMilliseconds(Duration d);
-ABSL_ATTRIBUTE_PURE_FUNCTION double ToDoubleSeconds(Duration d);
-ABSL_ATTRIBUTE_PURE_FUNCTION double ToDoubleMinutes(Duration d);
-ABSL_ATTRIBUTE_PURE_FUNCTION double ToDoubleHours(Duration d);
+ABSL_ATTRIBUTE_CONST_FUNCTION double ToDoubleNanoseconds(Duration d);
+ABSL_ATTRIBUTE_CONST_FUNCTION double ToDoubleMicroseconds(Duration d);
+ABSL_ATTRIBUTE_CONST_FUNCTION double ToDoubleMilliseconds(Duration d);
+ABSL_ATTRIBUTE_CONST_FUNCTION double ToDoubleSeconds(Duration d);
+ABSL_ATTRIBUTE_CONST_FUNCTION double ToDoubleMinutes(Duration d);
+ABSL_ATTRIBUTE_CONST_FUNCTION double ToDoubleHours(Duration d);
 
 // FromChrono()
 //
@@ -525,12 +557,18 @@ ABSL_ATTRIBUTE_PURE_FUNCTION double ToDoubleHours(Duration d);
 //
 //   std::chrono::milliseconds ms(123);
 //   absl::Duration d = absl::FromChrono(ms);
-constexpr Duration FromChrono(const std::chrono::nanoseconds& d);
-constexpr Duration FromChrono(const std::chrono::microseconds& d);
-constexpr Duration FromChrono(const std::chrono::milliseconds& d);
-constexpr Duration FromChrono(const std::chrono::seconds& d);
-constexpr Duration FromChrono(const std::chrono::minutes& d);
-constexpr Duration FromChrono(const std::chrono::hours& d);
+ABSL_ATTRIBUTE_PURE_FUNCTION constexpr Duration FromChrono(
+    const std::chrono::nanoseconds& d);
+ABSL_ATTRIBUTE_PURE_FUNCTION constexpr Duration FromChrono(
+    const std::chrono::microseconds& d);
+ABSL_ATTRIBUTE_PURE_FUNCTION constexpr Duration FromChrono(
+    const std::chrono::milliseconds& d);
+ABSL_ATTRIBUTE_PURE_FUNCTION constexpr Duration FromChrono(
+    const std::chrono::seconds& d);
+ABSL_ATTRIBUTE_PURE_FUNCTION constexpr Duration FromChrono(
+    const std::chrono::minutes& d);
+ABSL_ATTRIBUTE_PURE_FUNCTION constexpr Duration FromChrono(
+    const std::chrono::hours& d);
 
 // ToChronoNanoseconds()
 // ToChronoMicroseconds()
@@ -550,18 +588,21 @@ constexpr Duration FromChrono(const std::chrono::hours& d);
 //   auto y = absl::ToChronoNanoseconds(d);  // x == y
 //   auto z = absl::ToChronoSeconds(absl::InfiniteDuration());
 //   // z == std::chrono::seconds::max()
-std::chrono::nanoseconds ToChronoNanoseconds(Duration d);
-std::chrono::microseconds ToChronoMicroseconds(Duration d);
-std::chrono::milliseconds ToChronoMilliseconds(Duration d);
-std::chrono::seconds ToChronoSeconds(Duration d);
-std::chrono::minutes ToChronoMinutes(Duration d);
-std::chrono::hours ToChronoHours(Duration d);
+ABSL_ATTRIBUTE_CONST_FUNCTION std::chrono::nanoseconds ToChronoNanoseconds(
+    Duration d);
+ABSL_ATTRIBUTE_CONST_FUNCTION std::chrono::microseconds ToChronoMicroseconds(
+    Duration d);
+ABSL_ATTRIBUTE_CONST_FUNCTION std::chrono::milliseconds ToChronoMilliseconds(
+    Duration d);
+ABSL_ATTRIBUTE_CONST_FUNCTION std::chrono::seconds ToChronoSeconds(Duration d);
+ABSL_ATTRIBUTE_CONST_FUNCTION std::chrono::minutes ToChronoMinutes(Duration d);
+ABSL_ATTRIBUTE_CONST_FUNCTION std::chrono::hours ToChronoHours(Duration d);
 
 // FormatDuration()
 //
 // Returns a string representing the duration in the form "72h3m0.5s".
 // Returns "inf" or "-inf" for +/- `InfiniteDuration()`.
-std::string FormatDuration(Duration d);
+ABSL_ATTRIBUTE_CONST_FUNCTION std::string FormatDuration(Duration d);
 
