Auto merge of #53327 - wesleywiser:wip_optimize_nll, r=nikomatsakis

[nll] teach SCC about `'static`

r? @nikomatsakis

I think this is right? I am seeing better performance on the `html5ever` benchmark but I'd like a perf run to quantify the exact speedup. There's a few ui tests failing due to changes in the error messages. The main issue seems to be that returns aren't being detected correctly?

`mir_check_cast_unsize.rs` before:

```
error: unsatisfied lifetime constraints
  --> mir_check_cast_unsize.rs:17:46
   |
17 |   fn bar<'a>(x: &'a u32) -> &'static dyn Debug {
   |  ________--____________________________________^
   | |        |
   | |        lifetime `'a` defined here
18 | |     //~^ ERROR unsatisfied lifetime constraints
19 | |     x
20 | |     //~^ WARNING not reporting region error due to nll
21 | | }
   | |_^ return requires that `'a` must outlive `'static`
```

`mir_check_cast_unsize.rs` after:

```
error: unsatisfied lifetime constraints
  --> mir_check_cast_unsize.rs:19:5
   |
17 | fn bar<'a>(x: &'a u32) -> &'static dyn Debug {
   |        -- lifetime `'a` defined here
18 |     //~^ ERROR unsatisfied lifetime constraints
19 |     x
   |     ^ cast requires that `'a` must outlive `'static`
```

src/librustc/middle/resolve_lifetime.rs

@@ -2567,6 +2567,13 @@ fn insert_late_bound_lifetimes(
     // - do not appear in the where-clauses
     // - are not implicitly captured by `impl Trait`
     for param in &generics.params {
+        match param.kind {
+            hir::GenericParamKind::Lifetime { .. } => { /* fall through */ }
+
+            // Types are not late-bound.
+            hir::GenericParamKind::Type { .. } => continue,
+        }
+
         let lt_name = hir::LifetimeName::Param(param.name.modern());
         // appears in the where clauses? early-bound.
         if appears_in_where_clause.regions.contains(&lt_name) {

src/librustc_mir/borrow_check/nll/constraints/graph.rs

@@ -8,6 +8,7 @@
 // option. This file may not be copied, modified, or distributed
 // except according to those terms.
 
+use borrow_check::nll::type_check::Locations;
 use borrow_check::nll::constraints::{ConstraintIndex, ConstraintSet, OutlivesConstraint};
 use rustc::ty::RegionVid;
 use rustc_data_structures::graph;
@@ -31,6 +32,7 @@ crate type ReverseConstraintGraph = ConstraintGraph<Reverse>;
 crate trait ConstraintGraphDirecton: Copy + 'static {
     fn start_region(c: &OutlivesConstraint) -> RegionVid;
     fn end_region(c: &OutlivesConstraint) -> RegionVid;
+    fn is_normal() -> bool;
 }
 
 /// In normal mode, a `R1: R2` constraint results in an edge `R1 ->
@@ -48,6 +50,10 @@ impl ConstraintGraphDirecton for Normal {
     fn end_region(c: &OutlivesConstraint) -> RegionVid {
         c.sub
     }
+
+    fn is_normal() -> bool {
+        true
+    }
 }
 
 /// In reverse mode, a `R1: R2` constraint results in an edge `R2 ->
@@ -65,6 +71,10 @@ impl ConstraintGraphDirecton for Reverse {
     fn end_region(c: &OutlivesConstraint) -> RegionVid {
         c.sup
     }
+
+    fn is_normal() -> bool {
+        false
+    }
 }
 
 impl<D: ConstraintGraphDirecton> ConstraintGraph<D> {
@@ -98,32 +108,74 @@ impl<D: ConstraintGraphDirecton> ConstraintGraph<D> {
     /// Given the constraint set from which this graph was built
     /// creates a region graph so that you can iterate over *regions*
     /// and not constraints.
-    crate fn region_graph<'rg>(&'rg self, set: &'rg ConstraintSet) -> RegionGraph<'rg, D> {
-        RegionGraph::new(set, self)
+    crate fn region_graph<'rg>(
+        &'rg self,
+        set: &'rg ConstraintSet,
+        static_region: RegionVid,
+    ) -> RegionGraph<'rg, D> {
+        RegionGraph::new(set, self, static_region)
     }
 
