[Unity][Transform] Keep R.ExternFunc in dead-code elimination #16118
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Prior to this commit, the `DeadCodeElimination` and `FuseTIR` passes treated `R.ExternFunc` differently with respect to removal of internal functions: `DeadCodeElimination` treated these functions as internal, to be removed if there are no internal callers, while `FuseTIR` treated these functions as external, to be retained in all cases. Because the visibility of a function is determined by the `tvm::attr::kGlobalSymbol` attribute; which is present for `PrimFunc` and `relax::Function`, but missing for `relax::ExternFunc`; there is no information in the `IRModule` that can determine whether a `relax::ExternFunc` should be visible externally. For consistency, and to allow the use of `DeadCodeElimination` in future refactors of `FuseTIR`, this commit updates `DeadCodeElimination` to retain instances of `relax::ExternFunc`.
This was referenced Nov 13, 2023
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Prior to this commit, the
DeadCodeEliminationandFuseTIRpasses treatedR.ExternFuncdifferently with respect to removal of internal functions:DeadCodeEliminationtreated these functions as internal, to be removed if there are no internal callers, whileFuseTIRtreated these functions as external, to be retained in all cases.Because the visibility of a function is determined by the
tvm::attr::kGlobalSymbolattribute; which is present forPrimFuncandrelax::Function, but missing forrelax::ExternFunc; there is no information in theIRModulethat can determine whether arelax::ExternFuncshould be visible externally.For consistency, and to allow the use of
DeadCodeEliminationin future refactors ofFuseTIR, this commit updatesDeadCodeEliminationto retain instances ofrelax::ExternFunc.