[Arm64 Windows] Use portable MP optimized new/alloc

[sdmaclea]

dotnet/coreclr#12333 "[Arm64 / Windows] Use portable MP optimized new/alloc" did not include Windows due to a Contract violation. Debug contract violation and enable for Windows

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[AndyAyersMS]

Do we still want this for 3.0?

Also, we should probably reclassify this as a runtime issue.

[AndyAyersMS]

@jkotas is this worth doing for 3.0?

[jkotas]

Note that this is ARM64 Windows-specific issue. Is .NET Core 3.0 going to be officially supported on Windows ARM64?

In any case, the fix is just about removing an ifdef TODO and see whether the tests pass. I would expect that it will just work.

[jkotas]

Submitted dotnet/coreclr#22283 to see whether there is anything real left to fix.

[jkotas]

The problem is still there. Somebody with Windows ARM64 box needs to debug it.

[jkotas]

@adityamandaleeka Do you happen to have Windows ARM64 box around to debug this?

[adityamandaleeka]

Yes, I do. I'll take a look at this soon.

[AndyAyersMS]

Can you also look at dotnet/coreclr#13590? It may already be fixed.

[adityamandaleeka]

@jkotas I had a chance to look into this today.

The portable alloc fast paths are marked FCALL_CONTRACT which is GC_NOTRIGGER. The problem here is that JIT_NewArr1OBJ_MP_FastPortable calls SetArrayMethodTable which, in debug, calls ArrayBase::AssertArrayTypeDescLoaded to ensure that the type of the array is loaded.

LoadArrayTypeThrowing is GC_TRIGGERS unless FORBIDGC_LOADER_USE_ENABLED is true.

I'm not an expert in this area, but based on what I see, I think it may be okay to stick an ENABLE_FORBID_GC_LOADER_USE_IN_THIS_SCOPE in ArrayBase::AssertArrayTypeDescLoaded since we believe that the type is already loaded if that function is being called. Does that sound right, or am I missing something?

[adityamandaleeka]

@AndyAyersMS I think you're right.

[jkotas]

stick an ENABLE_FORBID_GC_LOADER_USE_IN_THIS_SCOPE in ArrayBase::AssertArrayTypeDescLoaded

Yes, that should work. Could you please try to do that?