[clr-interp] Fix issues found in the startup path with the interpreter (#118497)

- Fix virtual function resolution might not handle dispatch to a shared generic method if the exact type of the method is visible at compile time
- Fix ldelema for an array of reference types doesn't handle shared generics properly
- Fix issue where the readonly prefix for ldelema is ignored

Author: davidwrighton

src/coreclr/interpreter/compiler.cpp

@@ -3095,7 +3095,7 @@ void InterpCompiler::EmitCall(CORINFO_RESOLVED_TOKEN* pConstrainedToken, bool re
             break;
 
         case CORINFO_VIRTUALCALL_LDVIRTFTN:
-            if ((callInfo.sig.sigInst.methInstCount != 0) || (m_compHnd->getClassAttribs(resolvedCallToken.hClass) & CORINFO_FLG_SHAREDINST))
+            if ((callInfo.sig.sigInst.methInstCount != 0) || (m_compHnd->getMethodAttribs(callInfo.hMethod) & CORINFO_FLG_SHAREDINST))
             {
                 assert(extraParamArgLocation == INT_MAX);
                 // We should not have a type argument for the ldvirtftn path since we don't know
@@ -5805,17 +5805,34 @@ void InterpCompiler::GenerateCode(CORINFO_METHOD_INFO* methodInfo)
                 CorInfoType elemCorType = m_compHnd->asCorInfoType(elemClsHnd);
 
                 m_pStackPointer -= 2;
-                if (elemCorType == CORINFO_TYPE_CLASS)
+                if ((elemCorType == CORINFO_TYPE_CLASS) && !readonly)
                 {
-                    AddIns(INTOP_LDELEMA_REF);
-                    m_pLastNewIns->SetSVars2(m_pStackPointer[0].var, m_pStackPointer[1].var);
-                    PushInterpType(InterpTypeByRef, elemClsHnd);
-                    m_pLastNewIns->SetDVar(m_pStackPointer[-1].var);
-                    m_pLastNewIns->data[0] = m_compHnd->getClassSize(elemClsHnd);
-                    m_pLastNewIns->data[1] = GetDataItemIndex(elemClsHnd);
+                    CORINFO_GENERICHANDLE_RESULT embedInfo;
+                    m_compHnd->embedGenericHandle(&resolvedToken, false, m_methodInfo->ftn, &embedInfo);
+                    DeclarePointerIsClass((CORINFO_CLASS_HANDLE)embedInfo.compileTimeHandle);
+
+                    if (embedInfo.lookup.lookupKind.needsRuntimeLookup)
+                    {
+                        GenericHandleData handleData = GenericHandleToGenericHandleData(embedInfo);
+
+                        AddIns(INTOP_LDELEMA_REF_GENERIC);
+                        m_pLastNewIns->SetSVars3(m_pStackPointer[0].var, m_pStackPointer[1].var, handleData.genericVar);
+                        PushInterpType(InterpTypeByRef, elemClsHnd);
+                        m_pLastNewIns->SetDVar(m_pStackPointer[-1].var);
+                        m_pLastNewIns->data[0] = handleData.dataItemIndex;
+                    }
+                    else
+                    {
+                        AddIns(INTOP_LDELEMA_REF);
+                        m_pLastNewIns->SetSVars2(m_pStackPointer[0].var, m_pStackPointer[1].var);
+                        PushInterpType(InterpTypeByRef, elemClsHnd);
+                        m_pLastNewIns->SetDVar(m_pStackPointer[-1].var);
+                        m_pLastNewIns->data[0] = GetDataItemIndex(elemClsHnd);
+                    }
                 }
                 else
                 {
+                    readonly = false; // If readonly was set, it is no longer needed as its been handled.
                     AddIns(INTOP_LDELEMA);
                     m_pLastNewIns->SetSVars2(m_pStackPointer[0].var, m_pStackPointer[1].var);
                     PushInterpType(InterpTypeByRef, elemClsHnd);

src/coreclr/interpreter/intops.def

@@ -53,7 +53,8 @@ OPDEF(INTOP_STELEM_VT, "stelem.vt", 6, 0, 3, InterpOpTwoInts)
 OPDEF(INTOP_STELEM_VT_NOREF, "stelem.vt.noref", 5, 0, 3, InterpOpInt)
 
 OPDEF(INTOP_LDELEMA, "ldelema", 5, 1, 2, InterpOpInt)
-OPDEF(INTOP_LDELEMA_REF, "ldelema.ref", 6, 1, 2, InterpOpTwoInts)
+OPDEF(INTOP_LDELEMA_REF, "ldelema.ref", 5, 1, 2, InterpOpClassHandle)
+OPDEF(INTOP_LDELEMA_REF_GENERIC, "ldelema.ref.generic", 6, 1, 3, InterpOpGenericLookup)
 
 OPDEF(INTOP_MOV_I4_I1, "mov.i4.i1", 3, 1, 1, InterpOpNoArgs)
 OPDEF(INTOP_MOV_I4_U1, "mov.i4.u1", 3, 1, 1, InterpOpNoArgs)

src/coreclr/vm/interpexec.cpp

@@ -2459,11 +2459,38 @@ do {                                                                           \
                         COMPlusThrow(kIndexOutOfRangeException);
 
                     uint8_t* pData = arr->GetDataPtr();
-                    size_t elemSize = ip[4];
-                    void* elemAddr = pData + idx * elemSize;
+                    void* elemAddr = pData + idx * sizeof(void*);
 
                     MethodTable* arrayElemMT = arr->GetArrayElementTypeHandle().AsMethodTable();
-                    MethodTable* expectedMT = (MethodTable*)pMethod->pDataItems[ip[5]];
+                    MethodTable* expectedMT = (MethodTable*)pMethod->pDataItems[ip[4]];
+                    if (arrayElemMT != expectedMT)
+                    {
+                        COMPlusThrow(kArrayTypeMismatchException);
+                    }
+
+                    LOCAL_VAR(ip[1], void*) = elemAddr;
+                    ip += 5;
+                    break;
+                }
+
+                case INTOP_LDELEMA_REF_GENERIC:
+                {
+                    BASEARRAYREF arrayRef = LOCAL_VAR(ip[2], BASEARRAYREF);
+                    if (arrayRef == NULL)
+                        COMPlusThrow(kNullReferenceException);
+
+                    ArrayBase* arr = (ArrayBase*)OBJECTREFToObject(arrayRef);
+                    uint32_t len = arr->GetNumComponents();
+                    uint32_t idx = (uint32_t)LOCAL_VAR(ip[3], int32_t);
+                    if (idx >= len)
+                        COMPlusThrow(kIndexOutOfRangeException);
+
+                    uint8_t* pData = arr->GetDataPtr();
+                    void* elemAddr = pData + idx * sizeof(void*);
+
+                    MethodTable* arrayElemMT = arr->GetArrayElementTypeHandle().AsMethodTable();
+                    InterpGenericLookup *pLookup = (InterpGenericLookup*)&pMethod->pDataItems[ip[5]];
+                    MethodTable* expectedMT = (MethodTable*)DoGenericLookup(LOCAL_VAR(ip[4], void*), pLookup);
                     if (arrayElemMT != expectedMT)
                     {
                         COMPlusThrow(kArrayTypeMismatchException);