1 use rustc_data_structures::graph::iterate::{
2 NodeStatus, TriColorDepthFirstSearch, TriColorVisitor,
4 use rustc_hir::intravisit::FnKind;
5 use rustc_middle::mir::{BasicBlock, BasicBlocks, Body, Operand, TerminatorKind};
6 use rustc_middle::ty::subst::{GenericArg, InternalSubsts};
7 use rustc_middle::ty::{self, AssocItem, AssocItemContainer, Instance, TyCtxt};
8 use rustc_session::lint::builtin::UNCONDITIONAL_RECURSION;
10 use std::ops::ControlFlow;
12 pub(crate) fn check<'tcx>(tcx: TyCtxt<'tcx>, body: &Body<'tcx>) {
13 let def_id = body.source.def_id().expect_local();
15 if let Some(fn_kind) = tcx.hir().get_by_def_id(def_id).fn_kind() {
16 if let FnKind::Closure = fn_kind {
17 // closures can't recur, so they don't matter.
21 // If this is trait/impl method, extract the trait's substs.
22 let trait_substs = match tcx.opt_associated_item(def_id.to_def_id()) {
24 container: AssocItemContainer::TraitContainer(trait_def_id), ..
26 let trait_substs_count = tcx.generics_of(*trait_def_id).count();
27 &InternalSubsts::identity_for_item(tcx, def_id.to_def_id())[..trait_substs_count]
32 let mut vis = Search { tcx, body, reachable_recursive_calls: vec![], trait_substs };
33 if let Some(NonRecursive) =
34 TriColorDepthFirstSearch::new(&body.basic_blocks).run_from_start(&mut vis)
38 if vis.reachable_recursive_calls.is_empty() {
42 vis.reachable_recursive_calls.sort();
44 let hir_id = tcx.hir().local_def_id_to_hir_id(def_id);
45 let sp = tcx.sess.source_map().guess_head_span(tcx.hir().span_with_body(hir_id));
46 tcx.struct_span_lint_hir(UNCONDITIONAL_RECURSION, hir_id, sp, |lint| {
47 let mut db = lint.build("function cannot return without recursing");
48 db.span_label(sp, "cannot return without recursing");
49 // offer some help to the programmer.
50 for call_span in vis.reachable_recursive_calls {
51 db.span_label(call_span, "recursive call site");
53 db.help("a `loop` may express intention better if this is on purpose");
61 struct Search<'mir, 'tcx> {
63 body: &'mir Body<'tcx>,
64 trait_substs: &'tcx [GenericArg<'tcx>],
66 reachable_recursive_calls: Vec<Span>,
69 impl<'mir, 'tcx> Search<'mir, 'tcx> {
70 /// Returns `true` if `func` refers to the function we are searching in.
71 fn is_recursive_call(&self, func: &Operand<'tcx>, args: &[Operand<'tcx>]) -> bool {
72 let Search { tcx, body, trait_substs, .. } = *self;
73 // Resolving function type to a specific instance that is being called is expensive. To
74 // avoid the cost we check the number of arguments first, which is sufficient to reject
75 // most of calls as non-recursive.
76 if args.len() != body.arg_count {
79 let caller = body.source.def_id();
80 let param_env = tcx.param_env(caller);
82 let func_ty = func.ty(body, tcx);
83 if let ty::FnDef(callee, substs) = *func_ty.kind() {
84 let normalized_substs = tcx.normalize_erasing_regions(param_env, substs);
85 let (callee, call_substs) = if let Ok(Some(instance)) =
86 Instance::resolve(tcx, param_env, callee, normalized_substs)
88 (instance.def_id(), instance.substs)
90 (callee, normalized_substs)
93 // FIXME(#57965): Make this work across function boundaries
95 // If this is a trait fn, the substs on the trait have to match, or we might be
96 // calling into an entirely different method (for example, a call from the default
97 // method in the trait to `<A as Trait<B>>::method`, where `A` and/or `B` are
99 return callee == caller && &call_substs[..trait_substs.len()] == trait_substs;
106 impl<'mir, 'tcx> TriColorVisitor<BasicBlocks<'tcx>> for Search<'mir, 'tcx> {
107 type BreakVal = NonRecursive;
112 prior_status: Option<NodeStatus>,
113 ) -> ControlFlow<Self::BreakVal> {
114 // Back-edge in the CFG (loop).
115 if let Some(NodeStatus::Visited) = prior_status {
116 return ControlFlow::Break(NonRecursive);
119 match self.body[bb].terminator().kind {
120 // These terminators return control flow to the caller.
121 TerminatorKind::Abort
122 | TerminatorKind::GeneratorDrop
123 | TerminatorKind::Resume
124 | TerminatorKind::Return
125 | TerminatorKind::Unreachable
126 | TerminatorKind::Yield { .. } => ControlFlow::Break(NonRecursive),
128 // A diverging InlineAsm is treated as non-recursing
129 TerminatorKind::InlineAsm { destination, .. } => {
130 if destination.is_some() {
131 ControlFlow::CONTINUE
133 ControlFlow::Break(NonRecursive)
138 TerminatorKind::Assert { .. }
139 | TerminatorKind::Call { .. }
140 | TerminatorKind::Drop { .. }
141 | TerminatorKind::DropAndReplace { .. }
142 | TerminatorKind::FalseEdge { .. }
143 | TerminatorKind::FalseUnwind { .. }
144 | TerminatorKind::Goto { .. }
145 | TerminatorKind::SwitchInt { .. } => ControlFlow::CONTINUE,
149 fn node_settled(&mut self, bb: BasicBlock) -> ControlFlow<Self::BreakVal> {
150 // When we examine a node for the last time, remember it if it is a recursive call.
151 let terminator = self.body[bb].terminator();
152 if let TerminatorKind::Call { func, args, .. } = &terminator.kind {
153 if self.is_recursive_call(func, args) {
154 self.reachable_recursive_calls.push(terminator.source_info.span);
158 ControlFlow::CONTINUE
161 fn ignore_edge(&mut self, bb: BasicBlock, target: BasicBlock) -> bool {
162 let terminator = self.body[bb].terminator();
163 if terminator.unwind() == Some(&Some(target)) && terminator.successors().count() > 1 {
166 // Don't traverse successors of recursive calls or false CFG edges.
167 match self.body[bb].terminator().kind {
168 TerminatorKind::Call { ref func, ref args, .. } => self.is_recursive_call(func, args),
169 TerminatorKind::FalseEdge { imaginary_target, .. } => imaginary_target == target,