     /// Given a region `R`, iterate over all constraints `R: R1`.
-    crate fn outgoing_edges(&self, region_sup: RegionVid) -> Edges<'_, D> {
-        let first = self.first_constraints[region_sup];
-        Edges {
-            graph: self,
-            pointer: first,
+    crate fn outgoing_edges<'a>(
+        &'a self,
+        region_sup: RegionVid,
+        constraints: &'a ConstraintSet,
+        static_region: RegionVid,
+    ) -> Edges<'a, D> {
+        //if this is the `'static` region and the graph's direction is normal,
+        //then setup the Edges iterator to return all regions #53178
+        if region_sup == static_region && D::is_normal() {
+            Edges {
+                graph: self,
+                constraints,
+                pointer: None,
+                next_static_idx: Some(0),
+                static_region,
+            }
+        } else {
+            //otherwise, just setup the iterator as normal
+            let first = self.first_constraints[region_sup];
+            Edges {
+                graph: self,
+                constraints,
+                pointer: first,
+                next_static_idx: None,
+                static_region,
+           }
         }
     }
 }
 
 crate struct Edges<'s, D: ConstraintGraphDirecton> {
     graph: &'s ConstraintGraph<D>,
+    constraints: &'s ConstraintSet,
     pointer: Option<ConstraintIndex>,
+    next_static_idx: Option<usize>,
+    static_region: RegionVid,
 }
 
 impl<'s, D: ConstraintGraphDirecton> Iterator for Edges<'s, D> {
-    type Item = ConstraintIndex;
+    type Item = OutlivesConstraint;
 
     fn next(&mut self) -> Option<Self::Item> {
         if let Some(p) = self.pointer {
             self.pointer = self.graph.next_constraints[p];
-            Some(p)
+
+            Some(self.constraints[p])
+        } else if let Some(next_static_idx) = self.next_static_idx {
+            self.next_static_idx =
+                if next_static_idx == (self.graph.first_constraints.len() - 1) {
+                    None
+                } else {
+                    Some(next_static_idx + 1)
+                };
+
+            Some(OutlivesConstraint {
+                sup: self.static_region,
+                sub: next_static_idx.into(),
+                locations: Locations::All,
+            })
         } else {
             None
         }
@@ -136,40 +188,44 @@ impl<'s, D: ConstraintGraphDirecton> Iterator for Edges<'s, D> {
 crate struct RegionGraph<'s, D: ConstraintGraphDirecton> {
     set: &'s ConstraintSet,
     constraint_graph: &'s ConstraintGraph<D>,
+    static_region: RegionVid,
 }
 
 impl<'s, D: ConstraintGraphDirecton> RegionGraph<'s, D> {
     /// Create a "dependency graph" where each region constraint `R1:
     /// R2` is treated as an edge `R1 -> R2`. We use this graph to
     /// construct SCCs for region inference but also for error
     /// reporting.
-    crate fn new(set: &'s ConstraintSet, constraint_graph: &'s ConstraintGraph<D>) -> Self {
+    crate fn new(
+        set: &'s ConstraintSet,
+        constraint_graph: &'s ConstraintGraph<D>,
+        static_region: RegionVid,
+    ) -> Self {
         Self {
             set,
             constraint_graph,
+            static_region,
         }
     }
 
     /// Given a region `R`, iterate over all regions `R1` such that
     /// there exists a constraint `R: R1`.
     crate fn outgoing_regions(&self, region_sup: RegionVid) -> Successors<'_, D> {
         Successors {
-            set: self.set,
-            edges: self.constraint_graph.outgoing_edges(region_sup),
+            edges: self.constraint_graph.outgoing_edges(region_sup, self.set, self.static_region),
         }
     }
 }
 
 crate struct Successors<'s, D: ConstraintGraphDirecton> {
-    set: &'s ConstraintSet,
     edges: Edges<'s, D>,
 }
 
 impl<'s, D: ConstraintGraphDirecton> Iterator for Successors<'s, D> {
     type Item = RegionVid;
 
     fn next(&mut self) -> Option<Self::Item> {
-        self.edges.next().map(|c| D::end_region(&self.set[c]))
+        self.edges.next().map(|c| D::end_region(&c))
     }
 }
 

src/librustc_mir/borrow_check/nll/constraints/mod.rs

@@ -58,8 +58,9 @@ impl ConstraintSet {
     crate fn compute_sccs(
         &self,
         constraint_graph: &graph::NormalConstraintGraph,
+        static_region: RegionVid,
     ) -> Sccs<RegionVid, ConstraintSccIndex> {
-        let region_graph = &constraint_graph.region_graph(self);
+        let region_graph = &constraint_graph.region_graph(self, static_region);
         Sccs::new(region_graph)
     }
 }

src/librustc_mir/borrow_check/nll/region_infer/error_reporting/mod.rs

@@ -8,7 +8,8 @@
 // option. This file may not be copied, modified, or distributed
 // except according to those terms.
 
