Auto merge of #53109 - nikomatsakis:nll-escaping-into-return-revert, r=nikomatsakis

revert #52991

Reverts https://github.com/rust-lang/rust/pull/52991 which is flawed. I have an idea how to fix it but might as well revert first since it is so wildly flawed. That's what I get for opening PRs while on PTO =)

r? @pnkfelix

11 files changed, 108 insertions, 331 deletions

diff --git a/src/librustc_mir/borrow_check/nll/escaping_locals.rs b/src/librustc_mir/borrow_check/nll/escaping_locals.rs
deleted file mode 100644
index 7e39f3d3b08..00000000000
--- a/src/librustc_mir/borrow_check/nll/escaping_locals.rs
+++ /dev/null
@@ -1,229 +0,0 @@
-// Copyright 2016 The Rust Project Developers. See the COPYRIGHT
-// file at the top-level directory of this distribution and at
-// http://rust-lang.org/COPYRIGHT.
-//
-// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
-// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
-// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
-// option. This file may not be copied, modified, or distributed
-// except according to those terms.
-
-//! Identify those variables whose entire value will eventually be
-//! returned from the fn via the RETURN_PLACE. As an optimization, we
-//! can skip computing liveness results for those variables. The idea
-//! is that the return type of the fn only ever contains free
-//! regions. Therefore, the types of those variables are going to
-//! ultimately be contrained to outlive those free regions -- since
-//! free regions are always live for the entire body, this implies
-//! that the liveness results are not important for those regions.
-//! This is most important in the "fns" that we create to represent static
-//! values, since those are often really quite large, and all regions in them
-//! will ultimately be constrained to be `'static`. Two examples:
-//!
-//! ```
-//! fn foo() -> &'static [u32] { &[] }
-//! static FOO: &[u32] = &[];
-//! ```
-//!
-//! In both these cases, the return value will only have static lifetime.
-//!
-//! NB: The simple logic here relies on the fact that outlives
-//! relations in our analysis don't have locations. Otherwise, we
-//! would have to restrict ourselves to values that are
-//! *unconditionally* returned (which would still cover the "big
-//! static value" case).
-//!
-//! The way that this code works is to use union-find -- we iterate
-//! over the MIR and union together two variables X and Y if all
-//! regions in the value of Y are going to be stored into X -- that
-//! is, if `typeof(X): 'a` requires that `typeof(Y): 'a`. This means
-//! that e.g. we can union together `x` and `y` if we have something
-//! like `x = (y, 22)`, but not something like `x = y.f` (since there
-//! may be regions in the type of `y` that do not appear in the field
-//! `f`).
-
-use rustc::mir::visit::Visitor;
-use rustc::mir::*;
-
-use rustc_data_structures::indexed_vec::Idx;
-use rustc_data_structures::unify as ut;
-
-crate struct EscapingLocals {
-    unification_table: ut::UnificationTable<ut::InPlace<AssignedLocal>>,
-}
-
-impl EscapingLocals {
-    crate fn compute(mir: &Mir<'tcx>) -> Self {
-        let mut visitor = GatherAssignedLocalsVisitor::new();
-        visitor.visit_mir(mir);
-
-        EscapingLocals {
-            unification_table: visitor.unification_table,
-        }
-    }
-
-    /// True if `local` is known to escape into static
-    /// memory.
-    crate fn escapes_into_return(&mut self, local: Local) -> bool {
-        let return_place = AssignedLocal::from(RETURN_PLACE);
-        let other_place = AssignedLocal::from(local);
-        self.unification_table.unioned(return_place, other_place)
-    }
-}
-
-/// The MIR visitor gathering the union-find of the locals used in
-/// assignments.
-struct GatherAssignedLocalsVisitor {
-    unification_table: ut::UnificationTable<ut::InPlace<AssignedLocal>>,
-}
-
-#[derive(Copy, Clone, Debug, Hash, PartialEq, Eq)]
-struct AssignedLocal(u32);
-
-impl ut::UnifyKey for AssignedLocal {
-    type Value = ();
-
-    fn index(&self) -> u32 {
-        self.0
-    }
-
-    fn from_index(i: u32) -> AssignedLocal {
-        AssignedLocal(i)
-    }
-
-    fn tag() -> &'static str {
-        "AssignedLocal"
-    }
-}
-
-impl From<Local> for AssignedLocal {
-    fn from(item: Local) -> Self {
-        // newtype_indexes use usize but are u32s.
-        assert!(item.index() < ::std::u32::MAX as usize);
-        AssignedLocal(item.index() as u32)
-    }
-}
-
-impl GatherAssignedLocalsVisitor {
-    fn new() -> Self {
-        Self {
-            unification_table: ut::UnificationTable::new(),
-        }
-    }
-
-    fn union_locals_if_needed(&mut self, lvalue: Option<Local>, rvalue: Option<Local>) {
-        if let Some(lvalue) = lvalue {
-            if let Some(rvalue) = rvalue {
-                if lvalue != rvalue {
