Auto merge of #72494 - lcnr:predicate-cleanup, r=nikomatsakis

Pass more `Copy` types by value.

There are a lot of locations where we pass `&T where T: Copy` by reference,
which should both be slightly less performant and less readable IMO.

This PR currently consists of three fairly self contained commits:

- passes `ty::Predicate` by value and stops depending on `AsRef<ty::Predicate>`.
- changes `<&List<_>>::into_iter` to iterate over the elements by value. This would break `List`s
  of non copy types. But as the only list constructor requires `T` to be copy anyways, I think
  the improved readability is worth this potential future restriction.
- passes `mir::PlaceElem` by value. Mir currently has quite a few copy types which are passed by reference, e.g. `Local`. As I don't have a lot of experience working with MIR, I mostly did this to get some feedback from people who use MIR more frequently
- tries to reuse `ty::Predicate` in case it did not change in some places, which should hopefully
  fix the regression caused by #72055

r? @nikomatsakis for the first commit, which continues the work of #72055 and makes adding `PredicateKind::ForAll` slightly more pleasant. Feel free to reassign though

src/librustc_codegen_ssa/debuginfo/type_names.rs

@@ -48,7 +48,7 @@ pub fn push_debuginfo_type_name<'tcx>(
         }
         ty::Tuple(component_types) => {
             output.push('(');
-            for &component_type in component_types {
+            for component_type in component_types {
                 push_debuginfo_type_name(tcx, component_type.expect_ty(), true, output, visited);
                 output.push_str(", ");
             }

src/librustc_codegen_ssa/mir/analyze.rs

@@ -104,7 +104,7 @@ impl<Bx: BuilderMethods<'a, 'tcx>> LocalAnalyzer<'mir, 'a, 'tcx, Bx> {
     ) {
         let cx = self.fx.cx;
 
-        if let [proj_base @ .., elem] = place_ref.projection {
+        if let &[ref proj_base @ .., elem] = place_ref.projection {
             let mut base_context = if context.is_mutating_use() {
                 PlaceContext::MutatingUse(MutatingUseContext::Projection)
             } else {
@@ -186,7 +186,7 @@ impl<Bx: BuilderMethods<'a, 'tcx>> LocalAnalyzer<'mir, 'a, 'tcx, Bx> {
             // now that we have moved to the "slice of projections" representation.
             if let mir::ProjectionElem::Index(local) = elem {
                 self.visit_local(
-                    local,
+                    &local,
                     PlaceContext::NonMutatingUse(NonMutatingUseContext::Copy),
                     location,
                 );

src/librustc_codegen_ssa/mir/place.rs

@@ -429,7 +429,7 @@ impl<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>> FunctionCx<'a, 'tcx, Bx> {
                 self.codegen_consume(bx, mir::PlaceRef { local, projection: proj_base })
                     .deref(bx.cx())
             }
-            mir::PlaceRef { local, projection: [proj_base @ .., elem] } => {
+            mir::PlaceRef { local, projection: &[ref proj_base @ .., elem] } => {
                 // FIXME turn this recursion into iteration
                 let cg_base =
                     self.codegen_place(bx, mir::PlaceRef { local, projection: proj_base });
@@ -440,7 +440,7 @@ impl<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>> FunctionCx<'a, 'tcx, Bx> {
                         cg_base.project_field(bx, field.index())
                     }
                     mir::ProjectionElem::Index(index) => {
-                        let index = &mir::Operand::Copy(mir::Place::from(*index));
+                        let index = &mir::Operand::Copy(mir::Place::from(index));
                         let index = self.codegen_operand(bx, index);
                         let llindex = index.immediate();
                         cg_base.project_index(bx, llindex)
@@ -450,22 +450,22 @@ impl<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>> FunctionCx<'a, 'tcx, Bx> {
                         from_end: false,
                         min_length: _,
                     } => {
-                        let lloffset = bx.cx().const_usize(*offset as u64);
+                        let lloffset = bx.cx().const_usize(offset as u64);
                         cg_base.project_index(bx, lloffset)
                     }
                     mir::ProjectionElem::ConstantIndex {
                         offset,
                         from_end: true,
                         min_length: _,
                     } => {
-                        let lloffset = bx.cx().const_usize(*offset as u64);
+                        let lloffset = bx.cx().const_usize(offset as u64);
                         let lllen = cg_base.len(bx.cx());
                         let llindex = bx.sub(lllen, lloffset);
                         cg_base.project_index(bx, llindex)
                     }
                     mir::ProjectionElem::Subslice { from, to, from_end } => {
                         let mut subslice =
-                            cg_base.project_index(bx, bx.cx().const_usize(*from as u64));
+                            cg_base.project_index(bx, bx.cx().const_usize(from as u64));
                         let projected_ty =
                             PlaceTy::from_ty(cg_base.layout.ty).projection_ty(tcx, elem).ty;
                         subslice.layout = bx.cx().layout_of(self.monomorphize(&projected_ty));
@@ -474,7 +474,7 @@ impl<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>> FunctionCx<'a, 'tcx, Bx> {
                             assert!(from_end, "slice subslices should be `from_end`");
                             subslice.llextra = Some(bx.sub(
                                 cg_base.llextra.unwrap(),
-                                bx.cx().const_usize((*from as u64) + (*to as u64)),
+                                bx.cx().const_usize((from as u64) + (to as u64)),
                             ));
                         }
 
