Auto merge of #57880 - Zoxc:error-on-cycle, r=michaelwoerister

Always emit an error for a query cycle

r? @michaelwoerister

cc @nikomatsakis @wesleywiser

13 files changed, 149 insertions, 178 deletions

diff --git a/src/librustc/ich/impls_ty.rs b/src/librustc/ich/impls_ty.rs
index 1e1dbd0b621..6f04a68a6ed 100644
--- a/src/librustc/ich/impls_ty.rs
+++ b/src/librustc/ich/impls_ty.rs
@@ -206,6 +206,10 @@ impl<'gcx> HashStable<StableHashingContext<'gcx>> for ty::adjustment::AutoBorrow
     }
 }
 
+impl_stable_hash_for!(tuple_struct ty::util::NeedsDrop { value });
+
+impl_stable_hash_for!(tuple_struct ty::AdtSizedConstraint<'tcx> { list });
+
 impl_stable_hash_for!(struct ty::UpvarPath { hir_id });
 
 impl_stable_hash_for!(struct ty::UpvarId { var_path, closure_expr_id });
diff --git a/src/librustc/ty/mod.rs b/src/librustc/ty/mod.rs
index 1bb67b3ffaa..18dba3092ad 100644
--- a/src/librustc/ty/mod.rs
+++ b/src/librustc/ty/mod.rs
@@ -43,7 +43,7 @@ use syntax::ast::{self, Name, Ident, NodeId};
 use syntax::attr;
 use syntax::ext::hygiene::Mark;
 use syntax::symbol::{keywords, Symbol, LocalInternedString, InternedString};
-use syntax_pos::{DUMMY_SP, Span};
+use syntax_pos::Span;
 
 use smallvec;
 use rustc_data_structures::indexed_vec::{Idx, IndexVec};
@@ -2379,20 +2379,7 @@ impl<'a, 'gcx, 'tcx> AdtDef {
     /// Due to normalization being eager, this applies even if
     /// the associated type is behind a pointer (e.g., issue #31299).
     pub fn sized_constraint(&self, tcx: TyCtxt<'a, 'gcx, 'tcx>) -> &'tcx [Ty<'tcx>] {
-        match tcx.try_adt_sized_constraint(DUMMY_SP, self.did) {
-            Ok(tys) => tys,
-            Err(mut bug) => {
-                debug!("adt_sized_constraint: {:?} is recursive", self);
-                // This should be reported as an error by `check_representable`.
-                //
-                // Consider the type as Sized in the meanwhile to avoid
-                // further errors. Delay our `bug` diagnostic here to get
-                // emitted later as well in case we accidentally otherwise don't
-                // emit an error.
-                bug.delay_as_bug();
-                tcx.intern_type_list(&[tcx.types.err])
-            }
-        }
+        tcx.adt_sized_constraint(self.did).0
     }
 
     fn sized_constraint_for_ty(&self,
@@ -3083,6 +3070,9 @@ fn associated_item<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>, def_id: DefId) -> Asso
               parent_item.node)
 }
 
+#[derive(Clone)]
+pub struct AdtSizedConstraint<'tcx>(pub &'tcx [Ty<'tcx>]);
+
 /// Calculates the `Sized` constraint.
 ///
 /// In fact, there are only a few options for the types in the constraint:
@@ -3094,7 +3084,7 @@ fn associated_item<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>, def_id: DefId) -> Asso
 ///       check should catch this case.
 fn adt_sized_constraint<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>,
                                   def_id: DefId)
-                                  -> &'tcx [Ty<'tcx>] {
+                                  -> AdtSizedConstraint<'tcx> {
     let def = tcx.adt_def(def_id);
 
     let result = tcx.mk_type_list(def.variants.iter().flat_map(|v| {
@@ -3105,7 +3095,7 @@ fn adt_sized_constraint<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>,
 
     debug!("adt_sized_constraint: {:?} => {:?}", def, result);
 