 // Output stream operator.
 inline std::ostream& operator<<(std::ostream& os, Duration d) {
@@ -725,29 +766,49 @@ class Time {
 };
 
 // Relational Operators
-constexpr bool operator<(Time lhs, Time rhs) { return lhs.rep_ < rhs.rep_; }
-constexpr bool operator>(Time lhs, Time rhs) { return rhs < lhs; }
-constexpr bool operator>=(Time lhs, Time rhs) { return !(lhs < rhs); }
-constexpr bool operator<=(Time lhs, Time rhs) { return !(rhs < lhs); }
-constexpr bool operator==(Time lhs, Time rhs) { return lhs.rep_ == rhs.rep_; }
-constexpr bool operator!=(Time lhs, Time rhs) { return !(lhs == rhs); }
+ABSL_ATTRIBUTE_CONST_FUNCTION constexpr bool operator<(Time lhs, Time rhs) {
+  return lhs.rep_ < rhs.rep_;
+}
+ABSL_ATTRIBUTE_CONST_FUNCTION constexpr bool operator>(Time lhs, Time rhs) {
+  return rhs < lhs;
+}
+ABSL_ATTRIBUTE_CONST_FUNCTION constexpr bool operator>=(Time lhs, Time rhs) {
+  return !(lhs < rhs);
+}
+ABSL_ATTRIBUTE_CONST_FUNCTION constexpr bool operator<=(Time lhs, Time rhs) {
+  return !(rhs < lhs);
+}
+ABSL_ATTRIBUTE_CONST_FUNCTION constexpr bool operator==(Time lhs, Time rhs) {
+  return lhs.rep_ == rhs.rep_;
+}
+ABSL_ATTRIBUTE_CONST_FUNCTION constexpr bool operator!=(Time lhs, Time rhs) {
+  return !(lhs == rhs);
+}
 
 // Additive Operators
-inline Time operator+(Time lhs, Duration rhs) { return lhs += rhs; }
-inline Time operator+(Duration lhs, Time rhs) { return rhs += lhs; }
-inline Time operator-(Time lhs, Duration rhs) { return lhs -= rhs; }
-inline Duration operator-(Time lhs, Time rhs) { return lhs.rep_ - rhs.rep_; }
+ABSL_ATTRIBUTE_CONST_FUNCTION inline Time operator+(Time lhs, Duration rhs) {
+  return lhs += rhs;
+}
+ABSL_ATTRIBUTE_CONST_FUNCTION inline Time operator+(Duration lhs, Time rhs) {
+  return rhs += lhs;
+}
+ABSL_ATTRIBUTE_CONST_FUNCTION inline Time operator-(Time lhs, Duration rhs) {
+  return lhs -= rhs;
+}
+ABSL_ATTRIBUTE_CONST_FUNCTION inline Duration operator-(Time lhs, Time rhs) {
+  return lhs.rep_ - rhs.rep_;
+}
 
 // UnixEpoch()
 //
 // Returns the `absl::Time` representing "1970-01-01 00:00:00.0 +0000".
-constexpr Time UnixEpoch() { return Time(); }
+ABSL_ATTRIBUTE_CONST_FUNCTION constexpr Time UnixEpoch() { return Time(); }
 
