5.9: [MoveOnlyAddressChecker] Fix representation for initialized fields. #66960
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tbkka
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Jun 27, 2023
In preparation for having a third instance getting or creating the bits affected by an instruction, introduce a typealias for maps SILInstruction->SmallBitVector and a helper function that returns a reference to the SmallBitVector for an instruction and two others that set into those bits the bits from another bit vector or from a range.
The address checker records instructions that initialize fields in its initInsts map. Previously, that map mapped from an instruction to a range of fields of the type. But an instruction can initialize multiple discontiguous fields of a single value. (Indeed an attempt to add a second range that was initialized by an already initializing instruction--even if it were overlapping or adjacent--would have no effect and the map wouldn't be updated.) Here, this is fixed by fixing the representation and updating the storage whenver a new range is seen to be initialized by the instruction. As in swiftlang#66728 , a SmallBitVector is the representation chosen. rdar://111391893
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Description: Fix a class of miscompiles in the move-only address checker.
The move-only address checker records which instructions initialize ranges of fields of a move-only value. Previously, it recorded instructions which initialized and the initialized fields via a map from instructions to ranges of fields of the value. But a single instruction can initialize non-contiguous fields of the value being checked.
The fix is to change the the value stored corresponding to an instruction to have enough information to store all the non-contiguous fields of the value that it initializes. Here, as elsewhere, the representation of a bit vector is used.
Risk: Low. The change is straightforward and similar in spirit to #66738 and #66947 .
Scope: Narrow. This only affects move-only types.
Original PR: #66955
Reviewed By: Andrew Trick ( @atrick ), Michael Gottesman ( @gottesmm )
Testing: Added test that the move-only address checker previously miscompiled.
Resolves: rdar://111391893