rebased

src/Compilers/CSharp/Portable/CodeGen/EmitExpression.cs

@@ -384,8 +384,7 @@ private void EmitLoweredConditionalAccessExpression(BoundLoweredConditionalAcces
             // or if we have default(T) (to do box just once)
             var nullCheckOnCopy = LocalRewriter.CanChangeValueBetweenReads(receiver, localsMayBeAssignedOrCaptured: false) ||
                                    (receiverType.IsReferenceType && receiverType.TypeKind == TypeKind.TypeParameter) ||
-                                   (receiver.Kind == BoundKind.Local && IsStackLocal(((BoundLocal)receiver).LocalSymbol)) ||
-                                   (receiver.IsDefaultValue() && notConstrained);
+                                   (receiver.Kind == BoundKind.Local && IsStackLocal(((BoundLocal)receiver).LocalSymbol));
 
             // ===== RECEIVER
             if (nullCheckOnCopy)
@@ -502,7 +501,7 @@ private void EmitLoweredConditionalAccessExpression(BoundLoweredConditionalAcces
                 Debug.Assert(receiverTemp == null);
                 // receiver may be used as target of a struct call (if T happens to be a sruct)
                 receiverTemp = EmitReceiverRef(receiver, AddressKind.Constrained);
-                Debug.Assert(receiverTemp == null);
+                Debug.Assert(receiverTemp == null || receiver.IsDefaultValue());
             }
 
             EmitExpression(expression.WhenNotNull, used);

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

@@ -68,7 +68,7 @@ .maxstack  1
   IL_0000:  ldc.i4.s   42
   IL_0002:  stloc.0
   IL_0003:  ldloca.s   V_0
-  IL_0005:  call       ""ref readonly int Program.M(ref readonly int)""
+  IL_0005:  call       ""ref readonly int Program.M(in int)""
   IL_000a:  ldind.i4
   IL_000b:  call       ""void System.Console.WriteLine(int)""
   IL_0010:  ret
@@ -103,7 +103,7 @@ .locals init (int V_0)
   IL_0000:  ldc.i4.s   42
   IL_0002:  stloc.0
   IL_0003:  ldloca.s   V_0
-  IL_0005:  call       ""ref readonly int Program.M(ref readonly int)""
+  IL_0005:  call       ""ref readonly int Program.M(in int)""
   IL_000a:  ldind.i4
   IL_000b:  call       ""void System.Console.WriteLine(int)""
   IL_0010:  ret
@@ -137,14 +137,14 @@ public static void Main()
   // Code size       17 (0x11)
   .maxstack  1
   IL_0000:  ldsflda    ""int Program.F""
-  IL_0005:  call       ""ref readonly int Program.M(ref readonly int)""
+  IL_0005:  call       ""ref readonly int Program.M(in int)""
   IL_000a:  ldind.i4
   IL_000b:  call       ""void System.Console.WriteLine(int)""
   IL_0010:  ret
 }");
 
 
-            comp.VerifyIL("Program.M(ref readonly int)", @"
+            comp.VerifyIL("Program.M(in int)", @"
 {
   // Code size        2 (0x2)
   .maxstack  1
@@ -180,12 +180,12 @@ public static void Main()
 
             var comp = CompileAndVerify(text, parseOptions: TestOptions.Regular, verify: false, expectedOutput: "42");
 
-            comp.VerifyIL("Program.M(ref readonly int)", @"
+            comp.VerifyIL("Program.M(in int)", @"
 {
   // Code size        7 (0x7)
   .maxstack  1
   IL_0000:  ldarg.0
-  IL_0001:  call       ""ref readonly int Program.M1(ref readonly int)""
+  IL_0001:  call       ""ref readonly int Program.M1(in int)""
   IL_0006:  ret
 }");
         }