func findCallSite(fn *ssa.Function, call *ast.CallExpr) (ssa.CallInstruction, error) {
instr, _ := fn.ValueForExpr(call)
callInstr, _ := instr.(ssa.CallInstruction)
if instr == nil {
return nil, fmt.Errorf("this call site is unreachable in this analysis")
}
return callInstr, nil
}