Implement castclass & isinst for WebAssembly (#5325)

* Implement castclass & isinst for wasm (#4510)

Implement castclass and isinst opcodes in ILToWebAssemblyImporter by
doing related function calls to methods in System.Runtime.TypeCast.

Fix #4510

Add castclass & isinst test in HelloWasm.

This includes three types of casting:
* castclass/isinst to classes.
* castclass/isinst to interfaces.
* castclass/isinst to array types.

For now, the second and third part of test is failing due to runtime
implementation problems which should be further digged into.

src/ILCompiler.WebAssembly/src/CodeGen/ILToWebAssemblyImporter.cs

@@ -818,6 +818,25 @@ namespace Internal.IL
 
         private void ImportCasting(ILOpcode opcode, int token)
         {
+            TypeDesc type = ResolveTypeToken(token);
+            
+            //TODO: call GetCastingHelperNameForType from JitHelper.cs (needs refactoring)
+            string function;
+            bool throwing = opcode == ILOpcode.castclass;
+            if (type.IsArray)
+                function = throwing ? "CheckCastArray" : "IsInstanceOfArray";
+            else if (type.IsInterface)
+                function = throwing ? "CheckCastInterface" : "IsInstanceOfInterface";
+            else
+                function = throwing ? "CheckCastClass" : "IsInstanceOfClass";
+
+            var arguments = new StackEntry[]
+            {
+                _stack.Pop(),
+                new LoadExpressionEntry(StackValueKind.ValueType, "eeType", GetEETypePointerForTypeDesc(type, true), _compilation.TypeSystemContext.SystemModule.GetKnownType("System", "EETypePtr"))
+            };
+
+            _stack.Push(CallRuntime(_compilation.TypeSystemContext, TypeCast, function, arguments, type));
         }
 
         private void ImportLoadNull()
@@ -2344,6 +2363,7 @@ namespace Internal.IL
         private const string RuntimeExport = "RuntimeExports";
         private const string RuntimeImport = "RuntimeImports";
         private const string InternalCalls = "InternalCalls";
+        private const string TypeCast = "TypeCast";
         private ExpressionEntry CallRuntime(TypeSystemContext context, string className, string methodName, StackEntry[] arguments, TypeDesc forcedReturnType = null)
         {
             MetadataType helperType = context.SystemModule.GetKnownType("System.Runtime", className);

tests/src/Simple/HelloWasm/Program.cs

@@ -181,6 +181,27 @@ internal static class Program
 
         IntToStringTest();
 
+        CastingTestClass castingTest = new DerivedCastingTestClass1();
+        if (((DerivedCastingTestClass1)castingTest).GetValue() == 1 && !(castingTest is DerivedCastingTestClass2))
+        {
+            PrintLine("Type casting with isinst & castclass to class test: Ok.");
+        }
+
+        // Instead of checking the result of `GetValue`, we use null check by now until interface dispatch is implemented.
+        if ((ICastingTest1)castingTest != null && !(castingTest is ICastingTest2))
+        {
+            PrintLine("Type casting with isinst & castclass to interface test: Ok.");
+        }
+
+        object arrayCastingTest = new BoxStubTest[] { new BoxStubTest { Value = "Array" }, new BoxStubTest { Value = "Cast" }, new BoxStubTest { Value = "Test" } };
+        PrintLine(((BoxStubTest[])arrayCastingTest)[0].Value);
+        PrintLine(((BoxStubTest[])arrayCastingTest)[1].Value);
+        PrintLine(((BoxStubTest[])arrayCastingTest)[2].Value);
+        if (!(arrayCastingTest is CastingTestClass[]))
+        {   
+            PrintLine("Type casting with isinst & castclass to array test: Ok.");
+        }
+
         PrintLine("Done");
     }
 
@@ -367,3 +388,27 @@ public class TestDerivedClass : TestClass
     }
 }
 
+public interface ICastingTest1
+{
+    int GetValue();
+}
+
+public interface ICastingTest2
+{
+    int GetValue();
+}
+
+public abstract class CastingTestClass
+{
+    public abstract int GetValue();
+}
+
+public class DerivedCastingTestClass1 : CastingTestClass, ICastingTest1
+{
+    public override int GetValue() => 1;
+}
+
+public class DerivedCastingTestClass2 : CastingTestClass, ICastingTest2
+{
+    public override int GetValue() => 2;
+}