@@ -487,7 +487,7 @@ impl<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>> FunctionCx<'a, 'tcx, Bx> {
 
                         subslice
                     }
-                    mir::ProjectionElem::Downcast(_, v) => cg_base.project_downcast(bx, *v),
+                    mir::ProjectionElem::Downcast(_, v) => cg_base.project_downcast(bx, v),
                 }
             }
         };

src/librustc_infer/infer/canonical/mod.rs

@@ -87,7 +87,7 @@ impl<'cx, 'tcx> InferCtxt<'cx, 'tcx> {
     ) -> CanonicalVarValues<'tcx> {
         let var_values: IndexVec<BoundVar, GenericArg<'tcx>> = variables
             .iter()
-            .map(|info| self.instantiate_canonical_var(span, *info, &universe_map))
+            .map(|info| self.instantiate_canonical_var(span, info, &universe_map))
             .collect();
 
         CanonicalVarValues { var_values }

src/librustc_infer/infer/canonical/query_response.rs

@@ -464,12 +464,12 @@ impl<'cx, 'tcx> InferCtxt<'cx, 'tcx> {
                     if info.is_existential() {
                         match opt_values[BoundVar::new(index)] {
                             Some(k) => k,
-                            None => self.instantiate_canonical_var(cause.span, *info, |u| {
+                            None => self.instantiate_canonical_var(cause.span, info, |u| {
                                 universe_map[u.as_usize()]
                             }),
                         }
                     } else {
-                        self.instantiate_canonical_var(cause.span, *info, |u| {
+                        self.instantiate_canonical_var(cause.span, info, |u| {
                             universe_map[u.as_usize()]
                         })
                     }

src/librustc_infer/infer/mod.rs

@@ -970,7 +970,7 @@ impl<'a, 'tcx> InferCtxt<'a, 'tcx> {
         &self,
         cause: &ObligationCause<'tcx>,
         param_env: ty::ParamEnv<'tcx>,
-        predicate: &ty::PolySubtypePredicate<'tcx>,
+        predicate: ty::PolySubtypePredicate<'tcx>,
     ) -> Option<InferResult<'tcx, ()>> {
         // Subtle: it's ok to skip the binder here and resolve because
         // `shallow_resolve` just ignores anything that is not a type
@@ -993,7 +993,7 @@ impl<'a, 'tcx> InferCtxt<'a, 'tcx> {
 
         Some(self.commit_if_ok(|snapshot| {
             let (ty::SubtypePredicate { a_is_expected, a, b }, placeholder_map) =
-                self.replace_bound_vars_with_placeholders(predicate);
+                self.replace_bound_vars_with_placeholders(&predicate);
 
             let ok = self.at(cause, param_env).sub_exp(a_is_expected, a, b)?;
 
