#3075: Avoid processing already-transformed blocks by introducing BlockTransformContext.IndexOfFirstAlreadyTransformedInstruction, which allows us to track already transformed instructions after a block has been merged into another by ConditionDetection.

ICSharpCode.Decompiler/IL/ControlFlow/ConditionDetection.cs

@@ -93,6 +93,7 @@ namespace ICSharpCode.Decompiler.IL.ControlFlow
 			}
 			PickBetterBlockExit(block, ifInst);
 			OrderIfBlocks(ifInst);
+			context.IndexOfFirstAlreadyTransformedInstruction = block.Instructions.Count;
 		}
 
 		/// <summary>
@@ -150,6 +151,7 @@ namespace ICSharpCode.Decompiler.IL.ControlFlow
 			// The targetBlock was already processed, and is ready to embed
 			var targetBlock = ((Branch)exitInst).TargetBlock;
 			block.Instructions.RemoveAt(block.Instructions.Count - 1);
+			context.IndexOfFirstAlreadyTransformedInstruction = block.Instructions.Count;
 			block.Instructions.AddRange(targetBlock.Instructions);
 			targetBlock.Remove();
 

ICSharpCode.Decompiler/IL/Instructions/Block.cs

@@ -328,6 +328,7 @@ namespace ICSharpCode.Decompiler.IL
 			foreach (var transform in transforms)
 			{
 				context.CancellationToken.ThrowIfCancellationRequested();
+				Debug.Assert(context.IndexOfFirstAlreadyTransformedInstruction <= this.Instructions.Count);
 				context.StepStartGroup(transform.GetType().Name);
 				transform.Run(this, context);
 				this.CheckInvariant(ILPhase.Normal);

ICSharpCode.Decompiler/IL/Transforms/BlockTransform.cs

@@ -53,6 +53,15 @@ namespace ICSharpCode.Decompiler.IL.Transforms
 		/// </summary>
 		public ControlFlowGraph ControlFlowGraph { get; set; }
 
+		/// <summary>
+		/// Initially equal to Block.Instructions.Count indicating that nothing has been transformed yet.
+		/// Set by <see cref="ConditionDetection"/> when another already transformed block is merged into
+		/// the current block. Subsequent <see cref="IBlockTransform"/>s must update this value, for example,
+		/// by resetting it to Block.Instructions.Count. <see cref="StatementTransform"/> will use this value to
+		/// skip already transformed instructions.
+		/// </summary>
+		public int IndexOfFirstAlreadyTransformedInstruction { get; set; }
+
 		public BlockTransformContext(ILTransformContext context) : base(context)
 		{
 		}
@@ -103,6 +112,7 @@ namespace ICSharpCode.Decompiler.IL.Transforms
 
 			context.ControlFlowNode = cfgNode;
 			context.Block = block;
+			context.IndexOfFirstAlreadyTransformedInstruction = block.Instructions.Count;
 			block.RunTransforms(PreOrderTransforms, context);
 
 			// First, process the children in the dominator tree.
@@ -115,6 +125,7 @@ namespace ICSharpCode.Decompiler.IL.Transforms
 
 			context.ControlFlowNode = cfgNode;
 			context.Block = block;
+			context.IndexOfFirstAlreadyTransformedInstruction = block.Instructions.Count;
 			block.RunTransforms(PostOrderTransforms, context);
 			context.StepEndGroup();
 		}

ICSharpCode.Decompiler/IL/Transforms/CachedDelegateInitialization.cs

@@ -16,7 +16,6 @@
 // OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
 // DEALINGS IN THE SOFTWARE.
 
-using System;
 using System.Linq;
 
 using ICSharpCode.Decompiler.TypeSystem;
@@ -32,36 +31,42 @@ namespace ICSharpCode.Decompiler.IL.Transforms
 			this.context = context;
 			if (!context.Settings.AnonymousMethods)
 				return;
-			for (int i = block.Instructions.Count - 1; i >= 0; i--)
+			for (int i = context.IndexOfFirstAlreadyTransformedInstruction - 1; i >= 0; i--)
 			{
 				if (block.Instructions[i] is IfInstruction inst)
 				{
 					if (CachedDelegateInitializationWithField(inst))
 					{
 						block.Instructions.RemoveAt(i);
+						context.IndexOfFirstAlreadyTransformedInstruction = block.Instructions.Count;
 						continue;
 					}
 					if (CachedDelegateInitializationWithLocal(inst))
 					{
 						ILInlining.InlineOneIfPossible(block, i, InliningOptions.Aggressive, context);
+						context.IndexOfFirstAlreadyTransformedInstruction = block.Instructions.Count;
 						continue;
 					}
 					if (CachedDelegateInitializationRoslynInStaticWithLocal(inst) || CachedDelegateInitializationRoslynWithLocal(inst))
 					{
 						block.Instructions.RemoveAt(i);
+						context.IndexOfFirstAlreadyTransformedInstruction = block.Instructions.Count;
 						continue;
 					}
 					if (CachedDelegateInitializationVB(inst))
 					{
+						context.IndexOfFirstAlreadyTransformedInstruction = block.Instructions.Count;
 						continue;
 					}
 					if (CachedDelegateInitializationVBWithReturn(inst))
 					{
 						block.Instructions.RemoveAt(i);
+						context.IndexOfFirstAlreadyTransformedInstruction = block.Instructions.Count;
 						continue;
 					}
 					if (CachedDelegateInitializationVBWithClosure(inst))
 					{
+						context.IndexOfFirstAlreadyTransformedInstruction = block.Instructions.Count;
 						continue;
 					}
 				}

