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Eliminate bound checks for "arr[arr.Length - cns]" by EgorBo · Pull Request #84213 · dotnet/runtime · GitHub
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Eliminate bound checks for "arr[arr.Length - cns]" #84213

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Merged
merged 6 commits into from
Apr 2, 2023
Merged

Eliminate bound checks for "arr[arr.Length - cns]" #84213

merged 6 commits into from
Apr 2, 2023

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@EgorBo EgorBo commented Apr 1, 2023 •
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Motivation: #84210 (comment)

void Test1(int[] arr)
{
    if (arr.Length == 0 || arr[arr.Length - 1] == 0)
        Console.WriteLine();
}

void Test2(int[] arr)
{
    if (arr.Length < 10)
        return;
    
    if (arr[^10] == 0)
        Console.WriteLine();
}

Previous codegen:

; Method Test1(int[]):this
       sub      rsp, 40
       mov      eax, dword ptr [rdx+08H]
       test     eax, eax
       je       SHORT G_M32023_IG04
       lea      ecx, [rax-01H]
       cmp      ecx, eax
       jae      SHORT G_M32023_IG06
       mov      eax, ecx
       cmp      dword ptr [rdx+4*rax+10H], 0
       jne      SHORT G_M32023_IG05
G_M32023_IG04:
       add      rsp, 40
       tail.jmp [System.Console:WriteLine()]
G_M32023_IG05:
       add      rsp, 40
       ret      
G_M32023_IG06:
       call     CORINFO_HELP_RNGCHKFAIL
       int3     
; Total bytes of code: 48


; Method Test2(int[]):this
       sub      rsp, 40
       mov      eax, dword ptr [rdx+08H]
       cmp      eax, 10
       jge      SHORT G_M54292_IG04
       add      rsp, 40
       ret      
G_M54292_IG04:
       lea      ecx, [rax-0AH]
       cmp      ecx, eax
       jae      SHORT G_M54292_IG07
       mov      eax, ecx
       cmp      dword ptr [rdx+4*rax+10H], 0
       jne      SHORT G_M54292_IG06
       add      rsp, 40
       tail.jmp [System.Console:WriteLine()]
G_M54292_IG06:
       add      rsp, 40
       ret      
G_M54292_IG07:
       call     CORINFO_HELP_RNGCHKFAIL
       int3     
; Total bytes of code: 54

New codegen:

; Method Test1(int[]):this
       mov      eax, dword ptr [rdx+08H]
       test     eax, eax
       je       SHORT G_M32023_IG04
       dec      eax
       cmp      dword ptr [rdx+4*rax+10H], 0
       jne      SHORT G_M32023_IG05
G_M32023_IG04:
       tail.jmp [System.Console:WriteLine()]
G_M32023_IG05:
       ret      
; Total bytes of code: 23


; Method Test2(int[]):this
       mov      eax, dword ptr [rdx+08H]
       cmp      eax, 10
       jge      SHORT G_M54292_IG04
       ret      
G_M54292_IG04:
       add      eax, -10
       cmp      dword ptr [rdx+4*rax+10H], 0
       jne      SHORT G_M54292_IG06
       tail.jmp [System.Console:WriteLine()]
G_M54292_IG06:
       ret      
; Total bytes of code: 26

@ghost ghost added the area-CodeGen-coreclr CLR JIT compiler in src/coreclr/src/jit and related components such as SuperPMI label Apr 1, 2023
@ghost ghost assigned EgorBo Apr 1, 2023
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ghost commented Apr 1, 2023

Tagging subscribers to this area: @JulieLeeMSFT, @jakobbotsch, @kunalspathak
See info in area-owners.md if you want to be subscribed.

Issue Details 
void Test(int[] arr)
{
    if (arr.Length == 0 || arr[arr.Length - 1] == 0)
    {
        Console.WriteLine();
    }
}

Was:

; Method Prog:Test(int[]):this
       sub      rsp, 40
       mov      eax, dword ptr [rdx+08H]
       test     eax, eax
       je       SHORT G_M2580_IG04
       lea      ecx, [rax-01H]
       cmp      ecx, eax
       jae      SHORT G_M2580_IG07
       mov      eax, ecx
       cmp      dword ptr [rdx+4*rax+10H], 0
       jne      SHORT G_M2580_IG05
G_M2580_IG04:
       call     [System.Console:WriteLine()]
G_M2580_IG05:
       nop      
       add      rsp, 40
       ret      
G_M2580_IG07:
       call     CORINFO_HELP_RNGCHKFAIL
       int3     
; Total bytes of code: 45

New:

; Method Prog:Test(int[]):this
       sub      rsp, 40
       mov      eax, dword ptr [rdx+08H]
       test     eax, eax
       je       SHORT G_M2580_IG04
       dec      eax
       cmp      dword ptr [rdx+4*rax+10H], 0
       jne      SHORT G_M2580_IG05
G_M2580_IG04:
       call     [System.Console:WriteLine()]
G_M2580_IG05:
       nop   
       add      rsp, 40
       ret      
; Total bytes of code: 32
Author: EgorBo
Assignees: -
Labels:

area-CodeGen-coreclr
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EgorBo commented Apr 1, 2023

@AndyAyersMS @jakobbotsch @dotnet/jit-contrib PTAL

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EgorBo commented Apr 1, 2023

Diffs, no TP impact.

AndyAyersMS
AndyAyersMS approved these changes Apr 2, 2023
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LGTM.

@EgorBo EgorBo merged commit 443bf51 into dotnet:main Apr 2, 2023
@EgorBo EgorBo deleted the bound-checks-arr-add-cns branch April 2, 2023 15:55
@EgorBo EgorBo mentioned this pull request Apr 4, 2023
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@kunalspathak kunalspathak mentioned this pull request Apr 4, 2023
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@EgorBo EgorBo mentioned this pull request Apr 4, 2023
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@AndyAyersMS AndyAyersMS mentioned this pull request Apr 14, 2023
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@AndyAyersMS AndyAyersMS AndyAyersMS approved these changes

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