@@ -1006,11 +1006,11 @@ impl<'a, 'tcx> InferCtxt<'a, 'tcx> {
     pub fn region_outlives_predicate(
         &self,
         cause: &traits::ObligationCause<'tcx>,
-        predicate: &ty::PolyRegionOutlivesPredicate<'tcx>,
+        predicate: ty::PolyRegionOutlivesPredicate<'tcx>,
     ) -> UnitResult<'tcx> {
         self.commit_if_ok(|snapshot| {
             let (ty::OutlivesPredicate(r_a, r_b), placeholder_map) =
-                self.replace_bound_vars_with_placeholders(predicate);
+                self.replace_bound_vars_with_placeholders(&predicate);
             let origin = SubregionOrigin::from_obligation_cause(cause, || {
                 RelateRegionParamBound(cause.span)
             });

src/librustc_infer/infer/outlives/verify.rs

@@ -50,7 +50,7 @@ impl<'cx, 'tcx> VerifyBoundCx<'cx, 'tcx> {
                 // for further background and discussion.
                 let mut bounds = substs
                     .iter()
-                    .filter_map(|&child| match child.unpack() {
+                    .filter_map(|child| match child.unpack() {
                         GenericArgKind::Type(ty) => Some(self.type_bound(ty)),
                         GenericArgKind::Lifetime(_) => None,
                         GenericArgKind::Const(_) => Some(self.recursive_bound(child)),
@@ -334,10 +334,10 @@ impl<'cx, 'tcx> VerifyBoundCx<'cx, 'tcx> {
     fn collect_outlives_from_predicate_list(
         &self,
         compare_ty: impl Fn(Ty<'tcx>) -> bool,
-        predicates: impl Iterator<Item = impl AsRef<ty::Predicate<'tcx>>>,
+        predicates: impl Iterator<Item = ty::Predicate<'tcx>>,
     ) -> impl Iterator<Item = ty::OutlivesPredicate<Ty<'tcx>, ty::Region<'tcx>>> {
         predicates
-            .filter_map(|p| p.as_ref().to_opt_type_outlives())
+            .filter_map(|p| p.to_opt_type_outlives())
             .filter_map(|p| p.no_bound_vars())
             .filter(move |p| compare_ty(p.0))
     }

src/librustc_infer/traits/util.rs

@@ -8,52 +8,46 @@ use rustc_span::Span;
 
 pub fn anonymize_predicate<'tcx>(
     tcx: TyCtxt<'tcx>,
-    pred: &ty::Predicate<'tcx>,
+    pred: ty::Predicate<'tcx>,
 ) -> ty::Predicate<'tcx> {
-    match pred.kind() {
+    let kind = pred.kind();
+    let new = match kind {
         &ty::PredicateKind::Trait(ref data, constness) => {
             ty::PredicateKind::Trait(tcx.anonymize_late_bound_regions(data), constness)
-                .to_predicate(tcx)
         }
 
         ty::PredicateKind::RegionOutlives(data) => {
             ty::PredicateKind::RegionOutlives(tcx.anonymize_late_bound_regions(data))
-                .to_predicate(tcx)
         }
 
         ty::PredicateKind::TypeOutlives(data) => {
             ty::PredicateKind::TypeOutlives(tcx.anonymize_late_bound_regions(data))
-                .to_predicate(tcx)
         }
 
         ty::PredicateKind::Projection(data) => {
-            ty::PredicateKind::Projection(tcx.anonymize_late_bound_regions(data)).to_predicate(tcx)
+            ty::PredicateKind::Projection(tcx.anonymize_late_bound_regions(data))
         }
 
-        &ty::PredicateKind::WellFormed(data) => {
-            ty::PredicateKind::WellFormed(data).to_predicate(tcx)
-        }
+        &ty::PredicateKind::WellFormed(data) => ty::PredicateKind::WellFormed(data),
 
-        &ty::PredicateKind::ObjectSafe(data) => {
-            ty::PredicateKind::ObjectSafe(data).to_predicate(tcx)
-        }
+        &ty::PredicateKind::ObjectSafe(data) => ty::PredicateKind::ObjectSafe(data),
 
         &ty::PredicateKind::ClosureKind(closure_def_id, closure_substs, kind) => {
-            ty::PredicateKind::ClosureKind(closure_def_id, closure_substs, kind).to_predicate(tcx)
+            ty::PredicateKind::ClosureKind(closure_def_id, closure_substs, kind)
         }
 
         ty::PredicateKind::Subtype(data) => {
-            ty::PredicateKind::Subtype(tcx.anonymize_late_bound_regions(data)).to_predicate(tcx)
+            ty::PredicateKind::Subtype(tcx.anonymize_late_bound_regions(data))
         }
 
