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To avoid information loss, introduce a difference between unset stats and 0 for statistics that are supposed to be set once per entry point. Now, if the statistic is not set for an entry point, the corresponding CSV cell will be empty, and not 0. Thanks to this differentiation, I noticed that `PathRunningTime` was actually never set, and fixed that. Additionally, this patch enables the timers if `DumpEntryPointStatsToCSV` is set, because in most cases you dump these stats to get a detailed view on analyzer performance. Finally, I added a dedicated debug checker that demonstrates the use of a statistic and tested the set and unset scenarios explicitly. -- CPP-7097 --------- Co-authored-by: Donát Nagy <donat.nagy@ericsson.com>
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===================
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Analysis Statistics
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===================
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Clang Static Analyzer enjoys two facilities to collect statistics: per translation unit and per entry point.
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We use `llvm/ADT/Statistic.h`_ for numbers describing the entire translation unit.
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We use `clang/StaticAnalyzer/Core/PathSensitive/EntryPointStats.h`_ to collect data for each symbolic-execution entry point.
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.. _llvm/ADT/Statistic.h: https://github.com/llvm/llvm-project/blob/main/llvm/include/llvm/ADT/Statistic.h#L171
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.. _clang/StaticAnalyzer/Core/PathSensitive/EntryPointStats.h: https://github.com/llvm/llvm-project/blob/main/clang/include/clang/StaticAnalyzer/Core/PathSensitive/EntryPointStats.h
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In many cases, it makes sense to collect statistics on both translation-unit level and entry-point level. You can use the two macros defined in EntryPointStats.h for that:
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- ``STAT_COUNTER`` for additive statistics, for example, "the number of steps executed", "the number of functions inlined".
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- ``STAT_MAX`` for maximizing statistics, for example, "the maximum environment size", or "the longest execution path".
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If you want to define a statistic that makes sense only for the entire translation unit, for example, "the number of entry points", Statistic.h defines two macros: ``STATISTIC`` and ``ALWAYS_ENABLED_STATISTIC``.
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You should prefer ``ALWAYS_ENABLED_STATISTIC`` unless you have a good reason not to.
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``STATISTIC`` is controlled by ``LLVM_ENABLE_STATS`` / ``LLVM_FORCE_ENABLE_STATS``.
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However, note that with ``LLVM_ENABLE_STATS`` disabled, only storage of the values is disabled, the computations producing those values still carry on unless you took an explicit precaution to make them conditional too.
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If you want to define a statistic only for entry point, EntryPointStats.h has four classes at your disposal:
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- ``UnsignedEPStat`` - an unsigned value assigned at most once per entry point. For example: "the number of source characters in an entry-point body". If no value is assigned during analysis of an entry point, the corresponding CSV cell will be empty.
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- ``CounterEPStat`` - an additive statistic. It starts with 0 and you can add to it as many times as needed. For example: "the number of bugs discovered".
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- ``UnsignedMaxEPStat`` - a maximizing statistic. It starts with 0 and when you join it with a value, it picks the maximum of the previous value and the new one. For example, "the longest execution path of a bug".
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To produce a CSV file with all the statistics collected per entry point, use the ``dump-entry-point-stats-to-csv=<file>.csv`` parameter.
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Note, EntryPointStats.h is not meant to be complete, and if you feel it is lacking certain kind of statistic, odds are that it does.
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Feel free to extend it!
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