EXPERIMENT: derive Debug as a single function call #95637
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Rather than needing a bunch of method calls, build arrays of the names and values, leaving the loop up to the implementation in core.
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@bors try @rust-timer queue |
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Awaiting bors try build completion. @rustbot label: +S-waiting-on-perf |
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⌛ Trying commit 8aa2c66 with merge a6295bd5c15c45e144c1cb2460888cfcae521b7d... |
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☀️ Try build successful - checks-actions |
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Queued a6295bd5c15c45e144c1cb2460888cfcae521b7d with parent ec667fb, future comparison URL. |
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Finished benchmarking commit (a6295bd5c15c45e144c1cb2460888cfcae521b7d): comparison url. Summary:
If you disagree with this performance assessment, please file an issue in rust-lang/rustc-perf. Benchmarking this pull request likely means that it is perf-sensitive, so we're automatically marking it as not fit for rolling up. While you can manually mark this PR as fit for rollup, we strongly recommend not doing so since this PR led to changes in compiler perf. Next Steps: If you can justify the regressions found in this try perf run, please indicate this with @bors rollup=never Footnotes |
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I'll have to do more to fix diesel, apparently, so I don't need this open in the mean time. |
This commit adds new methods that combine sequences of existing
formatting methods.
- `Formatter::debug_{tuple,struct}_field[12345]_finish`, equivalent to a
`Formatter::debug_{tuple,struct}` + N x `Debug{Tuple,Struct}::field` +
`Debug{Tuple,Struct}::finish` call sequence.
- `Formatter::debug_{tuple,struct}_fields_finish` is similar, but can
handle any number of fields by using arrays.
These new methods are all marked as `doc(hidden)` and unstable. They are
intended for the compiler's own use.
Special-casing up to 5 fields gives significantly better performance
results than always using arrays (as was tried in rust-lang#95637).
The commit also changes the `Debug` deriving code to use these new methods. For
example, where the old `Debug` code for a struct with two fields would be like
this:
```
fn fmt(&self, f: &mut ::core::fmt::Formatter) -> ::core::fmt::Result {
match *self {
Self {
f1: ref __self_0_0,
f2: ref __self_0_1,
} => {
let debug_trait_builder = &mut ::core::fmt::Formatter::debug_struct(f, "S2");
let _ = ::core::fmt::DebugStruct::field(debug_trait_builder, "f1", &&(*__self_0_0));
let _ = ::core::fmt::DebugStruct::field(debug_trait_builder, "f2", &&(*__self_0_1));
::core::fmt::DebugStruct::finish(debug_trait_builder)
}
}
}
```
the new code is like this:
```
fn fmt(&self, f: &mut ::core::fmt::Formatter) -> ::core::fmt::Result {
match *self {
Self {
f1: ref __self_0_0,
f2: ref __self_0_1,
} => ::core::fmt::Formatter::debug_struct_field2_finish(
f,
"S2",
"f1",
&&(*__self_0_0),
"f2",
&&(*__self_0_1),
),
}
}
```
This shrinks the code produced for `Debug` instances
considerably, reducing compile times and binary sizes.
Co-authored-by: Scott McMurray <[email protected]>
Rather than needing a bunch of method calls, build arrays of the names and values, leaving the loop up to the implementation in core.
DebugStruct::fieldis already using&dyn Debug, after all.r? @ghost