Binary size optimization experiment #569
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EFanZh
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src/macros.rs
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| let lvl = $lvl; | ||
| if lvl <= $crate::STATIC_MAX_LEVEL && lvl <= $crate::max_level() { | ||
| match (::std::format_args!($($arg)+), $target, $kvs) { | ||
| (args, target, kvs) => if let ::std::option::Option::Some(literal) = ::std::fmt::Arguments::as_str(&args) { |
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I don't think this is necessary, since it is turned into an fmt::Argument<'_> again when constructing Record<'_>.
I think this actually prevents the Log implementation to take advantage of Argument::as_str.
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The idea is that passing an Arguments value is more costly than passing an str value: https://godbolt.org/z/bzbnfq1TM. I expect an application may contain a lot of logs that only contains string literals, so if we can reduce the cost of each log call, the total binary size could been reduced. Essentially, this implementation tries to bring back an old optimization that was reverted by #446.
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You can pass a reference to Arguments, then dereference it when building Records.
It implements Copy, so you can avoid copying it in each function while preserving the ability to take advantages of Arguments::as_str
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Aside from copying, building an Argument object also has costs: https://godbolt.org/z/a1eqr4bq5.
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It seems that passing Arguments and passing &Arguments have the same cost: https://godbolt.org/z/Wz35xYrsr.
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Is this PR trying to take advantages of rust-lang/rust#109999 ? |
Not exactly. This PR intends to minimize code generated by macro expansion. This is done by moving as much code logic as possible into functions that can be shared by each macro call. |
Thanks for explanation. |
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It seems that using "opt-level=z", the compiler won’t inline Maybe marking |
You could just pass |
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@NobodyXu: I have tested the effect of passing |
Your linked code does not actually use the Arguments, so the compiler might omits the copy requires to happen. In your PR, you passes the Arguments to log2, log1, log0 by value, that would require copying Arguments between stacks unless inlined. |
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OK, I think this is ready for the next step. This PR is just a proof of concept of some ideas I have, and should not be merged as is. I have tested this PR on my personal project and gained about 2.4% binary size reduction, which is significant to me. Now I want to implement these ideas in the
Also, is there a known open source project that uses |
In |
It seems that |
It uses many dependencies which depends on If you check the "details" which contained the dependency tree, you would find it actually heavily depends on |
| module_path_and_file: &'static (&'static str, &'static str), | ||
| line: u32, | ||
| level: L, | ||
| args: A, |
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I think you could try passing &Arguments<'_> here and in all log_* instead of passing generics here.
I still think losing Arguments::as_str as an optimization is bad and passing it by reference could make up for it.
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I have added a const function to check whether the format argument is a string literal as a not perfect replacement for Arguments::as_str, that’s why I used a generic argument here. Sometimes I need to pass &str as args.
As for &Arguments, I think I should do some test, then decide which one to use.
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I have added a const function to check whether the format argument is a string literal as a not perfect replacement for
Arguments::as_str
I was actually referring to using Argument::as_str in Log::log, the implementation might be able to avoid heap alloc using Argument::as_str, passing &str here breaks that optimization.
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I am not sure I understand. Log::log is not implemented by this crate, so how do I utilize Argument::as_str?
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I am not sure I understand.
Log::logis not implemented by this crate, so how do I utilizeArgument::as_str?
Implementator of Log::log could use Argument::as_str to avoid heap allocation.
Now that you decided to pass arg as &str if possible, they can no longer utilize this optimization.
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I see your point. Maybe this can be optimized by format_args! as a special case?
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I see your point. Maybe this can be optimized by
format_args!as a special case?
Ideally yes, but that will require the args to be &'static str, which involves lifetime and is a bit hard to do.
I guess we can ask @m-ou-se for this?
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A simpler approach could be impl<'a> From<&'a &'static str> for Arguments<'a>, utilizing Arguments::new_const.
src/__private_api.rs
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| impl LogKVs for &[(&str, &LogKvValue<'_>)] { | ||
| #[inline] | ||
| fn with(self, f: impl FnOnce(&[(&str, &LogKvValue)])) { |
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Why every Log* trait has to accept a closure here?
Can't they just return the value directly?
Returning the closure would only add more overhead and generate more code.
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For LogArgs, I can’t return a Arguments value from a &str value:
fn f(s: &str) -> Arguments<'_> {
format_args!("{s}") // Does not work because a local variable reference is captured.
}So I have to use a callback function.
For other ones, since they need to be converted into references, the trait method may need to take a &self argument, and I don’t feel like taking references from &str or a zero sized type, since the will get a &&str type and &ZST type. But I am not very insistent on this.
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So I have to use a callback function.
Yeah for LogArgs you have to use a callback due to limitation of Arguments<'_>, although I wonder
For other ones, since they need to be converted into references, the trait method may need to take a
&selfargument, and I don’t feed like taking references from&stror a zero sized type, since the will get a&&strtype and&ZSTtype. But I am not very insistent on this.
I don't think there's much issue with this since it will most likely be inlined.
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OK, now I have removed callback functions from LogTarget and LogKVs.
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I have tests this PR on cargo-binstall, and here is the binary size comparison:
You can reproduce the result using this program. |
Experiment for some ideas I have on binary size optimization.