[6.2 🍒][AutoDiff] Use LinkEntity::SecondaryPointer for diff witness
#82694
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If `LinkEntity::isTypeKind()` is true, `IRGenModule::getAddrOfLLVMVariable` assumes that we can safely call `LinkEntity::getType()`, which does `reinterpret_cast` of `LinkEntity::Pointer` to `TypeBase *`. However, for SIL differentiability witness, the pointer has `SILDifferentiabilityWitness *` type, which is not derived from `TypeBase`. So, such a cast is not allowed. Just as with `ProtocolWitnessTableLazyAccessFunction` and `ProtocolWitnessTableLazyCacheVariable` link entity kinds (which are also type kinds), we should use `SecondaryPointer` instead of `Pointer` for storing payload here, while setting `Pointer` to `nullptr`. (cherry picked from commit 77a3873)
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@swift-ci please test |
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cc @JaapWijnen |
bnbarham
approved these changes
Jul 2, 2025
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Explanation:
This cherry-pick addresses an unsafe
reinterpret_castinIRGenModule::getAddrOfLLVMVariablewhen handling certainLinkEntitykinds.Scope:
This change is narrowly scoped to
setForDifferentiabilityWitnessand only affects code paths related to autodiff.Issues:
No public issue is filed. The fix resolves a latent bug triggered in certain compiler configurations or IR generation flows involving
SILDifferentiabilityWitness.Original PRs:
[AutoDiff] Use
LinkEntity::SecondaryPointerfor diff witness #82412Risk:
Low. The patch follows existing patterns, and does not introduce new logic.
Testing:
We have tested this change across an internal suite of projects that utilize autodiff features heavily.
Reviewers:
@compnerd @asl @kovdan01