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Extract isinst opcode into a processor #289

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Merged
hazzik merged 3 commits into from
Oct 6, 2025
Merged

Extract isinst opcode into a processor #289

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a0df798
Extract isinst opcode into a processor
hazzik Oct 6, 2025
4abaab2
Remove comment
hazzik Oct 6, 2025
d220628
Code structure
hazzik Oct 6, 2025
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32 changes: 32 additions & 0 deletions src/DelegateDecompiler/OptimizeExpressionVisitor.cs
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Original file line number Diff line number Diff line change
Expand Up @@ -313,6 +313,12 @@ protected override Expression VisitBinary(BinaryExpression node)
{
var left = Visit(node.Left);
var right = Visit(node.Right);

if (TryOptimizeTypeAsComparison(node.NodeType, left, right, out var typeIsExpression))
{
return typeIsExpression;
}

if (node.Right is ConstantExpression rightConstant)
{
if (rightConstant.Value as bool? == false)
Expand Down Expand Up @@ -537,6 +543,32 @@ protected override Expression VisitParameter(ParameterExpression node)
}
}

static bool TryOptimizeTypeAsComparison(ExpressionType nodeType, Expression left, Expression right, out Expression result)
{
result = null;

// Pattern: (obj as Type) != null -> TypeIs(obj, Type)
// Pattern: (obj as Type) == null -> !TypeIs(obj, Type)
if (left.NodeType != ExpressionType.TypeAs || left is not UnaryExpression typeAs || !IsNullConstant(right))
return false;

switch (nodeType)
{
case ExpressionType.NotEqual:
{
result = Expression.TypeIs(typeAs.Operand, typeAs.Type);
return true;
}
case ExpressionType.Equal:
{
result = Expression.Not(Expression.TypeIs(typeAs.Operand, typeAs.Type));
return true;
}
default:
return false;
}
}

public static Expression Optimize(Expression expression)
{
return new GetValueOrDefaultToCoalesceConverter().Visit(new OptimizeExpressionVisitor().Visit(expression));
Expand Down
19 changes: 2 additions & 17 deletions src/DelegateDecompiler/Processor.cs
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Original file line number Diff line number Diff line change
Expand Up @@ -57,6 +57,7 @@ static Processor()
ConvertTypeProcessor.Register(processors);
DupProcessor.Register(processors);
InitObjProcessor.Register(processors);
IsinstProcessor.Register(processors);
LdargConstantProcessor.Register(processors);
LdargParameterProcessor.Register(processors);
LdcI4SProcessor.Register(processors);
Expand Down Expand Up @@ -145,6 +146,7 @@ static int ProcessInstruction(ProcessorState state, Instruction instruction)

if (instruction.OpCode == OpCodes.Nop ||
instruction.OpCode == OpCodes.Break ||
instruction.OpCode == OpCodes.Ret ||
instruction.OpCode.FlowControl == FlowControl.Branch)
{
// Do nothing
Expand All @@ -156,23 +158,6 @@ static int ProcessInstruction(ProcessorState state, Instruction instruction)
state.Stack.Push(expression);
return 1;
}
else if (instruction.OpCode == OpCodes.Isinst)
{
var val = state.Stack.Pop();
if (instruction.Next != null && instruction.Next.OpCode == OpCodes.Ldnull &&
instruction.Next.Next != null && instruction.Next.Next.OpCode == OpCodes.Cgt_Un)
{
state.Stack.Push(Expression.TypeIs(val, (Type)instruction.Operand));
// Skip the next two instructions as they're part of this pattern
return 2;
}

state.Stack.Push(Expression.TypeAs(val, (Type)instruction.Operand));
}
else if (instruction.OpCode == OpCodes.Ret)
{
// Return instruction - signal early return
}
else if (processors.TryGetValue(instruction.OpCode, out var processor))
{
processor.Process(state, instruction);
Expand Down
22 changes: 22 additions & 0 deletions src/DelegateDecompiler/Processors/IsinstProcessor.cs
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Original file line number Diff line number Diff line change
@@ -0,0 +1,22 @@
using System;
using System.Collections.Generic;
using System.Linq.Expressions;
using System.Reflection.Emit;
using Mono.Reflection;

namespace DelegateDecompiler.Processors
{
internal class IsinstProcessor : IProcessor
{
public static void Register(Dictionary<OpCode, IProcessor> processors)
{
processors.Register(new IsinstProcessor(), OpCodes.Isinst);
}

public void Process(ProcessorState state, Instruction instruction)
{
var val = state.Stack.Pop();
state.Stack.Push(Expression.TypeAs(val, (Type)instruction.Operand));
}
}
}