Rollup merge of rust-lang#61554 - spastorino:change_visit_api, r=oli-obk

Change visit api

r? @oli-obk

In the [first commit](rust-lang@37386d3) of this PR, I'm changing `visit_place` to be the function that traverses the `Place` and have only that responsibility. Then there are two other functions `visit_place_base` and `visit_projection` which are the ones in charge of visiting the base and the projection. Visitor implementors can implement any of those.

In the [second commit](rust-lang@e786f63) we can already see some things that confuses me, which I think this division will make more clear. The old code, first checked if the place was a base, did something with it and then called `super_place` [here](rust-lang@e786f63#diff-d583e4efe1a72516e274158e53223633L678). `super_place` checks again if it's a base [here](https://github.com/rust-lang/rust/blob/master/src/librustc/mir/visit.rs#L679-L684) and in case is a local, visits the local and stuff like that. That's not very obvious on the code, and if I'm not wrong it's not needed. In this PR or we have [this](rust-lang@e786f63#diff-d583e4efe1a72516e274158e53223633R673) as I did or we can just do `- => self.super_place_base(...)` and that will be obvious that I'm letting the default implementation process the base.

src/librustc/mir/visit.rs

@@ -151,17 +151,17 @@ macro_rules! make_mir_visitor {
                 self.super_place(place, context, location);
             }
 
-            fn visit_projection(&mut self,
-                                place: & $($mutability)? Projection<'tcx>,
+            fn visit_place_base(&mut self,
+                                place_base: & $($mutability)? PlaceBase<'tcx>,
                                 context: PlaceContext,
                                 location: Location) {
-                self.super_projection(place, context, location);
+                self.super_place_base(place_base, context, location);
             }
 
-            fn visit_projection_elem(&mut self,
-                                     place: & $($mutability)? PlaceElem<'tcx>,
-                                     location: Location) {
-                self.super_projection_elem(place, location);
+            fn visit_projection(&mut self,
+                                place: & $($mutability)? Projection<'tcx>,
+                                location: Location) {
+                self.super_projection(place, location);
             }
 
             fn visit_constant(&mut self,
@@ -676,36 +676,40 @@ macro_rules! make_mir_visitor {
                             context: PlaceContext,
                             location: Location) {
                 match place {
-                    Place::Base(PlaceBase::Local(local)) => {
-                        self.visit_local(local, context, location);
-                    }
-                    Place::Base(PlaceBase::Static(box Static { kind: _, ty })) => {
-                        self.visit_ty(& $($mutability)? *ty, TyContext::Location(location));
+                    Place::Base(place_base) => {
+                        self.visit_place_base(place_base, context, location);
                     }
                     Place::Projection(proj) => {
-                        self.visit_projection(proj, context, location);
+                        let context = if context.is_mutating_use() {
+                            PlaceContext::MutatingUse(MutatingUseContext::Projection)
+                        } else {
+                            PlaceContext::NonMutatingUse(NonMutatingUseContext::Projection)
+                        };
+
+                        self.visit_place(& $($mutability)? proj.base, context, location);
+                        self.visit_projection(proj, location);
                     }
                 }
             }
 
-            fn super_projection(&mut self,
-                                proj: & $($mutability)? Projection<'tcx>,
+            fn super_place_base(&mut self,
+                                place_base: & $($mutability)? PlaceBase<'tcx>,
                                 context: PlaceContext,
                                 location: Location) {
-                let Projection { base, elem } = proj;
-                let context = if context.is_mutating_use() {
-                    PlaceContext::MutatingUse(MutatingUseContext::Projection)
-                } else {
-                    PlaceContext::NonMutatingUse(NonMutatingUseContext::Projection)
-                };
-                self.visit_place(base, context, location);
-                self.visit_projection_elem(elem, location);
+                match place_base {
+                    PlaceBase::Local(local) => {
+                        self.visit_local(local, context, location);
+                    }
+                    PlaceBase::Static(box Static { kind: _, ty }) => {
+                        self.visit_ty(& $($mutability)? *ty, TyContext::Location(location));
+                    }
+                }
             }
 
-            fn super_projection_elem(&mut self,
-                                     proj: & $($mutability)? PlaceElem<'tcx>,
-                                     location: Location) {
-                match proj {
+            fn super_projection(&mut self,
+                                proj: & $($mutability)? Projection<'tcx>,
+                                location: Location) {
+                match & $($mutability)? proj.elem {
                     ProjectionElem::Deref => {
                     }
                     ProjectionElem::Subslice { from: _, to: _ } => {

src/librustc_mir/monomorphize/collector.rs

@@ -185,7 +185,7 @@ use rustc::ty::{self, TypeFoldable, Ty, TyCtxt, GenericParamDefKind, Instance};
 use rustc::ty::print::obsolete::DefPathBasedNames;
 use rustc::ty::adjustment::{CustomCoerceUnsized, PointerCast};
 use rustc::session::config::EntryFnType;
-use rustc::mir::{self, Location, Place, PlaceBase, Promoted, Static, StaticKind};
+use rustc::mir::{self, Location, PlaceBase, Promoted, Static, StaticKind};
 use rustc::mir::visit::Visitor as MirVisitor;
 use rustc::mir::mono::{MonoItem, InstantiationMode};
 use rustc::mir::interpret::{Scalar, GlobalId, GlobalAlloc, ErrorHandled};
@@ -655,14 +655,12 @@ impl<'a, 'tcx> MirVisitor<'tcx> for MirNeighborCollector<'a, 'tcx> {
         self.super_terminator_kind(kind, location);
     }
 
-    fn visit_place(&mut self,
-                    place: &mir::Place<'tcx>,
-                    context: mir::visit::PlaceContext,
-                    location: Location) {
-        match place {
-            Place::Base(
-                PlaceBase::Static(box Static{ kind:StaticKind::Static(def_id), .. })
-            ) => {
+    fn visit_place_base(&mut self,
+                        place_base: &mir::PlaceBase<'tcx>,
+                        _context: mir::visit::PlaceContext,
+                        location: Location) {
+        match place_base {
+            PlaceBase::Static(box Static { kind: StaticKind::Static(def_id), .. }) => {
                 debug!("visiting static {:?} @ {:?}", def_id, location);
 
                 let tcx = self.tcx;
@@ -671,10 +669,13 @@ impl<'a, 'tcx> MirVisitor<'tcx> for MirNeighborCollector<'a, 'tcx> {
                     self.output.push(MonoItem::Static(*def_id));
                 }
             }
-            _ => {}
+            PlaceBase::Static(box Static { kind: StaticKind::Promoted(_), .. }) => {
+                // FIXME: should we handle promoteds here instead of eagerly in collect_neighbours?
+            }
+            PlaceBase::Local(_) => {
+                // Locals have no relevance for collector
+            }
         }
-
-        self.super_place(place, context, location);
     }
 }