-                    debug!("EscapingLocals: union {:?} and {:?}", lvalue, rvalue);
-                    self.unification_table
-                        .union(AssignedLocal::from(lvalue), AssignedLocal::from(rvalue));
-                }
-            }
-        }
-    }
-}
-
-// Returns the potential `Local` associated to this `Place` or `PlaceProjection`
-fn find_local_in_place(place: &Place) -> Option<Local> {
-    match place {
-        Place::Local(local) => Some(*local),
-
-        // If you do e.g. `x = a.f` then only *part* of the type of
-        // `a` escapes into `x` (the part contained in `f`); if `a`'s
-        // type has regions that don't appear in `f`, those might not
-        // escape.
-        Place::Projection(..) => None,
-
-        Place::Static { .. } | Place::Promoted { .. } => None,
-    }
-}
-
-// Returns the potential `Local` in this `Operand`.
-fn find_local_in_operand(op: &Operand) -> Option<Local> {
-    // Conservatively check a subset of `Operand`s we know our
-    // benchmarks track, for example `html5ever`.
-    match op {
-        Operand::Copy(place) | Operand::Move(place) => find_local_in_place(place),
-        Operand::Constant(_) => None,
-    }
-}
-
-impl Visitor<'tcx> for GatherAssignedLocalsVisitor {
-    fn visit_mir(&mut self, mir: &Mir<'tcx>) {
-        // We need as many union-find keys as there are locals
-        for _ in 0..mir.local_decls.len() {
-            self.unification_table.new_key(());
-        }
-
-        self.super_mir(mir);
-    }
-
-    fn visit_assign(
-        &mut self,
-        block: BasicBlock,
-        place: &Place<'tcx>,
-        rvalue: &Rvalue<'tcx>,
-        location: Location,
-    ) {
-        let local = find_local_in_place(place);
-
-        // Find those cases where there is a `Place` consumed by
-        // `rvalue` and we know that all regions in its type will be
-        // incorporated into `place`, the `Place` we are assigning to.
-        match rvalue {
-            // `x = y` is the simplest possible case.
-            Rvalue::Use(op) => self.union_locals_if_needed(local, find_local_in_operand(op)),
-
-            // `X = &'r P` -- the type of `X` will be `&'r T_P`, where
-            // `T_P` is the type of `P`.
-            Rvalue::Ref(_, _, place) => {
-                // Special case: if you have `X = &*Y` (or `X = &**Y`
-                // etc), then the outlives relationships will ensure
-                // that all regions in `Y` are constrained by regions
-                // in `X` -- this is because the lifetimes of the
-                // references we deref through are required to outlive
-                // the borrow lifetime `'r` (which appears in `X`).
-                //
-                // (We don't actually need to check the type of `Y`:
-                // since `ProjectionElem::Deref` represents a built-in
-                // deref and not an overloaded deref, if the thing we
-                // deref through is not a reference, then it must be a
-                // `Box` or `*const`, in which case it contains no
-                // references.)
-                let mut place_ref = place;
-                while let Place::Projection(proj) = place_ref {
-                    if let ProjectionElem::Deref = proj.elem {
-                        place_ref = &proj.base;
-                    } else {
-                        break;
-                    }
-                }
-
-                self.union_locals_if_needed(local, find_local_in_place(place_ref))
-            }
-
-            Rvalue::Cast(kind, op, _) => match kind {
-                CastKind::Unsize => {
-                    // Casting a `&[T; N]` to `&[T]` or `&Foo` to `&Trait` --
-                    // in both cases, no regions are "lost".
-                    self.union_locals_if_needed(local, find_local_in_operand(op))
-                }
-                _ => (),
-            },
-
-            // Constructing an aggregate like `(x,)` or `Foo { x }`
-            // includes the full type of `x`.
-            Rvalue::Aggregate(_, ops) => {
-                for rvalue in ops.iter().map(find_local_in_operand) {
-                    self.union_locals_if_needed(local, rvalue);
-                }
-            }
-
-            // For other things, be conservative and do not union.
-            _ => (),
-        };
-
-        self.super_assign(block, place, rvalue, location);
-    }
-}
diff --git a/src/librustc_mir/borrow_check/nll/liveness_map.rs b/src/librustc_mir/borrow_check/nll/liveness_map.rs
index d018a9277d8..cbd9c9a4e1a 100644
--- a/src/librustc_mir/borrow_check/nll/liveness_map.rs
+++ b/src/librustc_mir/borrow_check/nll/liveness_map.rs
@@ -16,10 +16,9 @@
 //! liveness code so that it only operates over variables with regions in their
 //! types, instead of all variables.
 
