Do not visit rvalues twice.

Author: cjgillot

compiler/rustc_mir_transform/src/gvn.rs

@@ -741,7 +741,6 @@ impl<'tcx> MutVisitor<'tcx> for VnState<'_, 'tcx> {
     }
 
     fn visit_statement(&mut self, stmt: &mut Statement<'tcx>, location: Location) {
-        self.super_statement(stmt, location);
         if let StatementKind::Assign(box (_, ref mut rvalue)) = stmt.kind
             // Do not try to simplify a constant, it's already in canonical shape.
             && !matches!(rvalue, Rvalue::Use(Operand::Constant(_)))
@@ -755,6 +754,8 @@ impl<'tcx> MutVisitor<'tcx> for VnState<'_, 'tcx> {
                 *rvalue = Rvalue::Use(Operand::Copy(local.into()));
                 self.reused_locals.insert(local);
             }
+        } else {
+            self.super_statement(stmt, location);
         }
     }
 }