Rm allocation in uninhabited_enum_branching

Also convert `uninhabited_enum_branching` `Cow<[u128]>::to_mut`

Author: JulianKnodt

src/librustc_mir/transform/simplify_try.rs

@@ -246,12 +246,14 @@ fn get_arm_identity_info<'a, 'tcx>(
         tmp_assigned_vars.insert(*r);
     }
 
-    let mut dbg_info_to_adjust = Vec::new();
-    for (i, var_info) in debug_info.iter().enumerate() {
-        if tmp_assigned_vars.contains(var_info.place.local) {
-            dbg_info_to_adjust.push(i);
-        }
-    }
+    let dbg_info_to_adjust: Vec<_> =
+        debug_info
+            .iter()
+            .enumerate()
+            .filter_map(|(i, var_info)| {
+                if tmp_assigned_vars.contains(var_info.place.local) { Some(i) } else { None }
+            })
+            .collect();
 
     Some(ArmIdentityInfo {
         local_temp_0: local_tmp_s0,
@@ -461,14 +463,14 @@ fn match_get_variant_field<'tcx>(
     stmt: &Statement<'tcx>,
 ) -> Option<(Local, Local, VarField<'tcx>, &'tcx List<PlaceElem<'tcx>>)> {
     match &stmt.kind {
-        StatementKind::Assign(box (place_into, rvalue_from)) => match rvalue_from {
-            Rvalue::Use(Operand::Copy(pf) | Operand::Move(pf)) => {
-                let local_into = place_into.as_local()?;
-                let (local_from, vf) = match_variant_field_place(*pf)?;
-                Some((local_into, local_from, vf, pf.projection))
-            }
-            _ => None,
-        },
+        StatementKind::Assign(box (
+            place_into,
+            Rvalue::Use(Operand::Copy(pf) | Operand::Move(pf)),
+        )) => {
+            let local_into = place_into.as_local()?;
+            let (local_from, vf) = match_variant_field_place(*pf)?;
+            Some((local_into, local_from, vf, pf.projection))
+        }
         _ => None,
     }
 }
@@ -479,14 +481,11 @@ fn match_get_variant_field<'tcx>(
 /// ```
 fn match_set_variant_field<'tcx>(stmt: &Statement<'tcx>) -> Option<(Local, Local, VarField<'tcx>)> {
     match &stmt.kind {
-        StatementKind::Assign(box (place_from, rvalue_into)) => match rvalue_into {
-            Rvalue::Use(Operand::Move(place_into)) => {
-                let local_into = place_into.as_local()?;
-                let (local_from, vf) = match_variant_field_place(*place_from)?;
-                Some((local_into, local_from, vf))
-            }
-            _ => None,
-        },
+        StatementKind::Assign(box (place_from, Rvalue::Use(Operand::Move(place_into)))) => {
+            let local_into = place_into.as_local()?;
+            let (local_from, vf) = match_variant_field_place(*place_from)?;
+            Some((local_into, local_from, vf))
+        }
         _ => None,
     }
 }

src/librustc_mir/transform/uninhabited_enum_branching.rs

@@ -99,26 +99,18 @@ impl<'tcx> MirPass<'tcx> for UninhabitedEnumBranching {
             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!()
             }

src/librustc_mir/transform/unreachable_prop.rs

@@ -68,17 +68,6 @@ where
     F: Fn(BasicBlock) -> bool,
 {
     let terminator = match *terminator_kind {
-        TerminatorKind::FalseEdge { real_target, imaginary_target }
-            if predicate(real_target) && predicate(imaginary_target) =>
-        {
-            TerminatorKind::Unreachable
-        }
-        TerminatorKind::FalseUnwind { real_target, unwind }
-            if predicate(real_target) && unwind.map_or(true, &predicate) =>
-        {
-            TerminatorKind::Unreachable
-        }
-
         TerminatorKind::Goto { target } if predicate(target) => TerminatorKind::Unreachable,
         TerminatorKind::SwitchInt { ref discr, switch_ty, ref values, ref targets } => {
             let original_targets_len = targets.len();