6.1: [OSSACanonicalizeGuaranteed] Don't rewrite consuming uses of move-only values. #78574
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Replace large nested condition with early exit.
Allow rewriting of arguments to bail out. This is necessary because not all forwarding instructions allow rewriting of forward(copy) as copy(forward) (e.g. when forward produces a move-only value).
When visiting a consuming use of a move-only value (which can be produced by a forwarding operation), the inner rewriter must bail out. Otherwise, it would produce a copy of that move-only value. rdar://142520491
On main type annotations are not always required but on 6.1 they are.
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@swift-ci please test |
tbkka
approved these changes
Jan 13, 2025
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Explanation: Fix a miscompile which introduced a copy of a noncopyable value.
SILCombine uses the
CanonicalizeBorrowScopeutility to eliminate copies of guaranteed function arguments. The utility walks the def-use tree of the argument, walking through copies and moves, walking into the uses of forwarding operations, producing copies as needed for any consuming uses for the value produced by a chain of forwarding operations. These days, some forwarding operations produce noncopyable values such asstruct $Noncopyable, however. If the tree included a chain likeconsume(struct $Noncopyable(copy(%arg))), it was previously rewritten asconsume(copy(struct $Noncopyable(%arg))). This is invalid (copies of noncopyable values are invalid). Here, this is fixed by bailing out of rewriting uses of a particular def in the tree (e.g.struct $Noncopyable(copy(%arg))) if one of the uses is a consuming use of a noncopyable value. This bailout (two lines) required a bit of tweaking to the utility because it was written not to bailout when processing arguments--at the time, there were no cases in which it ought to.Scope: Affects optimized code.
Issue: rdar://142520491
Original PR: #78552
Risk: Low.
Testing: Added tests.
Reviewer: Meghana Gupta ( @meg-gupta )