ICSharpCode.Decompiler/IL/Transforms/LockTransform.cs

@@ -16,12 +16,6 @@
 // OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
 // DEALINGS IN THE SOFTWARE.
 
-using System;
-using System.Collections.Generic;
-using System.Linq;
-using System.Text;
-using System.Threading.Tasks;
-
 using ICSharpCode.Decompiler.TypeSystem;
 
 namespace ICSharpCode.Decompiler.IL.Transforms
@@ -35,18 +29,39 @@ namespace ICSharpCode.Decompiler.IL.Transforms
 			if (!context.Settings.LockStatement)
 				return;
 			this.context = context;
-			for (int i = block.Instructions.Count - 1; i >= 0; i--)
+			for (int i = context.IndexOfFirstAlreadyTransformedInstruction - 1; i >= 0; i--)
 			{
-				if (!TransformLockRoslyn(block, i))
+				bool changed = DoTransform(block, i);
-					if (!TransformLockV4(block, i))
+				if (changed)
-						if (!TransformLockV4YieldReturn(block, i))
+				{
-							if (!TransformLockV2(block, i))
+					context.IndexOfFirstAlreadyTransformedInstruction = block.Instructions.Count;
-								TransformLockMCS(block, i);
+				}
 				// This happens in some cases:
 				// Use correct index after transformation.
 				if (i >= block.Instructions.Count)
 					i = block.Instructions.Count;
 			}
+
+			bool DoTransform(Block block, int i)
+			{
+				if (TransformLockRoslyn(block, i))
+				{
+					return true;
+				}
+				if (TransformLockV4(block, i))
+				{
+					return true;
+				}
+				if (TransformLockV4YieldReturn(block, i))
+				{
+					return true;
+				}
+				if (TransformLockV2(block, i))
+				{
+					return true;
+				}
+				return TransformLockMCS(block, i);
+			}
 		}
 
 		/// <summary>

ICSharpCode.Decompiler/IL/Transforms/StatementTransform.cs

@@ -114,7 +114,11 @@ namespace ICSharpCode.Decompiler.IL.Transforms
 		{
 			var ctx = new StatementTransformContext(context);
 			int pos = 0;
-			ctx.rerunPosition = block.Instructions.Count - 1;
+			if (context.IndexOfFirstAlreadyTransformedInstruction == 0)
+			{
+				return;
+			}
+			ctx.rerunPosition = context.IndexOfFirstAlreadyTransformedInstruction - 1;
 			while (pos >= 0)
 			{
 				if (ctx.rerunPosition != null)

ICSharpCode.Decompiler/IL/Transforms/UsingTransform.cs

@@ -16,11 +16,7 @@
 // OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
 // DEALINGS IN THE SOFTWARE.
 
-using System;
-using System.Collections.Generic;
 using System.Linq;
-using System.Text;
-using System.Threading.Tasks;
 
 using ICSharpCode.Decompiler.TypeSystem;
 
@@ -35,18 +31,21 @@ namespace ICSharpCode.Decompiler.IL.Transforms
 			if (!context.Settings.UsingStatement)
 				return;
 			this.context = context;
-			for (int i = block.Instructions.Count - 1; i >= 0; i--)
+			for (int i = context.IndexOfFirstAlreadyTransformedInstruction - 1; i >= 0; i--)
 			{
 				if (TransformUsing(block, i))
 				{
+					context.IndexOfFirstAlreadyTransformedInstruction = block.Instructions.Count;
 					continue;
 				}
 				if (TransformUsingVB(block, i))
 				{
+					context.IndexOfFirstAlreadyTransformedInstruction = block.Instructions.Count;
 					continue;
 				}
 				if (TransformAsyncUsing(block, i))
 				{
+					context.IndexOfFirstAlreadyTransformedInstruction = block.Instructions.Count;
 					continue;
 				}
 			}