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Fix ValueType.GetHashCode not calling overriden method on nested field #98754

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merged 11 commits into from
Feb 26, 2024
Merged

Fix ValueType.GetHashCode not calling overriden method on nested field #98754

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1ae14c2
Handle overridden value type method
huoyaoyuan Feb 20, 2024
d5a84eb
Call virtual for NativeAot
huoyaoyuan Feb 21, 2024
80235f7
Add test
huoyaoyuan Feb 21, 2024
33e0177
Change to box
huoyaoyuan Feb 22, 2024
d6b8287
Fix test
huoyaoyuan Feb 23, 2024
758dead
Fold GetHashCodeImpl
huoyaoyuan Feb 23, 2024
3219160
NativeAOT cleanup
huoyaoyuan Feb 23, 2024
19e5618
Don't create duplicated HashCode
huoyaoyuan Feb 24, 2024
aea4b67
Pass ref HashCode to RegularGetValueTypeHashCode
huoyaoyuan Feb 25, 2024
2d27a42
Update test to not use default equals of nested field
huoyaoyuan Feb 25, 2024
b6fabf5
Return span from method instead
huoyaoyuan Feb 26, 2024
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11 changes: 9 additions & 2 deletions src/coreclr/System.Private.CoreLib/src/System/ValueType.cs
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Original file line number Diff line number Diff line change
Expand Up @@ -120,7 +120,7 @@ public override unsafe int GetHashCode()
else
{
object thisRef = this;
switch (GetHashCodeStrategy(pMT, ObjectHandleOnStack.Create(ref thisRef), out uint fieldOffset, out uint fieldSize))
switch (GetHashCodeStrategy(pMT, ObjectHandleOnStack.Create(ref thisRef), out uint fieldOffset, out uint fieldSize, out MethodTable* fieldMT))
{
case ValueTypeHashCodeStrategy.ReferenceField:
hashCode.Add(Unsafe.As<byte, object>(ref Unsafe.AddByteOffset(ref rawData, fieldOffset)).GetHashCode());
Expand All @@ -138,6 +138,12 @@ public override unsafe int GetHashCode()
Debug.Assert(fieldSize != 0);
hashCode.AddBytes(MemoryMarshal.CreateReadOnlySpan(ref Unsafe.AddByteOffset(ref rawData, fieldOffset), (int)fieldSize));
break;

case ValueTypeHashCodeStrategy.ValueTypeOverride:
Debug.Assert(fieldMT != null);
// Box the field to handle complicated cases like mutable method and shared generic
hashCode.Add(RuntimeHelpers.Box(fieldMT, ref Unsafe.AddByteOffset(ref rawData, fieldOffset))?.GetHashCode() ?? 0);
break;
}
}

Expand All @@ -152,11 +158,12 @@ private enum ValueTypeHashCodeStrategy
DoubleField,
SingleField,
FastGetHashCode,
ValueTypeOverride,
}

[LibraryImport(RuntimeHelpers.QCall, EntryPoint = "ValueType_GetHashCodeStrategy")]
private static unsafe partial ValueTypeHashCodeStrategy GetHashCodeStrategy(
MethodTable* pMT, ObjectHandleOnStack objHandle, out uint fieldOffset, out uint fieldSize);
MethodTable* pMT, ObjectHandleOnStack objHandle, out uint fieldOffset, out uint fieldSize, out MethodTable* fieldMT);

public override string? ToString()
{
Expand Down
35 changes: 12 additions & 23 deletions src/coreclr/nativeaot/System.Private.CoreLib/src/System/ValueType.cs
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Original file line number Diff line number Diff line change
Expand Up @@ -95,37 +95,24 @@ public override unsafe bool Equals([NotNullWhen(true)] object? obj)

public override unsafe int GetHashCode()
{
int hashCode = (int)this.GetMethodTable()->HashCode;
HashCode hashCode = default;
hashCode.Add((IntPtr)this.GetMethodTable());

hashCode ^= GetHashCodeImpl();

return hashCode;
}

private unsafe int GetHashCodeImpl()
{
int numFields = __GetFieldHelper(GetNumFields, out _);

