Merge pull request #15466 from TyOverby/9703-vb-bad-emit

avoid double-pop in an ignored conversion expression

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

@@ -15488,5 +15488,36 @@ public static void Main(string[] args)
                 expectedOutput: "0");
         }
 
+        [Fact, WorkItem(9703, "https://github.com/dotnet/roslyn/issues/9703")]
+        public void IgnoredConversion()
+        {
+            string source = @"
+using System;
+
+public class Form1 {
+    public class BadCompiler {
+        public DateTime? Value {get; set;}
+    }
+
+    private BadCompiler TestObj = new BadCompiler();
+
+    public void IPE() {
+        object o;
+        o = TestObj.Value;
+    }
+}";
+            var compilation = CompileAndVerify(source);
+            compilation.VerifyIL("Form1.IPE", @"
+{
+    // Code size       13 (0xd)
+    .maxstack  1
+    IL_0000:  ldarg.0
+    IL_0001:  ldfld      ""Form1.BadCompiler Form1.TestObj""
+    IL_0006:  callvirt   ""System.DateTime? Form1.BadCompiler.Value.get""
+    IL_000b:  pop
+    IL_000c:  ret
+}");
+        }
+
     }
 }

src/Compilers/VisualBasic/Portable/CodeGen/EmitConversion.vb

@@ -160,19 +160,15 @@ Namespace Microsoft.CodeAnalysis.VisualBasic.CodeGen
                 ElseIf typeFrom.IsNullableType Then
                     Debug.Assert(typeTo.IsReferenceType)
 
+                    EmitExpression(conversion.Operand, used:=True)
+
                     If (conversion.ConversionKind And ConversionKind.Narrowing) <> 0 Then
-                        EmitExpression(conversion.Operand, True)
                         EmitBox(typeFrom, conversion.Operand.Syntax)
                         _builder.EmitOpCode(ILOpCode.Castclass)
                         EmitSymbolToken(typeTo, conversion.Syntax)
-
-                    Else
+                    ElseIf used Then
                         ' boxing itself is CLR-widening, so no need to emit unused boxing
-                        EmitExpression(conversion.Operand, used)
-                        If used Then
-                            EmitBox(typeFrom, conversion.Operand.Syntax)
-                        End If
-
+                        EmitBox(typeFrom, conversion.Operand.Syntax)
                     End If
 
                 ElseIf typeTo.IsNullableType Then

src/Compilers/VisualBasic/Test/Emit/CodeGen/CodeGenTests.vb

@@ -13580,5 +13580,45 @@ End Class
 ]]>)
         End Sub
 
+
+        <Fact, WorkItem(9703, "https://github.com/dotnet/roslyn/issues/9703")>
+        Public Sub IgnoredConversion()
+            CompileAndVerify(
+                <compilation>
+                    <file name="ignoreNullableValue.vb">
+Module MainModule
+    Public Class Form1
+        Public Class BadCompiler
+            Public Property Value As Date?
+        End Class
+
+        Private TestObj As BadCompiler = New BadCompiler()
+
+        Public Sub IPE()
+            Dim o as Object
+            o = TestObj.Value
+        End Sub
+    End Class
+
+    Public Sub Main()
+        Dim f = new Form1
+        f.IPE()
+    End Sub
+End Module
+                    </file>
+                </compilation>).
+                            VerifyIL("MainModule.Form1.IPE",
+            <![CDATA[
+{
+// Code size       13 (0xd)
+.maxstack  1
+IL_0000:  ldarg.0
+IL_0001:  ldfld      "MainModule.Form1.TestObj As MainModule.Form1.BadCompiler"
+IL_0006:  callvirt   "Function MainModule.Form1.BadCompiler.get_Value() As Date?"
+IL_000b:  pop
+IL_000c:  ret
+}
+]]>)
+        End Sub
     End Class
 End Namespace