Optimize DateTime constructors (DateToTicks and IsLeapYear) #46245

EgorBo · 2020-12-19T10:31:54Z

Just a nano-optimization to make some of the DateTime constructors a bit faster, e.g.:

[Benchmark]
public DateTime CreateDate_const()
{
    return new DateTime(2021, 5, 20);
}

[Benchmark]
[Arguments(2021, 5, 20)]
public DateTime CreateDate_var(int y, int m, int d)
{
    return new DateTime(y, m, d); // and other constructors with DateToTicks/IsLeapYear checks inside
}

/*

            |           Method |      Mean |
            |----------------- |----------:|
     master | CreateDate_const | 0.3712 ns |
     PR     | CreateDate_const | 0.2356 ns |
     master |   CreateDate_var | 2.6116 ns |
     PR     |   CreateDate_var | 2.1922 ns |

*/

Codegen diff for CreateDate_var: https://www.diffchecker.com/BOTFFqql (336 bytes -> 286 bytes), for arm64: https://www.diffchecker.com/H8xUCOtO (448 bytes -> 400 bytes)

Feel free to close if you think the hacks aren't worth it 🙂

Dotnet-GitSync-Bot · 2020-12-19T10:31:57Z

I couldn't figure out the best area label to add to this PR. If you have write-permissions please help me learn by adding exactly one area label.

EgorBo · 2020-12-19T10:41:34Z

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

-            return (year & 3) == 0 && ((year & 15) == 0 || (year % 25) != 0);
+            return (year & 3) == 0 && ((year & 15) == 0 ||
+                   // TODO: optimize "(uint)year % 25 != 0" in JIT to produce:
+                   (year * -1030792151 > 171798691));
        }


https://godbolt.org/z/8qdPEK

EgorBo · 2020-12-19T10:44:58Z

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

-            int y = year - 1;
-            int n = y * 365 + y / 4 - y / 100 + y / 400 + days[month - 1] + day - 1;
+            uint y = (uint)(year - 1);
+            uint n = y * 365 + y / 4 - y / 100 + y / 400 + (uint)days[month - 1] + (uint)day - 1;
            return n * TicksPerDay;
        }


y is int but always is in the [1..9999] range so can be treated as unsigned (X /u C is faster than X / C) sharplab.io

jkotas · 2020-12-19T16:55:05Z

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

@@ -635,8 +635,8 @@ private static long DateToTicks(int year, int month, int day)
                ThrowHelper.ThrowArgumentOutOfRange_BadYearMonthDay();
            }

-            int y = year - 1;
-            int n = y * 365 + y / 4 - y / 100 + y / 400 + days[month - 1] + day - 1;
+            uint y = (uint)(year - 1);


A similar optimization is part of #46245

jkotas · 2020-12-19T16:56:39Z

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

@@ -1130,7 +1130,9 @@ public static bool IsLeapYear(int year)
            {
                ThrowHelper.ThrowArgumentOutOfRange_Year();
            }
-            return (year & 3) == 0 && ((year & 15) == 0 || (year % 25) != 0);
+            return (year & 3) == 0 && ((year & 15) == 0 ||
+                   // TODO: optimize "(uint)year % 25 != 0" in JIT to produce:


Yes, we should fix the JIT instead of sprinkling manually generated magic div and mod everywhere. I had the same comment in #45479 (comment)

ah didn't notice that pr 🙂

Optimize DateToTicks and IsLeapYear

0acacc6

EgorBo added the area-System.Runtime label Dec 19, 2020

EgorBo commented Dec 19, 2020

View reviewed changes

Update DateTime.cs

69f28bf

jkotas reviewed Dec 19, 2020

View reviewed changes

EgorBo closed this Dec 19, 2020

ghost locked as resolved and limited conversation to collaborators Jan 18, 2021

jeffhandley added area-System.DateTime and removed area-System.Runtime labels Nov 22, 2022

Provide feedback

Saved searches

Use saved searches to filter your results more quickly

Optimize DateTime constructors (DateToTicks and IsLeapYear) #46245

Optimize DateTime constructors (DateToTicks and IsLeapYear) #46245

EgorBo commented Dec 19, 2020 •

edited

Loading

Dotnet-GitSync-Bot commented Dec 19, 2020

EgorBo Dec 19, 2020

EgorBo Dec 19, 2020 •

edited

Loading

jkotas Dec 19, 2020

jkotas Dec 19, 2020

EgorBo Dec 19, 2020

Optimize DateTime constructors (DateToTicks and IsLeapYear) #46245

Optimize DateTime constructors (DateToTicks and IsLeapYear) #46245

Conversation

EgorBo commented Dec 19, 2020 • edited Loading

Dotnet-GitSync-Bot commented Dec 19, 2020

EgorBo Dec 19, 2020

Choose a reason for hiding this comment

EgorBo Dec 19, 2020 • edited Loading

Choose a reason for hiding this comment

jkotas Dec 19, 2020

Choose a reason for hiding this comment

jkotas Dec 19, 2020

Choose a reason for hiding this comment

EgorBo Dec 19, 2020

Choose a reason for hiding this comment

EgorBo commented Dec 19, 2020 •

edited

Loading

EgorBo Dec 19, 2020 •

edited

Loading