Refactor how SwitchInt stores jump targets

[rust.git] / compiler / rustc_mir / src / transform / uninhabited_enum_branching.rs

diff --git a/compiler/rustc_mir/src/transform/uninhabited_enum_branching.rs b/compiler/rustc_mir/src/transform/uninhabited_enum_branching.rs
index a6bfa0c7409f2d3dd6516ea256c0efbab0bcf6e7..465832c89fd00871b7f7117c0d28ee196152efc4 100644 (file)
--- a/compiler/rustc_mir/src/transform/uninhabited_enum_branching.rs
+++ b/compiler/rustc_mir/src/transform/uninhabited_enum_branching.rs
@@ -1,8 +1,10 @@
 //! A pass that eliminates branches on uninhabited enum variants.
 
 use crate::transform::MirPass;
+use rustc_data_structures::stable_set::FxHashSet;
 use rustc_middle::mir::{
-    BasicBlock, BasicBlockData, Body, Local, Operand, Rvalue, StatementKind, TerminatorKind,
+    BasicBlock, BasicBlockData, Body, Local, Operand, Rvalue, StatementKind, SwitchTargets,
+    TerminatorKind,
 };
 use rustc_middle::ty::layout::TyAndLayout;
 use rustc_middle::ty::{Ty, TyCtxt};
@@ -52,9 +54,13 @@ fn variant_discriminants<'tcx>(
     layout: &TyAndLayout<'tcx>,
     ty: Ty<'tcx>,
     tcx: TyCtxt<'tcx>,
-) -> Vec<u128> {
+) -> FxHashSet<u128> {
     match &layout.variants {
-        Variants::Single { index } => vec![index.as_u32() as u128],
+        Variants::Single { index } => {
+            let mut res = FxHashSet::default();
+            res.insert(index.as_u32() as u128);
+            res
+        }
         Variants::Multiple { variants, .. } => variants
             .iter_enumerated()
             .filter_map(|(idx, layout)| {
@@ -96,21 +102,15 @@ fn run_pass(&self, tcx: TyCtxt<'tcx>, body: &mut Body<'tcx>) {
 
             trace!("allowed_variants = {:?}", allowed_variants);
 
-            if let TerminatorKind::SwitchInt { values, targets, .. } =
+            if let TerminatorKind::SwitchInt { targets, .. } =
                 &mut body.basic_blocks_mut()[bb].terminator_mut().kind
             {
-                // 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));
+                let new_targets = SwitchTargets::new(
+                    targets.iter().filter(|(val, _)| allowed_variants.contains(val)),
+                    targets.otherwise(),
+                );
+
+                *targets = new_targets;
             } else {
                 unreachable!()
             }