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Auto merge of #68828 - oli-obk:inline_cycle, r=wesleywiser
Prevent query cycles in the MIR inliner r? `@eddyb` `@wesleywiser` cc `@rust-lang/wg-mir-opt` The general design is that we have a new query that is run on the `validated_mir` instead of on the `optimized_mir`. That query is forced before going into the optimization pipeline, so as to not try to read from a stolen MIR. The query should not be cached cross crate, as you should never call it for items from other crates. By its very design calls into other crates can never cause query cycles. This is a pessimistic approach to inlining, since we strictly have more calls in the `validated_mir` than we have in `optimized_mir`, but that's not a problem imo.
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,157 @@ | ||
| use rustc_data_structures::fx::{FxHashMap, FxHashSet}; | ||
| use rustc_data_structures::stack::ensure_sufficient_stack; | ||
| use rustc_hir::def_id::{DefId, LocalDefId}; | ||
| use rustc_middle::mir::TerminatorKind; | ||
| use rustc_middle::ty::TypeFoldable; | ||
| use rustc_middle::ty::{self, subst::SubstsRef, InstanceDef, TyCtxt}; | ||
|
|
||
| // FIXME: check whether it is cheaper to precompute the entire call graph instead of invoking | ||
| // this query riddiculously often. | ||
| #[instrument(skip(tcx, root, target))] | ||
| crate fn mir_callgraph_reachable( | ||
| tcx: TyCtxt<'tcx>, | ||
| (root, target): (ty::Instance<'tcx>, LocalDefId), | ||
| ) -> bool { | ||
| trace!(%root, target = %tcx.def_path_str(target.to_def_id())); | ||
| let param_env = tcx.param_env_reveal_all_normalized(target); | ||
| assert_ne!( | ||
| root.def_id().expect_local(), | ||
| target, | ||
| "you should not call `mir_callgraph_reachable` on immediate self recursion" | ||
| ); | ||
| assert!( | ||
| matches!(root.def, InstanceDef::Item(_)), | ||
| "you should not call `mir_callgraph_reachable` on shims" | ||
| ); | ||
| assert!( | ||
| !tcx.is_constructor(root.def_id()), | ||
| "you should not call `mir_callgraph_reachable` on enum/struct constructor functions" | ||
| ); | ||
| #[instrument(skip(tcx, param_env, target, stack, seen, recursion_limiter, caller))] | ||
| fn process( | ||
| tcx: TyCtxt<'tcx>, | ||
| param_env: ty::ParamEnv<'tcx>, | ||
| caller: ty::Instance<'tcx>, | ||
| target: LocalDefId, | ||
| stack: &mut Vec<ty::Instance<'tcx>>, | ||
| seen: &mut FxHashSet<ty::Instance<'tcx>>, | ||
| recursion_limiter: &mut FxHashMap<DefId, usize>, | ||
| ) -> bool { | ||
| trace!(%caller); | ||
| for &(callee, substs) in tcx.mir_inliner_callees(caller.def) { | ||
| let substs = caller.subst_mir_and_normalize_erasing_regions(tcx, param_env, substs); | ||
| let callee = match ty::Instance::resolve(tcx, param_env, callee, substs).unwrap() { | ||
| Some(callee) => callee, | ||
| None => { | ||
| trace!(?callee, "cannot resolve, skipping"); | ||
| continue; | ||
| } | ||
| }; | ||
|
|
||
| // Found a path. | ||
| if callee.def_id() == target.to_def_id() { | ||
| return true; | ||
| } | ||
|
|
||
| if tcx.is_constructor(callee.def_id()) { | ||
| trace!("constructors always have MIR"); | ||
| // Constructor functions cannot cause a query cycle. | ||
| continue; | ||
| } | ||
|
|
||
| match callee.def { | ||
| InstanceDef::Item(_) => { | ||
| // If there is no MIR available (either because it was not in metadata or | ||
| // because it has no MIR because it's an extern function), then the inliner | ||
| // won't cause cycles on this. | ||
| if !tcx.is_mir_available(callee.def_id()) { | ||
| trace!(?callee, "no mir available, skipping"); | ||
| continue; | ||
| } | ||
| } | ||
| // These have no own callable MIR. | ||
| InstanceDef::Intrinsic(_) | InstanceDef::Virtual(..) => continue, | ||
| // These have MIR and if that MIR is inlined, substituted and then inlining is run | ||
| // again, a function item can end up getting inlined. Thus we'll be able to cause | ||
| // a cycle that way | ||
| InstanceDef::VtableShim(_) | ||
| | InstanceDef::ReifyShim(_) | ||
| | InstanceDef::FnPtrShim(..) | ||
| | InstanceDef::ClosureOnceShim { .. } | ||
| | InstanceDef::CloneShim(..) => {} | ||
| InstanceDef::DropGlue(..) => { | ||
| // FIXME: A not fully substituted drop shim can cause ICEs if one attempts to | ||
| // have its MIR built. Likely oli-obk just screwed up the `ParamEnv`s, so this | ||
| // needs some more analysis. | ||
| if callee.needs_subst() { | ||
| continue; | ||
| } | ||
| } | ||
| } | ||
|
|
||
| if seen.insert(callee) { | ||
| let recursion = recursion_limiter.entry(callee.def_id()).or_default(); | ||
| trace!(?callee, recursion = *recursion); | ||
| if tcx.sess.recursion_limit().value_within_limit(*recursion) { | ||
| *recursion += 1; | ||
| stack.push(callee); | ||
| let found_recursion = ensure_sufficient_stack(|| { | ||
| process(tcx, param_env, callee, target, stack, seen, recursion_limiter) | ||
| }); | ||
| if found_recursion { | ||
| return true; | ||
| } | ||
| stack.pop(); | ||
| } else { | ||
| // Pessimistically assume that there could be recursion. | ||
| return true; | ||
| } | ||
| } | ||
| } | ||
| false | ||
| } | ||
| process( | ||
| tcx, | ||
| param_env, | ||
| root, | ||
| target, | ||
| &mut Vec::new(), | ||
| &mut FxHashSet::default(), | ||
| &mut FxHashMap::default(), | ||
| ) | ||
| } | ||
|
|
||
| crate fn mir_inliner_callees<'tcx>( | ||
| tcx: TyCtxt<'tcx>, | ||
| instance: ty::InstanceDef<'tcx>, | ||
| ) -> &'tcx [(DefId, SubstsRef<'tcx>)] { | ||
| let steal; | ||
| let guard; | ||
| let body = match (instance, instance.def_id().as_local()) { | ||
| (InstanceDef::Item(_), Some(def_id)) => { | ||
| let def = ty::WithOptConstParam::unknown(def_id); | ||
| steal = tcx.mir_promoted(def).0; | ||
| guard = steal.borrow(); | ||
| &*guard | ||
| } | ||
| // Functions from other crates and MIR shims | ||
| _ => tcx.instance_mir(instance), | ||
| }; | ||
| let mut calls = Vec::new(); | ||
| for bb_data in body.basic_blocks() { | ||
| let terminator = bb_data.terminator(); | ||
| if let TerminatorKind::Call { func, .. } = &terminator.kind { | ||
| let ty = func.ty(&body.local_decls, tcx); | ||
| let call = match ty.kind() { | ||
| ty::FnDef(def_id, substs) => (*def_id, *substs), | ||
| _ => continue, | ||
| }; | ||
| // We've seen this before | ||
| if calls.contains(&call) { | ||
| continue; | ||
| } | ||
| calls.push(call); | ||
| } | ||
| } | ||
| tcx.arena.alloc_slice(&calls) | ||
| } |
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