-    result
+    AdtSizedConstraint(result)
 }
 
 fn associated_item_def_ids<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>,
diff --git a/src/librustc/ty/query/config.rs b/src/librustc/ty/query/config.rs
index a3ee92f8e12..1870812893c 100644
--- a/src/librustc/ty/query/config.rs
+++ b/src/librustc/ty/query/config.rs
@@ -13,6 +13,7 @@ use crate::ty::subst::Substs;
 use crate::ty::query::queries;
 use crate::ty::query::Query;
 use crate::ty::query::QueryCache;
+use crate::ty::query::plumbing::CycleError;
 use crate::util::profiling::ProfileCategory;
 
 use std::borrow::Cow;
@@ -49,7 +50,7 @@ pub(super) trait QueryAccessors<'tcx>: QueryConfig<'tcx> {
         result: &Self::Value
     ) -> Option<Fingerprint>;
 
-    fn handle_cycle_error(tcx: TyCtxt<'_, 'tcx, '_>) -> Self::Value;
+    fn handle_cycle_error(tcx: TyCtxt<'_, 'tcx, '_>, error: CycleError<'tcx>) -> Self::Value;
 }
 
 pub(super) trait QueryDescription<'tcx>: QueryAccessors<'tcx> {
diff --git a/src/librustc/ty/query/job.rs b/src/librustc/ty/query/job.rs
index 16b4af53594..22211468412 100644
--- a/src/librustc/ty/query/job.rs
+++ b/src/librustc/ty/query/job.rs
@@ -73,30 +73,12 @@ impl<'tcx> QueryJob<'tcx> {
     }
 
     /// Awaits for the query job to complete.
-    ///
-    /// For single threaded rustc there's no concurrent jobs running, so if we are waiting for any
-    /// query that means that there is a query cycle, thus this always running a cycle error.
-    #[cfg(not(parallel_compiler))]
-    #[inline(never)]
-    #[cold]
-    pub(super) fn cycle_error<'lcx, 'a, D: QueryDescription<'tcx>>(
-        &self,
-        tcx: TyCtxt<'_, 'tcx, 'lcx>,
-        span: Span,
-    ) -> TryGetJob<'a, 'tcx, D> {
-        TryGetJob::JobCompleted(Err(Box::new(self.find_cycle_in_stack(tcx, span))))
-    }
-
-    /// Awaits for the query job to complete.
-    ///
-    /// For single threaded rustc there's no concurrent jobs running, so if we are waiting for any
-    /// query that means that there is a query cycle, thus this always running a cycle error.
     #[cfg(parallel_compiler)]
     pub(super) fn r#await<'lcx>(
         &self,
         tcx: TyCtxt<'_, 'tcx, 'lcx>,
         span: Span,
-    ) -> Result<(), Box<CycleError<'tcx>>> {
+    ) -> Result<(), CycleError<'tcx>> {
         tls::with_related_context(tcx, move |icx| {
             let mut waiter = Lrc::new(QueryWaiter {
                 query: icx.query.clone(),
@@ -111,13 +93,13 @@ impl<'tcx> QueryJob<'tcx> {
             let mut cycle = waiter.cycle.lock();
             match cycle.take() {
                 None => Ok(()),
-                Some(cycle) => Err(Box::new(cycle))
+                Some(cycle) => Err(cycle)
             }
         })
     }
 
     #[cfg(not(parallel_compiler))]
-    fn find_cycle_in_stack<'lcx>(
+    pub(super) fn find_cycle_in_stack<'lcx>(
         &self,
         tcx: TyCtxt<'_, 'tcx, 'lcx>,
         span: Span,
diff --git a/src/librustc/ty/query/mod.rs b/src/librustc/ty/query/mod.rs
index 3b191d4201f..740875109d0 100644
--- a/src/librustc/ty/query/mod.rs
+++ b/src/librustc/ty/query/mod.rs
@@ -34,15 +34,15 @@ use crate::traits::query::normalize::NormalizationResult;
 use crate::traits::query::outlives_bounds::OutlivesBound;
 use crate::traits::specialization_graph;
 use crate::traits::Clauses;
-use crate::ty::{self, CrateInherentImpls, ParamEnvAnd, Ty, TyCtxt};
+use crate::ty::{self, CrateInherentImpls, ParamEnvAnd, Ty, TyCtxt, AdtSizedConstraint};
 use crate::ty::steal::Steal;
 use crate::ty::subst::Substs;
+use crate::ty::util::NeedsDrop;
 use crate::util::nodemap::{DefIdSet, DefIdMap, ItemLocalSet};
 use crate::util::common::{ErrorReported};
 use crate::util::profiling::ProfileCategory::*;
 use crate::session::Session;
 
