Support loop cloning of class member arrays

[BruceForstall]

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

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Issue Details

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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;
    }
}

Author:	BruceForstall
Assignees:	-
Labels:	area-CodeGen-coreclr
Milestone:	8.0.0

[ChrML]

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?