JIT: Unchecked write barriers are emitted for stack allocated arrays

[jakobbotsch]

// Generated by Fuzzlyn v2.4 on 2025-02-19 20:47:50
// Run on X64 Windows
// Seed: 12432040051036532696-vectort,vector128,vector256,x86aes,x86avx,x86avx2,x86avx512bw,x86avx512bwvl,x86avx512cd,x86avx512cdvl,x86avx512dq,x86avx512dqvl,x86avx512f,x86avx512fvl,x86avx512fx64,x86bmi1,x86bmi1x64,x86bmi2,x86bmi2x64,x86fma,x86lzcnt,x86lzcntx64,x86pclmulqdq,x86popcnt,x86popcntx64,x86sse,x86ssex64,x86sse2,x86sse2x64,x86sse3,x86sse41,x86sse41x64,x86sse42,x86sse42x64,x86ssse3,x86x86base
// Reduced from 62.0 KiB to 0.5 KiB in 00:06:15
// Exits with error:
// Fatal error. System.AccessViolationException: Attempted to read or write protected memory. This is often an indication that other memory is corrupt.
//    at Program.Main(Fuzzlyn.ExecutionServer.IRuntime)
//    at Fuzzlyn.ExecutionServer.Program.<RunPairAsync>g__RunAndGetResultAsync|1_0(Byte[], <>c__DisplayClass1_0 ByRef)
//    at Fuzzlyn.ExecutionServer.Program.RunPairAsync(System.Runtime.Loader.AssemblyLoadContext, Fuzzlyn.ExecutionServer.ProgramPair)
//    at Fuzzlyn.ExecutionServer.Program+<>c__DisplayClass0_0.<Main>b__0()
//    at System.Threading.Thread+StartHelper.RunWorker()
//
using System;
using System.Numerics;
using System.Runtime.Intrinsics;
using System.Runtime.Intrinsics.X86;

public class Program
{
    public static void Main()
    {
        Vector256<byte>[][][] vr0 = default(Vector256<byte>[][][]);
        vr0 = new Vector256<byte>[][][]
        {
            new Vector256<byte>[][]
            {
                new Vector256<byte>[]
                {
                    Vector256.Create<byte>(0)
                }
            }
        };
        vr0[0] = vr0[0];
    }
}

Looks introduced by #112527, cc @AndyAyersMS

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[EgorBo]

Likely set by this one.
(not sure if should be just removed, or can take arrayObjVN and check whether it's stack-alloc or not)

[AndyAyersMS]

Odd that it wasn't caught by other tests.

[EgorBo]

Odd that it wasn't caught by other tests.

My fix seems to found 0 text diffs (at least in a few collections I tried) so that'd explain why