-use errors::DiagnosticBuilder;
 use rustc_data_structures::svh::Svh;
 use rustc_data_structures::bit_set::BitSet;
 use rustc_data_structures::indexed_vec::IndexVec;
@@ -154,7 +154,16 @@ define_queries! { <'tcx>
         [] fn trait_def: TraitDefOfItem(DefId) -> &'tcx ty::TraitDef,
         [] fn adt_def: AdtDefOfItem(DefId) -> &'tcx ty::AdtDef,
         [] fn adt_destructor: AdtDestructor(DefId) -> Option<ty::Destructor>,
-        [] fn adt_sized_constraint: SizedConstraint(DefId) -> &'tcx [Ty<'tcx>],
+
+        // The cycle error here should be reported as an error by `check_representable`.
+        // We consider the type as Sized in the meanwhile to avoid
+        // further errors (done in impl Value for AdtSizedConstraint).
+        // Use `cycle_delay_bug` to delay the cycle error here to be emitted later
+        // in case we accidentally otherwise don't emit an error.
+        [cycle_delay_bug] fn adt_sized_constraint: SizedConstraint(
+            DefId
+        ) -> AdtSizedConstraint<'tcx>,
+
         [] fn adt_dtorck_constraint: DtorckConstraint(
             DefId
         ) -> Result<DtorckConstraint<'tcx>, NoSolution>,
@@ -411,7 +420,16 @@ define_queries! { <'tcx>
         [] fn is_copy_raw: is_copy_dep_node(ty::ParamEnvAnd<'tcx, Ty<'tcx>>) -> bool,
         [] fn is_sized_raw: is_sized_dep_node(ty::ParamEnvAnd<'tcx, Ty<'tcx>>) -> bool,
         [] fn is_freeze_raw: is_freeze_dep_node(ty::ParamEnvAnd<'tcx, Ty<'tcx>>) -> bool,
-        [] fn needs_drop_raw: needs_drop_dep_node(ty::ParamEnvAnd<'tcx, Ty<'tcx>>) -> bool,
+
+        // The cycle error here should be reported as an error by `check_representable`.
+        // We consider the type as not needing drop in the meanwhile to avoid
+        // further errors (done in impl Value for NeedsDrop).
+        // Use `cycle_delay_bug` to delay the cycle error here to be emitted later
+        // in case we accidentally otherwise don't emit an error.
+        [cycle_delay_bug] fn needs_drop_raw: needs_drop_dep_node(
+            ty::ParamEnvAnd<'tcx, Ty<'tcx>>
+        ) -> NeedsDrop,
+
         [] fn layout_raw: layout_dep_node(ty::ParamEnvAnd<'tcx, Ty<'tcx>>)
                                     -> Result<&'tcx ty::layout::LayoutDetails,
                                                 ty::layout::LayoutError<'tcx>>,
@@ -731,32 +749,6 @@ define_queries! { <'tcx>
     },
 }
 
