From d3f8912d53c8a395ad45a71b648e86e70cf6c4a3 Mon Sep 17 00:00:00 2001
From: Siegfried Pammer <siegfriedpammer@gmail.com>
Date: Thu, 16 Jun 2022 00:54:15 +0200
Subject: [PATCH] Handle special-cases with addressof: - Never introduce casts
 for ldobj-address-chains - Add special-case to TransformExpressionTrees:
 transform addressof(ldloc) to ldloca - Classify foreach and using variables
 as readonly lvalues

---
 .../CSharp/ExpressionBuilder.cs               | 19 ++++++++++++++++++-
 .../IL/Transforms/ILInlining.cs               |  5 ++++-
 .../IL/Transforms/TransformExpressionTrees.cs |  8 ++++++++
 3 files changed, 30 insertions(+), 2 deletions(-)

diff --git a/ICSharpCode.Decompiler/CSharp/ExpressionBuilder.cs b/ICSharpCode.Decompiler/CSharp/ExpressionBuilder.cs
index e6a8584b7..cd3918ff6 100644
--- a/ICSharpCode.Decompiler/CSharp/ExpressionBuilder.cs
+++ b/ICSharpCode.Decompiler/CSharp/ExpressionBuilder.cs
@@ -3784,7 +3784,9 @@ namespace ICSharpCode.Decompiler.CSharp
 			// on a mutable lvalue, we would end up modifying the original lvalue, not just the copy.
 			// We solve this by introducing a "redundant" cast. Casts are classified as rvalue
 			// and ensure that the C# compiler will also create a copy.
-			if (classification == ExpressionClassification.MutableLValue && value.Expression is not CastExpression)
+			if (classification == ExpressionClassification.MutableLValue
+				&& !CanIgnoreCopy()
+				&& value.Expression is not CastExpression)
 			{
 				value = new CastExpression(ConvertType(inst.Type), value.Expression)
 					.WithoutILInstruction()
@@ -3793,6 +3795,21 @@ namespace ICSharpCode.Decompiler.CSharp
 			return new DirectionExpression(FieldDirection.Ref, value)
 				.WithILInstruction(inst)
 				.WithRR(new ByReferenceResolveResult(value.ResolveResult, ReferenceKind.Ref));
+
+			bool CanIgnoreCopy()
+			{
+				ILInstruction loadAddress = inst;
+				while (loadAddress.Parent is LdFlda parent)
+				{
+					loadAddress = parent;
+				}
+				if (loadAddress.Parent is LdObj)
+				{
+					// Ignore copy, never introduce a cast
+					return true;
+				}
+				return false;
+			}
 		}
 
 		protected internal override TranslatedExpression VisitAwait(Await inst, TranslationContext context)
diff --git a/ICSharpCode.Decompiler/IL/Transforms/ILInlining.cs b/ICSharpCode.Decompiler/IL/Transforms/ILInlining.cs
index 21c6e9d45..ecdb7d2b4 100644
--- a/ICSharpCode.Decompiler/IL/Transforms/ILInlining.cs
+++ b/ICSharpCode.Decompiler/IL/Transforms/ILInlining.cs
@@ -416,7 +416,10 @@ namespace ICSharpCode.Decompiler.IL.Transforms
 			{
 				case OpCode.LdLoc:
 				case OpCode.StLoc:
-					if (((IInstructionWithVariableOperand)inst).Variable.IsRefReadOnly)
+					ILVariable v = ((IInstructionWithVariableOperand)inst).Variable;
+					if (v.IsRefReadOnly
+						|| v.Kind == VariableKind.ForeachLocal
+						|| v.Kind == VariableKind.UsingLocal)
 					{
 						return ExpressionClassification.ReadonlyLValue;
 					}
diff --git a/ICSharpCode.Decompiler/IL/Transforms/TransformExpressionTrees.cs b/ICSharpCode.Decompiler/IL/Transforms/TransformExpressionTrees.cs
index 997a5dcbe..eef43cb7d 100644
--- a/ICSharpCode.Decompiler/IL/Transforms/TransformExpressionTrees.cs
+++ b/ICSharpCode.Decompiler/IL/Transforms/TransformExpressionTrees.cs
@@ -637,9 +637,17 @@ namespace ICSharpCode.Decompiler.IL.Transforms
 			{
 				case StackType.Ref:
 					if (target.ResultType == StackType.Ref)
+					{
 						return target;
+					}
+					else if (target is LdLoc ldloc)
+					{
+						return new LdLoca(ldloc.Variable).WithILRange(ldloc);
+					}
 					else
+					{
 						return new AddressOf(target, expectedType);
+					}
 				case StackType.O:
 					if (targetType.IsReferenceType == false)
 					{