Added FStructBaseChain to UStruct for faster IsA type checks.

Author: Fischsalat

Dumper/Engine/Private/OffsetFinder/OffsetFinder.cpp

@@ -743,6 +743,49 @@ int32_t OffsetFinder::FindMinAlignmentOffset()
 	return FindOffset(Infos);
 }
 
+int32_t OffsetFinder::FindStructBaseChainOffset()
+{
+	// UStruct inherits from FStructBaseChain, so the members of base chain should come right after UField
+
+	UEStruct Struct = ObjectArray::FindStructFast("Struct");
+	if (!Struct)
+		Struct = ObjectArray::FindStructFast("struct");
+
+	const int32 UStructStart = Struct.GetSuper().GetStructSize();
+	const int32 UStructEnd = UStructStart + Struct.GetStructSize();
+
+	// If the members of UStruct come right after UField, FStructBaseChain either doesn't exist or is empty
+	if (UStructStart == Off::UStruct::ChildProperties || UStructStart == Off::UStruct::Children)
+		return OffsetNotFound;
+
+	auto CountSuperClasses = [](const UEStruct InStruct) -> int32
+	{
+		int32 Count = 0;
+
+		UEStruct CurrentSuper = InStruct.GetSuper();
+		while (CurrentSuper)
+		{
+			Count++;
+			CurrentSuper = CurrentSuper.GetSuper();
+		}
+
+		return Count;
+	};
+
+	/* Pair<UStruct, NumSuperClasses> */
+	std::vector<std::pair<void*, int32_t>> Infos;
+
+	UEStruct APlayerController = ObjectArray::FindClassFast("PlayerController");
+	UEStruct AActor = ObjectArray::FindClassFast("Actor");
+
+	Infos.push_back({ Struct.GetAddress(),              CountSuperClasses(Struct)            });
+	Infos.push_back({ APlayerController.GetAddress(),   CountSuperClasses(APlayerController) });
+	Infos.push_back({ AActor.GetAddress(),              CountSuperClasses(AActor)            });
+
+	// FStructBaseChain::NumStructBasesInChainMinusOne is at offset 0x8, after a pointer
+	return FindOffset(Infos, UStructStart, UStructEnd) - sizeof(void*);
+}
+
 /* UFunction */
 int32_t OffsetFinder::FindFunctionFlagsOffset()
 {

Dumper/Engine/Private/OffsetFinder/Offsets.cpp

@@ -349,6 +349,10 @@ void Off::Init()
 		std::cerr << std::format("Off::FFieldClass::CastFlags: 0x{:X}\n\n", Off::FFieldClass::CastFlags);
 	}
 
+	Off::UStruct::StructBaseChain = OffsetFinder::FindStructBaseChainOffset();
+	if (Off::UStruct::StructBaseChain != OffsetFinder::OffsetNotFound)
+		std::cerr << std::format("Off::UStruct::StructBaseChain: 0x{:X}\n", Off::UStruct::StructBaseChain);
+
 	Off::UClass::ClassDefaultObject = OffsetFinder::FindDefaultObjectOffset();
 	std::cerr << std::format("Off::UClass::ClassDefaultObject: 0x{:X}\n", Off::UClass::ClassDefaultObject);
 

Dumper/Engine/Public/OffsetFinder/OffsetFinder.h

@@ -107,6 +107,7 @@ namespace OffsetFinder
 	int32_t FindChildPropertiesOffset();
 	int32_t FindStructSizeOffset();
 	int32_t FindMinAlignmentOffset();
+	int32_t FindStructBaseChainOffset();
 
 	/* UFunction */
 	int32_t FindFunctionFlagsOffset();

Dumper/Engine/Public/OffsetFinder/Offsets.h

@@ -195,6 +195,9 @@ namespace Off
 
 	namespace UStruct
 	{
+		/* Optional offset, if available we can generate a faster IsA implementation for the SDK. */
+		inline int32 StructBaseChain = -1;
+
 		inline int32 SuperStruct;
 		inline int32 Children;
 		inline int32 ChildProperties;