if (numFields == UseFastHelper)
return FastGetValueTypeHashCodeHelper(this.GetMethodTable(), ref this.GetRawData());
hashCode.AddBytes(GetSpanForField(this.GetMethodTable(), ref this.GetRawData()));
else
hashCode.Add(RegularGetValueTypeHashCode(ref this.GetRawData(), numFields));

return RegularGetValueTypeHashCode(ref this.GetRawData(), numFields);
return hashCode.ToHashCode();
}

private static unsafe int FastGetValueTypeHashCodeHelper(MethodTable* type, ref byte data)
private static unsafe ReadOnlySpan<byte> GetSpanForField(MethodTable* type, ref byte data)
{
// Sanity check - if there are GC references, we should not be hashing bytes
Debug.Assert(!type->ContainsGCPointers);

int size = (int)type->ValueTypeSize;
int hashCode = 0;

for (int i = 0; i < size / 4; i++)
{
hashCode ^= Unsafe.As<byte, int>(ref Unsafe.Add(ref data, i * 4));
}

return hashCode;
return new ReadOnlySpan<byte>(ref data, (int)type->ValueTypeSize);
}

private unsafe int RegularGetValueTypeHashCode(ref byte data, int numFields)
Expand All @@ -150,7 +137,9 @@ private unsafe int RegularGetValueTypeHashCode(ref byte data, int numFields)
}
else if (fieldType->IsPrimitive)
{
hashCode = FastGetValueTypeHashCodeHelper(fieldType, ref fieldData);
HashCode hash = default;
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The method should take ref HashCode argument instead of creating a new instance here.

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I meant change RegularGetValueTypeHashCode to take ref HashCode argument and delete HashCode hash = default; that this comment is attached to.

hash.AddBytes(GetSpanForField(fieldType, ref fieldData));
hashCode = hash.ToHashCode();
}
else if (fieldType->IsValueType)
{
Expand All @@ -164,7 +153,7 @@ private unsafe int RegularGetValueTypeHashCode(ref byte data, int numFields)
var fieldValue = (ValueType)RuntimeImports.RhBox(fieldType, ref fieldData);
if (fieldValue != null)
{
hashCode = fieldValue.GetHashCodeImpl();
hashCode = fieldValue.GetHashCode();
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I think GetHashCodeImpl can now be inlined into GetHashCode.

The only reason we had GetHashCodeImpl was because it was emulating CoreCLR behavior that did not call the GetHashCode on the field type (even if it had one) but instead used the fallback algorithm.

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Is it feasible to use System.HashCode for NativeAOT here? Will it bring unintended dependency or complexity?

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I think it would be fine to use System.HashCode. This was mirroring the CoreCLR-JIT logic but now it diverged because that's how forks usually end up.

If we really wanted to, we could probably unify this to the point of sharing a part of this file, maybe with an ifdef or two. From a quick look GetHashCodeStrategy could be implemented using NativeAOT's __GetFieldHelper.

}
else
{
Expand Down
19 changes: 14 additions & 5 deletions src/coreclr/vm/comutilnative.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -1703,9 +1703,10 @@ enum ValueTypeHashCodeStrategy
DoubleField,
SingleField,
FastGetHashCode,
ValueTypeOverride,
};

static ValueTypeHashCodeStrategy GetHashCodeStrategy(MethodTable* mt, QCall::ObjectHandleOnStack objHandle, UINT32* fieldOffset, UINT32* fieldSize)
static ValueTypeHashCodeStrategy GetHashCodeStrategy(MethodTable* mt, QCall::ObjectHandleOnStack objHandle, UINT32* fieldOffset, UINT32* fieldSize, MethodTable** fieldMTOut)
{
CONTRACTL
{
Expand Down Expand Up @@ -1772,10 +1773,18 @@ static ValueTypeHashCodeStrategy GetHashCodeStrategy(MethodTable* mt, QCall::Obj
*fieldSize = field->LoadSize();
ret = ValueTypeHashCodeStrategy::FastGetHashCode;
}
else if (HasOverriddenMethod(fieldMT,
CoreLibBinder::GetClass(CLASS__VALUE_TYPE),
CoreLibBinder::GetMethod(METHOD__VALUE_TYPE__GET_HASH_CODE)->GetSlot()))
{
*fieldOffset += field->GetOffsetUnsafe();
*fieldMTOut = fieldMT;
ret = ValueTypeHashCodeStrategy::ValueTypeOverride;
}
else
{
*fieldOffset += field->GetOffsetUnsafe();
ret = GetHashCodeStrategy(fieldMT, objHandle, fieldOffset, fieldSize);
ret = GetHashCodeStrategy(fieldMT, objHandle, fieldOffset, fieldSize, fieldMTOut);
}
}
}
Expand All @@ -1785,18 +1794,18 @@ static ValueTypeHashCodeStrategy GetHashCodeStrategy(MethodTable* mt, QCall::Obj
return ret;
}

