Type-driven automated program transformations and cost modelling for optimising streaming programs on FPGAs

In this paper we present a novel approach to program optimisation based on compiler-based type-driven program transformations and a fast and accurate cost/performance model for the target architecture. We target streaming programs for the problem domain of scientific computing, such as numerical weather prediction. We present our theoretical framework for type-driven program transformation, our target high-level language and intermediate representation languages and the cost model and demonstrate the effectiveness of our approach by comparison with a commercial toolchain

Optimal program variant generation for hybrid manycore systems

Field Programmable Gate Arrays promise to deliver superior energy efficiency in heterogeneous high performance computing, as compared to multicore CPUs and GPUs. The rate of adoption is however hampered by the relative difficulty of programming FPGAs. High-level synthesis tools such as Xilinx Vivado, Altera OpenCL or Intel's HLS address a large part of the programmability issue by synthesizing a Hardware Description Languages representation from a high-level specification of the application, given in programming languages such as OpenCL C, typically used to program CPUs and GPUs. Although HLS solutions make programming easier, they fail to also lighten the burden of optimization. Application developers must rely on expert knowledge to manually optimize their applications for each target device, meaning that traditional HLS solutions do not offer a solution to the issue of performance portability. This state of fact prompted the development of compiler frameworks such as TyTra that operate at an even higher level of abstraction that is amenable to the use of Design Space Exploration (DSE). With DSE the initial program specification can be seen as the starting location in a search-space of correct-by-construction program transformations. In TyTra the search-space is generated from the transitive-closure of term-level transformations derived from type-level transformations. Compiler frameworks such as TyTra theoretically solve the issue of performance portability by providing a way to automatically generate alternative correct program variants. They however suffer from the very practical issue that the generated space is often too large to fully explore. As a consequence, the globally optimal solution may be overlooked. In this work we provide a novel solution to issue performance portability by deriving an efficient yet effective DSE strategy for the TyTra compiler framework. We make use of categorical data types to derive categorical semantics for the formal languages that describe the terms, types, cost-performance estimates and their transformations. From these we define a category of interpretations for TyTra applications, from which we derive a DSE strategy that finds the globally optimal transformation sequence in polynomial time. This is achieved by reducing the size of the generated search space. We formally state and prove a theorem for this claim and then show that the polynomial run-time for our DSE strategy has practically negligible coefficients leading to sub-second exploration times for realistic applications

Efficient FPGA Cost-Performance Space Exploration Using Type-driven Program Transformations

Many numerical simulation applications from the scientific, financial and machine-learning domains require large amounts of compute capacity. They can often be implemented with a streaming data-flow architecture. Field Programmable Gate Arrays (FPGA) are particularly power-efficient hardware architectures suitable for streaming data-flow applications. Although numerous programming languages and frameworks target FPGAs, expert knowledge is still required to optimise the throughput of such applications for each target FPGA device. The process of selecting which optimising transformations to apply, and where to apply them is dubbed Design Space Exploration (DSE). We contribute an elegant and efficient compiler based DSE strategy for FPGAs by merging information sourced from the compiled application's semantic structure, an accurate cost-performance model and a description of hardware resource limits for particular FPGAs. Our work leverages developments in functional programming and dependent type theory to bring performance portability to the realm of High-Level Synthesis (HLS) tools targeting FPGAs. We showcase our approach by presenting achievable speedups for three example applications. Results indicate considerable improvements in throughput of up to 58× in one example. These results are obtained by traversing a minute fraction of the total Design Space

Capable : a mechanised imperative language with native multiparty session types

CAPABLE is lightweight mechanised imperative language that provides native support for Multiparty Session Types (MPSTs). Through mechanisation, we can explore and catalogue the changes required to extend similar languages with native support for MPSTs, as well as the interplay between the existing type-system and other novel extensions. Principally, our demo shows CAPABLE in action and what a language with native MPSTs can look like. We also look beneath the surface syntax and offer insight over how we created intrinsically typed sessions (and session types) within a dependently typed language. We show a compact well-scoped encoding of session types, mechanised proofs of soundness and completeness for projection, and how dependent types help with bidirectional type checking of typed sessions

Capable: A Mechanised Imperative Language with Native Multiparty Session Types

CAPABLE is lightweight mechanised imperative language that provides native support for Multiparty Session Types (MPSTs). Through mechanisation, we can explore and catalogue the changes required to extend similar languages with native support for MPSTs, as well as the interplay between the existing type-system and other novel extensions. Principally, our demo shows CAPABLE in action and what a language with native MPSTs can look like. We also look beneath the surface syntax and offer insight over how we created intrinsically typed sessions (and session types) within a dependently typed language. We show a compact well-scoped encoding of session types, mechanised proofs of soundness and completeness for projection, and how dependent types help with bidirectional type checking of typed sessions