librustc_mir: don't allocate vectors where slices will do.

Author: matthiaskrgr

src/librustc_mir/transform/generator.rs

@@ -117,7 +117,7 @@ impl<'tcx> MutVisitor<'tcx> for DerefArgVisitor<'tcx> {
                 place,
                 Place {
                     local: self_arg(),
-                    projection: self.tcx().intern_place_elems(&vec![ProjectionElem::Deref]),
+                    projection: self.tcx().intern_place_elems(&[ProjectionElem::Deref]),
                 },
                 self.tcx,
             );
@@ -153,7 +153,7 @@ impl<'tcx> MutVisitor<'tcx> for PinArgVisitor<'tcx> {
                 place,
                 Place {
                     local: self_arg(),
-                    projection: self.tcx().intern_place_elems(&vec![ProjectionElem::Field(
+                    projection: self.tcx().intern_place_elems(&[ProjectionElem::Field(
                         Field::new(0),
                         self.ref_gen_ty,
                     )]),

src/librustc_mir/transform/instcombine.rs

@@ -51,7 +51,7 @@ impl<'tcx> MutVisitor<'tcx> for InstCombineVisitor<'tcx> {
             let new_place = match rvalue {
                 Rvalue::Ref(_, _, place) => {
                     if let &[ref proj_l @ .., proj_r] = place.projection.as_ref() {
-                        place.projection = self.tcx().intern_place_elems(&vec![proj_r.clone()]);
+                        place.projection = self.tcx().intern_place_elems(&[proj_r.clone()]);
 
                         Place {
                             // Replace with dummy