 // UniversalEpoch()
 //
 // Returns the `absl::Time` representing "0001-01-01 00:00:00.0 +0000", the
 // epoch of the ICU Universal Time Scale.
-constexpr Time UniversalEpoch() {
+ABSL_ATTRIBUTE_CONST_FUNCTION constexpr Time UniversalEpoch() {
   // 719162 is the number of days from 0001-01-01 to 1970-01-01,
   // assuming the Gregorian calendar.
   return Time(
@@ -757,7 +818,7 @@ constexpr Time UniversalEpoch() {
 // InfiniteFuture()
 //
 // Returns an `absl::Time` that is infinitely far in the future.
-constexpr Time InfiniteFuture() {
+ABSL_ATTRIBUTE_CONST_FUNCTION constexpr Time InfiniteFuture() {
   return Time(time_internal::MakeDuration((std::numeric_limits<int64_t>::max)(),
                                           ~uint32_t{0}));
 }
@@ -765,7 +826,7 @@ constexpr Time InfiniteFuture() {
 // InfinitePast()
 //
 // Returns an `absl::Time` that is infinitely far in the past.
-constexpr Time InfinitePast() {
+ABSL_ATTRIBUTE_CONST_FUNCTION constexpr Time InfinitePast() {
   return Time(time_internal::MakeDuration((std::numeric_limits<int64_t>::min)(),
                                           ~uint32_t{0}));
 }
@@ -779,13 +840,13 @@ constexpr Time InfinitePast() {
 // FromUniversal()
 //
 // Creates an `absl::Time` from a variety of other representations.
-constexpr Time FromUnixNanos(int64_t ns);
-constexpr Time FromUnixMicros(int64_t us);
-constexpr Time FromUnixMillis(int64_t ms);
-constexpr Time FromUnixSeconds(int64_t s);
-constexpr Time FromTimeT(time_t t);
-Time FromUDate(double udate);
-Time FromUniversal(int64_t universal);
+ABSL_ATTRIBUTE_CONST_FUNCTION constexpr Time FromUnixNanos(int64_t ns);
+ABSL_ATTRIBUTE_CONST_FUNCTION constexpr Time FromUnixMicros(int64_t us);
+ABSL_ATTRIBUTE_CONST_FUNCTION constexpr Time FromUnixMillis(int64_t ms);
+ABSL_ATTRIBUTE_CONST_FUNCTION constexpr Time FromUnixSeconds(int64_t s);
+ABSL_ATTRIBUTE_CONST_FUNCTION constexpr Time FromTimeT(time_t t);
+ABSL_ATTRIBUTE_CONST_FUNCTION Time FromUDate(double udate);
+ABSL_ATTRIBUTE_CONST_FUNCTION Time FromUniversal(int64_t universal);
 
 // ToUnixNanos()
 // ToUnixMicros()
@@ -799,13 +860,13 @@ Time FromUniversal(int64_t universal);
 // these operations round down toward negative infinity where necessary to
 // adjust to the resolution of the result type.  Beware of possible time_t
 // over/underflow in ToTime{T,val,spec}() on 32-bit platforms.
-int64_t ToUnixNanos(Time t);
-int64_t ToUnixMicros(Time t);
-int64_t ToUnixMillis(Time t);
-int64_t ToUnixSeconds(Time t);
-time_t ToTimeT(Time t);
-double ToUDate(Time t);
-int64_t ToUniversal(Time t);
+ABSL_ATTRIBUTE_CONST_FUNCTION int64_t ToUnixNanos(Time t);
+ABSL_ATTRIBUTE_CONST_FUNCTION int64_t ToUnixMicros(Time t);
+ABSL_ATTRIBUTE_CONST_FUNCTION int64_t ToUnixMillis(Time t);
+ABSL_ATTRIBUTE_CONST_FUNCTION int64_t ToUnixSeconds(Time t);
+ABSL_ATTRIBUTE_CONST_FUNCTION time_t ToTimeT(Time t);
+ABSL_ATTRIBUTE_CONST_FUNCTION double ToUDate(Time t);
+ABSL_ATTRIBUTE_CONST_FUNCTION int64_t ToUniversal(Time t);
 
 // DurationFromTimespec()
 // DurationFromTimeval()
@@ -821,14 +882,14 @@ int64_t ToUniversal(Time t);
 // and gettimeofday(2)), so conversion functions are provided for both cases.
 // The "to timespec/val" direction is easily handled via overloading, but
 // for "from timespec/val" the desired type is part of the function name.
-Duration DurationFromTimespec(timespec ts);
-Duration DurationFromTimeval(timeval tv);
-timespec ToTimespec(Duration d);
-timeval ToTimeval(Duration d);
-Time TimeFromTimespec(timespec ts);
-Time TimeFromTimeval(timeval tv);
-timespec ToTimespec(Time t);
-timeval ToTimeval(Time t);
+ABSL_ATTRIBUTE_CONST_FUNCTION Duration DurationFromTimespec(timespec ts);
+ABSL_ATTRIBUTE_CONST_FUNCTION Duration DurationFromTimeval(timeval tv);
+ABSL_ATTRIBUTE_CONST_FUNCTION timespec ToTimespec(Duration d);
+ABSL_ATTRIBUTE_CONST_FUNCTION timeval ToTimeval(Duration d);
+ABSL_ATTRIBUTE_CONST_FUNCTION Time TimeFromTimespec(timespec ts);
+ABSL_ATTRIBUTE_CONST_FUNCTION Time TimeFromTimeval(timeval tv);
+ABSL_ATTRIBUTE_CONST_FUNCTION timespec ToTimespec(Time t);
+ABSL_ATTRIBUTE_CONST_FUNCTION timeval ToTimeval(Time t);
 
