Implement use-after-free detection in the lifetime safety analysis with two warning levels.
- Added a `LifetimeSafetyReporter` interface for reporting lifetime safety issues
- Created two warning levels:
- Definite errors (reported with `-Wexperimental-lifetime-safety-permissive`)
- Potential errors (reported with `-Wexperimental-lifetime-safety-strict`)
- Implemented a `LifetimeChecker` class that analyzes loan propagation and expired loans to detect use-after-free issues.
- Added tracking of use sites through a new `UseFact` class.
- Enhanced the `ExpireFact` to track the expressions where objects are destroyed.
- Added test cases for both definite and potential use-after-free scenarios.
The implementation now tracks pointer uses and can determine when a pointer is dereferenced after its loan has been expired, with appropriate diagnostics.
The two warning levels provide flexibility - definite errors for high-confidence issues and potential errors for cases that depend on control flow.
Fix a crash in the lifetime safety dataflow analysis when handling null CFG blocks.
Added a null check for adjacent blocks in the dataflow analysis algorithm to prevent dereferencing null pointers. This occurs when processing CFG blocks with unreachable successors or predecessors.
Original crash: https://compiler-explorer.com/z/qfzfqG5vM
Fixes https://github.com/llvm/llvm-project/issues/150095
This PR adds the `ExpiredLoansAnalysis` class to track which loans have expired. The analysis uses a dataflow lattice (`ExpiredLattice`) to maintain the set of expired loans at each program point.
This is a very light weight dataflow analysis and is expected to reach fixed point in ~2 iterations.
In principle, this does not need a dataflow analysis but is used for convenience in favour of lean code.
Refactor the Lifetime Safety Analysis infrastructure to support unit testing.
- Created a public API class `LifetimeSafetyAnalysis` that encapsulates the analysis functionality
- Added support for test points via a special `TestPointFact` that can be used to mark specific program points
- Added unit tests that verify loan propagation in various code patterns