         &ty::PredicateKind::ConstEvaluatable(def_id, substs) => {
-            ty::PredicateKind::ConstEvaluatable(def_id, substs).to_predicate(tcx)
+            ty::PredicateKind::ConstEvaluatable(def_id, substs)
         }
 
-        ty::PredicateKind::ConstEquate(c1, c2) => {
-            ty::PredicateKind::ConstEquate(c1, c2).to_predicate(tcx)
-        }
-    }
+        ty::PredicateKind::ConstEquate(c1, c2) => ty::PredicateKind::ConstEquate(c1, c2),
+    };
+
+    if new != *kind { new.to_predicate(tcx) } else { pred }
 }
 
 struct PredicateSet<'tcx> {
@@ -66,7 +60,7 @@ impl PredicateSet<'tcx> {
         Self { tcx, set: Default::default() }
     }
 
-    fn insert(&mut self, pred: &ty::Predicate<'tcx>) -> bool {
+    fn insert(&mut self, pred: ty::Predicate<'tcx>) -> bool {
         // We have to be careful here because we want
         //
         //    for<'a> Foo<&'a int>
@@ -81,10 +75,10 @@ impl PredicateSet<'tcx> {
     }
 }
 
-impl<T: AsRef<ty::Predicate<'tcx>>> Extend<T> for PredicateSet<'tcx> {
-    fn extend<I: IntoIterator<Item = T>>(&mut self, iter: I) {
+impl Extend<ty::Predicate<'tcx>> for PredicateSet<'tcx> {
+    fn extend<I: IntoIterator<Item = ty::Predicate<'tcx>>>(&mut self, iter: I) {
         for pred in iter {
-            self.insert(pred.as_ref());
+            self.insert(pred);
         }
     }
 }
@@ -132,7 +126,7 @@ pub fn elaborate_obligations<'tcx>(
     mut obligations: Vec<PredicateObligation<'tcx>>,
 ) -> Elaborator<'tcx> {
     let mut visited = PredicateSet::new(tcx);
-    obligations.retain(|obligation| visited.insert(&obligation.predicate));
+    obligations.retain(|obligation| visited.insert(obligation.predicate));
     Elaborator { stack: obligations, visited }
 }
 
@@ -172,7 +166,7 @@ impl Elaborator<'tcx> {
                 // cases. One common case is when people define
                 // `trait Sized: Sized { }` rather than `trait Sized { }`.
                 let visited = &mut self.visited;
-                let obligations = obligations.filter(|o| visited.insert(&o.predicate));
+                let obligations = obligations.filter(|o| visited.insert(o.predicate));
 
                 self.stack.extend(obligations);
             }
@@ -260,7 +254,7 @@ impl Elaborator<'tcx> {
                             }
                         })
                         .map(|predicate_kind| predicate_kind.to_predicate(tcx))
-                        .filter(|predicate| visited.insert(predicate))
+                        .filter(|&predicate| visited.insert(predicate))
                         .map(|predicate| predicate_obligation(predicate, None)),
                 );
             }

src/librustc_middle/mir/mod.rs

@@ -2077,10 +2077,10 @@ impl Debug for Place<'_> {
                 ProjectionElem::ConstantIndex { offset, min_length, from_end: true } => {
                     write!(fmt, "[-{:?} of {:?}]", offset, min_length)?;
                 }
-                ProjectionElem::Subslice { from, to, from_end: true } if *to == 0 => {
+                ProjectionElem::Subslice { from, to, from_end: true } if to == 0 => {
                     write!(fmt, "[{:?}:]", from)?;
                 }
-                ProjectionElem::Subslice { from, to, from_end: true } if *from == 0 => {
+                ProjectionElem::Subslice { from, to, from_end: true } if from == 0 => {
                     write!(fmt, "[:-{:?}]", to)?;
                 }
                 ProjectionElem::Subslice { from, to, from_end: true } => {

src/librustc_middle/mir/tcx.rs

@@ -56,8 +56,8 @@ impl<'tcx> PlaceTy<'tcx> {
     /// Convenience wrapper around `projection_ty_core` for
     /// `PlaceElem`, where we can just use the `Ty` that is already
     /// stored inline on field projection elems.
-    pub fn projection_ty(self, tcx: TyCtxt<'tcx>, elem: &PlaceElem<'tcx>) -> PlaceTy<'tcx> {
-        self.projection_ty_core(tcx, ty::ParamEnv::empty(), elem, |_, _, ty| ty)
+    pub fn projection_ty(self, tcx: TyCtxt<'tcx>, elem: PlaceElem<'tcx>) -> PlaceTy<'tcx> {
+        self.projection_ty_core(tcx, ty::ParamEnv::empty(), &elem, |_, _, ty| ty)
     }
 