 // FromChrono()
 //
@@ -839,7 +900,8 @@ timeval ToTimeval(Time t);
 //   auto tp = std::chrono::system_clock::from_time_t(123);
 //   absl::Time t = absl::FromChrono(tp);
 //   // t == absl::FromTimeT(123)
-Time FromChrono(const std::chrono::system_clock::time_point& tp);
+ABSL_ATTRIBUTE_PURE_FUNCTION Time
+FromChrono(const std::chrono::system_clock::time_point& tp);
 
 // ToChronoTime()
 //
@@ -852,7 +914,8 @@ Time FromChrono(const std::chrono::system_clock::time_point& tp);
 //   absl::Time t = absl::FromTimeT(123);
 //   auto tp = absl::ToChronoTime(t);
 //   // tp == std::chrono::system_clock::from_time_t(123);
-std::chrono::system_clock::time_point ToChronoTime(Time);
+ABSL_ATTRIBUTE_CONST_FUNCTION std::chrono::system_clock::time_point
+    ToChronoTime(Time);
 
 // AbslParseFlag()
 //
@@ -1124,22 +1187,25 @@ inline TimeZone LocalTimeZone() {
 //   absl::Time t = ...;
 //   absl::TimeZone tz = ...;
 //   const auto cd = absl::ToCivilDay(t, tz);
-inline CivilSecond ToCivilSecond(Time t, TimeZone tz) {
+ABSL_ATTRIBUTE_PURE_FUNCTION inline CivilSecond ToCivilSecond(Time t,
+                                                              TimeZone tz) {
   return tz.At(t).cs;  // already a CivilSecond
 }
-inline CivilMinute ToCivilMinute(Time t, TimeZone tz) {
+ABSL_ATTRIBUTE_PURE_FUNCTION inline CivilMinute ToCivilMinute(Time t,
+                                                              TimeZone tz) {
   return CivilMinute(tz.At(t).cs);
 }
-inline CivilHour ToCivilHour(Time t, TimeZone tz) {
+ABSL_ATTRIBUTE_PURE_FUNCTION inline CivilHour ToCivilHour(Time t, TimeZone tz) {
   return CivilHour(tz.At(t).cs);
 }
-inline CivilDay ToCivilDay(Time t, TimeZone tz) {
+ABSL_ATTRIBUTE_PURE_FUNCTION inline CivilDay ToCivilDay(Time t, TimeZone tz) {
   return CivilDay(tz.At(t).cs);
 }
-inline CivilMonth ToCivilMonth(Time t, TimeZone tz) {
+ABSL_ATTRIBUTE_PURE_FUNCTION inline CivilMonth ToCivilMonth(Time t,
+                                                            TimeZone tz) {
   return CivilMonth(tz.At(t).cs);
 }
-inline CivilYear ToCivilYear(Time t, TimeZone tz) {
+ABSL_ATTRIBUTE_PURE_FUNCTION inline CivilYear ToCivilYear(Time t, TimeZone tz) {
   return CivilYear(tz.At(t).cs);
 }
 
@@ -1155,7 +1221,8 @@ inline CivilYear ToCivilYear(Time t, TimeZone tz) {
 // being when two non-existent civil times map to the same transition time.
 //
 // Note: Accepts civil times of any alignment.
-inline Time FromCivil(CivilSecond ct, TimeZone tz) {
+ABSL_ATTRIBUTE_PURE_FUNCTION inline Time FromCivil(CivilSecond ct,
+                                                   TimeZone tz) {
   const auto ti = tz.At(ct);
   if (ti.kind == TimeZone::TimeInfo::SKIPPED) return ti.trans;
   return ti.pre;
@@ -1240,13 +1307,13 @@ inline Time FromDateTime(int64_t year, int mon, int day, int hour,
 // instant, so `tm_isdst != 0` returns the DST instant, and `tm_isdst == 0`
 // returns the non-DST instant, that would have matched if the transition never
 // happened.
-Time FromTM(const struct tm& tm, TimeZone tz);
+ABSL_ATTRIBUTE_PURE_FUNCTION Time FromTM(const struct tm& tm, TimeZone tz);
 
 // ToTM()
 //
 // Converts the given `absl::Time` to a struct tm using the given time zone.
 // See ctime(3) for a description of the values of the tm fields.
-struct tm ToTM(Time t, TimeZone tz);
+ABSL_ATTRIBUTE_PURE_FUNCTION struct tm ToTM(Time t, TimeZone tz);
 
