Rollup merge of #97079 - SparrowLii:successors, r=lcnr

Change `Successors` to `impl Iterator<Item = BasicBlock>`

This PR fixes the FIXME in `compiler\rustc_middle\src\mir\mod.rs`.
This can omit several `&`, `*` or `cloned` operations on Successros' generated elements

compiler/rustc_borrowck/src/dataflow.rs

@@ -199,7 +199,7 @@ impl<'tcx> OutOfScopePrecomputer<'_, 'tcx> {
                 // Add successor BBs to the work list, if necessary.
                 let bb_data = &self.body[bb];
                 debug_assert!(hi == bb_data.statements.len());
-                for &succ_bb in bb_data.terminator().successors() {
+                for succ_bb in bb_data.terminator().successors() {
                     if !self.visited.insert(succ_bb) {
                         if succ_bb == location.block && first_lo > 0 {
                             // `succ_bb` has been seen before. If it wasn't

compiler/rustc_borrowck/src/diagnostics/explain_borrow.rs

@@ -467,7 +467,7 @@ impl<'cx, 'tcx> MirBorrowckCtxt<'cx, 'tcx> {
                     block
                         .terminator()
                         .successors()
-                        .map(|bb| Location { statement_index: 0, block: *bb })
+                        .map(|bb| Location { statement_index: 0, block: bb })
                         .filter(|s| visited_locations.insert(*s))
                         .map(|s| {
                             if self.is_back_edge(location, s) {
@@ -526,7 +526,7 @@ impl<'cx, 'tcx> MirBorrowckCtxt<'cx, 'tcx> {
                 }
             } else {
                 for bb in block.terminator().successors() {
-                    let successor = Location { statement_index: 0, block: *bb };
+                    let successor = Location { statement_index: 0, block: bb };
 
                     if !visited_locations.contains(&successor)
                         && self.find_loop_head_dfs(successor, loop_head, visited_locations)

compiler/rustc_borrowck/src/diagnostics/find_use.rs

@@ -67,8 +67,8 @@ impl<'cx, 'tcx> UseFinder<'cx, 'tcx> {
                             block_data
                                 .terminator()
                                 .successors()
-                                .filter(|&bb| Some(&Some(*bb)) != block_data.terminator().unwind())
+                                .filter(|&bb| Some(&Some(bb)) != block_data.terminator().unwind())
-                                .map(|&bb| Location { statement_index: 0, block: bb }),
+                                .map(|bb| Location { statement_index: 0, block: bb }),
                         );
                     }
                 }

compiler/rustc_borrowck/src/nll.rs

@@ -108,7 +108,7 @@ fn populate_polonius_move_facts(
                     // We are at the terminator of an init that has a panic path,
                     // and where the init should not happen on panic
 
-                    for &successor in block_data.terminator().successors() {
+                    for successor in block_data.terminator().successors() {
                         if body[successor].is_cleanup {
                             continue;
                         }

compiler/rustc_codegen_ssa/src/mir/analyze.rs

@@ -328,7 +328,7 @@ pub fn cleanup_kinds(mir: &mir::Body<'_>) -> IndexVec<mir::BasicBlock, CleanupKi
                 bb, data, result[bb], funclet
             );
 
-            for &succ in data.terminator().successors() {
+            for succ in data.terminator().successors() {
                 let kind = result[succ];
                 debug!("cleanup_kinds: propagating {:?} to {:?}/{:?}", funclet, succ, kind);
                 match kind {

compiler/rustc_middle/src/mir/generic_graph.rs

@@ -24,7 +24,7 @@ pub fn mir_fn_to_generic_graph<'tcx>(tcx: TyCtxt<'tcx>, body: &Body<'_>) -> Grap
         let terminator = body[source].terminator();
         let labels = terminator.kind.fmt_successor_labels();
 
