Consider types with ref fields as managed and Allow pointers of managed types in some contexts

[jcouv]

The first commit reverts commit 76bd0d9.

Spec update for the relaxation: dotnet/csharplang#6453
Some context on EE logic: 02a3854

Note: I've built the runtime libraries locally with this change and some suppressions (as expected).

[RikkiGibson]

approving so we can ship .NET 7. Not thrilled about being able to do var ptr = &managed; but not Managed* ptr = &managed; :)

[RikkiGibson]

consider indicating that UnsafeRegion is also needed, since absence of that flag means no pointer types are allowed. #Resolved

[cston]

);

Can we run this code (using IncludeExpectedOutput(...) to run conditionally)?

Same question for the next several tests. #Resolved

[jcouv]

I haven't yet found out which unsafe operations are in fact safe from the JIT's perspective...
Since the IL is small and straightforward, I think it's sufficient.

[cston]

// 1

Consider removing comments // 1 and // 4. #Resolved

[cston]

}

Are we testing implicit stack alloc?

ref struct R { ref int F; }
var a = stackalloc[] { new R() };
``` #Resolved

[cston]

}

Are we testing assignment?

ref struct R { ref int F; }
unsafe static void Assign(IntPtr* p, ref R r)
{
    *(R*)p = r;
}
``` #Resolved

[Neme12]

Given the change that pointers to managed structs are now allowed and considered a warning instead of an error, could someone pls explain why the warning exists - i.e. why are pointers to managed structs considered unsafe (or "unsafe" unsafe) and why was it originally an error? What issues can I run into if I use pointers to managed structs?

There is no documentation for the new warning and I can't find any info on it.