-use borrow_check::nll::escaping_locals::EscapingLocals;
-use rustc::mir::{Local, Mir};
 use rustc::ty::TypeFoldable;
 use rustc_data_structures::indexed_vec::IndexVec;
+use rustc::mir::{Mir, Local};
 use util::liveness::LiveVariableMap;
 
 use rustc_data_structures::indexed_vec::Idx;
@@ -30,13 +29,14 @@ use rustc_data_structures::indexed_vec::Idx;
 crate struct NllLivenessMap {
     /// For each local variable, contains either None (if the type has no regions)
     /// or Some(i) with a suitable index.
-    from_local: IndexVec<Local, Option<LocalWithRegion>>,
-
+    pub from_local: IndexVec<Local, Option<LocalWithRegion>>,
     /// For each LocalWithRegion, maps back to the original Local index.
-    to_local: IndexVec<LocalWithRegion, Local>,
+    pub to_local: IndexVec<LocalWithRegion, Local>,
+
 }
 
 impl LiveVariableMap for NllLivenessMap {
+
     fn from_local(&self, local: Local) -> Option<Self::LiveVar> {
         self.from_local[local]
     }
@@ -55,43 +55,21 @@ impl LiveVariableMap for NllLivenessMap {
 impl NllLivenessMap {
     /// Iterates over the variables in Mir and assigns each Local whose type contains
     /// regions a LocalWithRegion index. Returns a map for converting back and forth.
-    crate fn compute(mir: &Mir<'tcx>) -> Self {
-        let mut escaping_locals = EscapingLocals::compute(mir);
-
+    pub fn compute(mir: &Mir) -> Self {
         let mut to_local = IndexVec::default();
-        let mut escapes_into_return = 0;
-        let mut no_regions = 0;
-        let from_local: IndexVec<Local, Option<_>> = mir
+        let from_local: IndexVec<Local,Option<_>> = mir
             .local_decls
             .iter_enumerated()
             .map(|(local, local_decl)| {
-                if escaping_locals.escapes_into_return(local) {
-                    // If the local escapes into the return value,
-                    // then the return value will force all of the
-                    // regions in its type to outlive free regions
-                    // (e.g., `'static`) and hence liveness is not
-                    // needed. This is particularly important for big
-                    // statics.
-                    escapes_into_return += 1;
-                    None
-                } else if local_decl.ty.has_free_regions() {
-                    let l = to_local.push(local);
-                    debug!("liveness_map: {:?} = {:?}", local, l);
-                    Some(l)
-                } else {
-                    no_regions += 1;
-                    None
+                if local_decl.ty.has_free_regions() {
+                    Some(to_local.push(local))
                 }
+                    else {
+                        None
+                    }
             }).collect();
 
-        debug!("liveness_map: {} variables need liveness", to_local.len());
-        debug!("liveness_map: {} escapes into return", escapes_into_return);
-        debug!("liveness_map: {} no regions", no_regions);
-
-        Self {
-            from_local,
-            to_local,
-        }
+        Self { from_local, to_local }
     }
 }
 
diff --git a/src/librustc_mir/borrow_check/nll/mod.rs b/src/librustc_mir/borrow_check/nll/mod.rs
index 44ed6b7676c..973568a67f0 100644
--- a/src/librustc_mir/borrow_check/nll/mod.rs
+++ b/src/librustc_mir/borrow_check/nll/mod.rs
@@ -39,9 +39,7 @@ use polonius_engine::{Algorithm, Output};
 use util as mir_util;
 use util::pretty::{self, ALIGN};
 
