Execution inside a process [VHDL]
This code does not describe a state machine, so the concepts of sequential statements or program execution don't apply here. The correct answer to your question is "無."

The sequential execution of a process will create a state machine only if there are wait statements, which are not allowed in processes with sensitivity lists. The order of statements is relevant for resolving signal assignments (last assignment to a signal wins), and for conditions based on variables (where assignments are visible to the following statements in the same process).

The two conditional statements only depend on signal values, only modify signal values and have no interdependencies, so their effects are concurrent even though they are technically part of a sequence. If you synthesize this design, you end up with completely independent circuits.

In a bigger scope, the entire process is optimized out, as there is only a single place driving a and b, and the only value ever assigned is 0.



You cannot have other concurrent statements or processes drive a and b either, as that would cause a conflict.