Move GetMethodTable to JIT (#105098)

Author: MichalPetryka

src/coreclr/System.Private.CoreLib/src/System/Runtime/CompilerServices/RuntimeHelpers.CoreCLR.cs

@@ -436,16 +436,8 @@ internal static unsafe bool ObjectHasComponentSize(object obj)
         //
         // GC.KeepAlive(o);
         //
-        [MethodImpl(MethodImplOptions.AggressiveInlining)]
         [Intrinsic]
-        internal static unsafe MethodTable* GetMethodTable(object obj)
-        {
-            // The body of this function will be replaced by the EE with unsafe code
-            // See getILIntrinsicImplementationForRuntimeHelpers for how this happens.
-
-            return (MethodTable*)Unsafe.Add(ref Unsafe.As<byte, IntPtr>(ref obj.GetRawData()), -1);
-        }
-
+        internal static unsafe MethodTable* GetMethodTable(object obj) => GetMethodTable(obj);
 
         [LibraryImport(QCall, EntryPoint = "MethodTable_AreTypesEquivalent")]
         [return: MarshalAs(UnmanagedType.Bool)]

src/coreclr/jit/importercalls.cpp

@@ -3561,6 +3561,12 @@ GenTree* Compiler::impIntrinsic(CORINFO_CLASS_HANDLE    clsHnd,
                 break;
             }
 
+            case NI_System_Runtime_CompilerServices_RuntimeHelpers_GetMethodTable:
+            {
+                retNode = gtNewMethodTableLookup(impPopStack().val);
+                break;
+            }
+
             case NI_System_Runtime_InteropService_MemoryMarshal_GetArrayDataReference:
             {
                 assert(sig->numArgs == 1);
@@ -10410,6 +10416,10 @@ NamedIntrinsic Compiler::lookupNamedIntrinsic(CORINFO_METHOD_HANDLE method)
                                 result =
                                     NI_System_Runtime_CompilerServices_RuntimeHelpers_IsReferenceOrContainsReferences;
                             }
+                            else if (strcmp(methodName, "GetMethodTable") == 0)
+                            {
+                                result = NI_System_Runtime_CompilerServices_RuntimeHelpers_GetMethodTable;
+                            }
                         }
                         else if (strcmp(className, "Unsafe") == 0)
                         {

src/coreclr/jit/namedintrinsiclist.h

@@ -114,6 +114,7 @@ enum NamedIntrinsic : unsigned short
     NI_System_Runtime_CompilerServices_RuntimeHelpers_InitializeArray,
     NI_System_Runtime_CompilerServices_RuntimeHelpers_IsKnownConstant,
     NI_System_Runtime_CompilerServices_RuntimeHelpers_IsReferenceOrContainsReferences,
+    NI_System_Runtime_CompilerServices_RuntimeHelpers_GetMethodTable,
 
     NI_System_Runtime_InteropService_MemoryMarshal_GetArrayDataReference,
 

src/coreclr/nativeaot/System.Private.CoreLib/src/System/Runtime/CompilerServices/RuntimeHelpers.NativeAot.cs

@@ -216,8 +216,8 @@ internal static unsafe ushort GetElementSize(this Array array)
             return array.GetMethodTable()->ComponentSize;
         }
 
-        internal static unsafe MethodTable* GetMethodTable(this object obj)
-            => obj.m_pEEType;
+        [Intrinsic]
+        internal static unsafe MethodTable* GetMethodTable(this object obj) => obj.GetMethodTable();
 
         internal static unsafe ref MethodTable* GetMethodTableRef(this object obj)
             => ref obj.m_pEEType;

src/coreclr/tools/Common/TypeSystem/IL/Stubs/RuntimeHelpersIntrinsics.cs

@@ -19,19 +19,6 @@ public static MethodIL EmitIL(MethodDesc method)
             Debug.Assert(((MetadataType)method.OwningType).Name == "RuntimeHelpers");
             string methodName = method.Name;
 
