Use dynamic dispatch for queries by Zoxc · Pull Request #108638 · rust-lang/rust...
source link: https://github.com/rust-lang/rust/pull/108638
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This replaces most concrete query values V with MaybeUninit<[u8; { size_of::<V>() }]> reducing the code instantiated by queries. The compile time of rustc_query_impl is reduced by 27%. It is an alternative to #107937 which uses unstable const generics while this uses a EraseType trait which maps query values to their erased variant.
This is achieved by introducing an Erased type which does sanity check with cfg(debug_assertions). The query caches gets instantiated with these erased types leaving the code in rustc_query_system unaware of them. rustc_query_system is changed to use instances of QueryConfig so that rustc_query_impl can pass in DynamicConfig which holds a pointer to a virtual table.
| Benchmark | Before | After | |
| Time | Time | % | |
 clap:check | 1.7055s | 1.6949s | -0.62% |
| hyper:check | 0.2547s | 0.2528s | -0.73% |
| regex:check | 0.9590s | 0.9553s | -0.39% |
| syn:check | 1.5457s | 1.5440s | -0.11% |
| syntex_syntax:check | 5.9092s | 5.9009s | -0.14% |
| Total | 10.3741s | 10.3479s | -0.25% |
| Summary | 1.0000s | 0.9960s | -0.40% |
| Benchmark | Before | After | |
| Time | Time | % | |
| clap:check:initial | 2.0605s | 2.0575s | -0.15% |
| hyper:check:initial | 0.3218s | 0.3216s | -0.07% |
| regex:check:initial | 1.1848s | 1.1839s | -0.07% |
| syn:check:initial | 1.9409s | 1.9376s | -0.17% |
| syntex_syntax:check:initial | 7.3105s | 7.2928s | -0.24% |
| Total | 12.8185s | 12.7935s | -0.20% |
| Summary | 1.0000s | 0.9986s | -0.14% |
| Benchmark | Before | After | |
| Time | Time | % | |
| clap:check:unchanged | 0.4606s | 0.4617s | 0.24% |
| hyper:check:unchanged | 0.1335s | 0.1336s | 0.08% |
| regex:check:unchanged | 0.3324s | 0.3346s | 0.65% |
| syn:check:unchanged | 0.6268s | 0.6307s | 0.64% |
| syntex_syntax:check:unchanged | 1.8248s | 1.8508s |  1.43% |
| Total | 3.3779s | 3.4113s | 0.99% |
| Summary | 1.0000s | 1.0061s | 0.61% |
It's based on #108167.
r? @cjgillot
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