-mod constraints;
 mod constraint_generation;
-mod escaping_locals;
 pub mod explain_borrow;
 mod facts;
 mod invalidation;
@@ -51,6 +49,8 @@ crate mod type_check;
 mod universal_regions;
 crate mod liveness_map;
 
+mod constraints;
+
 use self::facts::AllFacts;
 use self::region_infer::RegionInferenceContext;
 use self::universal_regions::UniversalRegions;
@@ -120,7 +120,6 @@ pub(in borrow_check) fn compute_regions<'cx, 'gcx, 'tcx>(
         location_table,
         borrow_set,
         &liveness,
-        &liveness_map,
         &mut all_facts,
         flow_inits,
         move_data,
@@ -206,7 +205,6 @@ pub(in borrow_check) fn compute_regions<'cx, 'gcx, 'tcx>(
     dump_mir_results(
         infcx,
         &liveness,
-        &liveness_map,
         MirSource::item(def_id),
         &mir,
         &regioncx,
@@ -223,7 +221,6 @@ pub(in borrow_check) fn compute_regions<'cx, 'gcx, 'tcx>(
 fn dump_mir_results<'a, 'gcx, 'tcx>(
     infcx: &InferCtxt<'a, 'gcx, 'tcx>,
     liveness: &LivenessResults<LocalWithRegion>,
-    liveness_map: &NllLivenessMap,
     source: MirSource,
     mir: &Mir<'tcx>,
     regioncx: &RegionInferenceContext,
@@ -233,6 +230,8 @@ fn dump_mir_results<'a, 'gcx, 'tcx>(
         return;
     }
 
+    let map = &NllLivenessMap::compute(mir);
+
     let regular_liveness_per_location: FxHashMap<_, _> = mir
         .basic_blocks()
         .indices()
@@ -240,7 +239,7 @@ fn dump_mir_results<'a, 'gcx, 'tcx>(
             let mut results = vec![];
             liveness
                 .regular
-                .simulate_block(&mir, bb, liveness_map, |location, local_set| {
+                .simulate_block(&mir, bb, map, |location, local_set| {
                     results.push((location, local_set.clone()));
                 });
             results
@@ -254,7 +253,7 @@ fn dump_mir_results<'a, 'gcx, 'tcx>(
             let mut results = vec![];
             liveness
                 .drop
-                .simulate_block(&mir, bb, liveness_map, |location, local_set| {
+                .simulate_block(&mir, bb, map, |location, local_set| {
                     results.push((location, local_set.clone()));
                 });
             results
diff --git a/src/librustc_mir/borrow_check/nll/type_check/liveness.rs b/src/librustc_mir/borrow_check/nll/type_check/liveness.rs
index d02f54dc4b8..2b9307db59a 100644
--- a/src/librustc_mir/borrow_check/nll/type_check/liveness.rs
+++ b/src/librustc_mir/borrow_check/nll/type_check/liveness.rs
@@ -37,7 +37,6 @@ pub(super) fn generate<'gcx, 'tcx>(
     cx: &mut TypeChecker<'_, 'gcx, 'tcx>,
     mir: &Mir<'tcx>,
     liveness: &LivenessResults<LocalWithRegion>,
-    liveness_map: &NllLivenessMap,
     flow_inits: &mut FlowAtLocation<MaybeInitializedPlaces<'_, 'gcx, 'tcx>>,
     move_data: &MoveData<'tcx>,
 ) {
@@ -45,10 +44,10 @@ pub(super) fn generate<'gcx, 'tcx>(
         cx,
         mir,
         liveness,
-        liveness_map,
         flow_inits,
         move_data,
         drop_data: FxHashMap(),
+        map: &NllLivenessMap::compute(mir),
     };
 
