Canonical Body - 2024.1 English

Inside the canonical region, the canonical body should follow these guidelines:

1. Use a local, non-static scalar or an array variable. A local variable is declared inside the function body (for dataflow in a function) or loop body (for dataflow inside a loop). Refer to Limitations of Control-Driven Task-Level Parallelism for additional limitations on arrays.
2. A sequence of function calls that pass data forward (with no feedback unless using hls::stream/hls::stream_of_blocks), from a function to one that is lexically later, under the following conditions:
   1. Variables (except scalar) can have only one reading process and one writing process.
   2. Use write before read (producer before consumer) if you are using local non-scalar variables, which then become channels. For scalar variables, both write before read and read before write are allowed.
   3. Function return type must be void.
   4. No loop-carried dependencies are allowed among different processes via variables except when FIFOs are used. Forward loop-carried dependencies are supported for arrays transformed to streams and both forward and backward dependencies are supported for hls::streams.
   5. No control whatsoever is supported inside a dataflow region, except inside function calls (that define processes).
      • For canonical dataflow, there should be no conditionals, no loops, no return or goto statements, and no C++ exceptions such as throw.