DI: Lower AssignInst in a post-processing pass [5.0] #21163
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- Handle DIMemoryUse::Kind::IndirectIn just like Load - Consolidate duplicated 'only touches trivial elements' check
Compiler passes that intermingle analysis with mutation of the CFG are fraught with danger. The bug here was that a single AssignInst could appear twice in DI's Uses list, once as a store use and once as a load use. When processing Uses, we would lower AssignInsts on the fly. We would take care to erase the instruction pointer from the current Use, but if a subsequent Use *also* referenced the now-deleted AssignInst, we would crash. Handle this in the standard way: instead of lowering assignments right away, just build a list of assignments that we're planning on lowering and process them all at the very end. This has the added benefit of simplifying the code, because we no longer have to work as hard to keep the state of the Uses list consistent while lowering AssignInsts. The rest of DI should not care that the lowering got postponed either, since it was already expected to handle any ordering of elements in the Uses list, so it could not assume that any particular AssignInst has been lowered. Fixes <https://bugs.swift.org/browse/SR-9451>.
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@swift-ci Please test |
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Build failed |
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Looks like a transient lldb failure:
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@swift-ci Please test macOS |
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Compiler passes that intermingle analysis with mutation of the CFG
are fraught with danger. The bug here was that a single AssignInst
could appear twice in DI's Uses list, once as a store use and once
as a load use.
When processing Uses, we would lower AssignInsts on the fly. We would
take care to erase the instruction pointer from the current Use, but
if a subsequent Use also referenced the now-deleted AssignInst, we
would crash.
Handle this in the standard way: instead of lowering assignments
right away, just build a list of assignments that we're planning on
lowering and process them all at the very end.
This has the added benefit of simplifying the code, because we no
longer have to work as hard to keep the state of the Uses list
consistent while lowering AssignInsts. The rest of DI should not
care that the lowering got postponed either, since it was already
expected to handle any ordering of elements in the Uses list, so
it could not assume that any particular AssignInst has been lowered.
Fixes https://bugs.swift.org/browse/SR-9451.