// If the constant pool entry for invokespecial is InterfaceMethodref,
// we need to add a separate cpCache entry for its resolution, because it is
// different than the resolution for invokeinterface with InterfaceMethodref.
// These cannot share cpCache entries. It's unclear if all invokespecial to
// InterfaceMethodrefs would resolve to the same thing so a new cpCache entry
// is created for each one. This was added with lambda.
void Rewriter::rewrite_invokespecial(address bcp, int offset, bool reverse, bool* invokespecial_error) {
...

We do in fact share cpCache entries for invokespecial/IMR combinations if the IMR is the same.

  // add a new CP cache entry beyond the normal cache for the special case of
  // invokespecial with InterfaceMethodref as cpool operand.
  int add_invokespecial_cp_cache_entry(int cp_index) {
    assert(_first_iteration_cp_cache_limit >= 0, "add these special cache entries after first iteration");
    // Don't add InterfaceMethodref if it already exists at the end.
    for (int i = _first_iteration_cp_cache_limit; i < _cp_cache_map.length(); i++) {
      if (cp_cache_entry_pool_index(i) == cp_index) {
        return i;
      }
    }