rustc_mir_transform/inline/
cycle.rs

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

rustc_mir_transform/inline/
cycle.rs
