make DateTime.UtcNow 5% faster to minimize the leap second performance impact

src/System.Private.CoreLib/shared/System/DateTime.cs

@@ -641,32 +641,38 @@ public int CompareTo(DateTime value)
 
         // Returns the tick count corresponding to the given year, month, and day.
         // Will check the if the parameters are valid.
+        [MethodImpl(MethodImplOptions.AggressiveInlining)]
         private static long DateToTicks(int year, int month, int day)
         {
-            if (year >= 1 && year <= 9999 && month >= 1 && month <= 12)
+            if (year < 1 || year > 9999 || month < 1 || month > 12 || day < 1)
             {
-                int[] days = IsLeapYear(year) ? s_daysToMonth366 : s_daysToMonth365;
-                if (day >= 1 && day <= days[month] - days[month - 1])
-                {
-                    int y = year - 1;
-                    int n = y * 365 + y / 4 - y / 100 + y / 400 + days[month - 1] + day - 1;
-                    return n * TicksPerDay;
-                }
+                ThrowHelper.ThrowArgumentOutOfRange_BadYearMonthDay();
+            }
+
+            int[] days = IsLeapYear(year) ? s_daysToMonth366 : s_daysToMonth365;
+            if (day > days[month] - days[month - 1])
+            {
+                ThrowHelper.ThrowArgumentOutOfRange_BadYearMonthDay();
             }
-            throw new ArgumentOutOfRangeException(null, SR.ArgumentOutOfRange_BadYearMonthDay);
+
+            int y = year - 1;
+            int n = y * 365 + y / 4 - y / 100 + y / 400 + days[month - 1] + day - 1;
+            return n * TicksPerDay;
         }
 
         // Return the tick count corresponding to the given hour, minute, second.
         // Will check the if the parameters are valid.
+        [MethodImpl(MethodImplOptions.AggressiveInlining)]
         private static long TimeToTicks(int hour, int minute, int second)
         {
             //TimeSpan.TimeToTicks is a family access function which does no error checking, so
             //we need to put some error checking out here.
-            if (hour >= 0 && hour < 24 && minute >= 0 && minute < 60 && second >= 0 && second < 60)
+            if (hour < 0 || hour >= 24 || minute < 0 || minute >= 60 || second < 0 || second >= 60)
             {
-                return (TimeSpan.TimeToTicks(hour, minute, second));
+                ThrowHelper.ThrowArgumentOutOfRange_BadHourMinuteSecond();
             }
-            throw new ArgumentOutOfRangeException(null, SR.ArgumentOutOfRange_BadHourMinuteSecond);
+
+            return (TimeSpan.TimeToTicks(hour, minute, second));
         }
 
         // Returns the number of days in the month given by the year and
@@ -1182,11 +1188,12 @@ public int Year
         // Checks whether a given year is a leap year. This method returns true if
         // year is a leap year, or false if not.
         //
+        [MethodImpl(MethodImplOptions.AggressiveInlining)]
         public static bool IsLeapYear(int year)
         {
             if (year < 1 || year > 9999)
             {
-                throw new ArgumentOutOfRangeException(nameof(year), SR.ArgumentOutOfRange_Year);
+                ThrowHelper.ThrowArgumentOutOfRange_Year();
             }
             return year % 4 == 0 && (year % 100 != 0 || year % 400 == 0);
         }

src/System.Private.CoreLib/shared/System/ThrowHelper.cs

@@ -131,6 +131,31 @@ internal static void ThrowCountArgumentOutOfRange_ArgumentOutOfRange_Count()
                                                     ExceptionResource.ArgumentOutOfRange_Count);
         }
 
+        [DoesNotReturn]
+        internal static void ThrowArgumentOutOfRange_Year()
+        {
+            throw GetArgumentOutOfRangeException(ExceptionArgument.year,
+                                                    ExceptionResource.ArgumentOutOfRange_Year);
+        }
+
+        [DoesNotReturn]
+        internal static void ThrowArgumentOutOfRange_BadYearMonthDay()
+        {
+            throw new ArgumentOutOfRangeException(null, SR.ArgumentOutOfRange_BadYearMonthDay);
+        }
+
+        [DoesNotReturn]
+        internal static void ThrowArgumentOutOfRange_BadHourMinuteSecond()
+        {
+            throw new ArgumentOutOfRangeException(null, SR.ArgumentOutOfRange_BadHourMinuteSecond);
+        }
+
+        [DoesNotReturn]
+        internal static void ThrowArgumentOutOfRange_TimeSpanTooLong()
+        {
+            throw new ArgumentOutOfRangeException(null, SR.Overflow_TimeSpanTooLong);
+        }
+
         [DoesNotReturn]
         internal static void ThrowWrongKeyTypeArgumentException<T>(T key, Type targetType)
         {
@@ -657,6 +682,8 @@ private static string GetArgumentName(ExceptionArgument argument)
                     return "elementType";
                 case ExceptionArgument.arrayIndex:
                     return "arrayIndex";
+                case ExceptionArgument.year:
+                    return "year";
                 default:
                     Debug.Fail("The enum value is not defined, please check the ExceptionArgument Enum.");
                     return "";
@@ -687,6 +714,8 @@ private static string GetResourceString(ExceptionResource resource)
                     return SR.ArgumentOutOfRange_IndexCountBuffer;
                 case ExceptionResource.ArgumentOutOfRange_Count:
                     return SR.ArgumentOutOfRange_Count;
+                case ExceptionResource.ArgumentOutOfRange_Year:
+                    return SR.ArgumentOutOfRange_Year;
                 case ExceptionResource.Arg_ArrayPlusOffTooSmall:
                     return SR.Arg_ArrayPlusOffTooSmall;
                 case ExceptionResource.NotSupported_ReadOnlyCollection:
@@ -901,6 +930,7 @@ internal enum ExceptionArgument
         endIndex,
         elementType,
         arrayIndex,
+        year,
     }
 
     //
@@ -912,6 +942,7 @@ internal enum ExceptionResource
         ArgumentOutOfRange_IndexCount,
         ArgumentOutOfRange_IndexCountBuffer,
         ArgumentOutOfRange_Count,
+        ArgumentOutOfRange_Year,
         Arg_ArrayPlusOffTooSmall,
         NotSupported_ReadOnlyCollection,
         Arg_RankMultiDimNotSupported,

src/System.Private.CoreLib/shared/System/TimeSpan.cs

@@ -3,6 +3,7 @@
 // See the LICENSE file in the project root for more information.
 
 using System.Globalization;
+using System.Runtime.CompilerServices;
 
 namespace System
 {
@@ -288,13 +289,14 @@ public static TimeSpan FromTicks(long value)
             return new TimeSpan(value);
         }
 
+        [MethodImpl(MethodImplOptions.AggressiveInlining)]
         internal static long TimeToTicks(int hour, int minute, int second)
         {
             // totalSeconds is bounded by 2^31 * 2^12 + 2^31 * 2^8 + 2^31,
             // which is less than 2^44, meaning we won't overflow totalSeconds.
             long totalSeconds = (long)hour * 3600 + (long)minute * 60 + (long)second;
             if (totalSeconds > MaxSeconds || totalSeconds < MinSeconds)
-                throw new ArgumentOutOfRangeException(null, SR.Overflow_TimeSpanTooLong);
+                ThrowHelper.ThrowArgumentOutOfRange_TimeSpanTooLong();
             return totalSeconds * TicksPerSecond;
         }