Use more compact storage for impl lookup buckets. #4351
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jonmeow
approved these changes
Sep 27, 2024
toolchain/sem_ir/impl.h
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| // An ID of either a single impl or a lookup bucket. | ||
| class ImplOrLookupBucketId : public IdBase { | ||
| public: | ||
| using IdBase::IdBase; |
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Had you considered making the constructor private in order to emphasize use of the factory functions?
| @@ -57,22 +57,110 @@ struct Impl : public EntityWithParamsBase, | |||
| // A collection of `Impl`s, which can be accessed by the self type and | |||
| // constraint implemented. | |||
| class ImplStore { | |||
| private: | |||
| // An ID of either a single impl or a lookup bucket. | |||
| class ImplOrLookupBucketId : public IdBase { | |||
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Abstractly, we have a couple other things which have TinyPtrVector-like TODOs. Particularly NameScope's extended_scopes had seemed similar, but this approach won't work for it (I think it'd need to own the vector). I think this approach is fine, but I wanted to note this because I don't think this approach would work directly in other use-cases; I'm not sure precisely where the trade-offs stand to try to get something generally applicable.
If the bucket is of size zero or one, which is expected to be the common case, then store it directly. For the remaining cases, use a side table of lookup buckets.
Co-authored-by: Jon Ross-Perkins <jperkins@google.com>
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If the bucket is of size zero or one, which is expected to be the common
case, then store it directly. For the remaining cases, use a side table
of lookup buckets.