Pragma Unroll with variable loop bound

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Is it compulsory for the loop bound to be constant for unrolling?

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No. However, for minimum area overhead and maximum performance, it is best if the loop bound is known at compile-time and is divisible by the unroll factor.

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Would the below kernel generate 50 times hw replication? What will happen if host sets the k = 60?

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The compiler will create a pipeline that can process 50 iteration per clock by using more FPGA resources. If you set k = 60, then the pipeline will work for two clocks + pipeline latency; nothing will go wrong, just the pipeline utilization will be low in the last clock.

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