Bounds checks for "a[i] followed by a[j] when j > i"

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#112,694 1 comment 0 reactions 1 assignee View on GitHub

@EgorBo is already working on this.

Since Feb 19, 2025.

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Description

area-CodeGen-coreclr

Minimal repro for a case with a redundant bounds check

void Test(byte[] arr, int i, int j)
{
    if (j <= i && j >= 0) // hints
    {
        arr[i] = 0;
        arr[j] = 0; // redundant bounds check
    }
}

Current codegen:

; Assembly listing for method Bench:Test(ubyte[],int,int)
       sub      rsp, 40
       cmp      r8d, edx
       jg       SHORT G_M58188_IG04
       test     r8d, r8d
       jl       SHORT G_M58188_IG04
       mov      eax, dword ptr [rcx+0x08]
       cmp      edx, eax
       jae      SHORT G_M58188_IG05
       mov      edx, edx
       mov      byte  ptr [rcx+rdx+0x10], 0
       cmp      r8d, eax
       jae      SHORT G_M58188_IG05 ;; <---------------- redundant check
       mov      eax, r8d
       mov      byte  ptr [rcx+rax+0x10], 0
G_M58188_IG04:
       add      rsp, 40
       ret      
G_M58188_IG05:
       call     CORINFO_HELP_RNGCHKFAIL
       int3     
; Total bytes of code 52
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