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Allow optimizing out panic_bounds_check in Unicode checks.

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This commit is contained in:
Markus Reiter 2025-03-05 01:04:10 +01:00
parent e6af292f91
commit 222adac953
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3 changed files with 65 additions and 53 deletions
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73
library/core/src/unicode/unicode_data.rs
View file

@ -55,24 +55,31 @@ fn decode_length(short_offset_run_header: u32) -> usize {
(short_offset_run_header >> 21) as usize
}
/// # Safety
///
/// The last element of `short_offset_runs` must be greater than `std::char::MAX`.
#[inline(always)]
fn skip_search<const SOR: usize, const OFFSETS: usize>(
needle: u32,
unsafe fn skip_search<const SOR: usize, const OFFSETS: usize>(
needle: char,
short_offset_runs: &[u32; SOR],
offsets: &[u8; OFFSETS],
) -> bool {
// Note that this *cannot* be past the end of the array, as the last
// element is greater than std::char::MAX (the largest possible needle).
//
// So, we cannot have found it (i.e. Ok(idx) + 1 != length) and the correct
// location cannot be past it, so Err(idx) != length either.
//
// This means that we can avoid bounds checking for the accesses below, too.
let needle = needle as u32;
let last_idx =
match short_offset_runs.binary_search_by_key(&(needle << 11), |header| header << 11) {
Ok(idx) => idx + 1,
Err(idx) => idx,
};
// SAFETY: `last_idx` *cannot* be past the end of the array, as the last
// element is greater than `std::char::MAX` (the largest possible needle)
// as guaranteed by the caller.
//
// So, we cannot have found it (i.e. `Ok(idx) => idx + 1 != length`) and the
// correct location cannot be past it, so `Err(idx) => idx != length` either.
//
// This means that we can avoid bounds checking for the accesses below, too.
unsafe { crate::hint::assert_unchecked(last_idx < SOR) };
let mut offset_idx = decode_length(short_offset_runs[last_idx]);
let length = if let Some(next) = short_offset_runs.get(last_idx + 1) {
@ -169,11 +176,9 @@ pub mod alphabetic {
0, 0, 0, 0, 5, 0, 0,
];
pub fn lookup(c: char) -> bool {
super::skip_search(
c as u32,
&SHORT_OFFSET_RUNS,
&OFFSETS,
)
const { assert!(*SHORT_OFFSET_RUNS.last().unwrap() > (char::MAX as u32)); }
// SAFETY: We just ensured the last element of `SHORT_OFFSET_RUNS` is greater than `std::char::MAX`.
unsafe { super::skip_search(c, &SHORT_OFFSET_RUNS, &OFFSETS) }
}
}
@ -222,11 +227,9 @@ pub mod case_ignorable {
1, 61, 4, 0, 5, 254, 2, 0, 7, 109, 8, 0, 5, 0, 1, 30, 96, 128, 240, 0,
];
pub fn lookup(c: char) -> bool {
super::skip_search(
c as u32,
&SHORT_OFFSET_RUNS,
&OFFSETS,
)
const { assert!(*SHORT_OFFSET_RUNS.last().unwrap() > (char::MAX as u32)); }
// SAFETY: We just ensured the last element of `SHORT_OFFSET_RUNS` is greater than `std::char::MAX`.
unsafe { super::skip_search(c, &SHORT_OFFSET_RUNS, &OFFSETS) }
}
}
@ -252,11 +255,9 @@ pub mod cased {
8, 0, 10, 1, 20, 6, 6, 0, 62, 0, 68, 0, 26, 6, 26, 6, 26, 0,
];
pub fn lookup(c: char) -> bool {
super::skip_search(
c as u32,
&SHORT_OFFSET_RUNS,
&OFFSETS,
)
const { assert!(*SHORT_OFFSET_RUNS.last().unwrap() > (char::MAX as u32)); }
// SAFETY: We just ensured the last element of `SHORT_OFFSET_RUNS` is greater than `std::char::MAX`.
unsafe { super::skip_search(c, &SHORT_OFFSET_RUNS, &OFFSETS) }
}
}
@ -269,11 +270,9 @@ pub mod cc {
0, 32, 95, 33, 0,
];
pub fn lookup(c: char) -> bool {
super::skip_search(
c as u32,
&SHORT_OFFSET_RUNS,
&OFFSETS,
)
const { assert!(*SHORT_OFFSET_RUNS.last().unwrap() > (char::MAX as u32)); }
// SAFETY: We just ensured the last element of `SHORT_OFFSET_RUNS` is greater than `std::char::MAX`.
unsafe { super::skip_search(c, &SHORT_OFFSET_RUNS, &OFFSETS) }
}
}
@ -320,11 +319,9 @@ pub mod grapheme_extend {
(c as u32) >= 0x300 && lookup_slow(c)
}
fn lookup_slow(c: char) -> bool {
super::skip_search(
c as u32,
&SHORT_OFFSET_RUNS,
&OFFSETS,
)
const { assert!(*SHORT_OFFSET_RUNS.last().unwrap() > (char::MAX as u32)); }
// SAFETY: We just ensured the last element of `SHORT_OFFSET_RUNS` is greater than `std::char::MAX`.
unsafe { super::skip_search(c, &SHORT_OFFSET_RUNS, &OFFSETS) }
}
}
@ -459,11 +456,9 @@ pub mod n {
10, 247, 10, 0, 9, 128, 10, 0, 59, 1, 3, 1, 4, 76, 45, 1, 15, 0, 13, 0, 10, 0,
];
pub fn lookup(c: char) -> bool {
super::skip_search(
c as u32,
&SHORT_OFFSET_RUNS,
&OFFSETS,
)
const { assert!(*SHORT_OFFSET_RUNS.last().unwrap() > (char::MAX as u32)); }
// SAFETY: We just ensured the last element of `SHORT_OFFSET_RUNS` is greater than `std::char::MAX`.
unsafe { super::skip_search(c, &SHORT_OFFSET_RUNS, &OFFSETS) }
}
}

