ICSharpCode.ILSpy.AssertionFailedException: Container should not have any unreachable blocks

[greenozon]

Input code

save as project

Erroneous output

Error decompiling @060033A7 
in assembly "C:\Tmp\1\err145.dll"
 ---> ICSharpCode.ILSpy.AssertionFailedException: Container should not have any unreachable blocks
   at ICSharpCode.ILSpy.ILSpyTraceListener.Fail(String message, String detailMessage) in offset 379
   at System.Diagnostics.TraceInternal.Fail(String message, String detailMessage) in offset 48
   at System.Diagnostics.Debug.Fail(String message, String detailMessage) in offset 0
   at ICSharpCode.Decompiler.IL.BlockContainer.CheckInvariant(ILPhase phase) in BlockContainer.cs:line 202
   at ICSharpCode.Decompiler.IL.ILInstruction.CheckInvariant(ILPhase phase) in ILInstruction.cs:line 95
   at ICSharpCode.Decompiler.IL.ILInstruction.CheckInvariant(ILPhase phase) in ILInstruction.cs:line 95
   at ICSharpCode.Decompiler.IL.Block.CheckInvariant(ILPhase phase) in Block.cs:line 108
   at ICSharpCode.Decompiler.IL.ILInstruction.CheckInvariant(ILPhase phase) in ILInstruction.cs:line 95
   at ICSharpCode.Decompiler.IL.BlockContainer.CheckInvariant(ILPhase phase) in BlockContainer.cs:line 196
   at ICSharpCode.Decompiler.IL.ILInstruction.CheckInvariant(ILPhase phase) in ILInstruction.cs:line 95
   at ICSharpCode.Decompiler.IL.ILFunction.CheckInvariant(ILPhase phase) in ILFunction.cs:line 260
   at ICSharpCode.Decompiler.CSharp.CSharpDecompiler.DecompileBody(IMethod method, EntityDeclaration entityDecl, DecompileRun decompileRun, ITypeResolveContext decompilationContext) in CSharpDecompiler.cs:line 1760
-- continuing with outer exception (ICSharpCode.Decompiler.DecompilerException) --
   at ICSharpCode.Decompiler.CSharp.CSharpDecompiler.DecompileBody(IMethod method, EntityDeclaration entityDecl, DecompileRun decompileRun, ITypeResolveContext decompilationContext) in CSharpDecompiler.cs:line 1795
   at ICSharpCode.Decompiler.CSharp.CSharpDecompiler.DoDecompile(IMethod method, DecompileRun decompileRun, ITypeResolveContext decompilationContext) in CSharpDecompiler.cs:line 1644
   at ICSharpCode.Decompiler.CSharp.CSharpDecompiler.<>c__DisplayClass75_0.<DoDecompile>g__DoDecompileMember|0(IEntity entity, RecordDecompiler recordDecompiler, PartialTypeInfo partialType) in CSharpDecompiler.cs:line 1519
   at ICSharpCode.Decompiler.CSharp.CSharpDecompiler.DoDecompile(ITypeDefinition typeDef, DecompileRun decompileRun, ITypeResolveContext decompilationContext) in CSharpDecompiler.cs:line 1382
   at ICSharpCode.Decompiler.CSharp.CSharpDecompiler.DoDecompileTypes(IEnumerable`1 types, DecompileRun decompileRun, ITypeResolveContext decompilationContext, SyntaxTree syntaxTree) in CSharpDecompiler.cs:line 656
   at ICSharpCode.Decompiler.CSharp.CSharpDecompiler.DecompileTypes(IEnumerable`1 types) in CSharpDecompiler.cs:line 955
   at ICSharpCode.Decompiler.CSharp.ProjectDecompiler.WholeProjectDecompiler.<>c__DisplayClass46_0.<WriteCodeFilesInProject>b__5(IGrouping`2 file) in WholeProjectDecompiler.cs:line 289
   at System.Threading.Tasks.Parallel.<>c__DisplayClass43_0`2.<PartitionerForEachWorker>b__1(IEnumerator& partitionState, Int64 timeout, Boolean& replicationDelegateYieldedBeforeCompletion) in offset 259
   at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw() in offset 17
   at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw(Exception source) in offset 0
   at System.Threading.Tasks.Parallel.<>c__DisplayClass43_0`2.<PartitionerForEachWorker>b__1(IEnumerator& partitionState, Int64 timeout, Boolean& replicationDelegateYieldedBeforeCompletion) in offset 609
   at System.Threading.Tasks.TaskReplicator.Replica.Execute() in offset 35

Details

• ILSpy version 9.0.0.7832-preview3+1134313515d9c4ad908eb024942e740b591aaac5
  .NET version 8.0.8+08338fcaa5c9b9a8190abb99222fed12aaba956c

err145.zip

[dgrunwald]

The exception occurs after the async/await decompiler has finished.

In MoveNext, IL_0586 is originally reachable via IL_03b2->IL_03d5->IL_0586 and from the catch(NotSupportedException): IL_03c2->IL_03d5->IL_0586.
However, "Inline catch block with await">"Remove jump-table entry" severs the link from IL_03d5 to IL_0586, and instead lets IL_03b2 directly jump to IL_0586.
As far as I can tell, this is the expected behavior, we are eliminating a compiler generated variable and simplifying the control flow accordingly.

Later, the AwaitInFinallyTransform runs, which causes a different block to become dead (IL_0382). This actually dominates IL_03b2, so effectively IL_0586 also becomes unreachable here.
All of the blocks that became unreachable contain compiler-generated exception handling machinery (await-in-catch/finally).

Finally, the AwaitInFinallyTransform performs cleanup. This ends up deleting unreachable code in all modified block containers, including IL_03b2. But IL_0586 actually lives in a different block container that is not getting cleaned up.