     for bb in mir.basic_blocks().indices() {
@@ -66,10 +65,10 @@ where
     cx: &'gen mut TypeChecker<'typeck, 'gcx, 'tcx>,
     mir: &'gen Mir<'tcx>,
     liveness: &'gen LivenessResults<LocalWithRegion>,
-    liveness_map: &'gen NllLivenessMap,
     flow_inits: &'gen mut FlowAtLocation<MaybeInitializedPlaces<'flow, 'gcx, 'tcx>>,
     move_data: &'gen MoveData<'tcx>,
     drop_data: FxHashMap<Ty<'tcx>, DropData<'tcx>>,
+    map: &'gen NllLivenessMap,
 }
 
 struct DropData<'tcx> {
@@ -87,9 +86,9 @@ impl<'gen, 'typeck, 'flow, 'gcx, 'tcx> TypeLivenessGenerator<'gen, 'typeck, 'flo
 
         self.liveness
             .regular
-            .simulate_block(self.mir, bb, self.liveness_map, |location, live_locals| {
+            .simulate_block(self.mir, bb, self.map, |location, live_locals| {
                 for live_local in live_locals.iter() {
-                    let local = self.liveness_map.from_live_var(live_local);
+                    let local = self.map.from_live_var(live_local);
                     let live_local_ty = self.mir.local_decls[local].ty;
                     Self::push_type_live_constraint(&mut self.cx, live_local_ty, location);
                 }
@@ -98,7 +97,7 @@ impl<'gen, 'typeck, 'flow, 'gcx, 'tcx> TypeLivenessGenerator<'gen, 'typeck, 'flo
         let mut all_live_locals: Vec<(Location, Vec<LocalWithRegion>)> = vec![];
         self.liveness
             .drop
-            .simulate_block(self.mir, bb, self.liveness_map, |location, live_locals| {
+            .simulate_block(self.mir, bb, self.map, |location, live_locals| {
                 all_live_locals.push((location, live_locals.iter().collect()));
             });
         debug!(
@@ -125,7 +124,7 @@ impl<'gen, 'typeck, 'flow, 'gcx, 'tcx> TypeLivenessGenerator<'gen, 'typeck, 'flo
                     });
                 }
 
-                let local = self.liveness_map.from_live_var(live_local);
+                let local = self.map.from_live_var(live_local);
                 let mpi = self.move_data.rev_lookup.find_local(local);
                 if let Some(initialized_child) = self.flow_inits.has_any_child_of(mpi) {
                     debug!(
@@ -134,7 +133,7 @@ impl<'gen, 'typeck, 'flow, 'gcx, 'tcx> TypeLivenessGenerator<'gen, 'typeck, 'flo
                         self.move_data.move_paths[initialized_child]
                     );
 
