[5.7][Autolink Extract] Filter out common Swift libraries from being linked more than once #59115
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…d more than once A partial solution to swiftlang#58380
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nkcsgexi
approved these changes
May 31, 2022
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Cherry-pick of #59063
• Explanation: #58380 brought up an issue of excessive memory consumption at link-time on Linux. The cause of memory-consumption explosion appears to be due to the linker invocation command having duplicated
-lxxxflags which come from theswift-autolink-extracttool which aggregates auto-linking directives across all input object files. For common Swift libraries that every Swift object file links (e.g.swiftCore) this means that they appear on the linker invocation as many times as the number of object files in the project. Which for large projects means possibly thousands of times. The linker is not able to de-duplicate these flags because duplicate linked libraries in a certain order has a semantic meaning, and apparently it loads them into memory as many times as they appear on the linker command-line. This change addresses this issue at least partially by making sure that the common Swift libraries, at least, are de-duplicated across all object files and are only linked once:SwiftCore,SwiftOnoneSupport, andSwiftConcurrency.• Scope of Issue: High memory consumption when building modules with many object files on Linux.
• Risk: Low, this change only filters common Swift libraries and should leave behavior of other linked libraries largely unchanged.
• Automated Testing: Automated test added to the compiler test suite