[Dependency Scanning] Only omit Clang VFS overlays from Swift dependencies if unused by their Clang dependencies #71691
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artemcm force-pushed the DepScanSmartVFSOpt branch from 183271d to d013a02 Compare 
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artemcm requested review from Bigcheese, cachemeifyoucan, nkcsgexi, tshortli and xymus artemcm changed the title artemcm force-pushed the DepScanSmartVFSOpt branch from d013a02 to ce8f7b3 Compare | @swift-ci smoke test |
artemcm force-pushed the DepScanSmartVFSOpt branch from ce8f7b3 to 75babdb Compare | @swift-ci smoke test |
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LGTM with a small improvement suggestion in line.
I had an idea of fixing this problem completely long term by:
- switch clang importer to use direct cc1 only: #71118
- do a dependency scanning for clang importer for each swift invocation and use the returning cc1 arg to construct clang importer
Then any optimization can be done in clang scanner, swift will get it for free.
I had a prototype for clang importer dep scanning too. I just need to find it somewhere.
…ncies if unused by Clang dependencies We previously blanket omitted `-Xcc -vfsoverlay` flags from Swift module dependencies' command-line recipes. This is incorrect as the Swift module must have an exact matching VFS overlay that its Clang dependencies use, in order to load said Clang dependnecies successfully and resolve their headers as expected and as was done during the scan. Resolves rdar://122667530
artemcm force-pushed the DepScanSmartVFSOpt branch from 75babdb to 500d2e5 Compare | @swift-ci smoke test |
I think this sounds very promising! I assume we would do this faux-scan after we actually resolved all the Clang dependencies so that it is as near to free as possible? Would be cool to get the benefit of all the command-line optimization work Clang is doing "for free". |
cachemeifyoucan approved these changes Feb 17, 2024
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We previously blanket omitted
-Xcc -vfsoverlayflags from Swift module dependencies' command-line recipes. This is incorrect as the Swift module must have an exact matching VFS overlay that its Clang dependencies use, in order to load said Clang dependnecies successfully and resolve their headers as expected and as was done during the scan.Resolves rdar://122667530