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Optimized away usually means your test design has no significant functionality that requires the respective resources.
I didn't yet use carry and carry_sum primitive, but I think your design has connections that can't be mapped to real hardware. As far as I understand, CIN can't be driven by regular logic output and COUT can't drive an regular logic input. CIN and COUT can be connected to each other or must be left unconnected.
Obligatory question with posts like this: What do you want to achieve?
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Assume there is a Carry chain, the first cin and the last cout must be floating according your comments? If it is true, how can i use the chain? becasue i must input my signal into this chain!!! Thanks for you reply, anyway!
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