 // RFC3339_full
 // RFC3339_sec
@@ -1305,13 +1372,14 @@ ABSL_DLL extern const char RFC1123_no_wday[];  // %d %b %E4Y %H:%M:%S %z
 // `absl::InfinitePast()`, the returned string will be exactly "infinite-past".
 // In both cases the given format string and `absl::TimeZone` are ignored.
 //
-std::string FormatTime(absl::string_view format, Time t, TimeZone tz);
+ABSL_ATTRIBUTE_PURE_FUNCTION std::string FormatTime(absl::string_view format,
+                                                    Time t, TimeZone tz);
 
 // Convenience functions that format the given time using the RFC3339_full
 // format.  The first overload uses the provided TimeZone, while the second
 // uses LocalTimeZone().
-std::string FormatTime(Time t, TimeZone tz);
-std::string FormatTime(Time t);
+ABSL_ATTRIBUTE_PURE_FUNCTION std::string FormatTime(Time t, TimeZone tz);
+ABSL_ATTRIBUTE_PURE_FUNCTION std::string FormatTime(Time t);
 
 // Output stream operator.
 inline std::ostream& operator<<(std::ostream& os, Time t) {
@@ -1389,18 +1457,20 @@ namespace time_internal {
 // Creates a Duration with a given representation.
 // REQUIRES: hi,lo is a valid representation of a Duration as specified
 // in time/duration.cc.
-constexpr Duration MakeDuration(int64_t hi, uint32_t lo = 0) {
+ABSL_ATTRIBUTE_CONST_FUNCTION constexpr Duration MakeDuration(int64_t hi,
+                                                              uint32_t lo = 0) {
   return Duration(hi, lo);
 }
 
-constexpr Duration MakeDuration(int64_t hi, int64_t lo) {
+ABSL_ATTRIBUTE_CONST_FUNCTION constexpr Duration MakeDuration(int64_t hi,
+                                                              int64_t lo) {
   return MakeDuration(hi, static_cast<uint32_t>(lo));
 }
 
 // Make a Duration value from a floating-point number, as long as that number
 // is in the range [ 0 .. numeric_limits<int64_t>::max ), that is, as long as
 // it's positive and can be converted to int64_t without risk of UB.
-inline Duration MakePosDoubleDuration(double n) {
+ABSL_ATTRIBUTE_CONST_FUNCTION inline Duration MakePosDoubleDuration(double n) {
   const int64_t int_secs = static_cast<int64_t>(n);
   const uint32_t ticks = static_cast<uint32_t>(
       std::round((n - static_cast<double>(int_secs)) * kTicksPerSecond));
@@ -1413,23 +1483,28 @@ inline Duration MakePosDoubleDuration(double n) {
 // pair. sec may be positive or negative.  ticks must be in the range
 // -kTicksPerSecond < *ticks < kTicksPerSecond.  If ticks is negative it
 // will be normalized to a positive value in the resulting Duration.
-constexpr Duration MakeNormalizedDuration(int64_t sec, int64_t ticks) {
+ABSL_ATTRIBUTE_CONST_FUNCTION constexpr Duration MakeNormalizedDuration(
+    int64_t sec, int64_t ticks) {
   return (ticks < 0) ? MakeDuration(sec - 1, ticks + kTicksPerSecond)
                      : MakeDuration(sec, ticks);
 }
 
 // Provide access to the Duration representation.
-constexpr int64_t GetRepHi(Duration d) { return d.rep_hi_; }
-constexpr uint32_t GetRepLo(Duration d) { return d.rep_lo_; }
+ABSL_ATTRIBUTE_CONST_FUNCTION constexpr int64_t GetRepHi(Duration d) {
+  return d.rep_hi_;
+}
+ABSL_ATTRIBUTE_CONST_FUNCTION constexpr uint32_t GetRepLo(Duration d) {
+  return d.rep_lo_;
+}
 
 // Returns true iff d is positive or negative infinity.
-constexpr bool IsInfiniteDuration(Duration d) {
+ABSL_ATTRIBUTE_CONST_FUNCTION constexpr bool IsInfiniteDuration(Duration d) {
   return GetRepLo(d) == ~uint32_t{0};
 }
 
