RFR(L): 8185556: [MVT] C2 compiler support for non-flattened value type fields

[Roland Westrelin]

> Yes but Node::set_req would register the node as modified and we would at least fail with "modified node was not 
> processed by IGVN.transform_old()" if it was not transformed.

Fair enough. Your change looks good to me.

Roland.