Storage optimization by replacing some flip-flops with latches

Conventionally, when a synchronous sequential circuit is synthesized, storage units are implemented in either edge-triggered flip-flops or level-sensitive latches, but not both, depending on the clocking scheme (one- or two-phase) used. We propose that, in the former case, some of the flip-flops can be replaced with latches. Since a latch is generally smaller, faster and less power-consuming than a flip-flop, this replacement leads to improvements in circuit area, performance and power consumption. Whether a flip-flop can be replaced with a latch depends on not only its structural context but also its temporal behavior. We first present conditions under which a straightforward replacement can be made; then, we propose two retiming-based transformations that increase the number of replaceable flip-flops. We have implemented the proposed idea in a software called FF2Latch. Experimental results on a set of control-dominated circuits from the high-level synthesis benchmark set show that a large number of the flip-flops can be replaced with latches. Up to 22% reduction in the circuit area and up to 73% reduction in the power consumption have been achieved.