-// `try_get_query` can't be public because it uses the private query
-// implementation traits, so we provide access to it selectively.
-impl<'a, 'tcx, 'lcx> TyCtxt<'a, 'tcx, 'lcx> {
-    pub fn try_adt_sized_constraint(
-        self,
-        span: Span,
-        key: DefId,
-    ) -> Result<&'tcx [Ty<'tcx>], Box<DiagnosticBuilder<'a>>> {
-        self.try_get_query::<queries::adt_sized_constraint<'_>>(span, key)
-    }
-    pub fn try_needs_drop_raw(
-        self,
-        span: Span,
-        key: ty::ParamEnvAnd<'tcx, Ty<'tcx>>,
-    ) -> Result<bool, Box<DiagnosticBuilder<'a>>> {
-        self.try_get_query::<queries::needs_drop_raw<'_>>(span, key)
-    }
-    pub fn try_optimized_mir(
-        self,
-        span: Span,
-        key: DefId,
-    ) -> Result<&'tcx mir::Mir<'tcx>, Box<DiagnosticBuilder<'a>>> {
-        self.try_get_query::<queries::optimized_mir<'_>>(span, key)
-    }
-}
-
 //////////////////////////////////////////////////////////////////////
 // These functions are little shims used to find the dep-node for a
 // given query when there is not a *direct* mapping:
diff --git a/src/librustc/ty/query/plumbing.rs b/src/librustc/ty/query/plumbing.rs
index 19b39be8a4d..37cb6753ed5 100644
--- a/src/librustc/ty/query/plumbing.rs
+++ b/src/librustc/ty/query/plumbing.rs
@@ -19,6 +19,8 @@ use errors::FatalError;
 use rustc_data_structures::fx::{FxHashMap};
 use rustc_data_structures::sync::{Lrc, Lock};
 use rustc_data_structures::thin_vec::ThinVec;
+#[cfg(not(parallel_compiler))]
+use rustc_data_structures::cold_path;
 use std::mem;
 use std::ptr;
 use std::collections::hash_map::Entry;
@@ -114,7 +116,7 @@ impl<'a, 'tcx, Q: QueryDescription<'tcx>> JobOwner<'a, 'tcx, Q> {
             if let Some(value) = lock.results.get(key) {
                 profq_msg!(tcx, ProfileQueriesMsg::CacheHit);
                 tcx.sess.profiler(|p| p.record_query_hit(Q::NAME, Q::CATEGORY));
-                let result = Ok((value.value.clone(), value.index));
+                let result = (value.value.clone(), value.index);
                 #[cfg(debug_assertions)]
                 {
                     lock.cache_hits += 1;
@@ -160,9 +162,11 @@ impl<'a, 'tcx, Q: QueryDescription<'tcx>> JobOwner<'a, 'tcx, Q> {
             mem::drop(lock);
 
             // If we are single-threaded we know that we have cycle error,
-            // so we just turn the errror
+            // so we just return the error
             #[cfg(not(parallel_compiler))]
-            return job.cycle_error(tcx, span);
+            return TryGetJob::Cycle(cold_path(|| {
+                Q::handle_cycle_error(tcx, job.find_cycle_in_stack(tcx, span))
+            }));
 
             // With parallel queries we might just have to wait on some other
             // thread
@@ -172,7 +176,7 @@ impl<'a, 'tcx, Q: QueryDescription<'tcx>> JobOwner<'a, 'tcx, Q> {
                 tcx.sess.profiler(|p| p.query_blocked_end(Q::NAME, Q::CATEGORY));
 
                 if let Err(cycle) = result {
-                    return TryGetJob::JobCompleted(Err(cycle));
+                    return TryGetJob::Cycle(Q::handle_cycle_error(tcx, cycle));
                 }
             }
         }
@@ -238,7 +242,10 @@ pub(super) enum TryGetJob<'a, 'tcx: 'a, D: QueryDescription<'tcx> + 'a> {
     /// The query was already completed.
     /// Returns the result of the query and its dep node index
     /// if it succeeded or a cycle error if it failed
-    JobCompleted(Result<(D::Value, DepNodeIndex), Box<CycleError<'tcx>>>),
+    JobCompleted((D::Value, DepNodeIndex)),
+
+    /// Trying to execute the query resulted in a cycle.
+    Cycle(D::Value),
 }
 
 impl<'a, 'gcx, 'tcx> TyCtxt<'a, 'gcx, 'tcx> {
@@ -279,8 +286,8 @@ impl<'a, 'gcx, 'tcx> TyCtxt<'a, 'gcx, 'tcx> {
     #[cold]
     pub(super) fn report_cycle(
         self,
-        box CycleError { usage, cycle: stack }: Box<CycleError<'gcx>>
-    ) -> Box<DiagnosticBuilder<'a>>
+        CycleError { usage, cycle: stack }: CycleError<'gcx>
+    ) -> DiagnosticBuilder<'a>
     {
         assert!(!stack.is_empty());
 
