The shift-register primitive does not use the register available in the same slice. To implement a fully synchronous read and write shift register, output pin Q must be connected to a flip-flop. Both the shift register and the flip-flop share the same clock as shown in the following figure.
Figure 1. Synchronous Shift Register
This configuration provides a better timing solution and simplifies the design. Because the flip-flop must be considered to be the last register in the shift-register chain, the static or dynamic address should point to the desired length minus one. If needed, the cascadable output can also be registered in a flip-flop.