Fix ILVerify failure: yield break in catch blocks within async iterators

src/Compilers/CSharp/Portable/Lowering/AsyncRewriter/AsyncIteratorMethodToStateMachineRewriter.cs

@@ -366,21 +366,24 @@
         public override BoundNode VisitTryStatement(BoundTryStatement node)
         {
             var savedDisposalLabel = _currentDisposalLabel;
+            LabelSymbol finallyEntry = null;
+            bool hasCatchBlocks = !node.CatchBlocks.IsEmpty;
+
             if (node.FinallyBlockOpt is object)
             {
-                var finallyEntry = F.GenerateLabel("finallyEntry");
+                finallyEntry = F.GenerateLabel("finallyEntry");
                 _currentDisposalLabel = finallyEntry;
 
-                // Add finallyEntry label:
-                //  try
-                //  {
-                //      ...
-                //      finallyEntry:
-                //  }
-
-                node = node.Update(
-                    tryBlock: F.Block(node.TryBlock, F.Label(finallyEntry)),
-                    node.CatchBlocks, node.FinallyBlockOpt, node.FinallyLabelOpt, node.PreferFaultHandler);
+                // When there are no catch blocks, we can place the finallyEntry label at the end
+                // of the try block (original behavior). But when there are catch blocks, we must
+                // place it after the entire try-catch-finally structure to avoid invalid IL
+                // (leaving from a catch block into a try block).
+                if (!hasCatchBlocks)
+                {
+                    node = node.Update(
+                        tryBlock: F.Block(node.TryBlock, F.Label(finallyEntry)),
+                        node.CatchBlocks, node.FinallyBlockOpt, node.FinallyLabelOpt, node.PreferFaultHandler);
+                }
             }
             else if (node.FinallyLabelOpt is object)
             {
@@ -391,6 +394,30 @@
 
             _currentDisposalLabel = savedDisposalLabel;
 
+            if (finallyEntry != null && hasCatchBlocks)
+            {
+                // When there are catch blocks, place the finallyEntry label after the try-catch-finally:
+                //  try
+                //  {
+                //      ...
+                //      if (disposeMode) leave to finallyEntry;
+                //  }
+                //  catch
+                //  {
+                //      ...
+                //      if (disposeMode) leave to finallyEntry;
+                //  }
+                //  finally
+                //  {
+                //      ...
+                //  }
+                //  finallyEntry:
+                //  if (disposeMode) goto currentDisposalLabel;
+                result = F.Block(
+                    result,
+                    F.Label(finallyEntry));
+            }
+
             if (node.FinallyBlockOpt != null && _currentDisposalLabel is object)
             {
                 // Append:

src/Compilers/CSharp/Test/Emit/CodeGen/CodeGenAsyncIteratorTests.cs

@@ -4729,11 +4729,7 @@ public static async System.Collections.Generic.IAsyncEnumerable<int> M()
 }";
             var comp = CreateCompilationWithAsyncIterator(new[] { Run(iterations), source }, options: TestOptions.DebugExe);
             comp.VerifyDiagnostics();
-            var verifier = CompileAndVerify(comp, expectedOutput: expectedOutput,
-                verify: Verification.FailsILVerify with
-                {
-                    ILVerifyMessage = "[MoveNext]: Leave into try block. { Offset = 0x11a }"
-                });
+            var verifier = CompileAndVerify(comp, expectedOutput: expectedOutput);
 
             verifier.VerifyIL("C.<M>d__0.System.Runtime.CompilerServices.IAsyncStateMachine.MoveNext()", """
                 {
@@ -4859,7 +4855,7 @@ .locals init (int V_0,
                         IL_00f9:  ldarg.0
                         IL_00fa:  ldfld      "bool C.<M>d__0.<>w__disposeMode"
                         IL_00ff:  brfalse.s  IL_0103
-                        IL_0101:  br.s       IL_0104
+                        IL_0101:  leave.s    IL_0130
                         IL_0103:  nop
                         IL_0104:  leave.s    IL_011c
                       }
@@ -4873,7 +4869,7 @@ .locals init (int V_0,
                         IL_0113:  ldarg.0
                         IL_0114:  ldc.i4.1
                         IL_0115:  stfld      "bool C.<M>d__0.<>w__disposeMode"
-                        IL_011a:  leave.s    IL_0104
+                        IL_011a:  leave.s    IL_0130
                       }
                       IL_011c:  leave.s    IL_0130
                     }