@@ -314,7 +321,7 @@ impl<'a, 'gcx, 'tcx> TyCtxt<'a, 'gcx, 'tcx> {
                               &format!("cycle used when {}", query.describe(self)));
             }
 
-            return Box::new(err)
+            err
         })
     }
 
@@ -346,13 +353,12 @@ impl<'a, 'gcx, 'tcx> TyCtxt<'a, 'gcx, 'tcx> {
     }
 
     #[inline(never)]
-    fn try_get_with<Q: QueryDescription<'gcx>>(
+    pub(super) fn get_query<Q: QueryDescription<'gcx>>(
         self,
         span: Span,
         key: Q::Key)
-    -> Result<Q::Value, Box<CycleError<'gcx>>>
-    {
-        debug!("ty::queries::{}::try_get_with(key={:?}, span={:?})",
+    -> Q::Value {
+        debug!("ty::query::get_query<{}>(key={:?}, span={:?})",
                Q::NAME,
                key,
                span);
@@ -366,11 +372,10 @@ impl<'a, 'gcx, 'tcx> TyCtxt<'a, 'gcx, 'tcx> {
 
         let job = match JobOwner::try_get(self, span, &key) {
             TryGetJob::NotYetStarted(job) => job,
-            TryGetJob::JobCompleted(result) => {
-                return result.map(|(v, index)| {
-                    self.dep_graph.read_index(index);
-                    v
-                })
+            TryGetJob::Cycle(result) => return result,
+            TryGetJob::JobCompleted((v, index)) => {
+                self.dep_graph.read_index(index);
+                return v
             }
         };
 
@@ -378,7 +383,7 @@ impl<'a, 'gcx, 'tcx> TyCtxt<'a, 'gcx, 'tcx> {
         // expensive for some DepKinds.
         if !self.dep_graph.is_fully_enabled() {
             let null_dep_node = DepNode::new_no_params(crate::dep_graph::DepKind::Null);
-            return Ok(self.force_query_with_job::<Q>(key, job, null_dep_node).0);
+            return self.force_query_with_job::<Q>(key, job, null_dep_node).0;
         }
 
         let dep_node = Q::to_dep_node(self, &key);
@@ -407,7 +412,7 @@ impl<'a, 'gcx, 'tcx> TyCtxt<'a, 'gcx, 'tcx> {
 
             job.complete(&result, dep_node_index);
 
-            return Ok(result);
+            return result;
         }
 
         if !dep_node.kind.is_input() {
@@ -427,13 +432,13 @@ impl<'a, 'gcx, 'tcx> TyCtxt<'a, 'gcx, 'tcx> {
             });
             if let Some((result, dep_node_index)) = loaded {
                 job.complete(&result, dep_node_index);
-                return Ok(result);
+                return result;
             }
         }
 
         let (result, dep_node_index) = self.force_query_with_job::<Q>(key, job, dep_node);
         self.dep_graph.read_index(dep_node_index);
-        Ok(result)
+        result
     }
 
