Why is the dangling signal with perserve_for_debug attribute still optimized away after compilation?

Description

Due to a problem in the Intel® Quartus® Prime Pro Edition Software v22.3 and earlier, you might see the dangling signal is optimized away, although it has preserve_for_debug synthesis attribute.

Resolution

To work around this problem, connect the dangling signal to the top-level pin to avoid synthesis optimization. 

This problem is fixed starting with the Intel® Quartus® Prime Pro Edition Software version 22.4.