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Fold "new T[size].Length" into "size" #114845

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merged 1 commit into from
Apr 22, 2025
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Fold "new T[size].Length" into "size" #114845

merged 1 commit into from
Apr 22, 2025
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@EgorBo EgorBo commented Apr 20, 2025 •
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Closes #114744

static void Test(int count)
{
    int[] arrA = new int[count];
    float[] arrB = new float[count];
    for (int i = 0; i < count; i++)
    {
        arrA[i] = 0;     // bounds check
        arrB[i] = 0.0f;  // bounds check
    }
}

Codegen diff: https://www.diffchecker.com/7iCHeDLt/

Seems like this transformation produces nice SPMI diffs.

@ghost ghost added the area-CodeGen-coreclr CLR JIT compiler in src/coreclr/src/jit and related components such as SuperPMI label Apr 20, 2025
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@EgorBo EgorBo mentioned this pull request Apr 20, 2025
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@EgorBo EgorBo marked this pull request as ready for review April 20, 2025 17:02
@Copilot Copilot AI review requested due to automatic review settings April 20, 2025 17:02
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Pull Request Overview

This PR implements an optimization to fold the expression new T[size].Length into the original size argument, reducing unnecessary bounds checks and streamlining array length calculations.

  • Introduces a new folding case for ARR_LENGTH with new array expressions.
  • Handles different type cases (TYP_LONG and TYP_INT) to extract the original size.

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EgorBo commented Apr 20, 2025

PTAL @AndyAyersMS @jakobbotsch @dotnet/jit-contrib simple opt with diffs.

@EgorBo EgorBo requested a review from AndyAyersMS April 20, 2025 17:04
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@EgorBot EgorBot mentioned this pull request Apr 21, 2025
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@EgorBo EgorBo merged commit 8af737a into dotnet:main Apr 22, 2025
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@EgorBo EgorBo deleted the fold-arr-len-pattern branch April 22, 2025 11:33
This was referenced Apr 29, 2025
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JIT: Redundant bounds check for when loopUpperBound==arrayLength
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