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Optimize more bound checks around logical operators#122263

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EgorBo merged 6 commits intodotnet:mainfrom
EgorBo:simplify-range-check
Jan 13, 2026
Merged

Optimize more bound checks around logical operators#122263
EgorBo merged 6 commits intodotnet:mainfrom
EgorBo:simplify-range-check

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@EgorBo EgorBo commented Dec 6, 2025

Closes #122150
Example:

int Test(byte inData)
{
    ReadOnlySpan<byte> base64 = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/="u8;
    return base64[((inData & 0x03) << 4) | ((inData & 0xf0) >> 4)];
}

Was:

; Method Program:Test(byte):int:this (FullOpts)
       sub      rsp, 40
       movzx    rax, dl
       mov      ecx, eax
       and      ecx, 3
       shl      ecx, 4
       and      eax, 240
       sar      eax, 4
       or       eax, ecx
       cmp      eax, 65
       jae      SHORT G_M54716_IG04
       mov      rcx, 0x196B4CC2D88      ; static handle
       movzx    rax, byte  ptr [rcx+rax]
       add      rsp, 40
       ret      
G_M54716_IG04:
       call     CORINFO_HELP_RNGCHKFAIL
       int3     
; Total bytes of code: 55

Now:

; Method Program:Test(byte):int:this (FullOpts)
       movzx    rax, dl
       mov      ecx, eax
       and      ecx, 3
       shl      ecx, 4
       and      eax, 240
       sar      eax, 4
       or       eax, ecx
       mov      rcx, 0x171D74A2D88      ; static handle
       movzx    rax, byte  ptr [rcx+rax]
       ret      
; Total bytes of code: 36

As the result, was able to optimize bound checks in Convert.ConvertToBase64Array

@github-actions github-actions bot added the area-CodeGen-coreclr CLR JIT compiler in src/coreclr/src/jit and related components such as SuperPMI label Dec 6, 2025
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EgorBo commented Dec 6, 2025

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am11
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dotnet-policy-service bot commented Jan 6, 2026

Draft Pull Request was automatically closed for 30 days of inactivity. Please let us know if you'd like to reopen it.

@EgorBo EgorBo reopened this Jan 9, 2026
@EgorBo EgorBo closed this Jan 11, 2026
@EgorBo EgorBo force-pushed the simplify-range-check branch from 90ae7aa to d2e3c3c Compare January 11, 2026 19:43
@EgorBo EgorBo reopened this Jan 11, 2026
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EgorBo commented Jan 11, 2026

/azp run Fuzzlyn

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@EgorBo EgorBo marked this pull request as ready for review January 11, 2026 21:12
Copilot AI review requested due to automatic review settings January 11, 2026 21:12
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Pull request overview

This PR optimizes bounds check elimination for expressions involving bitwise AND, OR, and shift operations. The JIT compiler's range check analysis is enhanced to understand value ranges produced by these operations, enabling automatic elimination of bounds checks in patterns like base64 encoding where bitwise operations produce values that are provably within array bounds.

Changes:

  • Enhanced JIT range check analysis to compute ranges for GT_AND, GT_OR, and GT_UMOD operations
  • Refactored ComputeRangeForBinOp to use a cleaner switch-based dispatch and lambda for range computation
  • Modified System.Private.CoreLib's Convert.ConvertToBase64Array to use ReadOnlySpan instead of fixed pointers, relying on the enhanced range check elimination
  • Added natvis debugging visualizations for Limit and Range types

Reviewed changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated 2 comments.

File Description
src/libraries/System.Private.CoreLib/src/System/Convert.cs Changed ConvertToBase64Array from using fixed pointer to ReadOnlySpan, removing one level of indentation; logic otherwise unchanged
src/coreclr/jit/rangecheck.h Added new range operations: ShiftLeft, And, Or, and UnsignedMod to compute value ranges for these binary operations
src/coreclr/jit/rangecheck.cpp Refactored ComputeRangeForBinOp to use switch statement dispatch and added support for GT_OR; removed GT_RSZ from range computation
src/coreclr/jit/clrjit.natvis Added debugging visualizers for Limit and Range types

@EgorBo EgorBo force-pushed the simplify-range-check branch from 1e09cca to b082f0e Compare January 11, 2026 23:30
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EgorBo commented Jan 12, 2026

PTAL @dotnet/jit-contrib
A small refactoring in range check + allowed OR binary operator. I recommend reviewing with disabled whitespaces

@EgorBo EgorBo requested a review from a team January 12, 2026 12:54
AndyAyersMS
AndyAyersMS reviewed Jan 12, 2026
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EgorBo commented Jan 13, 2026

@AndyAyersMS I've addressed the feedback

@EgorBo EgorBo enabled auto-merge (squash) January 13, 2026 16:25
@EgorBo EgorBo merged commit d2dda32 into dotnet:main Jan 13, 2026
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@EgorBo EgorBo deleted the simplify-range-check branch January 13, 2026 16:25
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@AndyAyersMS AndyAyersMS AndyAyersMS approved these changes

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Bound Check for arr[(X & 0x3) << 4] pattern

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