Deriving WCET Bounds by Abstract Execution

• Standard static WCET analysis methods today are based on the IPET technique, where WCET estimation is formulated as an integer linear programming (ILP) problem subject to linear program flow constraints with an objective function derived from the hardware timing model. The estimate is then calculated by an ILP solver. The hardware cost model, as well as the program flow constraints, are often derived using a static program analysis framework such as abstract interpretation. An alternative idea to estimate the WCET is to add time as an explicit variable, incremented for each basic block in the code. The possible values of this variable can then be bound by a value analysis. We have implemented this idea by integrating the time estimation in our Abstract Execution method for calculating program flow constraints. This method is in principle a very detailed value analysis. As it computes intervals bounding variable values, it bounds both the BCET and the WCET. In addition, it derives the explicit execution paths through the program which correspond to the calculated BCET and WCET bounds. We have compared the precision and the analysis time with the traditional IPET technique for a number of benchmark programs, and show that the new method typically is capable of calculating as tight or even tighter WCET estimates in shorter time. Our current implementation can handle simple timing models with constant execution times for basic blocks and edges in the CFG, but it is straightforward to extend the method to more detailed hardware timing models.

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NATURVETENSKAP  -- Data- och informationsvetenskap -- Datavetenskap (hsv//swe)

NATURAL SCIENCES  -- Computer and Information Sciences -- Computer Sciences (hsv//eng)

NATURVETENSKAP  -- Data- och informationsvetenskap (hsv//swe)

NATURAL SCIENCES  -- Computer and Information Sciences (hsv//eng)

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