16. A computer program product comprising a computer readable storage medium comprising computer-readable code, the computer-readable code causing a computing system, in response to executing the computer-readable code, to perform the following: running an environment for designing operation of circuitry, the running the environment comprising performing at least the following for providing simulations and evaluations of one or more user-defined modules of circuitry comprising one or more pipeline stages in a pipeline: automatically generating a model of the pipeline by using a pipeline block diagram, where the model is generated in a high-level modeling language able to perform simulations of circuitry with the pipeline; automatically generating an interface between the one or more user-defined modules and the generated model of the pipeline, the interface comprising access to the pipeline, wherein the pipeline access allows the one or more user-defined modules to interact indirectly; performing evaluation of the one or more user-defined modules using the automatically generated model of the pipeline and the automatically generated interface; and directly connecting the user-defined modules to ports allowing the one or more user-defined modules to interact directly to replace the pipeline access between the one or more user-defined modules and the generated model of the pipeline.
17. The computer program product of claim 16 , wherein the automatically generating the model and the automatically generating the interface are for a simulation flow supported by the environment, and wherein in response to a request to create synthesized versions of the one or more user-defined modules the environment performs a synthesis flow wherein: automatically generating an interface further comprises synthesizing the interface at least by converting the set of access methods to the pipeline to a set of ports in a hardware description language; and performing simulations further comprises performing simulations on the one or more user-defined modules with workloads using the automatically generated model of the pipeline and the automatically generated model of the interface to determine one or more design evaluation metrics of the one or more user-defined modules.