refactoring: move replace_base utility function to root of rustc_mir_transform crate.

incorporated review feedback: simplify replace_base via Place::project_deeper

Author: pnkfelix

compiler/rustc_mir_transform/src/generator.rs

@@ -182,14 +182,7 @@ impl<'tcx> MutVisitor<'tcx> for PinArgVisitor<'tcx> {
     }
 }
 
-fn replace_base<'tcx>(place: &mut Place<'tcx>, new_base: Place<'tcx>, tcx: TyCtxt<'tcx>) {
-    place.local = new_base.local;
-
-    let mut new_projection = new_base.projection.to_vec();
-    new_projection.append(&mut place.projection.to_vec());
-
-    place.projection = tcx.mk_place_elems(&new_projection);
-}
+use crate::replace_base;
 
 const SELF_ARG: Local = Local::from_u32(1);
 

compiler/rustc_mir_transform/src/lib.rs

@@ -626,3 +626,7 @@ fn promoted_mir(tcx: TyCtxt<'_>, def: LocalDefId) -> &IndexVec<Promoted, Body<'_
 
     tcx.arena.alloc(promoted)
 }
+
+fn replace_base<'tcx>(place: &mut Place<'tcx>, new_base: Place<'tcx>, tcx: TyCtxt<'tcx>) {
+    *place = new_base.project_deeper(&place.projection[..], tcx)
+}