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Extending Optimising Compilation to Support Worst-Case Execution Time Analysis
Raimund Kirner, TU Wien
The calculation of the WCET needs the knowledge of additional control-flow information so-called flow facts. For convenience, it is preferred to specify this information at the source code level. To perform a precise WCET analysis at object code level it is necessary to map the information onto the object code. For precise WCET analysis of programs optimised by the compiler, the flow facts have to be transformed in parallel to the code transformations performed during optimisation. This talk presents a framework to maintain correct flow facts during code optimisation. Previous solutions are either based on matching the debug information with the source code or on logging of only restricted code transformations. The talk presents a novel concept to transform flow information in parallel to the code transformations performed by the compiler. The code transformations are abstracted to their relevant structural changes. From the structural update and the known semantic control-flow information of the performed code transformation, a safe and precise transformation of the flow information is induced. A graphical transformation framework to describe the performed code transformations supports the compiler developer in understanding the required update of flow facts. The abstract representation of the control flow graph allows the modelling of blocks with multiple branching edges which enables the integration of this method into various compilers. The result is a framework that supports high-quality WCET analysis of optimised code.