Remove duplicated temporaries creating during box derefs elaboration

Temporaries created with `MirPatch::new_temp` will be declared after patch application. Remove manually created duplicate declarations. Removing duplicates exposes another issue. Visitor elaborates terminator twice and attempts to access new, but not yet available, local declarations. Remove duplicated call to `visit_terminator`.
rust-lang · bors · Sep 2, 2022 · Aug 1, 2022 · Aug 1, 2022 · Aug 1, 2022
commit 18a21e13b49320bc20836d5d20da82375fac2bbd
diff --git a/compiler/rustc_mir_transform/src/elaborate_box_derefs.rs b/compiler/rustc_mir_transform/src/elaborate_box_derefs.rs
@@ -70,7 +70,6 @@ impl<'tcx, 'a> MutVisitor<'tcx> for ElaborateBoxDerefVisitor<'tcx, 'a> {
                 build_ptr_tys(tcx, base_ty.boxed_ty(), self.unique_did, self.nonnull_did);
 
             let ptr_local = self.patch.new_temp(ptr_ty, source_info.span);
-            self.local_decls.push(LocalDecl::new(ptr_ty, source_info.span));
 
             self.patch.add_statement(location, StatementKind::StorageLive(ptr_local));
 
@@ -125,13 +124,6 @@ impl<'tcx> MirPass<'tcx> for ElaborateBoxDerefs {
                     index += 1;
                 }
 
-                if let Some(terminator) = terminator
-                && !matches!(terminator.kind, TerminatorKind::Yield{..})
-                {
-                    let location = Location { block, statement_index: index };
-                    visitor.visit_terminator(terminator, location);
-                }
-
                 let location = Location { block, statement_index: index };
                 match terminator {
                     // yielding into a box is handled when lowering generators