-                    let local = self.liveness_map.from_live_var(live_local);
+                    let local = self.map.from_live_var(live_local);
                     let live_local_ty = self.mir.local_decls[local].ty;
                     self.add_drop_live_constraint(live_local, live_local_ty, location);
                 }
diff --git a/src/librustc_mir/borrow_check/nll/type_check/mod.rs b/src/librustc_mir/borrow_check/nll/type_check/mod.rs
index 15afc6c52bf..a18e2368bf7 100644
--- a/src/librustc_mir/borrow_check/nll/type_check/mod.rs
+++ b/src/librustc_mir/borrow_check/nll/type_check/mod.rs
@@ -15,12 +15,9 @@ use borrow_check::borrow_set::BorrowSet;
 use borrow_check::location::LocationTable;
 use borrow_check::nll::constraints::{ConstraintSet, OutlivesConstraint};
 use borrow_check::nll::facts::AllFacts;
-use borrow_check::nll::liveness_map::NllLivenessMap;
-use borrow_check::nll::region_infer::values::{LivenessValues, RegionValueElements};
+use borrow_check::nll::region_infer::values::{RegionValueElements, LivenessValues};
 use borrow_check::nll::region_infer::{ClosureRegionRequirementsExt, TypeTest};
-use borrow_check::nll::type_check::free_region_relations::{
-    CreateResult, UniversalRegionRelations,
-};
+use borrow_check::nll::type_check::free_region_relations::{CreateResult, UniversalRegionRelations};
 use borrow_check::nll::universal_regions::UniversalRegions;
 use borrow_check::nll::LocalWithRegion;
 use borrow_check::nll::ToRegionVid;
@@ -119,7 +116,6 @@ pub(crate) fn type_check<'gcx, 'tcx>(
     location_table: &LocationTable,
     borrow_set: &BorrowSet<'tcx>,
     liveness: &LivenessResults<LocalWithRegion>,
-    liveness_map: &NllLivenessMap,
     all_facts: &mut Option<AllFacts>,
     flow_inits: &mut FlowAtLocation<MaybeInitializedPlaces<'_, 'gcx, 'tcx>>,
     move_data: &MoveData<'tcx>,
@@ -170,7 +166,7 @@ pub(crate) fn type_check<'gcx, 'tcx>(
             Some(&mut borrowck_context),
             Some(errors_buffer),
             |cx| {
-                liveness::generate(cx, mir, liveness, liveness_map, flow_inits, move_data);
+                liveness::generate(cx, mir, liveness, flow_inits, move_data);
                 cx.equate_inputs_and_outputs(
                     mir,
                     mir_def_id,
diff --git a/src/test/ui/borrowck/issue-52713-bug.rs b/src/test/ui/borrowck/issue-52713-bug.rs
new file mode 100644
index 00000000000..4ecba64b271
--- /dev/null
+++ b/src/test/ui/borrowck/issue-52713-bug.rs
@@ -0,0 +1,29 @@
+// Copyright 2014 The Rust Project Developers. See the COPYRIGHT
+// file at the top-level directory of this distribution and at
+// http://rust-lang.org/COPYRIGHT.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+// Regression test for a bug in #52713: this was an optimization for
+// computing liveness that wound up accidentally causing the program
+// below to be accepted.
+
+#![feature(nll)]
+
+fn foo<'a>(x: &'a mut u32) -> u32 {
+    let mut x = 22;
+    let y = &x;
+    if false {
+        return x;
+    }
+
+    x += 1; //~ ERROR
+    println!("{}", y);
+    return 0;
+}
+
+fn main() { }
diff --git a/src/test/ui/borrowck/issue-52713-bug.stderr b/src/test/ui/borrowck/issue-52713-bug.stderr
new file mode 100644
index 00000000000..7d9b57400dd
--- /dev/null
+++ b/src/test/ui/borrowck/issue-52713-bug.stderr
@@ -0,0 +1,14 @@
+error[E0506]: cannot assign to `x` because it is borrowed
+  --> $DIR/issue-52713-bug.rs:24:5
+   |
+LL |     let y = &x;
+   |             -- borrow of `x` occurs here
+...
+LL |     x += 1; //~ ERROR
+   |     ^^^^^^ assignment to borrowed `x` occurs here
+LL |     println!("{}", y);
+   |                    - borrow later used here
+
+error: aborting due to previous error
+
+For more information about this error, try `rustc --explain E0506`.
diff --git a/src/test/ui/borrowck/promote-ref-mut-in-let-issue-46557.nll.stderr b/src/test/ui/borrowck/promote-ref-mut-in-let-issue-46557.nll.stderr
index 52f1547bce6..95acdab3e80 100644
--- a/src/test/ui/borrowck/promote-ref-mut-in-let-issue-46557.nll.stderr
+++ b/src/test/ui/borrowck/promote-ref-mut-in-let-issue-46557.nll.stderr
@@ -1,24 +1,30 @@
 error[E0597]: borrowed value does not live long enough
   --> $DIR/promote-ref-mut-in-let-issue-46557.rs:15:21
    |
-LL |     let ref mut x = 1234543; //~ ERROR
-   |                     ^^^^^^^ temporary value does not live long enough
-LL |     x
-LL | }
-   | - temporary value only lives until here
-   |
-   = note: borrowed value must be valid for the static lifetime...
+LL |   fn gimme_static_mut_let() -> &'static mut u32 {
+   |  _______________________________________________-
+LL | |     let ref mut x = 1234543; //~ ERROR
+   | |                     ^^^^^^^ temporary value does not live long enough
+LL | |     x
+LL | | }
+   | | -
+   | | |
+   | |_temporary value only lives until here
+   |   borrow later used here
 