Dumper/Generator/Private/Generators/CppGenerator.cpp

@@ -1893,6 +1893,15 @@ void CppGenerator::InitPredefinedMembers()
 		});
 	}
 
+	if (Off::UStruct::StructBaseChain != -1)
+	{
+		UStructPredefs.Members.push_back({
+			.Comment = "NOT AUTO-GENERATED PROPERTY",
+			.Type = "struct FStructBaseChain", .Name = "BaseChain", .Offset = Off::UStruct::StructBaseChain, .Size = sizeof(void*) + sizeof(int32) + sizeof(uint32) /* PAD */, .ArrayDim = 0x1, .Alignment = alignof(void*),
+			.bIsStatic = false, .bIsZeroSizeMember = false, .bIsBitField = false, .BitIndex = 0xFF
+		});
+	}
+
 	PredefinedElements& UFunctionPredefs = PredefinedMembers[ObjectArray::FindClassFast("Function").GetIndex()];
 	UFunctionPredefs.Members =
 	{
@@ -2507,11 +2516,7 @@ R"({{
 
 	PredefinedElements& UStructPredefs = PredefinedMembers[UStructIdx];
 
-	UStructPredefs.Functions =
-	{
-		PredefinedFunction {
-			.CustomComment = "Checks if this class has a certain base",
-			.ReturnType = "bool", .NameWithParams = "IsSubclassOf(const UStruct* Base)", .Body =
+	const char* IsStructOfTypeCode =
 R"({
 	if (!Base)
 		return false;
@@ -2523,7 +2528,25 @@ R"({
 	}
 
 	return false;
-})",
+})";
+
+	if (Off::UStruct::StructBaseChain != -1)
+	{
+		IsStructOfTypeCode =
+R"({
+	if (!Base)
+		return false;
+
+	const int32 NumParentStructBasesInChainMinusOne = Base->BaseChain.NumStructBasesInChainMinusOne;
+	return NumParentStructBasesInChainMinusOne <= BaseChain.NumStructBasesInChainMinusOne && BaseChain.StructBaseChainArray[NumParentStructBasesInChainMinusOne] == &Base->BaseChain;
+})";
+	}
+
+	UStructPredefs.Functions =
+	{
+		PredefinedFunction {
+			.CustomComment = "Checks if this class has a certain base",
+			.ReturnType = "bool", .NameWithParams = "IsSubclassOf(const UStruct* Base)", .Body = IsStructOfTypeCode,
 			.bIsStatic = false, .bIsConst = true, .bIsBodyInline = false
 		},
 		PredefinedFunction {
@@ -4697,6 +4720,28 @@ class TSubclassOf
 };
 )";
 
+	/* struct FStructBaseChain */
+	PredefinedStruct FStructBaseChain = PredefinedStruct{
+		.UniqueName = "FStructBaseChain", .Size = sizeof(void*) + sizeof(int32), .Alignment = alignof(void*), .bUseExplictAlignment = false, .bIsFinal = false, .bIsClass = false, .bIsUnion = false, .Super = nullptr
+	};
+
+	FStructBaseChain.Properties =
+	{
+		PredefinedMember {
+			.Comment = "NOT AUTO-GENERATED PROPERTY",
+			.Type = "FStructBaseChain**", .Name = "StructBaseChainArray", .Offset = 0x0, .Size = sizeof(void*), .ArrayDim = 0x1, .Alignment = alignof(void*),
+			.bIsStatic = false, .bIsZeroSizeMember = false, .bIsBitField = false, .BitIndex = 0xFF
+		},
+		PredefinedMember {
+			.Comment = "NOT AUTO-GENERATED PROPERTY",
+			.Type = "int32", .Name = "NumStructBasesInChainMinusOne", .Offset = sizeof(void*), .Size = sizeof(int32), .ArrayDim = 0x1, .Alignment = alignof(void*),
+			.bIsStatic = false, .bIsZeroSizeMember = false, .bIsBitField = false, .BitIndex = 0xFF
+		},
+	};
+
+	GenerateStruct(&FStructBaseChain, BasicHpp, BasicCpp, BasicHpp, AssertionsFile);
+
+
 	const int32 TextDataSize = (Off::InSDK::Text::InTextDataStringOffset + sizeof(FString));
 
 	/* class FTextData */
@@ -4713,7 +4758,8 @@ class TSubclassOf
 		},
 	};
 
-	BasicHpp << R"(namespace FTextImpl
+	BasicHpp << R"(
+namespace FTextImpl
 {)";
 	GenerateStruct(&FTextData, BasicHpp, BasicCpp, BasicHpp, AssertionsFile);
 	BasicHpp << "}\n";