Using high level synthesis (HLS) and linked hardware description language (HDL) libraries to implement a circuit design includes generating, using computer hardware, a data flow graph from a model that includes an HDL model block coupled to a non-HDL model block, wherein the HDL model block is derived from HDL code, and dividing, using the computer hardware, the data flow graph into a first sub-graph corresponding to the HDL model block and a second sub-graph corresponding to the non-HDL model block. Using the computer hardware, a first HDL core is generated from the first sub-graph, synthesizable program code is generated form the second sub-graph, HLS is performed on the synthesizable program code to generate a second HDL core, and the circuit design is generated including the first HDL core connected to the second HDL core.