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[cDAC] Fix IsSharedByGenericInstantiations for non-shared canonical MTs #129721

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Merged
max-charlamb merged 1 commit into from
Jun 23, 2026
+11 −7
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[cDAC] Fix IsSharedByGenericInstantiations for non-shared canonical MTs #129721

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8 changes: 5 additions & 3 deletions docs/design/datacontracts/RuntimeTypeSystem.md
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Original file line number Diff line number Diff line change
Expand Up @@ -326,8 +326,9 @@ internal partial struct RuntimeTypeSystem_1
internal enum WFLAGS_LOW : uint
{
GenericsMask = 0x00000030,
GenericsMask_NonGeneric = 0x00000000, // no instantiation
GenericsMask_TypicalInstantiation = 0x00000030, // the type instantiated at its formal parameters, e.g. List<T>
GenericsMask_NonGeneric = 0x00000000, // no instantiation
GenericsMask_SharedInst = 0x00000020, // shared instantiation, e.g. List<__Canon> or List<MyValueType<__Canon>>
GenericsMask_TypicalInstantiation = 0x00000030, // the type instantiated at its formal parameters, e.g. List<T>

StringArrayValues = GenericsMask_NonGeneric,
}
Expand Down Expand Up @@ -402,6 +403,7 @@ internal partial struct RuntimeTypeSystem_1
public bool IsDynamicStatics => GetFlag(WFLAGS2_ENUM.DynamicStatics) != 0;
public bool IsTrackedReferenceWithFinalizer => GetFlag(WFLAGS_HIGH.IsTrackedReferenceWithFinalizer) != 0;
public bool IsGenericTypeDefinition => TestFlagWithMask(WFLAGS_LOW.GenericsMask, WFLAGS_LOW.GenericsMask_TypicalInstantiation);
public bool IsSharedByGenericInstantiations => TestFlagWithMask(WFLAGS_LOW.GenericsMask, WFLAGS_LOW.GenericsMask_SharedInst);
}

[Flags]
Expand Down Expand Up @@ -1837,7 +1839,7 @@ Determining where a shared generic method obtains its generic context:
return true;
}
MethodTable mt = _methodTables[md.MethodTable];
return mt.IsCanonMT && mt.Flags.HasInstantiation;
return mt.Flags.IsSharedByGenericInstantiations;
}
```

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2 changes: 1 addition & 1 deletion src/coreclr/vm/methodtable.h
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Expand Up @@ -3701,7 +3701,7 @@ public :
// AS YOU ADD NEW FLAGS PLEASE CONSIDER WHETHER Generics::NewInstantiation NEEDS
// TO BE UPDATED IN ORDER TO ENSURE THAT METHODTABLES DUPLICATED FOR GENERIC INSTANTIATIONS
// CARRY THE CORECT FLAGS.
// [cDAC] [RuntimeTypeSystem]: Contract depends on the values of enum_flag_GenericsMask, enum_flag_GenericsMask_NonGeneric, and enum_flag_GenericsMask_TypicalInst.
// [cDAC] [RuntimeTypeSystem]: Contract depends on the values of enum_flag_GenericsMask, enum_flag_GenericsMask_NonGeneric, enum_flag_GenericsMask_SharedInst, and enum_flag_GenericsMask_TypicalInst.

// We are overloading the low 2 bytes of m_dwFlags to be a component size for Strings
// and Arrays and some set of flags which we can be assured are of a specified state
Expand Down
2 changes: 1 addition & 1 deletion .../cdac/Microsoft.Diagnostics.DataContractReader.Contracts/Contracts/RuntimeTypeSystem_1.cs
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Expand Up @@ -1435,7 +1435,7 @@ private bool IsSharedByGenericInstantiations(MethodDesc methodDesc)

// Check class-level sharing: canonical MethodTable with generic instantiation
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MethodTable mt = GetOrCreateMethodTable(methodDesc);
return mt.IsCanonMT && mt.Flags.HasInstantiation;
return mt.Flags.IsSharedByGenericInstantiations;
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}

private bool IsAbstract(MethodDesc methodDesc)
Expand Down
6 changes: 4 additions & 2 deletions ...t.Diagnostics.DataContractReader.Contracts/RuntimeTypeSystemHelpers/MethodTableFlags_1.cs
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Expand Up @@ -22,8 +22,9 @@ internal enum EEClassOrCanonMTBits
internal enum WFLAGS_LOW : uint
{
GenericsMask = 0x00000030,
GenericsMask_NonGeneric = 0x00000000, // no instantiation
GenericsMask_TypicalInstantiation = 0x00000030, // the type instantiated at its formal parameters, e.g. List<T>
GenericsMask_NonGeneric = 0x00000000, // no instantiation
GenericsMask_SharedInst = 0x00000020, // shared instantiation, e.g. List<__Canon> or List<MyValueType<__Canon>>
GenericsMask_TypicalInstantiation = 0x00000030, // the type instantiated at its formal parameters, e.g. List<T>

StringArrayValues =
GenericsMask_NonGeneric |
Expand Down Expand Up @@ -108,6 +109,7 @@ private bool TestFlagWithMask(WFLAGS2_ENUM mask, WFLAGS2_ENUM flag)
public bool IsTrackedReferenceWithFinalizer => GetFlag(WFLAGS_HIGH.IsTrackedReferenceWithFinalizer) != 0;
public bool IsDynamicStatics => GetFlag(WFLAGS2_ENUM.DynamicStatics) != 0;
public bool IsGenericTypeDefinition => TestFlagWithMask(WFLAGS_LOW.GenericsMask, WFLAGS_LOW.GenericsMask_TypicalInstantiation);
public bool IsSharedByGenericInstantiations => TestFlagWithMask(WFLAGS_LOW.GenericsMask, WFLAGS_LOW.GenericsMask_SharedInst);
public bool ContainsGenericVariables => GetFlag(WFLAGS_HIGH.ContainsGenericVariables) != 0;

internal static EEClassOrCanonMTBits GetEEClassOrCanonMTBits(TargetPointer eeClassOrCanonMTPtr)
Expand Down
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