     fn load_from_disk_and_cache_in_memory<Q: QueryDescription<'gcx>>(
@@ -631,57 +636,28 @@ impl<'a, 'gcx, 'tcx> TyCtxt<'a, 'gcx, 'tcx> {
         // Ensure that only one of them runs the query
         let job = match JobOwner::try_get(self, span, &key) {
             TryGetJob::NotYetStarted(job) => job,
-            TryGetJob::JobCompleted(result) => {
-                if let Err(e) = result {
-                    self.report_cycle(e).emit();
-                }
+            TryGetJob::Cycle(_) |
+            TryGetJob::JobCompleted(_) => {
                 return
             }
         };
         self.force_query_with_job::<Q>(key, job, dep_node);
     }
-
-    pub(super) fn try_get_query<Q: QueryDescription<'gcx>>(
-        self,
-        span: Span,
-        key: Q::Key,
-    ) -> Result<Q::Value, Box<DiagnosticBuilder<'a>>> {
-        match self.try_get_with::<Q>(span, key) {
-            Ok(e) => Ok(e),
-            Err(e) => Err(self.report_cycle(e)),
-        }
-    }
-
-    // FIXME: Try uninlining this
-    #[inline(always)]
-    pub(super) fn get_query<Q: QueryDescription<'gcx>>(
-        self,
-        span: Span,
-        key: Q::Key,
-    ) -> Q::Value {
-        self.try_get_with::<Q>(span, key).unwrap_or_else(|e| {
-            self.emit_error::<Q>(e)
-        })
-    }
-
-    #[inline(never)]
-    #[cold]
-    fn emit_error<Q: QueryDescription<'gcx>>(
-        self,
-        e: Box<CycleError<'gcx>>,
-    ) -> Q::Value {
-        self.report_cycle(e).emit();
-        Q::handle_cycle_error(self)
-    }
 }
 
 macro_rules! handle_cycle_error {
-    ([][$this: expr]) => {{
-        Value::from_cycle_error($this.global_tcx())
+    ([][$tcx: expr, $error:expr]) => {{
+        $tcx.report_cycle($error).emit();
+        Value::from_cycle_error($tcx.global_tcx())
+    }};
+    ([fatal_cycle$(, $modifiers:ident)*][$tcx:expr, $error:expr]) => {{
+        $tcx.report_cycle($error).emit();
+        $tcx.sess.abort_if_errors();
+        unreachable!()
     }};
-    ([fatal_cycle$(, $modifiers:ident)*][$this:expr]) => {{
-        $this.sess.abort_if_errors();
-        unreachable!();
+    ([cycle_delay_bug$(, $modifiers:ident)*][$tcx:expr, $error:expr]) => {{
+        $tcx.report_cycle($error).delay_as_bug();
+        Value::from_cycle_error($tcx.global_tcx())
     }};
     ([$other:ident$(, $modifiers:ident)*][$($args:tt)*]) => {
         handle_cycle_error!([$($modifiers),*][$($args)*])
@@ -995,8 +971,11 @@ macro_rules! define_queries_inner {
                 hash_result!([$($modifiers)*][_hcx, _result])
             }
 
-            fn handle_cycle_error(tcx: TyCtxt<'_, 'tcx, '_>) -> Self::Value {
-                handle_cycle_error!([$($modifiers)*][tcx])
+            fn handle_cycle_error(
+                tcx: TyCtxt<'_, 'tcx, '_>,
+                error: CycleError<'tcx>
+            ) -> Self::Value {
+                handle_cycle_error!([$($modifiers)*][tcx, error])
             }
         })*
 
diff --git a/src/librustc/ty/query/values.rs b/src/librustc/ty/query/values.rs
index 11f55208d6e..a4b8d365a12 100644
--- a/src/librustc/ty/query/values.rs
+++ b/src/librustc/ty/query/values.rs
@@ -1,4 +1,5 @@
-use crate::ty::{self, Ty, TyCtxt};
+use crate::ty::{self, Ty, TyCtxt, AdtSizedConstraint};
+use crate::ty::util::NeedsDrop;
 
 use syntax::symbol::Symbol;
 
