rustc_mir_transform/inline/
cycle.rs

1use rustc_data_structures::Limit;
2use rustc_data_structures::fx::{FxHashMap, FxHashSet, FxIndexSet};
3use rustc_data_structures::stack::ensure_sufficient_stack;
4use rustc_data_structures::unord::UnordSet;
5use rustc_hir::def_id::{DefId, LocalDefId};
6use rustc_middle::mir::TerminatorKind;
7use rustc_middle::ty::{self, GenericArgsRef, InstanceKind, ShimKind, TyCtxt, TypeVisitableExt};
8use rustc_span::sym;
9use tracing::{instrument, trace};
10
11#[instrument(level = "debug", skip(tcx), ret)]
12fn should_recurse<'tcx>(tcx: TyCtxt<'tcx>, callee: ty::Instance<'tcx>) -> bool {
13    match callee.def {
14        // If there is no MIR available (either because it was not in metadata or
15        // because it has no MIR because it's an extern function), then the inliner
16        // won't cause cycles on this.
17        InstanceKind::Item(_) => {
18            if !tcx.is_mir_available(callee.def_id()) {
19                return false;
20            }
21        }
22
23        // These have no own callable MIR.
24        InstanceKind::Intrinsic(_) | InstanceKind::LlvmIntrinsic(_) | InstanceKind::Virtual(..) => {
25            return false;
26        }
27
28        // These have MIR and if that MIR is inlined, instantiated and then inlining is run
29        // again, a function item can end up getting inlined. Thus we'll be able to cause
30        // a cycle that way
31        InstanceKind::Shim(ShimKind::VTable(_))
32        | InstanceKind::Shim(ShimKind::Reify(..))
33        | InstanceKind::Shim(ShimKind::FnPtr(..))
34        | InstanceKind::Shim(ShimKind::ClosureOnce { .. })
35        | InstanceKind::Shim(ShimKind::ConstructCoroutineInClosure { .. })
36        | InstanceKind::Shim(ShimKind::ThreadLocal { .. })
37        | InstanceKind::Shim(ShimKind::Clone(..)) => {}
38
39        // This shim does not call any other functions, thus there can be no recursion.
40        InstanceKind::Shim(ShimKind::FnPtrAddr(..)) => return false,
41
42        // FIXME: A not fully instantiated drop shim can cause ICEs if one attempts to
43        // have its MIR built. Likely oli-obk just screwed up the `ParamEnv`s, so this
44        // needs some more analysis.
45        InstanceKind::Shim(ShimKind::DropGlue(..))
46        | InstanceKind::Shim(ShimKind::FutureDropPoll(..))
47        | InstanceKind::Shim(ShimKind::AsyncDropGlue(..))
48        | InstanceKind::Shim(ShimKind::AsyncDropGlueCtor(..)) => {
49            if callee.has_param() {
50                return false;
51            }
52        }
53    }
54
55    crate::pm::should_run_pass(tcx, &crate::inline::Inline, crate::pm::Optimizations::Allowed)
56        || crate::inline::ForceInline::should_run_pass_for_callee(tcx, callee.def.def_id())
57}
58
59#[instrument(
60    level = "debug",
61    skip(tcx, typing_env, seen, involved, recursion_limiter, recursion_limit),
62    ret
63)]
64fn process<'tcx>(
65    tcx: TyCtxt<'tcx>,
66    typing_env: ty::TypingEnv<'tcx>,
67    caller: ty::Instance<'tcx>,
68    target: LocalDefId,
69    seen: &mut FxHashMap<ty::Instance<'tcx>, bool>,
70    involved: &mut FxHashSet<LocalDefId>,
71    recursion_limiter: &mut FxHashMap<DefId, usize>,
72    recursion_limit: Limit,
73) -> Option<bool> {
74    trace!(%caller);
75    let mut reaches_root = false;
76
77    for &(callee_def_id, args) in tcx.mir_inliner_callees(caller.def) {
78        let Ok(args) = caller.try_instantiate_mir_and_normalize_erasing_regions(
79            tcx,
80            typing_env,
81            ty::EarlyBinder::bind(tcx, args),
82        ) else {
83            trace!(?caller, ?typing_env, ?args, "cannot normalize, skipping");
84            continue;
85        };
86        let Ok(Some(callee)) = ty::Instance::try_resolve(tcx, typing_env, callee_def_id, args)
87        else {
88            trace!(?callee_def_id, "cannot resolve, skipping");
89            continue;
90        };
91
92        // Found a path.
93        if callee.def_id() == target.to_def_id() {
94            reaches_root = true;
95            seen.insert(callee, true);
96            continue;
97        }
98
99        if tcx.is_constructor(callee.def_id()) {
100            trace!("constructors always have MIR");
101            // Constructor functions cannot cause a query cycle.
