Add zero field offsets where it was missed.

And don't add it as `ADD(,0)` in another.

Author: Sergey Andreenko

src/coreclr/src/jit/morph.cpp

@@ -10347,11 +10347,20 @@ GenTree* Compiler::fgMorphCopyBlock(GenTree* tree)
                     CORINFO_CLASS_HANDLE classHnd = srcVarDsc->lvVerTypeInfo.GetClassHandle();
                     CORINFO_FIELD_HANDLE fieldHnd =
                         info.compCompHnd->getFieldInClass(classHnd, srcFieldVarDsc->lvFldOrdinal);
-                    FieldSeqNode* curFieldSeq     = GetFieldSeqStore()->CreateSingleton(fieldHnd);
-                    unsigned      srcFieldOffset  = lvaGetDesc(srcFieldLclNum)->lvFldOffset;
-                    GenTree*      fieldOffsetNode = gtNewIconNode(srcFieldVarDsc->lvFldOffset, curFieldSeq);
+                    FieldSeqNode* curFieldSeq = GetFieldSeqStore()->CreateSingleton(fieldHnd);
+
+                    unsigned srcFieldOffset = lvaGetDesc(srcFieldLclNum)->lvFldOffset;
+
+                    if (srcFieldOffset == 0)
+                    {
+                        fgAddFieldSeqForZeroOffset(dstFld, curFieldSeq);
+                    }
+                    else
+                    {
+                        GenTree* fieldOffsetNode = gtNewIconNode(srcFieldVarDsc->lvFldOffset, curFieldSeq);
+                        dstFld                   = gtNewOperNode(GT_ADD, TYP_BYREF, dstFld, fieldOffsetNode);
+                    }
 
-                    dstFld = gtNewOperNode(GT_ADD, TYP_BYREF, dstFld, fieldOffsetNode);
                     dstFld = gtNewIndir(srcFieldVarDsc->TypeGet(), dstFld);
 
                     // !!! The destination could be on stack. !!!
@@ -10427,15 +10436,18 @@ GenTree* Compiler::fgMorphCopyBlock(GenTree* tree)
                             }
                         }
                     }
-                    else // if (lvaGetDesc(fieldLclNum)->lvFldOffset != 0)
-                    {
-                        srcFld = gtNewOperNode(GT_ADD, TYP_BYREF, srcFld,
-                                               new (this, GT_CNS_INT)
-                                                   GenTreeIntCon(TYP_I_IMPL, lvaGetDesc(dstFieldLclNum)->lvFldOffset,
-                                                                 curFieldSeq));
-                    }
                     if (!done)
                     {
+                        unsigned fldOffset = lvaGetDesc(dstFieldLclNum)->lvFldOffset;
+                        if (fldOffset == 0)
+                        {
+                            fgAddFieldSeqForZeroOffset(srcFld, curFieldSeq);
+                        }
+                        else
+                        {
+                            GenTreeIntCon* fldOffsetNode = gtNewIconNode(fldOffset, curFieldSeq);
+                            srcFld                       = gtNewOperNode(GT_ADD, TYP_BYREF, srcFld, fldOffsetNode);
+                        }
                         srcFld = gtNewIndir(destType, srcFld);
                     }
                 }