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Auto merge of #122102 - Urgau:optimize-symbol-integer, r=cjgillot

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Optimize `Symbol::integer` by utilizing in-place formatting

This PR optimize `Symbol::integer` by utilizing `itoa` in-place formatting instead of going through a dynamically allocated `String` and the format machinery.

<details>

For some context: I was profiling `rustc --check-cfg` with callgrind and due to the way we currently setup all the targets and we end-up calling `Symbol::integer` multiple times for all the targets. Using `itoa` reduced the number of instructions.

</details>
This commit is contained in:
bors 2024-03-09 08:47:57 +00:00
commit 9d272a1b05
3 changed files with 6 additions and 2 deletions
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6
compiler/rustc_span/src/symbol.rs
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@ -2327,13 +2327,15 @@ pub mod sym {
///
/// The first few non-negative integers each have a static symbol and therefore
/// are fast.
pub fn integer<N: TryInto<usize> + Copy + ToString>(n: N) -> Symbol {
pub fn integer<N: TryInto<usize> + Copy + itoa::Integer>(n: N) -> Symbol {
if let Result::Ok(idx) = n.try_into() {
if idx < 10 {
return Symbol::new(super::SYMBOL_DIGITS_BASE + idx as u32);
}
}
Symbol::intern(&n.to_string())
let mut buffer = itoa::Buffer::new();
let printed = buffer.format(n);
Symbol::intern(printed)
}
}