-use borrow_check::nll::region_infer::{ConstraintIndex, RegionInferenceContext};
+use borrow_check::nll::constraints::OutlivesConstraint;
+use borrow_check::nll::region_infer::RegionInferenceContext;
 use borrow_check::nll::type_check::Locations;
 use rustc::hir::def_id::DefId;
 use rustc::infer::error_reporting::nice_region_error::NiceRegionError;
@@ -53,7 +54,7 @@ impl fmt::Display for ConstraintCategory {
 #[derive(Copy, Clone, PartialEq, Eq)]
 enum Trace {
     StartRegion,
-    FromConstraint(ConstraintIndex),
+    FromOutlivesConstraint(OutlivesConstraint),
     NotVisited,
 }
 
@@ -80,12 +81,11 @@ impl<'tcx> RegionInferenceContext<'tcx> {
         debug!(
             "best_blame_constraint: path={:#?}",
             path.iter()
-                .map(|&ci| format!(
-                    "{:?}: {:?} ({:?}: {:?})",
-                    ci,
-                    &self.constraints[ci],
-                    self.constraint_sccs.scc(self.constraints[ci].sup),
-                    self.constraint_sccs.scc(self.constraints[ci].sub),
+                .map(|&c| format!(
+                    "{:?} ({:?}: {:?})",
+                    c,
+                    self.constraint_sccs.scc(c.sup),
+                    self.constraint_sccs.scc(c.sub),
                 ))
                 .collect::<Vec<_>>()
         );
@@ -121,7 +121,7 @@ impl<'tcx> RegionInferenceContext<'tcx> {
         // highlight (e.g., a call site or something).
         let target_scc = self.constraint_sccs.scc(target_region);
         let best_choice = (0..path.len()).rev().find(|&i| {
-            let constraint = &self.constraints[path[i]];
+            let constraint = path[i];
 
             let constraint_sup_scc = self.constraint_sccs.scc(constraint.sup);
 
@@ -164,7 +164,7 @@ impl<'tcx> RegionInferenceContext<'tcx> {
         &self,
         from_region: RegionVid,
         target_test: impl Fn(RegionVid) -> bool,
-    ) -> Option<(Vec<ConstraintIndex>, RegionVid)> {
+    ) -> Option<(Vec<OutlivesConstraint>, RegionVid)> {
         let mut context = IndexVec::from_elem(Trace::NotVisited, &self.definitions);
         context[from_region] = Trace::StartRegion;
 
@@ -185,9 +185,9 @@ impl<'tcx> RegionInferenceContext<'tcx> {
                         Trace::NotVisited => {
                             bug!("found unvisited region {:?} on path to {:?}", p, r)
                         }
-                        Trace::FromConstraint(c) => {
+                        Trace::FromOutlivesConstraint(c) => {
                             result.push(c);
-                            p = self.constraints[c].sup;
+                            p = c.sup;
                         }
 
                         Trace::StartRegion => {
@@ -201,11 +201,14 @@ impl<'tcx> RegionInferenceContext<'tcx> {
             // Otherwise, walk over the outgoing constraints and
             // enqueue any regions we find, keeping track of how we
             // reached them.
-            for constraint in self.constraint_graph.outgoing_edges(r) {
-                assert_eq!(self.constraints[constraint].sup, r);
-                let sub_region = self.constraints[constraint].sub;
+            let fr_static = self.universal_regions.fr_static;
+            for constraint in self.constraint_graph.outgoing_edges(r,
+                                                                   &self.constraints,
+                                                                   fr_static) {
+                assert_eq!(constraint.sup, r);
+                let sub_region = constraint.sub;
                 if let Trace::NotVisited = context[sub_region] {
-                    context[sub_region] = Trace::FromConstraint(constraint);
+                    context[sub_region] = Trace::FromOutlivesConstraint(constraint);
                     deque.push_back(sub_region);
                 }
             }
@@ -216,8 +219,7 @@ impl<'tcx> RegionInferenceContext<'tcx> {
 
     /// This function will return true if a constraint is interesting and false if a constraint
     /// is not. It is useful in filtering constraint paths to only interesting points.
-    fn constraint_is_interesting(&self, index: ConstraintIndex) -> bool {
-        let constraint = self.constraints[index];
+    fn constraint_is_interesting(&self, constraint: OutlivesConstraint) -> bool {
         debug!(
             "constraint_is_interesting: locations={:?} constraint={:?}",
             constraint.locations, constraint
@@ -232,19 +234,18 @@ impl<'tcx> RegionInferenceContext<'tcx> {
     /// This function classifies a constraint from a location.
     fn classify_constraint(
         &self,
-        index: ConstraintIndex,
+        constraint: OutlivesConstraint,
         mir: &Mir<'tcx>,
         tcx: TyCtxt<'_, '_, 'tcx>,
     ) -> (ConstraintCategory, Span) {
-        let constraint = self.constraints[index];
         debug!("classify_constraint: constraint={:?}", constraint);
         let span = constraint.locations.span(mir);
         let location = constraint
             .locations
             .from_location()
             .unwrap_or(Location::START);
 
-        if !self.constraint_is_interesting(index) {
+        if !self.constraint_is_interesting(constraint) {
             return (ConstraintCategory::Boring, span);
         }