HercuLeS is an extensible HLS environment that allows pluggable analyses and optimizations. It can be used for push-button synthesis from ANSI C and other source languages to custom hardware.

HercuLeS confronts shortcomings and omissions of current HLS flows such as the lack of extensibility, the use of opaque intermediate representations (IRs), and vendor- and technology-dependent HDL code generation. In contrast to rival HLS tools, HercuLeS uses open specifications throughout the HLS process. It exposes both its bit-accurate, typed-assembly IR named NAC (N-Address Code) and a low-level Graphviz-based IR for third-party interfacing of new frontends, analyses and optimizations.

I am the sole developer of HercuLeS so AMA :)

HercuLeS high-level synthesis overview
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