C++: Measure bounds for Enum constants and reduce getBoundsLimit#21313
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MathiasVP wants to merge 4 commits intogithub:mainfrom
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C++: Measure bounds for Enum constants and reduce getBoundsLimit#21313MathiasVP wants to merge 4 commits intogithub:mainfrom
Enum constants and reduce getBoundsLimit#21313MathiasVP wants to merge 4 commits intogithub:mainfrom
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cpp/ql/lib/semmle/code/cpp/rangeanalysis/RangeAnalysisUtils.qll
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Pull request overview
Improves C++ SimpleRangeAnalysis performance by ensuring enum-typed expressions get appropriate type bounds (so the bounds estimator stays functional) and by lowering the widening trigger threshold to avoid pathological blowups.
Changes:
- Add enum underlying-type handling to type-bound computation used by range analysis utilities.
- Reduce
BoundsEstimate.getBoundsLimitfrom2^40to2^29. - Add a regression test (
missing_bounds.cpp) and update rangeanalysis test expectations.
Reviewed changes
Copilot reviewed 7 out of 7 changed files in this pull request and generated 2 comments.
Show a summary per file
| File | Description |
|---|---|
| cpp/ql/lib/semmle/code/cpp/rangeanalysis/RangeAnalysisUtils.qll | Extend type-bound logic to cover Enum types via an inferred/explicit underlying integral type. |
| cpp/ql/lib/semmle/code/cpp/rangeanalysis/SimpleRangeAnalysis.qll | Lower the bounds-estimate limit used to decide when to enable widening. |
| cpp/ql/test/library-tests/rangeanalysis/SimpleRangeAnalysis/missing_bounds.cpp | New regression test exercising enum constants / flag-like operations for bounds estimation. |
| cpp/ql/test/library-tests/rangeanalysis/SimpleRangeAnalysis/nrOfBounds.ql | Tighten functionality test to assert expected estimator behavior for the new regression input. |
| cpp/ql/test/library-tests/rangeanalysis/SimpleRangeAnalysis/nrOfBounds.expected | Updated expected results for bounds-estimation test output. |
| cpp/ql/test/library-tests/rangeanalysis/SimpleRangeAnalysis/lowerBound.expected | Updated expected lower-bound results for the new regression input. |
| cpp/ql/test/library-tests/rangeanalysis/SimpleRangeAnalysis/upperBound.expected | Updated expected upper-bound results for the new regression input. |
| @@ -513,7 +513,7 @@ private module BoundsEstimate { | |||
| float getBoundsLimit() { | |||
| // This limit is arbitrary, but low enough that it prevents timeouts on | |||
| // specific observed customer databases (and the in the tests). | |||
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Comment text has a grammatical typo: "(and the in the tests)" reads incorrectly. Consider changing it to "(and in the tests)" (or similar).
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| // specific observed customer databases (and the in the tests). | |
| // specific observed customer databases (and in the tests). |
cpp/ql/test/library-tests/rangeanalysis/SimpleRangeAnalysis/missing_bounds.cpp
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This PR fixes a
SimpleRangeAnalysisperformance problem we've seen at Microsoft.There were two problems (both of which are fixed in this PR):
Enumtypes. This let toanalyzableExprnot being satisfied for expressions ofEnumtypes, which let tonrOfBoundsExprnot having a result for expressionsEnum.getBoundsLimittreshold was set way too high. Since this was just the arbitrary default value picked in C++: Range analysis measure bounds #20645 to fix the initial performance problem that PR was meant to solve, I think it's fair to reduce it to a more sane value now that we have yet another performance problem. Reducing it from 2^40 to 2^29 fixes this performance problem, and on anything greater we'll timeout even duringcodeql test run.Commit-by-commit review recommended.