VVMReturnSlot.h

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// Copyright Epic Games, Inc. All Rights Reserved.
 
#pragma once
 
#if WITH_VERSE_VM || defined(__INTELLISENSE__)
 
#include "VerseVM/VVMContext.h"
#include "VerseVM/VVMRestValue.h"
#include "VerseVM/VVMWriteBarrier.h"
 
namespace Verse
{
struct VFrame;
 
struct VReturnSlot
{
    enum class EReturnKind : uint8
    {
        RestValue,
        Value,
    };
 
    template <typename ReturnSlotType>
    VReturnSlot(FAllocationContext Context, ReturnSlotType ReturnSlot)
    {
        Set(Context, ReturnSlot);
    }
 
    VValue Get(FAllocationContext Context)
    {
        if (Kind == EReturnKind::RestValue)
        {
            if (RestValue)
            {
                return RestValue->Get(Context);
            }
            else
            {
                return VValue();
            }
        }
        else
        {
            return Value.Get();
        }
    }
 
    void Set(FAllocationContext Context, VRestValue* InRestValue)
    {
        RestValue = InRestValue;
        Kind = EReturnKind::RestValue;
    }
 
    void SetTransactionally(FAllocationContext Context, VRestValue* InRestValue)
    {
        AutoRTFM::RecordOpenWrite(&RestValue);
        RestValue = InRestValue;
        AutoRTFM::RecordOpenWrite(&Kind);
        Kind = EReturnKind::RestValue;
    }
 
    void Set(FAllocationContext Context, VValue InValue)
    {
        Value.Set(Context, InValue);
        Kind = EReturnKind::Value;
    }
 
    void SetTransactionally(FAllocationContext Context, VValue InValue)
    {
        Value.SetTransactionally(Context, InValue);
        AutoRTFM::RecordOpenWrite(&Kind);
        Kind = EReturnKind::Value;
    }
 
    void Reset()
    {
        EffectToken.Reset(0);
        Kind = EReturnKind::RestValue;
        RestValue = nullptr;
    }
 
    template <typename TVisitor>
    friend void Visit(TVisitor& Visitor, VReturnSlot& Value)
    {
        Visitor.Visit(Value.EffectToken, TEXT("ReturnEffectToken"));
        if (Value.Kind == EReturnKind::Value)
        {
            Visitor.Visit(Value.Value, TEXT("ReturnSlot"));
        }
    }
 
    friend class FInterpreter;
    friend struct VFrame;
 
private:
    VRestValue EffectToken{0};
    union
    {
        // This points into Frame or the C++ stack, so we don't need to tell GC about it.
        VRestValue* RestValue;
        TWriteBarrier<VValue> Value;
    };
    EReturnKind Kind;
};
} // namespace Verse
 
#endif