Suboptimal codegen for DateTime.IsLeapYear

EgorBo commented 5 years ago

I was looking for opportunities to improve performance of DateTime.UtcNow and noticed that JIT doesn't use magic tricks/peephole optimizations to improve codegen for this:

    bool IsLeapYear(int year)
    {
        if (year > 0 && year < 9999)
            return year % 4 == 0 && (year % 100 != 0 || year % 400 == 0);

        return false; // exception
    }

Currently generates (tier1):

; Method Program:IsLeapYear(int):bool:this

G_M62763_IG01:
       mov      ecx, edx

G_M62763_IG02:
       test     ecx, ecx
       jle      SHORT G_M62763_IG08
       cmp      ecx, 0x270F
       jge      SHORT G_M62763_IG08
       mov      eax, ecx
       sar      eax, 31
       and      eax, 3
       add      eax, ecx
       and      eax, -4
       mov      edx, ecx
       sub      edx, eax
       jne      SHORT G_M62763_IG06
       mov      edx, 0xD1FFAB1E
       mov      eax, edx
       imul     edx:eax, ecx
       mov      eax, edx
       shr      eax, 31
       sar      edx, 5
       add      eax, edx
       imul     eax, eax, 100
       mov      edx, ecx
       sub      edx, eax
       jne      SHORT G_M62763_IG04
       mov      edx, 0xD1FFAB1E
       mov      eax, edx
       imul     edx:eax, ecx
       mov      eax, edx
       shr      eax, 31
       sar      edx, 7
       add      eax, edx
       imul     eax, eax, 400
       sub      ecx, eax
       sete     al
       movzx    rax, al

G_M62763_IG03:
       ret      

G_M62763_IG04:
       mov      eax, 1

G_M62763_IG05:
       ret      

G_M62763_IG06:
       xor      eax, eax

G_M62763_IG07:
       ret      

G_M62763_IG08:
       xor      eax, eax

G_M62763_IG09:
       ret      
; Total bytes of code: 107

And here is the difference between what GCC generates and RyuJIT: