Entire indirect stores denormalize normalize-on-store locals

[SingleAccretion]

Reproduction:

Console.WriteLine(Problem(0));

[MethodImpl(MethodImplOptions.NoInlining | MethodImplOptions.AggressiveOptimization)]
static short Problem(byte x)
{
    short a = -1;
    Unsafe.InitBlock(&a, x, 2);
    
    return a;
}

Compile and run.

Expected result: the program prints 0.

Actual result: the program prints -65536.

Cause: normalize-on-store assumes all entire stores overwrite the full stack slot.

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Issue Details

---

Reproduction:

Console.WriteLine(Problem(0));

[MethodImpl(MethodImplOptions.NoInlining | MethodImplOptions.AggressiveOptimization)]
static short Problem(byte x)
{
    short a = -1;
    Unsafe.InitBlock(&a, x, 2);
    
    return a;
}

Compile and run.

Expected result: the program prints 0.

Actual result: the program prints -65536.

Cause: normalize-on-store assumes all entire stores overwrite the full stack slot.

Author:	SingleAccretion
Assignees:	-
Labels:	bug, area-CodeGen-coreclr
Milestone:	Future

[SingleAccretion]

We may need to address-expose normalize-on-store locals written this way, to make them normalize-on-load.