smite-ir: split determinism out of has_side_effects - #198
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LookupShortChannelId is a read-only operation, but it was marked as having side effects to stop CSE from merging two lookups whose results differ. Add is_deterministic and is_pure so CSE and the reorder mutator can ask about purity while DCE keeps asking about side effects.
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Follow-up to #155, where we agreed
LookupShortChannelIddoesn't really have side effects and that CSE wants a separate question answered.has_side_effectswas being asked three different questions by three callers: DCE wants to know whether an instruction can be dropped, CSE wants to know whether two instructions can be merged, andInstructionReorderMutatorwants to know whether an instruction's position matters. Those coincide for every operation we had untilLookupShortChannelId, which is read-only but nondeterministic, so it was marked as side-effecting to keep CSE away from it.Add
is_deterministic, andis_pureon top of it, so each caller asks what it actually means. DCE keeps usinghas_side_effects, while CSE and the reorder mutator switch tois_pure.LookupShortChannelIdbecomes side-effect free and nondeterministic, andCreateFundingTransactionand theRecvoperations are marked nondeterministic too since their results come from the wallet and from the target.The only behavior change is that DCE can now drop a
LookupShortChannelIdwhose result nothing consumes. I checked every operation, and it is the only one where!is_pure()differs fromhas_side_effects(), so CSE's skip set and the reorder mutator's candidate set are unchanged.Ref: #155