[pmo] Eliminate dead flat namespace tuple numbering from PMOMemoryUseCollector. #21645
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…Collector. TLDR: This does not eliminate the struct/tuple flat namespace from Predictable Mem Opts. Just the tuple specific flat namespace code from PMOMemoryUseCollector that we were computing and then throwing away. I explain below in more detail. First note that this is cruft from when def-init and pmo were one pass. What we were doing here was maintaing a flattened tuple namespace while we were collecting uses in PMOMemoryUseCollector. We never actually used them for anything since we recomputed this information including information about structs in PMO itself! So this information was truly completely dead. This commit removes that and related logic and from a maintenance standpoint makes PMOMemoryUseCollector a simple visitor that doesn't have any real special logic in it beyond the tuple scalarization.
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@swift-ci smoke test |
gottesmm
commented
Jan 4, 2019
| // | ||
| // This will cause the dataflow to stop propagating any information at the | ||
| // use block. | ||
| addElementUses(User, PMOUseKind::Escape); |
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This part of the change requires a bit of explanation. Previously what was happening is that PredictableMemOpts was completely ignoring the field, type here. So we basically had PredictableMemOpts processing the same use multiple times. The effect is the same as just having one use: stopping the propagation of available values.
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NOTE: I split this commit into two parts. 7175e17 only removes the flat namespace tuple numbering to ease review, while 7b7ccdc removes additional code that becomes dead. I did this to ease review.