use question mark operator in a few places.

src/libcore/iter/adapters/mod.rs

@@ -1894,9 +1894,7 @@ where
             let to_skip = self.n;
             self.n = 0;
             // nth(n) skips n+1
-            if self.iter.nth(to_skip - 1).is_none() {
-                return None;
-            }
+            self.iter.nth(to_skip - 1)?;
         }
         self.iter.nth(n)
     }
@@ -1916,9 +1914,7 @@ where
     fn last(mut self) -> Option<I::Item> {
         if self.n > 0 {
             // nth(n) skips n+1
-            if self.iter.nth(self.n - 1).is_none() {
-                return None;
-            }
+            self.iter.nth(self.n - 1)?;
         }
         self.iter.last()
     }

src/librustc/hir/map/mod.rs

@@ -338,9 +338,8 @@ impl<'hir> Map<'hir> {
             Node::Variant(_) => DefKind::Variant,
             Node::Ctor(variant_data) => {
                 // FIXME(eddyb) is this even possible, if we have a `Node::Ctor`?
-                if variant_data.ctor_hir_id().is_none() {
-                    return None;
-                }
+                variant_data.ctor_hir_id()?;
+
                 let ctor_of = match self.find(self.get_parent_node(hir_id)) {
                     Some(Node::Item(..)) => def::CtorOf::Struct,
                     Some(Node::Variant(..)) => def::CtorOf::Variant,

src/librustc/ty/instance.rs

@@ -115,9 +115,7 @@ impl<'tcx> Instance<'tcx> {
         }
 
         // If this a non-generic instance, it cannot be a shared monomorphization.
-        if self.substs.non_erasable_generics().next().is_none() {
-            return None;
-        }
+        self.substs.non_erasable_generics().next()?;
 
         match self.def {
             InstanceDef::Item(def_id) => tcx

src/librustc_incremental/persist/work_product.rs

@@ -13,9 +13,7 @@ pub fn copy_cgu_workproducts_to_incr_comp_cache_dir(
     files: &[(WorkProductFileKind, PathBuf)],
 ) -> Option<(WorkProductId, WorkProduct)> {
     debug!("copy_cgu_workproducts_to_incr_comp_cache_dir({:?},{:?})", cgu_name, files);
-    if sess.opts.incremental.is_none() {
-        return None;
-    }
+    sess.opts.incremental.as_ref()?;
 
     let saved_files = files
         .iter()