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const_range_contains: avoid the second comparison if possible.

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

Also, I find the new formulation easier to read.
This commit is contained in:
Nicholas Nethercote 2022-06-08 14:49:32 +10:00
parent ca983054e1
commit 7e4ec35d0c
1 changed files with 11 additions and 8 deletions
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19
compiler/rustc_mir_build/src/build/matches/test.rs
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@ -769,14 +769,17 @@ impl<'a, 'tcx> Builder<'a, 'tcx> {
use std::cmp::Ordering::*;
let tcx = self.tcx;
let a = compare_const_vals(tcx, range.lo, value, self.param_env, range.lo.ty())?;
let b = compare_const_vals(tcx, value, range.hi, self.param_env, range.lo.ty())?;
match (b, range.end) {
(Less, _) | (Equal, RangeEnd::Included) if a != Greater => Some(true),
_ => Some(false),
}
let param_env = self.param_env;
let ty = range.lo.ty();
// For performance, it's important to only do the second
// `compare_const_vals` if necessary.
Some(
matches!(compare_const_vals(tcx, range.lo, value, param_env, ty)?, Less | Equal)
&& matches!(
(compare_const_vals(tcx, value, range.hi, param_env, ty)?, range.end),
(Less, _) | (Equal, RangeEnd::Included)
),
)
}
fn values_not_contained_in_range(