[wasm coreclr] unboxing stubs

[radekdoulik]

We are missing unboxing stubs on wasm as these are currently emitted as native code on other platforms.

This can be reached through

TestCallingConvention0(1, 2.0f, 3, 4.0, 5, 6.0);

static void TestCallingConvention0(int a, float b, int c, double d, int e, double f)
{
    Console.WriteLine("TestCallingConvention0: a = {0}, b = {1}, c = {2}, d = {3}, e = {4}, f = {5}", a, b, c, d, e, f);
}

and results in

ASSERT FAILED
	Expression: false && "The EmitComputedInstantiatingMethodStub is not implemented on wasm"
	Location:   line 81 in /Users/rodo/git/runtime-main/src/coreclr/vm/wasm/cgencpu.h
	Function:   EmitComputedInstantiatingMethodStub
	Process:    42
Frame (InterpreterFrame): 0x4fee58
   0) System.Text.ValueStringBuilder::AppendFormatHelper, IR_051c
   1) System.IO.StreamWriter::WriteFormatHelper, IR_007c
   2) System.IO.StreamWriter::WriteLine, IR_0034
   3) System.Console::WriteLine, IR_0013
   4) Program::<<Main>$>g__TestCallingConvention0|0_0, IR_00b4
   5) Program::<Main>$, IR_001c

the native part

StubLinkerCPU::EmitComputedInstantiatingMethodStub(MethodDesc*, ShuffleEntry*, void*) (src/coreclr/vm/wasm/cgencpu.h:81)
MakeUnboxingStubWorker(MethodDesc*) (src/coreclr/vm/prestub.cpp:1723)
MethodDesc::DoPrestub(MethodTable*, CallerGCMode) (src/coreclr/vm/prestub.cpp:2263)
CallPreStub(MethodDesc*)::$_1::operator()(CallPreStub(MethodDesc*)::Param*) const (src/coreclr/vm/interpexec.cpp:641)
CallPreStub(MethodDesc*) (src/coreclr/vm/interpexec.cpp:643)
InterpExecMethod(InterpreterFrame*, InterpMethodContextFrame*, InterpThreadContext*, ExceptionClauseArgs*) (src/coreclr/vm/interpexec.cpp:2453)

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[radekdoulik]

@AaronRobinsonMSFT @davidwrighton do you have time to look at it?

[jkotas]

For now, we should be able to get around this by disabling FEATURE_PORTABLE_SHUFFLE_THUNKS for Wasm and always taking the implementation under FEATURE_INSTANTIATINGSTUB_AS_IL.

This may not be the best option for eventual partial R2R, but that's a problem for future.

[radekdoulik]

OK, I will try that. Do you see some intermediate solution for time before we get R2R? Like adding fcalls for some of these stubs?

[jkotas]

Do you see some intermediate solution for time before we get R2R?

What I have said: "For now, we should be able to get around this by disabling FEATURE_PORTABLE_SHUFFLE_THUNKS for Wasm and always taking the implementation under FEATURE_INSTANTIATINGSTUB_AS_IL."

[radekdoulik]

So how would that look like here?

runtime/src/coreclr/vm/prestub.cpp

Lines 1730 to 1748 in 6cf9c6b

	#ifdef FEATURE_INSTANTIATINGSTUB_AS_IL
	#ifndef FEATURE_PORTABLE_SHUFFLE_THUNKS
	if (pUnboxedMD->RequiresInstMethodTableArg())
	#endif // !FEATURE_PORTABLE_SHUFFLE_THUNKS
	{
	_ASSERTE(pUnboxedMD->RequiresInstMethodTableArg());
	pstub = CreateUnboxingILStubForSharedGenericValueTypeMethods(pUnboxedMD);
	}
	#ifndef FEATURE_PORTABLE_SHUFFLE_THUNKS
	else
	#endif // !FEATURE_PORTABLE_SHUFFLE_THUNKS
	#endif // FEATURE_INSTANTIATINGSTUB_AS_IL
	#ifndef FEATURE_PORTABLE_SHUFFLE_THUNKS
	{
	CPUSTUBLINKER sl;
	sl.EmitUnboxMethodStub(pUnboxedMD);
	pstub = sl.Link(pMD->GetLoaderAllocator()->GetStubHeap(), NEWSTUB_FL_NONE, "UnboxingStub");
	}
	#endif // !FEATURE_PORTABLE_SHUFFLE_THUNKS

Should we use the CreateUnboxingILStubForSharedGenericValueTypeMethods on wasm even when pUnboxedMD->RequiresInstMethodTableArg() is false or would we need new method to create the IL stub for the else branch?

I have quickly tried the former and getting InvalidProgramException, don't know yet where does it come from yet though.

[jkotas]

Try to add if (pUnboxedMD->RequiresInstMethodTableArg()) condition around // Push the hidden context param

If it works, you may want to rename CreateUnboxingILStubForSharedGenericValueTypeMethods to just CreateUnboxingILStubForValueTypeMethods since it does not work just for shared generics anymore.

[radekdoulik]

That works. I think I will refactor CreateUnboxingILStubForSharedGenericValueTypeMethods to have inner part, which will return PCODE. And use it for TARGET_WASM directly to avoid creating the Stub.

[jkotas]

I will refactor CreateUnboxingILStubForSharedGenericValueTypeMethods to have inner part, which will return PCODE

I am not sure whether it is worth it. There are multiple of these paths that pass around Stub. You would have to do the same for all of them. These paths handle rare cases. The extra temporary allocation on these paths is not a problem.