Compiling for Time-Predictability with Dual-Issue Single-Path Code

Designed for real-time systems, the Patmos instruction-set architecture's features ensure a high degree of predictability.One such feature is its dual-issue pipeline, which can issue and execute bundles of up to two instructions at a time.Executing instructions in the second issue slot is a predictable way to increase the throughput of a processor, but without dedicated support from the compiler, this benefit cannot be unlocked.A compiler generates highly predictable programs by generating single-path code.This technique produces code that always follows the same trace of instructions.While Patmos' compiler can already produce single-path code, it does not assign any instructions to the second issue-slot.This limitation is unfortunate, as single-path code inherently possesses a high degree of instruction-level parallelism.In this paper, we present a singlepath code generation technique with support for dual-issue pipelines.It can also support different bundling algorithms, which allows changing algorithms without having to edit other parts of the compiler.We present a simple bundling algorithm plugged into the single-path code generator.It looks for branches and bundles the basic blocks on each path of the branch.While this specific bundling algorithm is too simple to provide a real-world benefit, it highlights the potential that further work on bundling algorithms can unlock.