[ShrinkBorrowScope] Leave under rewritten copies. #61655
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When shrinking a borrow scope like
%borrow = begin_borrow %value
barrier
%copy = copy_value %borrow
end_borrow %borrow
the copy will be rewritten to be a copy of the borrowee:
%borrow = begin_borrow %value
barrier
%copy = copy_value %value
^^^^^^
end_borrow %borrow
If, as here, shrinking next encounters a barrier, then the insertion
point will be that rewritten copy_value instruction.
In such a case, when rather than creating a new end_borrow there and
deleting the old, just reuse the old one. The lifetime of the value
being copied will be canonicalized by CopyPropagation regardless.
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@swift-ci please test |
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@swift-ci please benchmark |
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@swift-ci please test source compatibility |
nate-chandler
deleted the
shrink_borrow_scope/dont_hoist_over_only_rewritten_copies
branch
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When shrinking a borrow scope like
the copy will be rewritten to be a copy of the borrowee:
If, as here, shrinking next encounters a barrier, then the insertion point will be that rewritten
copy_valueinstruction.In such a case, rather than creating a new
end_borrowthere and deleting the old, just reuse the old one. The lifetime of the value being copied will be canonicalized byCopyPropagationregardless.