25
src/tools/unicode-table-generator/src/range_search.rs
View file

@ -53,24 +53,31 @@ fn decode_length(short_offset_run_header: u32) -> usize {
(short_offset_run_header >> 21) as usize
}
/// # Safety
///
/// The last element of `short_offset_runs` must be greater than `std::char::MAX`.
#[inline(always)]
fn skip_search<const SOR: usize, const OFFSETS: usize>(
needle: u32,
unsafe fn skip_search<const SOR: usize, const OFFSETS: usize>(
needle: char,
short_offset_runs: &[u32; SOR],
offsets: &[u8; OFFSETS],
) -> bool {
// Note that this *cannot* be past the end of the array, as the last
// element is greater than std::char::MAX (the largest possible needle).
//
// So, we cannot have found it (i.e. Ok(idx) + 1 != length) and the correct
// location cannot be past it, so Err(idx) != length either.
//
// This means that we can avoid bounds checking for the accesses below, too.
let needle = needle as u32;
let last_idx =
match short_offset_runs.binary_search_by_key(&(needle << 11), |header| header << 11) {
Ok(idx) => idx + 1,
Err(idx) => idx,
};
// SAFETY: `last_idx` *cannot* be past the end of the array, as the last
// element is greater than `std::char::MAX` (the largest possible needle)
// as guaranteed by the caller.
//
// So, we cannot have found it (i.e. `Ok(idx) => idx + 1 != length`) and the
// correct location cannot be past it, so `Err(idx) => idx != length` either.
//
// This means that we can avoid bounds checking for the accesses below, too.
unsafe { crate::hint::assert_unchecked(last_idx < SOR) };
let mut offset_idx = decode_length(short_offset_runs[last_idx]);
let length = if let Some(next) = short_offset_runs.get(last_idx + 1) {

20
src/tools/unicode-table-generator/src/skiplist.rs
View file

@ -108,11 +108,21 @@ impl RawEmitter {
} else {
writeln!(&mut self.file, "pub fn lookup(c: char) -> bool {{").unwrap();
}
writeln!(&mut self.file, " super::skip_search(",).unwrap();
writeln!(&mut self.file, " c as u32,").unwrap();
writeln!(&mut self.file, " &SHORT_OFFSET_RUNS,").unwrap();
writeln!(&mut self.file, " &OFFSETS,").unwrap();
writeln!(&mut self.file, " )").unwrap();
writeln!(
&mut self.file,
" const {{ assert!(*SHORT_OFFSET_RUNS.last().unwrap() > (char::MAX as u32)); }}",
)
.unwrap();
writeln!(
&mut self.file,
" // SAFETY: We just ensured the last element of `SHORT_OFFSET_RUNS` is greater than `std::char::MAX`.",
)
.unwrap();
writeln!(
&mut self.file,
" unsafe {{ super::skip_search(c, &SHORT_OFFSET_RUNS, &OFFSETS) }}"
)
.unwrap();
writeln!(&mut self.file, "}}").unwrap();
}
}