-        for (&target, label) in terminator.successors().zip(labels) {
+        for (target, label) in terminator.successors().zip(labels) {
             let src = node(def_id, source);
             let trg = node(def_id, target);
             edges.push(Edge::new(src, trg, label.to_string()));

compiler/rustc_middle/src/mir/mod.rs

@@ -1355,10 +1355,7 @@ pub enum InlineAsmOperand<'tcx> {
 /// Type for MIR `Assert` terminator error messages.
 pub type AssertMessage<'tcx> = AssertKind<Operand<'tcx>>;
 
-// FIXME: Change `Successors` to `impl Iterator<Item = BasicBlock>`.
+pub type Successors<'a> = impl Iterator<Item = BasicBlock> + 'a;
-#[allow(rustc::pass_by_value)]
-pub type Successors<'a> =
-    iter::Chain<option::IntoIter<&'a BasicBlock>, slice::Iter<'a, BasicBlock>>;
 pub type SuccessorsMut<'a> =
     iter::Chain<option::IntoIter<&'a mut BasicBlock>, slice::IterMut<'a, BasicBlock>>;
 
@@ -3434,13 +3431,13 @@ impl<'tcx> graph::WithStartNode for Body<'tcx> {
 impl<'tcx> graph::WithSuccessors for Body<'tcx> {
     #[inline]
     fn successors(&self, node: Self::Node) -> <Self as GraphSuccessors<'_>>::Iter {
-        self.basic_blocks[node].terminator().successors().cloned()
+        self.basic_blocks[node].terminator().successors()
     }
 }
 
 impl<'a, 'b> graph::GraphSuccessors<'b> for Body<'a> {
     type Item = BasicBlock;
-    type Iter = iter::Cloned<Successors<'b>>;
+    type Iter = Successors<'b>;
 }
 
 impl<'tcx, 'graph> graph::GraphPredecessors<'graph> for Body<'tcx> {

compiler/rustc_middle/src/mir/patch.rs

@@ -166,9 +166,7 @@ impl<'tcx> MirPatch<'tcx> {
             // get terminator's targets and apply the statement to all of them.
             if loc.statement_index > body[loc.block].statements.len() {
                 let term = body[loc.block].terminator();
-                let successors = term.successors().clone();
+                for i in term.successors() {
-
-                for i in successors {
                     stmts_and_targets
                         .push((Statement { source_info, kind: stmt.clone() }, i.clone()));
                 }

compiler/rustc_middle/src/mir/predecessors.rs

@@ -43,7 +43,7 @@ impl PredecessorCache {
             let mut preds = IndexVec::from_elem(SmallVec::new(), basic_blocks);
             for (bb, data) in basic_blocks.iter_enumerated() {
                 if let Some(term) = &data.terminator {
-                    for &succ in term.successors() {
+                    for succ in term.successors() {
                         preds[succ].push(bb);
                     }
                 }

