Move unboxing helpers to managed code #109135
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,124 @@ | ||
| // Licensed to the .NET Foundation under one or more agreements. | ||
| // The .NET Foundation licenses this file to you under the MIT license. | ||
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| using System.Diagnostics; | ||
| using System.Runtime.InteropServices; | ||
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| namespace System.Runtime.CompilerServices | ||
| { | ||
| [StackTraceHidden] | ||
| [DebuggerStepThrough] | ||
| internal static unsafe partial class BoxingHelpers | ||
| { | ||
| [DebuggerHidden] | ||
| private static unsafe void InitValueClass(ref byte destBytes, MethodTable *pMT) | ||
| { | ||
| uint numInstanceFieldBytes = pMT->GetNumInstanceFieldBytes(); | ||
| if (((uint)Unsafe.AsPointer(ref destBytes) | numInstanceFieldBytes & ((uint)sizeof(void*) - 1)) != 0) | ||
| { | ||
| // If we have a non-pointer aligned instance field bytes count, or a non-aligned destBytes, we can zero out the data byte by byte | ||
| // And we do not need to concern ourselves with references | ||
| SpanHelpers.ClearWithoutReferences(ref destBytes, numInstanceFieldBytes); | ||
| } | ||
| else | ||
| { | ||
| // Otherwise, use the helper which is safe for that situation | ||
| SpanHelpers.ClearWithReferences(ref Unsafe.As<byte, IntPtr>(ref destBytes), (nuint)numInstanceFieldBytes / (nuint)sizeof(IntPtr)); | ||
| } | ||
| } | ||
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| [DebuggerHidden] | ||
| [MethodImpl(MethodImplOptions.NoInlining)] | ||
| private static bool AreTypesEquivalent(MethodTable* pMTa, MethodTable* pMTb) | ||
| { | ||
| if (pMTa == pMTb) | ||
| { | ||
| return true; | ||
| } | ||
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| if (pMTa->HasTypeEquivalence && pMTb->HasTypeEquivalence) | ||
| { | ||
| return false; | ||
| } | ||
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| return RuntimeHelpers.AreTypesEquivalent(pMTa, pMTb); | ||
| } | ||
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| [DebuggerHidden] | ||
| private static bool IsNullableForType(MethodTable* typeMT, MethodTable* boxedMT) | ||
| { | ||
| if (!typeMT->IsNullable) | ||
| { | ||
| return false; | ||
| } | ||
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| MethodTable *pMTNullableArg = typeMT->InstantiationArg0(); | ||
| if (pMTNullableArg == boxedMT) | ||
| { | ||
| return true; | ||
| } | ||
| else | ||
| { | ||
| return AreTypesEquivalent(pMTNullableArg, boxedMT); | ||
| } | ||
| } | ||
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| [DebuggerHidden] | ||
| internal static void Unbox_Nullable(ref byte destPtr, MethodTable* typeMT, object? obj) | ||
| { | ||
| if (obj == null) | ||
| { | ||
| InitValueClass(ref destPtr, typeMT); | ||
| } | ||
| else | ||
| { | ||
| if (!IsNullableForType(typeMT, RuntimeHelpers.GetMethodTable(obj))) | ||
| { | ||
| // For safety's sake, also allow true nullables to be unboxed normally. | ||
| // This should not happen normally, but we want to be robust | ||
| if (typeMT == RuntimeHelpers.GetMethodTable(obj)) | ||
| { | ||
| Unsafe.CopyBlockUnaligned(ref destPtr, ref RuntimeHelpers.GetRawData(obj), typeMT->GetNumInstanceFieldBytes()); | ||
| return; | ||
| } | ||
| CastHelpers.ThrowInvalidCastException(obj, typeMT); | ||
| } | ||
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| // Set the hasValue field on the Nullable type. It MUST always be placed at the start of the object. | ||
| *(bool*)destPtr = true; | ||
|
There was a problem hiding this comment. This doesn't look correct. The cast is casting the value of the reference into pointer. There was a problem hiding this comment. Yeah, that seems wrong. I kept waffling between refs and pointers here. Thanks. |
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| ref byte destValuePtr = ref typeMT->GetNullableValueFieldReferenceAndSize(ref destPtr, out uint size); | ||
| Unsafe.CopyBlockUnaligned(ref destValuePtr, ref RuntimeHelpers.GetRawData(obj), size); | ||
| } | ||
| } | ||
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| internal static ref byte Unbox_Helper(MethodTable* pMT1, object obj) | ||
| { | ||
| // must be a value type | ||
| Debug.Assert(pMT1->IsValueType); | ||
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| MethodTable* pMT2 = RuntimeHelpers.GetMethodTable(obj); | ||
| if ((pMT1->IsPrimitive && pMT2->IsPrimitive && | ||
| pMT1->GetPrimitiveCorElementType() == pMT2->GetPrimitiveCorElementType()) || | ||
| AreTypesEquivalent(pMT1, pMT2)) | ||
| { | ||
| return ref RuntimeHelpers.GetRawData(obj); | ||
| } | ||
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| CastHelpers.ThrowInvalidCastException(obj, pMT1); | ||
| return ref Unsafe.AsRef<byte>(null); | ||
| } | ||
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| internal static void Unbox_TypeTest(MethodTable *pMT1, MethodTable *pMT2) | ||
| { | ||
| if (pMT1 == pMT2 || | ||
| (pMT1->IsPrimitive && pMT2->IsPrimitive && | ||
| pMT1->GetPrimitiveCorElementType() == pMT2->GetPrimitiveCorElementType()) || | ||
| AreTypesEquivalent(pMT1, pMT2)) | ||
| { | ||
| return; | ||
| } | ||
|
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| CastHelpers.ThrowInvalidCastException(pMT1, pMT2); | ||
| } | ||
| } | ||
| } | ||
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Most of these types are going to be loaded on startup path. It feels a bit too fine grained to have separate type for the few unboxing helpers.
Would it be better for the unboxing helpers to live in CastHelpers? They are coupled anyway.
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Sure, seems reasonable to me. I had thought I might be moving the allocation based helpers over too so this class wouldn't be so small, but honestly, just copying the assembly routines from NativeAOT seems like a better path for most of those.