Why does a comma expression return the result of the last expression? -From another perspective, C ++

Auto V = func1 (), func2 (), func3 ();

This is because a function call requires parameter pressure stacks, calls are complete, and there is also a process of rollback (stack cleaning.
The stack rollback can be performed by the caller or the called, so there are two different call conventions:
_ Cdecl and _ stdcall, of course this is far away. The register is also used to eliminate the unique thiscall of the fastcall and C ++ of the stack.
Because function calling is a process that constantly goes into and out of the stack, the comma expression returns the result of the last expression.
Otherwise, if the result of the first expression is returned, where is the result stored?