Overview

Dahlia is a programming language for designing hardware accelerators. It provides abstractions that guarantee predictable hardware realizability after type checking.

The goal of this project is to build an end-to-end pipeline for compiling high level programming languages into performant hardware designs. Instead of targeting unrestricted programming languages like C or C++ or building domain specific languages, we're building an imperative programming language that leverages an affine type system to constrain programs to only represent valid hardware designs.

The current state of the art in High Level Synthesis (HLS) tools take unconstrained programming languages like C/C++ or various subsets thereof and compile them down to hardware designs. The compilation process is imprecise and depends heavily on a scheduling pass. Scheduling is a catch-all term for the various dependency analysis passes (such as alias analysis) and hardware module instantiation passes that an HLS tools must to extract static designs from C programs.

Furthermore, while HLS tools claim to transparently compile C/C++ programs, such codebases do not result in performant hardware designs. To circumvent this, the HLS toolchains provide static annotations (pragmas) for C programs that guide the toolchain in making decisions such as memory paritioning and loop pipelining. The complicated interactions between these source level pragmas and the scheduling passes result in unexpected hardware designs, complicated developer workflows, and manual effort spent optimizing the designs. All of this stands in opposition to the claim that HLS tools improve productivity and produce usable designs.

Instead of using these ad hoc techniques, we aim to develop a precise semantics and compiler toolchain and leverage modern programming language techniques (such as affine type systems) to build modular and agile HLS flows. We do this by treating scheduling as a first class problem in the langugage.

The intellectual goal of this project is to study HLS as a language design and compilers problem and build open source tools that help programming language and architecture researchers to explore this problem.

Status

Dahlia is still early in its development. The current reference compiler can generate Vivado HLS C code using Dahlia code. We have several ongoing projects:

Dahlia: The language constructs and the reference compiler. We are focusing our efforts on building precise semantics and compiling down to various HLS backends to study their properties.

Calyx: An intermediary language for compiling high level languages down to RTL. Distinct from IRs like FIRRTL which target the lower level problem of optimizing RTL code.

Dahlia-to-RTL: Ongoing project to directly generate RTL code from Dahlia source programs using Calyx.

Open Source

In the spirit of free and open research, all of our research prototypes are open source under a permissive license and we welcome any collaborations from industry and academic research groups.