Improve DWARF symbolization performance#1541
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Change Unit to store its gimli::Unit and language in OnceCell wrappers, introducing ensure_dw_unit() as the single access point. All units continue to be eagerly constructed via Unit::new() for now, but the OnceCell plumbing prepares for deferring construction when .debug_aranges data is available. Signed-off-by: Daniel Müller <deso@posteo.net>
Move the .debug_aranges lookup before gimli::Unit construction in Units::parse(). When aranges provide address ranges for a CU, use Unit::new_deferred() to skip the expensive abbreviation and line program header parsing entirely. The full gimli::Unit is constructed lazily on first access via ensure_dw_unit(). This changes the range source priority: .debug_aranges is now checked before DW_AT_ranges. This is necessary because we cannot read DW_AT_ranges without constructing the gimli::Unit (which is the expensive operation we are deferring). In practice both sources are assumed to agree since they are generated by the same toolchain. Our main vmlinux based symbolization benchmarks see a vast improvement from the lazy unit construction, because less work needs to happen overall (the vast majority of CUs are not queried): > main/symbolize_dwarf_no_lines > time: [11.456 ms 11.798 ms 12.163 ms] > change: [−92.099% −91.860% −91.645%] (p = 0.00 < 0.02) > Performance has improved. > main/symbolize_dwarf > time: [11.102 ms 11.165 ms 11.253 ms] > change: [−92.389% −92.322% −92.250%] (p = 0.00 < 0.02) > Performance has improved. Signed-off-by: Daniel Müller <deso@posteo.net>
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## main #1541 +/- ##
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- Coverage 95.50% 95.27% -0.23%
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Files 56 56
Lines 9534 9579 +45
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+ Hits 9105 9126 +21
- Misses 429 453 +24 ☔ View full report in Codecov by Sentry. 🚀 New features to boost your workflow:
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