extern "C" INT32 QCALLTYPE ValueType_GetHashCodeStrategy(MethodTable* mt, QCall::ObjectHandleOnStack objHandle, UINT32* fieldOffset, UINT32* fieldSize)
extern "C" INT32 QCALLTYPE ValueType_GetHashCodeStrategy(MethodTable* mt, QCall::ObjectHandleOnStack objHandle, UINT32* fieldOffset, UINT32* fieldSize, MethodTable** fieldMT)
{
QCALL_CONTRACT;

ValueTypeHashCodeStrategy ret = ValueTypeHashCodeStrategy::None;
*fieldOffset = 0;
*fieldSize = 0;
*fieldMT = NULL;

BEGIN_QCALL;


ret = GetHashCodeStrategy(mt, objHandle, fieldOffset, fieldSize);
ret = GetHashCodeStrategy(mt, objHandle, fieldOffset, fieldSize, fieldMT);

END_QCALL;

Expand Down
2 changes: 1 addition & 1 deletion src/coreclr/vm/comutilnative.h
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Original file line number Diff line number Diff line change
Expand Up @@ -252,7 +252,7 @@ class MethodTableNative {

extern "C" BOOL QCALLTYPE MethodTable_AreTypesEquivalent(MethodTable* mta, MethodTable* mtb);
extern "C" BOOL QCALLTYPE MethodTable_CanCompareBitsOrUseFastGetHashCode(MethodTable* mt);
extern "C" INT32 QCALLTYPE ValueType_GetHashCodeStrategy(MethodTable* mt, QCall::ObjectHandleOnStack objHandle, UINT32* fieldOffset, UINT32* fieldSize);
extern "C" INT32 QCALLTYPE ValueType_GetHashCodeStrategy(MethodTable* mt, QCall::ObjectHandleOnStack objHandle, UINT32* fieldOffset, UINT32* fieldSize, MethodTable** fieldMT);

class StreamNative {
public:
Expand Down
30 changes: 30 additions & 0 deletions src/libraries/System.Runtime/tests/System.Runtime.Tests/System/ValueTypeTests.cs
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Expand Up @@ -315,6 +315,21 @@ public static void StructContainsPointerNestedCompareTest()
Assert.Equal(obj1.GetHashCode(), obj2.GetHashCode());
}

[Fact]
public static void StructWithNestedOverriddenNotBitwiseComparableTest()
{
StructWithNestedOverriddenNotBitwiseComparable obj1 = new StructWithNestedOverriddenNotBitwiseComparable();
obj1.value1.value = 0.0;
obj1.value2.value = 1.0;

StructWithNestedOverriddenNotBitwiseComparable obj2 = new StructWithNestedOverriddenNotBitwiseComparable();
obj2.value1.value = -0.0;
obj2.value2.value = 1.0;

Assert.True(obj1.Equals(obj2));
Assert.Equal(obj1.GetHashCode(), obj2.GetHashCode());
}

public struct S
{
public int x;
Expand Down Expand Up @@ -413,5 +428,20 @@ public struct StructContainsPointerNested
public object o;
public StructNonOverriddenEqualsOrGetHasCode value;
}

public struct StructOverriddenNotBitwiseComparable
{
public double value;

public override bool Equals(object obj) => obj is StructOverriddenNotBitwiseComparable other && value.Equals(other.value);

public override int GetHashCode() => value.GetHashCode();
}

public struct StructWithNestedOverriddenNotBitwiseComparable
{
public StructOverriddenNotBitwiseComparable value1;
public StructOverriddenNotBitwiseComparable value2;
}
}
}
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