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Perf: Optimize target_for_value lookup #149186

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Perf: Optimize target_for_value lookup #149186

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9 changes: 8 additions & 1 deletion compiler/rustc_middle/src/mir/terminator.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -84,7 +84,14 @@ impl SwitchTargets {
/// branch if there's not a specific match for the value.
#[inline]
pub fn target_for_value(&self, value: u128) -> BasicBlock {
self.iter().find_map(|(v, t)| (v == value).then_some(t)).unwrap_or_else(|| self.otherwise())
let value = Pu128(value);
if let Some(idx) = self.values.iter().position(|&v| v == value) {
// SAFETY: Invariant ensures targets.len() == values.len() + 1.
// If index is in values, it is valid in targets.
unsafe { *self.targets.get_unchecked(idx) }
} else {
self.otherwise()
}
}

/// Adds a new target to the switch. Panics if you add an already present value.
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