Streamline some inputs/output traversals.

Author: nnethercote

Diff for: compiler/rustc_middle/src/ty/flags.rs

@@ -251,8 +251,7 @@ impl FlagComputation {
             }
 
             &ty::FnPtr(sig_tys, _) => self.bound_computation(sig_tys, |computation, sig_tys| {
-                computation.add_tys(sig_tys.inputs());
-                computation.add_ty(sig_tys.output());
+                computation.add_tys(sig_tys.inputs_and_output);
             }),
         }
     }

Diff for: compiler/rustc_middle/src/ty/walk.rs

@@ -189,11 +189,9 @@ fn push_inner<'tcx>(stack: &mut TypeWalkerStack<'tcx>, parent: GenericArg<'tcx>)
                 stack.extend(args.iter().rev());
             }
             ty::Tuple(ts) => stack.extend(ts.iter().rev().map(GenericArg::from)),
-            ty::FnPtr(sig_tys, hdr) => {
-                let fn_sig = sig_tys.with(hdr);
-                stack.push(fn_sig.skip_binder().output().into());
+            ty::FnPtr(sig_tys, _hdr) => {
                 stack.extend(
-                    fn_sig.skip_binder().inputs().iter().copied().rev().map(|ty| ty.into()),
+                    sig_tys.skip_binder().inputs_and_output.iter().rev().map(|ty| ty.into()),
                 );
             }
         },