Rollup merge of #75485 - RalfJung:pin, r=nagisa

[rust.git] / src / librustc_mir / transform / uninhabited_enum_branching.rs

diff --git a/src/librustc_mir/transform/uninhabited_enum_branching.rs b/src/librustc_mir/transform/uninhabited_enum_branching.rs
index e3b182b88492f10e81f5b2e7430dd3c3a6114452..4cca4d223c0cb6dd7c2f6cff5e71b762b549012b 100644 (file)
--- a/src/librustc_mir/transform/uninhabited_enum_branching.rs
+++ b/src/librustc_mir/transform/uninhabited_enum_branching.rs
@@ -99,26 +99,18 @@ fn run_pass(&self, tcx: TyCtxt<'tcx>, source: MirSource<'tcx>, body: &mut Body<'
             if let TerminatorKind::SwitchInt { values, targets, .. } =
                 &mut body.basic_blocks_mut()[bb].terminator_mut().kind
             {
-                let vals = &*values;
-                let zipped = vals.iter().zip(targets.iter());
-
-                let mut matched_values = Vec::with_capacity(allowed_variants.len());
-                let mut matched_targets = Vec::with_capacity(allowed_variants.len() + 1);
-
-                for (val, target) in zipped {
-                    if allowed_variants.contains(val) {
-                        matched_values.push(*val);
-                        matched_targets.push(*target);
-                    } else {
-                        trace!("eliminating {:?} -> {:?}", val, target);
-                    }
-                }
-
-                // handle the "otherwise" branch
-                matched_targets.push(targets.pop().unwrap());
-
-                *values = matched_values.into();
-                *targets = matched_targets;
+                // take otherwise out early
+                let otherwise = targets.pop().unwrap();
+                assert_eq!(targets.len(), values.len());
+                let mut i = 0;
+                targets.retain(|_| {
+                    let keep = allowed_variants.contains(&values[i]);
+                    i += 1;
+                    keep
+                });
+                targets.push(otherwise);
+
+                values.to_mut().retain(|var| allowed_variants.contains(var));
             } else {
                 unreachable!()
             }