102            continue;
103        }
104
105        if !should_recurse(tcx, callee) {
106            continue;
107        }
108
109        let callee_reaches_root = if let Some(&c) = seen.get(&callee) {
110            // Even if we have seen this callee before, and thus don't need
111            // to recurse into it, we still need to propagate whether it reaches
112            // the root so that we can mark all the involved callers, in case we
113            // end up reaching that same recursive callee through some *other* cycle.
114            c
115        } else {
116            seen.insert(callee, false);
117            let recursion = recursion_limiter.entry(callee.def_id()).or_default();
118            trace!(?callee, recursion = *recursion);
119            let callee_reaches_root = if recursion_limit.value_within_limit(*recursion) {
120                *recursion += 1;
121                ensure_sufficient_stack(|| {
122                    process(
123                        tcx,
124                        typing_env,
125                        callee,
126                        target,
127                        seen,
128                        involved,
129                        recursion_limiter,
130                        recursion_limit,
131                    )
132                })?
133            } else {
134                return None;
135            };
136            seen.insert(callee, callee_reaches_root);
137            callee_reaches_root
138        };
139        if callee_reaches_root {
140            if let Some(callee_def_id) = callee.def_id().as_local() {
141                // Calling `optimized_mir` of a non-local definition cannot cycle.
142                involved.insert(callee_def_id);
143            }
144            reaches_root = true;
145        }
146    }
147
148    Some(reaches_root)
149}
150
151#[instrument(level = "debug", skip(tcx), ret)]
152pub(crate) fn mir_callgraph_cyclic<'tcx>(
153    tcx: TyCtxt<'tcx>,
154    root: LocalDefId,
155) -> Option<UnordSet<LocalDefId>> {
156    assert!(
157        !tcx.is_constructor(root.to_def_id()),
158        "you should not call `mir_callgraph_reachable` on enum/struct constructor functions"
159    );
160
161    // FIXME(-Znext-solver=no): Remove this hack when trait solver overflow can return an error.
162    // In code like that pointed out in #128887, the type complexity we ask the solver to deal with
163    // grows as we recurse into the call graph. If we use the same recursion limit here and in the
164    // solver, the solver hits the limit first and emits a fatal error. But if we use a reduced
165    // limit, we will hit the limit first and give up on looking for inlining. And in any case,
166    // the default recursion limits are quite generous for us. If we need to recurse 64 times
167    // into the call graph, we're probably not going to find any useful MIR inlining.
168    let recursion_limit = tcx.recursion_limit() / 8;
169    let mut involved = FxHashSet::default();
170    let typing_env = ty::TypingEnv::post_analysis(tcx, root);
171    let root_instance =
172        ty::Instance::new_raw(root.to_def_id(), ty::GenericArgs::identity_for_item(tcx, root));
173    if !should_recurse(tcx, root_instance) {
174        trace!("cannot walk, skipping");
175        return Some(involved.into());
176    }
177    match process(
178        tcx,
179        typing_env,
180        root_instance,
181        root,
182        &mut FxHashMap::default(),
183        &mut involved,
184        &mut FxHashMap::default(),
185        recursion_limit,
186    ) {
187        Some(_) => Some(involved.into()),
188        _ => None,
189    }
190}
191
192pub(crate) fn mir_inliner_callees<'tcx>(
193    tcx: TyCtxt<'tcx>,
194    instance: ty::InstanceKind<'tcx>,
195) -> &'tcx [(DefId, GenericArgsRef<'tcx>)] {
196    let steal;
197    let guard;
198    let body = match (instance, instance.def_id().as_local()) {
199        (InstanceKind::Item(_), Some(def_id)) => {
200            steal = tcx.mir_promoted(def_id).0;
201            guard = steal.borrow();
202            &*guard
203        }
204        // Functions from other crates and MIR shims
205        _ => tcx.instance_mir(instance),
206    };
207    let mut calls = FxIndexSet::default();
208    for bb_data in body.basic_blocks.iter() {
209        let terminator = bb_data.terminator();
210        if let TerminatorKind::Call { func, args: call_args, .. } = &terminator.kind {
211            let ty = func.ty(&body.local_decls, tcx);
212            let ty::FnDef(def_id, generic_args) = ty.kind() else {
213                continue;
214            };
215            let call = if tcx.is_intrinsic(*def_id, sym::const_eval_select) {
216                let func = &call_args[2].node;
217                let ty = func.ty(&body.local_decls, tcx);
218                let ty::FnDef(def_id, generic_args) = ty.kind() else {
219                    continue;
220                };
221                (*def_id, *generic_args)
222            } else {
223                (*def_id, *generic_args)
224            };
225            calls.insert(call);
226        }
227    }
228    tcx.arena.alloc_from_iter(calls.iter().map(|(did, args)| (*did, args.no_bound_vars().unwrap())))
229}
rustc_mir_transform/inline/cycle.rs

rustc_mir_transform/inline/
cycle.rs
