Dataflow: Add type-based call-edge pruning. #13982
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Postponing type-based pruning until stage 3 seems to generally perform better and filters the same set of FPs. |
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…v call edge pruning.
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hvitved
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Sep 18, 2023
csharp/ql/lib/semmle/code/csharp/dataflow/internal/DataFlowPrivate.qll
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This extends data flow with a cartesian over-approximation of precise type-based call-contexts. Essentially this boils down to a type-flow analysis interleaved with data-flow.
Using a pruned call graph the type flow analysis determines possible types for arguments and parameters and uses this to filter impossible call edges. As one of the primary motivations, this improves dispatch to lambda callbacks, but it also improves on things like
Object.toStringdispatch and dispatch in e.g. the visitor pattern.Currently this is enabled for Java and C#. Other languages may follow, e.g. by defining a simple type system that merely distinguishes different lambdas. By assigning a specific type to a lambda and the value of the instance argument in the lambda body, the data flow library is able to link the two and improve dispatch.