@@ -31,3 +32,14 @@ impl<'tcx> Value<'tcx> for ty::SymbolName {
     }
 }
 
+impl<'tcx> Value<'tcx> for NeedsDrop {
+    fn from_cycle_error(_: TyCtxt<'_, 'tcx, 'tcx>) -> Self {
+        NeedsDrop(false)
+    }
+}
+
+impl<'tcx> Value<'tcx> for AdtSizedConstraint<'tcx> {
+    fn from_cycle_error(tcx: TyCtxt<'_, 'tcx, 'tcx>) -> Self {
+        AdtSizedConstraint(tcx.intern_type_list(&[tcx.types.err]))
+    }
+}
diff --git a/src/librustc/ty/util.rs b/src/librustc/ty/util.rs
index 0578162f84d..1ba7c3bba79 100644
--- a/src/librustc/ty/util.rs
+++ b/src/librustc/ty/util.rs
@@ -755,7 +755,7 @@ impl<'a, 'tcx> ty::TyS<'tcx> {
                       tcx: TyCtxt<'a, 'tcx, 'tcx>,
                       param_env: ty::ParamEnv<'tcx>)
                       -> bool {
-        tcx.needs_drop_raw(param_env.and(self))
+        tcx.needs_drop_raw(param_env.and(self)).0
     }
 
     pub fn same_type(a: Ty<'tcx>, b: Ty<'tcx>) -> bool {
@@ -992,29 +992,22 @@ fn is_freeze_raw<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>,
         ))
 }
 
+#[derive(Clone)]
+pub struct NeedsDrop(pub bool);
+
 fn needs_drop_raw<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>,
                             query: ty::ParamEnvAnd<'tcx, Ty<'tcx>>)
-                            -> bool
+                            -> NeedsDrop
 {
     let (param_env, ty) = query.into_parts();
 
     let needs_drop = |ty: Ty<'tcx>| -> bool {
-        tcx.try_needs_drop_raw(DUMMY_SP, param_env.and(ty)).unwrap_or_else(|mut bug| {
-            // Cycles should be reported as an error by `check_representable`.
-            //
-            // Consider the type as not needing drop in the meanwhile to
-            // avoid further errors.
-            //
-            // In case we forgot to emit a bug elsewhere, delay our
-            // diagnostic to get emitted as a compiler bug.
-            bug.delay_as_bug();
-            false
-        })
+        tcx.needs_drop_raw(param_env.and(ty)).0
     };
 
     assert!(!ty.needs_infer());
 
-    match ty.sty {
+    NeedsDrop(match ty.sty {
         // Fast-path for primitive types
         ty::Infer(ty::FreshIntTy(_)) | ty::Infer(ty::FreshFloatTy(_)) |
         ty::Bool | ty::Int(_) | ty::Uint(_) | ty::Float(_) | ty::Never |
@@ -1072,7 +1065,7 @@ fn needs_drop_raw<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>,
             def.variants.iter().any(
                 |variant| variant.fields.iter().any(
                     |field| needs_drop(field.ty(tcx, substs)))),
-    }
+    })
 }
 
 pub enum ExplicitSelf<'tcx> {
diff --git a/src/librustc_data_structures/lib.rs b/src/librustc_data_structures/lib.rs
index 08b453cf493..2bfb1b24a81 100644
--- a/src/librustc_data_structures/lib.rs
+++ b/src/librustc_data_structures/lib.rs
@@ -41,6 +41,12 @@ extern crate rustc_cratesio_shim;
 
 pub use rustc_serialize::hex::ToHex;
 
+#[inline(never)]
+#[cold]
+pub fn cold_path<F: FnOnce() -> R, R>(f: F) -> R {
+      f()
+}
+
 #[macro_export]
 macro_rules! likely {
       ($e:expr) => {
diff --git a/src/librustc_mir/transform/inline.rs b/src/librustc_mir/transform/inline.rs
index 4cb78266984..07ebbf6d0eb 100644
--- a/src/librustc_mir/transform/inline.rs
+++ b/src/librustc_mir/transform/inline.rs
@@ -98,22 +98,34 @@ impl<'a, 'tcx> Inliner<'a, 'tcx> {
                     continue;
                 }
 
