[5.9] Fix MandatoryARCOpts tryJoiningCopyValueLiveRangeWithOperand. #64866
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@swift-ci test |
meg-gupta
approved these changes
Apr 3, 2023
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The unit test needs to be fixed before I can merge this. |
Fix a miscompile in Debug builds at -Onone. This optimization ignores uses of owned values that aren't enclosed in borrow scopes. This is fairly eggregious since project_box instructions are never borrowed, which means that all local variables have this problem. This is a well-known issue that occurs throughout OSSA optimizations. The reason that we don't see the problem often is that the optimizations are hidden behind a pile of ad-hoc pattern matching, so they only kick in for simple cases. This approach to optimization is great at hiding problems for a long time. We're attempting to design away this class of problems in the next release. Until then, it's one miscompile at a time. Fixes rdar://107420448 (Variable mutation in block isn't reflected in outer scope: new behavior in swift 5.9) (cherry picked from commit 26a6264)
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@tbkka can you approve this for 5.9? |
tbkka
approved these changes
Apr 4, 2023
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Fix a miscompile in Debug builds at -Onone.
This optimization ignores uses of owned values that aren't enclosed in borrow scopes. This is fairly eggregious since project_box instructions are never borrowed, which means that all local variables have this problem.
This is a well-known issue that occurs throughout OSSA optimizations. The reason that we don't see the problem often is that the optimizations are hidden behind a pile of ad-hoc pattern matching, so they only kick in for simple cases. This approach to optimization is great at hiding problems for a long time.
We're attempting to design away this class of problems in the next release. Until then, it's one miscompile at a time.
Fixes rdar://107420448 (Variable mutation in block isn't reflected in outer scope: new behavior in swift 5.9)
(cherry picked from commit 26a6264)