The question about union of rvalue

Hi there! I have a question about clang, especially rvalue class.
Is there any method to find union at rvalue class?
I mean, if there exist code line like under, I want to know that this rvalue have union variable.
Please answer me is there any method to find this union variable! Thank you.

[code line]
union union_example
int int_A;
float float_A;

A(int x) { printf(“A function”);};

int main
union_example union_var;
union_var.int_A = 3;
return 0;