-                let callee_mir = match self.tcx.try_optimized_mir(callsite.location.span,
-                                                                  callsite.callee) {
-                    Ok(callee_mir) if self.consider_optimizing(callsite, callee_mir) => {
-                        self.tcx.subst_and_normalize_erasing_regions(
-                            &callsite.substs,
-                            param_env,
-                            callee_mir,
-                        )
+                let self_node_id = self.tcx.hir().as_local_node_id(self.source.def_id()).unwrap();
+                let callee_node_id = self.tcx.hir().as_local_node_id(callsite.callee);
+
+                let callee_mir = if let Some(callee_node_id) = callee_node_id {
+                    // Avoid a cycle here by only using `optimized_mir` only if we have
+                    // a lower node id than the callee. This ensures that the callee will
+                    // not inline us. This trick only works without incremental compilation.
+                    // So don't do it if that is enabled.
+                    if !self.tcx.dep_graph.is_fully_enabled()
+                        && self_node_id.as_u32() < callee_node_id.as_u32() {
+                        self.tcx.optimized_mir(callsite.callee)
+                    } else {
+                        continue;
                     }
-                    Ok(_) => continue,
+                } else {
+                    // This cannot result in a cycle since the callee MIR is from another crate
+                    // and is already optimized.
+                    self.tcx.optimized_mir(callsite.callee)
+                };
 
-                    Err(mut bug) => {
-                        // FIXME(#43542) shouldn't have to cancel an error
-                        bug.cancel();
-                        continue
-                    }
+                let callee_mir = if self.consider_optimizing(callsite, callee_mir) {
+                    self.tcx.subst_and_normalize_erasing_regions(
+                        &callsite.substs,
+                        param_env,
+                        callee_mir,
+                    )
+                } else {
+                    continue;
                 };
 
                 let start = caller_mir.basic_blocks().len();
diff --git a/src/test/mir-opt/inline-any-operand.rs b/src/test/mir-opt/inline-any-operand.rs
index 5fafc2c50ca..b5455003719 100644
--- a/src/test/mir-opt/inline-any-operand.rs
+++ b/src/test/mir-opt/inline-any-operand.rs
@@ -6,16 +6,16 @@ fn main() {
     println!("{}", bar());
 }
 
-#[inline(always)]
-fn foo(x: i32, y: i32) -> bool {
-    x == y
-}
-
 fn bar() -> bool {
     let f = foo;
     f(1, -1)
 }
 
+#[inline(always)]
+fn foo(x: i32, y: i32) -> bool {
+    x == y
+}
+
 // END RUST SOURCE
 // START rustc.bar.Inline.after.mir
 // ...
diff --git a/src/test/mir-opt/inline-retag.rs b/src/test/mir-opt/inline-retag.rs
index e91a5c22351..6cdbcfdb0ad 100644
--- a/src/test/mir-opt/inline-retag.rs
+++ b/src/test/mir-opt/inline-retag.rs
@@ -6,16 +6,16 @@ fn main() {
     println!("{}", bar());
 }
 
-#[inline(always)]
-fn foo(x: &i32, y: &i32) -> bool {
-    *x == *y
-}
-
 fn bar() -> bool {
     let f = foo;
     f(&1, &-1)
 }
 
+#[inline(always)]
+fn foo(x: &i32, y: &i32) -> bool {
+    *x == *y
+}
+
 // END RUST SOURCE
 // START rustc.bar.Inline.after.mir
 // ...
diff --git a/src/test/mir-opt/inline-trait-method_2.rs b/src/test/mir-opt/inline-trait-method_2.rs
index aa756f4a233..8f9f2535aa5 100644
--- a/src/test/mir-opt/inline-trait-method_2.rs
+++ b/src/test/mir-opt/inline-trait-method_2.rs
@@ -1,14 +1,14 @@
 // compile-flags: -Z span_free_formats -Z mir-opt-level=3
 
+fn test2(x: &dyn X) -> bool {
+    test(x)
+}
+
 #[inline]
 fn test(x: &dyn X) -> bool {
     x.y()
 }
 
-fn test2(x: &dyn X) -> bool {
-    test(x)
-}
-
 trait X {
     fn y(&self) -> bool {
         false