rust-lang / rust-lang/polonius
Idea: condense CFG
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Description
Currently we have an awful lot of points. However, it is rare that we need so many. I'm not sure of the exact conditions when we can compress two points, but it seems clear that we can. For example, if we have two points P and Q where
- P has one successor (Q)
- Q has one predecessor (P)
- The set of live regions at P is equal to set of live regions at Q
- There are no outlives relations at P or Q
then I think pretty clearly the subset relation would be the same during both of them.
We often know the first condition (one succ, one pred) just structurally: only the start of a basic block can have multiple preds, and only the mid point of a terminator can have multiple successors. The set of live regions is also easily approximated using the set of live variables, I imagine.
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First steps
- Read the whole issue, then the project's contributing guide.
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Research direction
Start by examining Polonius's current control-flow graph representation and how live regions, live variables, and outlives relations are computed. Define the conditions under which adjacent points preserve the subset relation, then validate the condensation behavior against representative CFGs; the issue names no files or tests.
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Assessment
- Tech stack
- rust
- Domain
- compilers
- Issue type
- Refactor
- Difficulty
- 5/5
- Estimated time
- Over a week
- Activity status
- Stale
- Clarity
- Needs clarification
- Newbie friendliness
- 25/100