     /// `place_ty.projection_ty_core(tcx, elem, |...| { ... })`
@@ -124,7 +124,7 @@ impl<'tcx> Place<'tcx> {
     {
         projection
             .iter()
-            .fold(PlaceTy::from_ty(local_decls.local_decls()[local].ty), |place_ty, elem| {
+            .fold(PlaceTy::from_ty(local_decls.local_decls()[local].ty), |place_ty, &elem| {
                 place_ty.projection_ty(tcx, elem)
             })
     }

src/librustc_middle/mir/visit.rs

@@ -903,7 +903,7 @@ macro_rules! visit_place_fns {
             let mut projection = Cow::Borrowed(projection);
 
             for i in 0..projection.len() {
-                if let Some(elem) = projection.get(i) {
+                if let Some(&elem) = projection.get(i) {
                     if let Some(elem) = self.process_projection_elem(elem, location) {
                         // This converts the borrowed projection into `Cow::Owned(_)` and returns a
                         // clone of the projection so we can mutate and reintern later.
@@ -921,19 +921,19 @@ macro_rules! visit_place_fns {
 
         fn process_projection_elem(
             &mut self,
-            elem: &PlaceElem<'tcx>,
+            elem: PlaceElem<'tcx>,
             location: Location,
         ) -> Option<PlaceElem<'tcx>> {
             match elem {
                 PlaceElem::Index(local) => {
-                    let mut new_local = *local;
+                    let mut new_local = local;
                     self.visit_local(
                         &mut new_local,
                         PlaceContext::NonMutatingUse(NonMutatingUseContext::Copy),
                         location,
                     );
 
-                    if new_local == *local { None } else { Some(PlaceElem::Index(new_local)) }
+                    if new_local == local { None } else { Some(PlaceElem::Index(new_local)) }
                 }
                 PlaceElem::Deref
                 | PlaceElem::Field(..)
@@ -959,7 +959,7 @@ macro_rules! visit_place_fns {
             &mut self,
             local: Local,
             proj_base: &[PlaceElem<'tcx>],
-            elem: &PlaceElem<'tcx>,
+            elem: PlaceElem<'tcx>,
             context: PlaceContext,
             location: Location,
         ) {
@@ -990,7 +990,7 @@ macro_rules! visit_place_fns {
             location: Location,
         ) {
             let mut cursor = projection;
-            while let [proj_base @ .., elem] = cursor {
+            while let &[ref proj_base @ .., elem] = cursor {
                 cursor = proj_base;
                 self.visit_projection_elem(local, cursor, elem, context, location);
             }
@@ -1000,7 +1000,7 @@ macro_rules! visit_place_fns {
             &mut self,
             _local: Local,
             _proj_base: &[PlaceElem<'tcx>],
-            elem: &PlaceElem<'tcx>,
+            elem: PlaceElem<'tcx>,
             _context: PlaceContext,
             location: Location,
         ) {
@@ -1010,7 +1010,7 @@ macro_rules! visit_place_fns {
                 }
                 ProjectionElem::Index(local) => {
                     self.visit_local(
-                        local,
+                        &local,
                         PlaceContext::NonMutatingUse(NonMutatingUseContext::Copy),
                         location,
                     );

src/librustc_middle/ty/flags.rs

@@ -129,7 +129,7 @@ impl FlagComputation {
             &ty::Dynamic(ref obj, r) => {
                 let mut computation = FlagComputation::new();
                 for predicate in obj.skip_binder().iter() {
-                    match *predicate {
+                    match predicate {
                         ty::ExistentialPredicate::Trait(tr) => computation.add_substs(tr.substs),
                         ty::ExistentialPredicate::Projection(p) => {
                             let mut proj_computation = FlagComputation::new();