5.9: [MoveOnlyAddressChecker] Fix representation for used fields. #66738
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According to language rules, such lifetimes are fixed and the relative order of their deinits is guaranteed. rdar://110913116
The members were declared but undefined.
Its storage vector is intended to be of some type like `std::vector<std::pair<Key, Optional<Value>>>`, i.e., some collection of pairs whose `second` is an `Optional<Value>`. So when constructing a default instance of that pair, just construct an Optional in the None case.
FieldSensitivePrunedLiveness is used as a vectorization of
PrunedLiveness. An instance of FSPL with N elements needs to be able to
represent the same states as N instances of PL.
Previously, it failed to do that in two significant ways:
(1) It attempted to save space for which elements were live by using
a range. This failed to account for instructions which are users of
non-contiguous fields of an aggregate.
apply(
@owned (struct_element_addr %s, #S.f1),
@owned (struct_element_addr %s, #S.f3)
)
(2) It used a single bit to represent whether the instruction was
consuming. This failed to account for instructions which consumed
some fields and borrowed others.
apply(
@owned (struct_element_addr %s, #S.f1),
@guaranteed (struct_element_addr %s, #S.f2)
)
The fix for (1) is to use a bit vector to represent which elements
are used by the instruction. The fix for (2) is to use a second bit
vector to represent which elements are _consumed_ by the instruction.
Adapted the move-checker to use the new representation.
rdar://110909290
Dumped more info and called llvm_unreachable on bad state.
Previously, the checker inserted destroys after each last use. Here, extend the lifetimes of fields as far as possible within their original (unchecked) limits. rdar://99681073
It's always the first line of the function, so try to do better.
Passing ``` -Xllvm -move-only-address-checker-disable-lifetime-extension=true ``` will skip the maximization of unconsumed field lifetimes.
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The address checker records uses in its livenessUses map. Previously, that map mapped from an instruction to a range of fields of the type. But an instruction can use multiple discontiguous fields of a single value. Here, such instructions are properly recorded by fixing the map to store a bit vector for each instruction. rdar://110676577
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@swift-ci please test |
tbkka
approved these changes
Jun 19, 2023
This was referenced Jun 27, 2023
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Description: Fix a class of miscompiles in the move-only address checker.
The move-only address checker records which instructions use ranges of fields of a move-only value. Previously, it recorded instructions with uses and the used fields via a map from instructions to ranges of fields of the value. But a single instruction can use non-gontiguous 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 uses. Here, the representation of a bit vector is implemented.
Risk: Low. The change is involved, but the previous representation was wrong.
Scope: Narrow. This only affects move-only types.
Original PR: #66728
Reviewed By: Andrew Trick ( @atrick )
Testing: Added test that the move-only address checker previously miscompiled.
Resolves: rdar://110676577