Fully integrating the Flang Fortran compiler with standard MLIR

TL;DR

This paper demonstrates that fully integrating the Flang Fortran compiler with standard MLIR can significantly improve performance, achieving up to three times speedup over existing Flang approaches in HPC benchmarks.

Contribution

The paper introduces a complete mapping between Fortran and standard MLIR, enabling full integration and substantial performance improvements over the current Flang compiler.

Findings

Up to three times speedup in benchmark performance

Full MLIR integration enhances Flang's efficiency

Performance gains across diverse HPC benchmarks

Abstract

Fortran is the lingua franca of HPC code development and as such it is crucial that we as a community have open source Fortran compilers capable of generating high performance executables. Flang is LLVM's Fortran compiler and leverages MLIR which is a reusable compiler infrastructure which, as part of LLVM, has become popular in recent years. However, whilst Flang leverages MLIR it does not fully integrate with it and instead provides bespoke translation and optimisation passes to target LLVM-IR. In this paper we first explore the performance of Flang against other compilers popular in HPC for a range of benchmarks before describing a mapping between Fortran and standard MLIR, exploring the performance of this. The result of this work is an up to three times speed up compared with Flang's existing approach across the benchmarks and experiments run, demonstrating that the Flang community should seriously consider leveraging standard MLIR.