 // Returns an infinite Duration with the opposite sign.
 // REQUIRES: IsInfiniteDuration(d)
-constexpr Duration OppositeInfinity(Duration d) {
+ABSL_ATTRIBUTE_CONST_FUNCTION constexpr Duration OppositeInfinity(Duration d) {
   return GetRepHi(d) < 0
              ? MakeDuration((std::numeric_limits<int64_t>::max)(), ~uint32_t{0})
              : MakeDuration((std::numeric_limits<int64_t>::min)(),
@@ -1437,7 +1512,8 @@ constexpr Duration OppositeInfinity(Duration d) {
 }
 
 // Returns (-n)-1 (equivalently -(n+1)) without avoidable overflow.
-constexpr int64_t NegateAndSubtractOne(int64_t n) {
+ABSL_ATTRIBUTE_CONST_FUNCTION constexpr int64_t NegateAndSubtractOne(
+    int64_t n) {
   // Note: Good compilers will optimize this expression to ~n when using
   // a two's-complement representation (which is required for int64_t).
   return (n < 0) ? -(n + 1) : (-n) - 1;
@@ -1447,23 +1523,30 @@ constexpr int64_t NegateAndSubtractOne(int64_t n) {
 // functions depend on the above mentioned choice of the Unix epoch for the
 // Time representation (and both need to be Time friends).  Without this
 // knowledge, we would need to add-in/subtract-out UnixEpoch() respectively.
-constexpr Time FromUnixDuration(Duration d) { return Time(d); }
-constexpr Duration ToUnixDuration(Time t) { return t.rep_; }
+ABSL_ATTRIBUTE_CONST_FUNCTION constexpr Time FromUnixDuration(Duration d) {
+  return Time(d);
+}
+ABSL_ATTRIBUTE_CONST_FUNCTION constexpr Duration ToUnixDuration(Time t) {
+  return t.rep_;
+}
 
 template <std::intmax_t N>
-constexpr Duration FromInt64(int64_t v, std::ratio<1, N>) {
+ABSL_ATTRIBUTE_CONST_FUNCTION constexpr Duration FromInt64(int64_t v,
+                                                           std::ratio<1, N>) {
   static_assert(0 < N && N <= 1000 * 1000 * 1000, "Unsupported ratio");
   // Subsecond ratios cannot overflow.
   return MakeNormalizedDuration(
       v / N, v % N * kTicksPerNanosecond * 1000 * 1000 * 1000 / N);
 }
-constexpr Duration FromInt64(int64_t v, std::ratio<60>) {
+ABSL_ATTRIBUTE_CONST_FUNCTION constexpr Duration FromInt64(int64_t v,
+                                                           std::ratio<60>) {
   return (v <= (std::numeric_limits<int64_t>::max)() / 60 &&
           v >= (std::numeric_limits<int64_t>::min)() / 60)
              ? MakeDuration(v * 60)
              : v > 0 ? InfiniteDuration() : -InfiniteDuration();
 }
-constexpr Duration FromInt64(int64_t v, std::ratio<3600>) {
+ABSL_ATTRIBUTE_CONST_FUNCTION constexpr Duration FromInt64(int64_t v,
+                                                           std::ratio<3600>) {
   return (v <= (std::numeric_limits<int64_t>::max)() / 3600 &&
           v >= (std::numeric_limits<int64_t>::min)() / 3600)
              ? MakeDuration(v * 3600)
@@ -1483,40 +1566,44 @@ constexpr auto IsValidRep64(char) -> bool {
 
 // Converts a std::chrono::duration to an absl::Duration.
 template <typename Rep, typename Period>
-constexpr Duration FromChrono(const std::chrono::duration<Rep, Period>& d) {
+ABSL_ATTRIBUTE_PURE_FUNCTION constexpr Duration FromChrono(
+    const std::chrono::duration<Rep, Period>& d) {
   static_assert(IsValidRep64<Rep>(0), "duration::rep is invalid");
   return FromInt64(int64_t{d.count()}, Period{});
 }
 
