[5.6] Fix OwnershipLiveRange for @owned values getting transformed to none values via switch_enum #60104
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…values via switch_enum rdar://95039799 We are currently not computing OwnershipLiveRange correctly in the presence of switch_enum transforming the owned value to a none value. We can end up with illegal SIL with LoadCopyToLoadBorrowOptimization, due to this. Example: sil [ossa] @switch_enum_test : $@convention(thin) (@inout StructWithEnum) -> () { bb0(%0 : $*StructWithEnum): %1 = struct_element_addr %0 : $*StructWithEnum, #StructWithEnum.val %2 = struct_element_addr %0 : $*StructWithEnum, #StructWithEnum.val %3 = load [copy] %2 : $*EnumA destroy_addr %1 : $*EnumA switch_enum %3 : $EnumA, case #EnumA.sometrivial!enumelt: bb1, case #EnumA.somenontrivial!enumelt:bb2, case #EnumA.none!enumelt: bb3 bb1(%6 : $TrivialStruct): %f = function_ref @get_enum : $@convention(thin) () -> @owned EnumA %r = apply %f() : $@convention(thin) () -> @owned EnumA %ele = struct_element_addr %0 : $*StructWithEnum, #StructWithEnum.val store %r to [init] %ele :$*EnumA %9999 = tuple() return %9999 : $() bb2(%7 : @owned $NonTrivialStruct): unreachable bb3: unreachable } can get transformed to: sil [ossa] @switch_enum_test : $@convention(thin) (@inout StructWithEnum) -> () { bb0(%0 : $*StructWithEnum): %1 = struct_element_addr %0 : $*StructWithEnum, #StructWithEnum.val %2 = struct_element_addr %0 : $*StructWithEnum, #StructWithEnum.val %3 = load_borrow %2 : $*EnumA destroy_addr %1 : $*EnumA switch_enum %3 : $EnumA, case #EnumA.sometrivial!enumelt: bb1, case #EnumA.somenontrivial!enumelt: bb2, case #EnumA.none!enumelt: bb3 bb1(%6 : $TrivialStruct): end_borrow %3 : $EnumA %8 = function_ref @get_enum : $@convention(thin) () -> @owned EnumA %9 = apply %8() : $@convention(thin) () -> @owned EnumA %10 = struct_element_addr %0 : $*StructWithEnum, #StructWithEnum.val store %9 to [init] %10 : $*EnumA %12 = tuple () return %12 : $() bb2(%14 : @guaranteed $NonTrivialStruct): unreachable bb3: unreachable } which is incorrect: Write: destroy_addr %1 : $*EnumA SIL verification failed: Found load borrow that is invalidated by a local write?!: loadBorrowImmutabilityAnalysis.isImmutable(LBI) Verifying instruction: %2 = struct_element_addr %0 : $*StructWithEnum, #StructWithEnum.val -> %3 = load_borrow %2 : $*EnumA switch_enum %3 : $EnumA, case #EnumA.sometrivial!enumelt: bb1, case #EnumA.somenontrivial!enumelt: bb2, case #EnumA.none!enumelt: bb3 end_borrow %3 : $EnumA
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Jul 25, 2022
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This is a cherry-pick of #60101
Fixes rdar://95039799
Description:
We are currently not computing OwnershipLiveRange correctly in the presence of switch_enum transforming the owned value to a none value in the presence of dead end blocks. We can end up with illegal SIL with LoadCopyToLoadBorrowOptimization, due to this. This won't cause a miscompile, but will raise a verifier error.
End-user impact: May see verifier error while using switch statement on enums with dead-end paths on all non-trivial paths.
Risk: Low
This change is just bailing out on seeing a switch_enum transforming the owned value to a none value, while computing OwnershipLiveRange.