Optimization of a compiler for a custom microprocessor

Abstract: New systems have higher and higher requirements in terms of reliability, safety, power consumption and performance. To meet those requirements, a custom processor can be a solution. That is why Thales is developing a processor that includes many features that make its architecture different from common architectures of general-purpose processors. To become widely usable, a fully optimizing compiler is the cornerstone that leads to its success. While most of the existing compilers manage to deal with code optimization for general purpose processors, their efficiency can considerably decrease when optimizing code for a custom processor whose architecture differs from general purpose processors. A new compiler had to be developed to translate C source code into highly optimized assembly code that would be able to deal with this processor's abilities, such as DSP-like instructions, in the best way possible, while introducing key features necessary to meet the requirements of Thales' line of products. Code optimizations have been introduced and enhanced, using pattern detection, control flow analysis or peephole optimization. At the same time, new key features have been added to the compiler, such as a compilation report, built-in functions support, and also fixed-point representation support. Many of these resources were lacking in existing compilers, which brings a noticeable added value to this compiler. As the processor is still under development, tests were carried out using a VHDL simulation model of the processor designed specifically to test the entire platform. The set of tests focused both on general purpose applications, and also on data processing algorithms. The optimization of this compiler led to an 18.3% shorter execution time for the set of tests, while reducing the total program size by 13.1% at least. Moreover, important features that existing compilers are lacking, have been added to the compiler. It helped improving the user-friendliness of the pair compiler/processor and it has proven to be of great interest for programmers.