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Don't compile regex at every function call. #76818

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Sep 20, 2020
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Don't compile regex at every function call. #76818

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10 changes: 9 additions & 1 deletion compiler/rustc_mir/src/dataflow/framework/graphviz.rs
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Original file line number Diff line number Diff line change
@@ -1,6 +1,7 @@
//! A helpful diagram for debugging dataflow problems.
use std::borrow::Cow;
use std::lazy::SyncOnceCell;
use std::{io, ops, str};

use regex::Regex;
Expand Down Expand Up @@ -570,6 +571,13 @@ where
}
}

macro_rules! regex {
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@ecstatic-morse ecstatic-morse Sep 17, 2020 •
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I quite like this. I think it would be a good addition to the regex crate (behind a feature for now). WDYT @hbina?

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I have opened an issue here rust-lang/regex#709
I am still new to this so I haven't open a PR yet.

($re:literal $(,)?) => {{
static RE: SyncOnceCell<regex::Regex> = SyncOnceCell::new();
RE.get_or_init(|| Regex::new($re).unwrap())
Comment on lines +576 to +577
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@ecstatic-morse ecstatic-morse Sep 17, 2020 •
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It seems like this should use SyncLazy instead. @matklad is using Lazy preferable to OnceCell when possible?

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Depends on code-style I guess. My preference would be to use OnceCell here, rather than lazy. I generally like to use the smallest tool for the job, and, as we are not really going to use Lazy's deref in any notable capacity here, OnceCell seems preferable.

But I also can see "don't overthink this and use just Lazy" line of thought there :-)

}};
}

fn diff_pretty<T, C>(new: T, old: T, ctxt: &C) -> String
where
T: DebugWithContext<C>,
Expand All @@ -578,7 +586,7 @@ where
return String::new();
}

let re = Regex::new("\t?\u{001f}([+-])").unwrap();
let re = regex!("\t?\u{001f}([+-])");

let raw_diff = format!("{:#?}", DebugDiffWithAdapter { new, old, ctxt });

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1 change: 1 addition & 0 deletions compiler/rustc_mir/src/lib.rs
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Expand Up @@ -27,6 +27,7 @@ Rust MIR: a lowered representation of Rust.
#![feature(trait_alias)]
#![feature(option_expect_none)]
#![feature(or_patterns)]
#![feature(once_cell)]
#![recursion_limit = "256"]

#[macro_use]
Expand Down