Remove extraneous dependencies from libclangDependencyScanning to fix regression in clangd size #10173
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benlangmuir
commented
Mar 5, 2025
benlangmuir
commented
- Explanation: After clangd added support for c++ modules, its binary size doubled unnecessarily due to extraneous dependencies on clang's codegen and llvm target libraries that were present in clang's dep scanner. The changes here remove those dependencies, with a small refactoring to split the ObjectFilePCHContainer reader (needed) from the writer (not needed by the scanner). This fixes the regression, reducing clangd size by ~half.
- Scope: Change should be NFC. If something has gone wrong, it will affect the dependency scanner and/or clangd.
- Risk: Low. This is a straightforward refactoring. The most likely risk would be at build time that we were accidentally depending on one of these transitive dependencies and it fails to link, but I have spot checked users of this library and they look okay and no build failures have been observed with BUILD_SHARED_LIBS=1.
- Tests: clangd size checkd manually, existing tests pass
- Issues: rdar://144790713
- Original PRs: [clang] Split ObjectFilePCHContainerReader from ObjectFilePCHContainerWriter llvm/llvm-project#99599 and [clang][deps] Remove dependency on llvm targets from lib DependencyScanning llvm/llvm-project#129774
- Reviewers: @benlangmuir and @jansvoboda11 for the first PR, @jansvoboda11 and @Bigcheese for the latter one.
…rWriter (llvm#99599) Close llvm#99479 See llvm#99479 for details (cherry picked from commit d64eccf) Conflicts: clang/lib/Tooling/DependencyScanning/CMakeLists.txt clang/tools/c-index-test/CMakeLists.txt clang/tools/c-index-test/core_main.cpp clang/tools/driver/cc1_main.cpp (cherry picked from commit 756acd5)
…perations (cherry picked from commit d213597)
…anning (llvm#129774) In d64eccf we split the object file reader from the writer and removed the dependency on clangCodeGen from the dependency scanner. However, we were still initializing all the llvm targets, which was needed for writing object file pcms but not reading them. This caused us to link more llvm target code than necessary. Shrinks clangd by nearly 50% for me. rdar://144790713 (cherry picked from commit f8ba0df) (cherry picked from commit c0eb45d)
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@swift-ci please test |
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@swift-ci please test llvm |
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@swift-ci please test Windows |
fredriss
approved these changes
Mar 6, 2025
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