 template <typename Ratio>
-int64_t ToInt64(Duration d, Ratio) {
+ABSL_ATTRIBUTE_CONST_FUNCTION int64_t ToInt64(Duration d, Ratio) {
   // Note: This may be used on MSVC, which may have a system_clock period of
   // std::ratio<1, 10 * 1000 * 1000>
   return ToInt64Seconds(d * Ratio::den / Ratio::num);
 }
 // Fastpath implementations for the 6 common duration units.
-inline int64_t ToInt64(Duration d, std::nano) {
+ABSL_ATTRIBUTE_CONST_FUNCTION inline int64_t ToInt64(Duration d, std::nano) {
   return ToInt64Nanoseconds(d);
 }
-inline int64_t ToInt64(Duration d, std::micro) {
+ABSL_ATTRIBUTE_CONST_FUNCTION inline int64_t ToInt64(Duration d, std::micro) {
   return ToInt64Microseconds(d);
 }
-inline int64_t ToInt64(Duration d, std::milli) {
+ABSL_ATTRIBUTE_CONST_FUNCTION inline int64_t ToInt64(Duration d, std::milli) {
   return ToInt64Milliseconds(d);
 }
-inline int64_t ToInt64(Duration d, std::ratio<1>) {
+ABSL_ATTRIBUTE_CONST_FUNCTION inline int64_t ToInt64(Duration d,
+                                                     std::ratio<1>) {
   return ToInt64Seconds(d);
 }
-inline int64_t ToInt64(Duration d, std::ratio<60>) {
+ABSL_ATTRIBUTE_CONST_FUNCTION inline int64_t ToInt64(Duration d,
+                                                     std::ratio<60>) {
   return ToInt64Minutes(d);
 }
-inline int64_t ToInt64(Duration d, std::ratio<3600>) {
+ABSL_ATTRIBUTE_CONST_FUNCTION inline int64_t ToInt64(Duration d,
+                                                     std::ratio<3600>) {
   return ToInt64Hours(d);
 }
 
 // Converts an absl::Duration to a chrono duration of type T.
 template <typename T>
-T ToChronoDuration(Duration d) {
+ABSL_ATTRIBUTE_CONST_FUNCTION T ToChronoDuration(Duration d) {
   using Rep = typename T::rep;
   using Period = typename T::period;
   static_assert(IsValidRep64<Rep>(0), "duration::rep is invalid");
@@ -1530,7 +1617,8 @@ T ToChronoDuration(Duration d) {
 
 }  // namespace time_internal
 
-constexpr bool operator<(Duration lhs, Duration rhs) {
+ABSL_ATTRIBUTE_CONST_FUNCTION constexpr bool operator<(Duration lhs,
+                                                       Duration rhs) {
   return time_internal::GetRepHi(lhs) != time_internal::GetRepHi(rhs)
              ? time_internal::GetRepHi(lhs) < time_internal::GetRepHi(rhs)
          : time_internal::GetRepHi(lhs) == (std::numeric_limits<int64_t>::min)()
@@ -1539,12 +1627,13 @@ constexpr bool operator<(Duration lhs, Duration rhs) {
              : time_internal::GetRepLo(lhs) < time_internal::GetRepLo(rhs);
 }
 
-constexpr bool operator==(Duration lhs, Duration rhs) {
+ABSL_ATTRIBUTE_CONST_FUNCTION constexpr bool operator==(Duration lhs,
+                                                        Duration rhs) {
   return time_internal::GetRepHi(lhs) == time_internal::GetRepHi(rhs) &&
          time_internal::GetRepLo(lhs) == time_internal::GetRepLo(rhs);
 }
 
-constexpr Duration operator-(Duration d) {
+ABSL_ATTRIBUTE_CONST_FUNCTION constexpr Duration operator-(Duration d) {
   // This is a little interesting because of the special cases.
   //
   // If rep_lo_ is zero, we have it easy; it's safe to negate rep_hi_, we're
@@ -1570,47 +1659,53 @@ constexpr Duration operator-(Duration d) {
                              time_internal::GetRepLo(d));
 }
 
-constexpr Duration InfiniteDuration() {
+ABSL_ATTRIBUTE_CONST_FUNCTION constexpr Duration InfiniteDuration() {
   return time_internal::MakeDuration((std::numeric_limits<int64_t>::max)(),
                                      ~uint32_t{0});
 }
 
-constexpr Duration FromChrono(const std::chrono::nanoseconds& d) {
+ABSL_ATTRIBUTE_PURE_FUNCTION constexpr Duration FromChrono(
+    const std::chrono::nanoseconds& d) {
   return time_internal::FromChrono(d);
 }
-constexpr Duration FromChrono(const std::chrono::microseconds& d) {
+ABSL_ATTRIBUTE_PURE_FUNCTION constexpr Duration FromChrono(
+    const std::chrono::microseconds& d) {
   return time_internal::FromChrono(d);
 }
-constexpr Duration FromChrono(const std::chrono::milliseconds& d) {
+ABSL_ATTRIBUTE_PURE_FUNCTION constexpr Duration FromChrono(
+    const std::chrono::milliseconds& d) {
   return time_internal::FromChrono(d);
 }
-constexpr Duration FromChrono(const std::chrono::seconds& d) {
+ABSL_ATTRIBUTE_PURE_FUNCTION constexpr Duration FromChrono(
+    const std::chrono::seconds& d) {
   return time_internal::FromChrono(d);
 }
-constexpr Duration FromChrono(const std::chrono::minutes& d) {
+ABSL_ATTRIBUTE_PURE_FUNCTION constexpr Duration FromChrono(
+    const std::chrono::minutes& d) {
   return time_internal::FromChrono(d);
 }
-constexpr Duration FromChrono(const std::chrono::hours& d) {
+ABSL_ATTRIBUTE_PURE_FUNCTION constexpr Duration FromChrono(
+    const std::chrono::hours& d) {
   return time_internal::FromChrono(d);
 }
 