compiler/rustc_middle/src/mir/terminator.rs

@@ -416,32 +416,36 @@ impl<'tcx> TerminatorKind<'tcx> {
             | Return
             | Unreachable
             | Call { destination: None, cleanup: None, .. }
-            | InlineAsm { destination: None, cleanup: None, .. } => None.into_iter().chain(&[]),
+            | InlineAsm { destination: None, cleanup: None, .. } => {
-            Goto { target: ref t }
+                None.into_iter().chain((&[]).into_iter().copied())
-            | Call { destination: None, cleanup: Some(ref t), .. }
-            | Call { destination: Some((_, ref t)), cleanup: None, .. }
-            | Yield { resume: ref t, drop: None, .. }
-            | DropAndReplace { target: ref t, unwind: None, .. }
-            | Drop { target: ref t, unwind: None, .. }
-            | Assert { target: ref t, cleanup: None, .. }
-            | FalseUnwind { real_target: ref t, unwind: None }
-            | InlineAsm { destination: Some(ref t), cleanup: None, .. }
-            | InlineAsm { destination: None, cleanup: Some(ref t), .. } => {
-                Some(t).into_iter().chain(&[])
             }
-            Call { destination: Some((_, ref t)), cleanup: Some(ref u), .. }
+            Goto { target: t }
-            | Yield { resume: ref t, drop: Some(ref u), .. }
+            | Call { destination: None, cleanup: Some(t), .. }
-            | DropAndReplace { target: ref t, unwind: Some(ref u), .. }
+            | Call { destination: Some((_, t)), cleanup: None, .. }
-            | Drop { target: ref t, unwind: Some(ref u), .. }
+            | Yield { resume: t, drop: None, .. }
-            | Assert { target: ref t, cleanup: Some(ref u), .. }
+            | DropAndReplace { target: t, unwind: None, .. }
-            | FalseUnwind { real_target: ref t, unwind: Some(ref u) }
+            | Drop { target: t, unwind: None, .. }
-            | InlineAsm { destination: Some(ref t), cleanup: Some(ref u), .. } => {
+            | Assert { target: t, cleanup: None, .. }
-                Some(t).into_iter().chain(slice::from_ref(u))
+            | FalseUnwind { real_target: t, unwind: None }
+            | InlineAsm { destination: Some(t), cleanup: None, .. }
+            | InlineAsm { destination: None, cleanup: Some(t), .. } => {
+                Some(t).into_iter().chain((&[]).into_iter().copied())
             }
-            SwitchInt { ref targets, .. } => None.into_iter().chain(&targets.targets),
+            Call { destination: Some((_, t)), cleanup: Some(ref u), .. }
-            FalseEdge { ref real_target, ref imaginary_target } => {
+            | Yield { resume: t, drop: Some(ref u), .. }
-                Some(real_target).into_iter().chain(slice::from_ref(imaginary_target))
+            | DropAndReplace { target: t, unwind: Some(ref u), .. }
+            | Drop { target: t, unwind: Some(ref u), .. }
+            | Assert { target: t, cleanup: Some(ref u), .. }
+            | FalseUnwind { real_target: t, unwind: Some(ref u) }
+            | InlineAsm { destination: Some(t), cleanup: Some(ref u), .. } => {
+                Some(t).into_iter().chain(slice::from_ref(u).into_iter().copied())
             }
+            SwitchInt { ref targets, .. } => {
+                None.into_iter().chain(targets.targets.iter().copied())
+            }
+            FalseEdge { real_target, ref imaginary_target } => Some(real_target)
+                .into_iter()
+                .chain(slice::from_ref(imaginary_target).into_iter().copied()),
         }
     }
 

compiler/rustc_middle/src/mir/traversal.rs

@@ -180,7 +180,7 @@ impl<'a, 'tcx> Postorder<'a, 'tcx> {
         // two iterations yield `C` and finally `A` for a final traversal of [E, D, B, C, A]
         loop {
             let bb = if let Some(&mut (_, ref mut iter)) = self.visit_stack.last_mut() {
-                if let Some(&bb) = iter.next() {
+                if let Some(bb) = iter.next() {
                     bb
                 } else {
                     break;

compiler/rustc_mir_dataflow/src/framework/graphviz.rs

@@ -125,7 +125,7 @@ where
     }
 
     fn target(&self, edge: &Self::Edge) -> Self::Node {
-        self.body[edge.source].terminator().successors().nth(edge.index).copied().unwrap()
+        self.body[edge.source].terminator().successors().nth(edge.index).unwrap()
     }
 }
 

compiler/rustc_mir_transform/src/coverage/debug.rs

@@ -701,7 +701,7 @@ pub(super) fn dump_coverage_graphviz<'tcx>(
         edge_labels.retain(|label| label != "unreachable");
         let edge_counters = from_terminator
             .successors()
-            .map(|&successor_bb| graphviz_data.get_edge_counter(from_bcb, successor_bb));
+            .map(|successor_bb| graphviz_data.get_edge_counter(from_bcb, successor_bb));
         iter::zip(&edge_labels, edge_counters)
             .map(|(label, some_counter)| {
                 if let Some(counter) = some_counter {

