std::hashmap: Tighter representation for the Bucket#9212
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bluss wants to merge 1 commit intorust-lang:masterfrom
bluss:tighter-bucket
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std::hashmap: Tighter representation for the Bucket#9212bluss wants to merge 1 commit intorust-lang:masterfrom bluss:tighter-bucket
bluss wants to merge 1 commit intorust-lang:masterfrom
bluss:tighter-bucket
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Replace `Option<Bucket<K, V>>` with a custom
`enum Bucket { Unused, Filled(hash, key, value) }`. The non-nullable
pointer optimization for enums with two variants will be active with the
new representation, while it was not with the old. This is if either
K or V is a non-nullable pointer type.
With these changes, now `Bucket<int,int>` is 32 bytes and
`Bucket<~str,int>` is 24 bytes on 64-bit, so we save the 8 bytes of enum
tag per bucket.
Contributor
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I think we should just make the the |
Contributor
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cc @jld |
Contributor
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We probably should improve the optimization. (And that should get its own issue if it doesn't have one yet.) The monomorphizer would need to know enough about whatever |
Contributor
Contributor
Author
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Closing this Pull unmerged, in favor of the linked issue I opened. |
flip1995
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Jul 31, 2023
New lint [`four_forward_slashes`] Closes rust-lang#9212 changelog: New lint [`four_forward_slashes`]
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Replace
Option<Bucket<K, V>>with a customenum Bucket { Unused, Filled(hash, key, value) }. The non-nullablepointer optimization for enums with two variants will be active with the
new representation, while it was not with the old. This is if either
K or V is a non-nullable pointer type.
With these changes, now
Bucket<int,int>is 32 bytes (like before) butBucket<~str,int>is 24 bytes on 64-bit, so we save the 8 bytes of enumtag per bucket.