VHDL shift or rotate: difference between concatenation and builtin functions (sll, sra,…)

Question

When you want to implement a shift/rotate operation in VHDL you can use either concatenation or built-in function of VHDL such as sll, sra, ror. Now my question is: what is the difference between the two (if there is one), both in terms of simulation performance (if applicable) and in particular in terms of synthesis results?

In my opinion concatenation could provide some advantages because it's just a matter of moving wires, while I don't know how built-in functions are treated by the synthesizer. But I am not totally certain and I'd like to understand which one is the best.

Thank you very much.

Answer 1

See Arithmetic and logical shifts and rotates are done with functions in VHDL, not operators ,"You've come to this page because you've asked about shift operators in VHDL". Concatenation should certainly be more compact.