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sort_candidates: avoid the second comparison if possible.

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This is a performance win for `unicode-normalization`.

The commit also removes the closure, which isn't necessary. And
reformulates the comparison into a form I find easier to read.
This commit is contained in:
Nicholas Nethercote 2022-06-08 17:02:06 +10:00
parent 7e4ec35d0c
commit c4cd04480b
1 changed files with 18 additions and 24 deletions
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42
compiler/rustc_mir_build/src/build/matches/test.rs
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@ -632,39 +632,33 @@ pub(super) fn sort_candidate<'pat>(
}
(&TestKind::Range(test), &PatKind::Range(pat)) => {
use std::cmp::Ordering::*;
if test == pat {
self.candidate_without_match_pair(match_pair_index, candidate);
return Some(0);
}
let no_overlap = (|| {
use rustc_hir::RangeEnd::*;
use std::cmp::Ordering::*;
let tcx = self.tcx;
let test_ty = test.lo.ty();
let tcx = self.tcx;
let test_ty = test.lo.ty();
let lo = compare_const_vals(tcx, test.lo, pat.hi, self.param_env, test_ty)?;
let hi = compare_const_vals(tcx, test.hi, pat.lo, self.param_env, test_ty)?;
match (test.end, pat.end, lo, hi) {
// pat < test
(_, _, Greater, _) |
(_, Excluded, Equal, _) |
// pat > test
(_, _, _, Less) |
(Excluded, _, _, Equal) => Some(true),
_ => Some(false),
}
})();
if let Some(true) = no_overlap {
// Testing range does not overlap with pattern range,
// so the pattern can be matched only if this test fails.
// For performance, it's important to only do the second
// `compare_const_vals` if necessary.
let no_overlap = if matches!(
(compare_const_vals(tcx, test.hi, pat.lo, self.param_env, test_ty)?, test.end),
(Less, _) | (Equal, RangeEnd::Excluded) // test < pat
) || matches!(
(compare_const_vals(tcx, test.lo, pat.hi, self.param_env, test_ty)?, pat.end),
(Greater, _) | (Equal, RangeEnd::Excluded) // test > pat
) {
Some(1)
} else {
None
}
};
// If the testing range does not overlap with pattern range,
// the pattern can be matched only if this test fails.
no_overlap
}
(&TestKind::Range(range), &PatKind::Constant { value }) => {