Don't hash the key when searching in an empty table. #305
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In rustc, approximately one third of all non-modifying lookups are on an empty table!
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Other workloads won't have this many lookups on empty tables, but it's simple and cheap enough to be worth considering. rust-lang/rust#92239 has details on the improvements seen in rustc. |
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Nice! @bors r+ |
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📌 Commit dec8e8c has been approved by |
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☀️ Test successful - checks-actions |
CAFxX
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Feb 25, 2022
Comment on lines
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| if self.table.is_empty() { | ||
| None | ||
| } else { | ||
| let hash = make_hash::<K, Q, S>(&self.hash_builder, k); | ||
| self.table.get(hash, equivalent_key(k)) | ||
| } |
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it may make sense, if the map contains a single element and the table is small, to skip hashing and compare directly the key with the key of the single entry in the table
vtjnash
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Feb 25, 2022
Avoids hashing the input key for empty dictionaries. Inspired by rust-lang/hashbrown#305.
staticfloat
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Mar 2, 2022
…ng#44341) Avoids hashing the input key for empty dictionaries. Inspired by rust-lang/hashbrown#305.
LilithHafner
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Mar 8, 2022
…ng#44341) Avoids hashing the input key for empty dictionaries. Inspired by rust-lang/hashbrown#305.
hargoniX
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kim-em
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kim-em
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In rustc, approximately one third of all non-modifying lookups are on an
empty table!