-            if (methodName == "GetMethodTable")
-            {
-                ILEmitter emit = new ILEmitter();
-                ILCodeStream codeStream = emit.NewCodeStream();
-                codeStream.EmitLdArg(0);
-                codeStream.Emit(ILOpcode.ldflda, emit.NewToken(method.Context.SystemModule.GetKnownType("System.Runtime.CompilerServices", "RawData").GetField("Data")));
-                codeStream.EmitLdc(-method.Context.Target.PointerSize);
-                codeStream.Emit(ILOpcode.add);
-                codeStream.Emit(ILOpcode.ldind_i);
-                codeStream.Emit(ILOpcode.ret);
-                return emit.Link(method);
-            }
-
             // All the methods handled below are per-instantiation generic methods
             if (method.Instantiation.Length != 1 || method.IsTypicalMethodDefinition)
                 return null;

src/coreclr/vm/corelib.h

@@ -632,7 +632,6 @@ DEFINE_METHOD(RTFIELD,              GET_FIELDHANDLE,        GetFieldHandle,
 
 DEFINE_CLASS(RUNTIME_HELPERS,       CompilerServices,       RuntimeHelpers)
 DEFINE_METHOD(RUNTIME_HELPERS,      IS_BITWISE_EQUATABLE,    IsBitwiseEquatable, NoSig)
-DEFINE_METHOD(RUNTIME_HELPERS,      GET_METHOD_TABLE,        GetMethodTable,     NoSig)
 DEFINE_METHOD(RUNTIME_HELPERS,      GET_RAW_DATA,            GetRawData,         NoSig)
 DEFINE_METHOD(RUNTIME_HELPERS,      GET_UNINITIALIZED_OBJECT, GetUninitializedObject, SM_Type_RetObj)
 DEFINE_METHOD(RUNTIME_HELPERS,      ENUM_EQUALS,            EnumEquals, NoSig)

src/coreclr/vm/jitinterface.cpp

@@ -7332,43 +7332,6 @@ bool getILIntrinsicImplementationForRuntimeHelpers(MethodDesc * ftn,
         return true;
     }
 
-    if (tk == CoreLibBinder::GetMethod(METHOD__RUNTIME_HELPERS__GET_METHOD_TABLE)->GetMemberDef())
-    {
-        mdToken tokRawData = CoreLibBinder::GetField(FIELD__RAW_DATA__DATA)->GetMemberDef();
-
-        // In the CLR, an object is laid out as follows.
-        // [ object_header || MethodTable* (64-bit pointer) || instance_data ]
-        //                    ^                                ^-- ref <theObj>.firstField points here
-        //                    `-- <theObj> reference (type O) points here
-        //
-        // So essentially what we want to do is to turn an object reference (type O) into a
-        // native int&, then dereference it to get the MethodTable*. (Essentially, an object
-        // reference is a MethodTable**.) Per ECMA-335, Sec. III.1.5, we can add
-        // (but not subtract) a & and an int32 to produce a &. So we'll get a reference to
-        // <theObj>.firstField (type &), then back up one pointer length to get a value of
-        // essentially type (MethodTable*)&. Both of these are legal GC-trackable references
-        // to <theObj>, regardless of <theObj>'s actual length.
-
-        static BYTE ilcode[] = { CEE_LDARG_0,         // stack contains [ O ] = <theObj>
-                                 CEE_LDFLDA,0,0,0,0,  // stack contains [ & ] = ref <theObj>.firstField
-                                 CEE_LDC_I4_S,(BYTE)(-TARGET_POINTER_SIZE), // stack contains [ &, int32 ] = -IntPtr.Size
-                                 CEE_ADD,             // stack contains [ & ] = ref <theObj>.methodTablePtr
-                                 CEE_LDIND_I,         // stack contains [ native int ] = <theObj>.methodTablePtr
-                                 CEE_RET };
-
-        ilcode[2] = (BYTE)(tokRawData);
-        ilcode[3] = (BYTE)(tokRawData >> 8);
-        ilcode[4] = (BYTE)(tokRawData >> 16);
-        ilcode[5] = (BYTE)(tokRawData >> 24);
-
-        methInfo->ILCode = const_cast<BYTE*>(ilcode);
-        methInfo->ILCodeSize = sizeof(ilcode);
-        methInfo->maxStack = 2;
-        methInfo->EHcount = 0;
-        methInfo->options = (CorInfoOptions)0;
-        return true;
-    }
-
     if (tk == CoreLibBinder::GetMethod(METHOD__RUNTIME_HELPERS__ENUM_EQUALS)->GetMemberDef())
     {
         // Normally we would follow the above pattern and unconditionally replace the IL,