-constexpr Time FromUnixNanos(int64_t ns) {
+ABSL_ATTRIBUTE_CONST_FUNCTION constexpr Time FromUnixNanos(int64_t ns) {
   return time_internal::FromUnixDuration(Nanoseconds(ns));
 }
 
-constexpr Time FromUnixMicros(int64_t us) {
+ABSL_ATTRIBUTE_CONST_FUNCTION constexpr Time FromUnixMicros(int64_t us) {
   return time_internal::FromUnixDuration(Microseconds(us));
 }
 
-constexpr Time FromUnixMillis(int64_t ms) {
+ABSL_ATTRIBUTE_CONST_FUNCTION constexpr Time FromUnixMillis(int64_t ms) {
   return time_internal::FromUnixDuration(Milliseconds(ms));
 }
 
-constexpr Time FromUnixSeconds(int64_t s) {
+ABSL_ATTRIBUTE_CONST_FUNCTION constexpr Time FromUnixSeconds(int64_t s) {
   return time_internal::FromUnixDuration(Seconds(s));
 }
 
-constexpr Time FromTimeT(time_t t) {
+ABSL_ATTRIBUTE_CONST_FUNCTION constexpr Time FromTimeT(time_t t) {
   return time_internal::FromUnixDuration(Seconds(t));
 }
 
diff --git a/absl/time/time_benchmark.cc b/absl/time/time_benchmark.cc
index 99e62799..93a7c41b 100644
--- a/absl/time/time_benchmark.cc
+++ b/absl/time/time_benchmark.cc
@@ -185,9 +185,11 @@ void BM_Time_FromCivil_Absl(benchmark::State& state) {
   int i = 0;
   while (state.KeepRunning()) {
     if ((i & 1) == 0) {
-      absl::FromCivil(absl::CivilSecond(2014, 12, 18, 20, 16, 18), tz);
+      benchmark::DoNotOptimize(
+          absl::FromCivil(absl::CivilSecond(2014, 12, 18, 20, 16, 18), tz));
     } else {
-      absl::FromCivil(absl::CivilSecond(2013, 11, 15, 18, 30, 27), tz);
+      benchmark::DoNotOptimize(
+          absl::FromCivil(absl::CivilSecond(2013, 11, 15, 18, 30, 27), tz));
     }
     ++i;
   }
@@ -224,7 +226,8 @@ BENCHMARK(BM_Time_FromCivil_Libc);
 void BM_Time_FromCivilUTC_Absl(benchmark::State& state) {
   const absl::TimeZone tz = absl::UTCTimeZone();
   while (state.KeepRunning()) {
-    absl::FromCivil(absl::CivilSecond(2014, 12, 18, 20, 16, 18), tz);
+    benchmark::DoNotOptimize(
+        absl::FromCivil(absl::CivilSecond(2014, 12, 18, 20, 16, 18), tz));
   }
 }
 BENCHMARK(BM_Time_FromCivilUTC_Absl);
@@ -235,9 +238,11 @@ void BM_Time_FromCivilDay0_Absl(benchmark::State& state) {
   int i = 0;
   while (state.KeepRunning()) {
     if ((i & 1) == 0) {
-      absl::FromCivil(absl::CivilSecond(2014, 12, 0, 20, 16, 18), tz);
+      benchmark::DoNotOptimize(
+          absl::FromCivil(absl::CivilSecond(2014, 12, 0, 20, 16, 18), tz));
     } else {
-      absl::FromCivil(absl::CivilSecond(2013, 11, 0, 18, 30, 27), tz);
+      benchmark::DoNotOptimize(
+          absl::FromCivil(absl::CivilSecond(2013, 11, 0, 18, 30, 27), tz));
     }
     ++i;
   }