compiler/rustc_mir_transform/src/coverage/graph.rs

@@ -484,17 +484,17 @@ fn bcb_filtered_successors<'a, 'tcx>(
     body: &'tcx &'a mir::Body<'tcx>,
     term_kind: &'tcx TerminatorKind<'tcx>,
 ) -> Box<dyn Iterator<Item = BasicBlock> + 'a> {
-    let mut successors = term_kind.successors();
     Box::new(
         match &term_kind {
             // SwitchInt successors are never unwind, and all of them should be traversed.
-            TerminatorKind::SwitchInt { .. } => successors,
+            TerminatorKind::SwitchInt { ref targets, .. } => {
+                None.into_iter().chain(targets.all_targets().into_iter().copied())
+            }
             // For all other kinds, return only the first successor, if any, and ignore unwinds.
             // NOTE: `chain(&[])` is required to coerce the `option::iter` (from
             // `next().into_iter()`) into the `mir::Successors` aliased type.
-            _ => successors.next().into_iter().chain(&[]),
+            _ => term_kind.successors().next().into_iter().chain((&[]).into_iter().copied()),
         }
-        .copied()
         .filter(move |&successor| body[successor].terminator().kind != TerminatorKind::Unreachable),
     )
 }

compiler/rustc_mir_transform/src/inline.rs

@@ -450,7 +450,7 @@ impl<'tcx> Inliner<'tcx> {
             }
 
             if !is_drop {
-                for &succ in term.successors() {
+                for succ in term.successors() {
                     work_list.push(succ);
                 }
             }

compiler/rustc_mir_transform/src/remove_noop_landing_pads.rs

@@ -65,7 +65,7 @@ impl RemoveNoopLandingPads {
             | TerminatorKind::SwitchInt { .. }
             | TerminatorKind::FalseEdge { .. }
             | TerminatorKind::FalseUnwind { .. } => {
-                terminator.successors().all(|&succ| nop_landing_pads.contains(succ))
+                terminator.successors().all(|succ| nop_landing_pads.contains(succ))
             }
             TerminatorKind::GeneratorDrop
             | TerminatorKind::Yield { .. }

compiler/rustc_mir_transform/src/simplify.rs

@@ -81,7 +81,7 @@ impl<'a, 'tcx> CfgSimplifier<'a, 'tcx> {
 
         for (_, data) in traversal::preorder(body) {
             if let Some(ref term) = data.terminator {
-                for &tgt in term.successors() {
+                for tgt in term.successors() {
                     pred_count[tgt] += 1;
                 }
             }
@@ -235,8 +235,8 @@ impl<'a, 'tcx> CfgSimplifier<'a, 'tcx> {
         };
 
         let first_succ = {
-            if let Some(&first_succ) = terminator.successors().next() {
+            if let Some(first_succ) = terminator.successors().next() {
-                if terminator.successors().all(|s| *s == first_succ) {
+                if terminator.successors().all(|s| s == first_succ) {
                     let count = terminator.successors().count();
                     self.pred_count[first_succ] -= (count - 1) as u32;
                     first_succ

src/tools/clippy/clippy_lints/src/redundant_clone.rs

@@ -114,7 +114,7 @@ impl<'tcx> LateLintPass<'tcx> for RedundantClone {
             }
 
             // Give up on loops
-            if terminator.successors().any(|s| *s == bb) {
+            if terminator.successors().any(|s| s == bb) {
                 continue;
             }
 
@@ -440,7 +440,7 @@ fn visit_clone_usage(cloned: mir::Local, clone: mir::Local, mir: &mir::Body<'_>,
             // Short-circuit
             if (usage.cloned_used && usage.clone_consumed_or_mutated) ||
                 // Give up on loops
-                tdata.terminator().successors().any(|s| *s == bb)
+                tdata.terminator().successors().any(|s| s == bb)
             {
                 return CloneUsage {
                     cloned_used: true,