 error[E0597]: borrowed value does not live long enough
   --> $DIR/promote-ref-mut-in-let-issue-46557.rs:20:25
    |
-LL |     let (ref mut x, ) = (1234543, ); //~ ERROR
-   |                         ^^^^^^^^^^^ temporary value does not live long enough
-LL |     x
-LL | }
-   | - temporary value only lives until here
-   |
-   = note: borrowed value must be valid for the static lifetime...
+LL |   fn gimme_static_mut_let_nested() -> &'static mut u32 {
+   |  ______________________________________________________-
+LL | |     let (ref mut x, ) = (1234543, ); //~ ERROR
+   | |                         ^^^^^^^^^^^ temporary value does not live long enough
+LL | |     x
+LL | | }
+   | | -
+   | | |
+   | |_temporary value only lives until here
+   |   borrow later used here
 
 error[E0597]: borrowed value does not live long enough
   --> $DIR/promote-ref-mut-in-let-issue-46557.rs:25:11
diff --git a/src/test/ui/nll/get_default.nll.stderr b/src/test/ui/nll/get_default.nll.stderr
index 580dce3c0fe..b955a51e38d 100644
--- a/src/test/ui/nll/get_default.nll.stderr
+++ b/src/test/ui/nll/get_default.nll.stderr
@@ -63,18 +63,9 @@ LL |         match map.get() {
 LL |             Some(v) => {
 LL |                 map.set(String::new()); // Both AST and MIR error here
    |                 ^^^^^^^^^^^^^^^^^^^^^^ mutable borrow occurs here
-   |
-note: borrowed value must be valid for the anonymous lifetime #1 defined on the function body at 41:1...
-  --> $DIR/get_default.rs:41:1
-   |
-LL | / fn err(map: &mut Map) -> &String {
-LL | |     loop {
-LL | |         match map.get() {
-LL | |             Some(v) => {
-...  |
-LL | |     }
-LL | | }
-   | |_^
+...
+LL |                 return v;
+   |                        - borrow later used here
 
 error[E0502]: cannot borrow `*map` as mutable because it is also borrowed as immutable (Mir)
   --> $DIR/get_default.rs:51:17
diff --git a/src/test/ui/nll/get_default.stderr b/src/test/ui/nll/get_default.stderr
index 2f8eab907c7..75194bf55bc 100644
--- a/src/test/ui/nll/get_default.stderr
+++ b/src/test/ui/nll/get_default.stderr
@@ -63,18 +63,9 @@ LL |         match map.get() {
 LL |             Some(v) => {
 LL |                 map.set(String::new()); // Both AST and MIR error here
    |                 ^^^ mutable borrow occurs here
-   |
-note: borrowed value must be valid for the anonymous lifetime #1 defined on the function body at 41:1...
-  --> $DIR/get_default.rs:41:1
-   |
-LL | / fn err(map: &mut Map) -> &String {
-LL | |     loop {
-LL | |         match map.get() {
-LL | |             Some(v) => {
-...  |
-LL | |     }
-LL | | }
-   | |_^
+...
+LL |                 return v;
+   |                        - borrow later used here
 
 error[E0502]: cannot borrow `*map` as mutable because it is also borrowed as immutable (Mir)
   --> $DIR/get_default.rs:51:17
diff --git a/src/test/ui/nll/return-ref-mut-issue-46557.stderr b/src/test/ui/nll/return-ref-mut-issue-46557.stderr
index f441085f242..f40e38c63f5 100644
--- a/src/test/ui/nll/return-ref-mut-issue-46557.stderr
+++ b/src/test/ui/nll/return-ref-mut-issue-46557.stderr
@@ -1,13 +1,16 @@
 error[E0597]: borrowed value does not live long enough
   --> $DIR/return-ref-mut-issue-46557.rs:17:21
    |
-LL |     let ref mut x = 1234543; //~ ERROR borrowed value does not live long enough [E0597]
-   |                     ^^^^^^^ temporary value does not live long enough
-LL |     x
-LL | }
-   | - temporary value only lives until here
-   |
-   = note: borrowed value must be valid for the static lifetime...
+LL |   fn gimme_static_mut() -> &'static mut u32 {
+   |  ___________________________________________-
+LL | |     let ref mut x = 1234543; //~ ERROR borrowed value does not live long enough [E0597]
+   | |                     ^^^^^^^ temporary value does not live long enough
+LL | |     x
+LL | | }
+   | | -
+   | | |
+   | |_temporary value only lives until here
+   |   borrow later used here
 
 error: aborting due to previous error