Support loop cloning of class member arrays

Currently, if the array being iterated is a class member (and not a function local), we can't analyze the access (e.g., can't determine if the array object is loop-invariant).

e.g.,

public class Program
{
    int[] array = new int[1000003];

    public int Sum()
    {
        int sum = 0;
        for (int i = 0; i < array.Length; i++)
            sum += array[i];
        return sum;
    }
}

category:cq
theme:loop-opt
skill-level:expert
cost:large
impact:medium

Just a question out of curiousity: I guess you can't guarantee that someone else doesn't change the array reference while looping.

What would be the criterias for assuming that the code up to the element-access is "short" enough / that it's safe to fetch the instance once, check and then access it without bound-checks?

Just a question out of curiousity: I guess you can't guarantee that someone else doesn't change the array reference while looping.

What would be the criterias for assuming that the code up to the element-access is "short" enough / that it's safe to fetch the instance once, check and then access it without bound-checks?

Our memory model allows us to hoist the array access regardless of the loop's length. Developers are expected to use volatile if that behavior is not desired (preferably, lock actually since lock-free is extremely difficult to do correctly).

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Support loop cloning of class member arrays #77071

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Support loop cloning of class member arrays #77071

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ChrML commented on Apr 16, 2024

EgorBo commented on Mar 20, 2025

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