Auto merge of #123572 - Mark-Simulacrum:vtable-methods, r=oli-obk

Increase vtable layout size

This improves LLVM's codegen by allowing vtable loads to be hoisted out of loops (as just one example). The calculation here is an under-approximation but works for simple trait hierarchies (e.g., FnMut will be improved). We have a runtime assert that the approximation is accurate, so there's no risk of UB as a result of getting this wrong.

```rust
#[no_mangle]
pub fn foo(elements: &[u32], callback: &mut dyn Callback) {
    for element in elements.iter() {
        if *element != 0 {
            callback.call(*element);
        }
    }
}

pub trait Callback {
    fn call(&mut self, _: u32);
}
```

Simplifying a bit (e.g., numbering ends up different):

```diff
 ; Function Attrs: nonlazybind uwtable
-define void `@foo(ptr` noalias noundef nonnull readonly align 4 %elements.0, i64 noundef %elements.1, ptr noundef nonnull align 1 %callback.0, ptr noalias nocapture noundef readonly align 8 dereferenceable(24) %callback.1) unnamed_addr #0 {
+define void `@foo(ptr` noalias noundef nonnull readonly align 4 %elements.0, i64 noundef %elements.1, ptr noundef nonnull align 1 %callback.0, ptr noalias nocapture noundef readonly align 8 dereferenceable(32) %callback.1) unnamed_addr #0 {
 start:
   %_15 = getelementptr inbounds i32, ptr %elements.0, i64 %elements.1
`@@` -13,4 +13,5 `@@`
 bb4.lr.ph:                                        ; preds = %start
   %1 = getelementptr inbounds i8, ptr %callback.1, i64 24
+  %2 = load ptr, ptr %1, align 8, !nonnull !3
   br label %bb4

 bb6:                                              ; preds = %bb4
-  %4 = load ptr, ptr %1, align 8, !invariant.load !3, !nonnull !3
-  tail call void %4(ptr noundef nonnull align 1 %callback.0, i32 noundef %_9)
+  tail call void %2(ptr noundef nonnull align 1 %callback.0, i32 noundef %_9)
   br label %bb7
 }
```

Author: bors

clippy_lints/src/len_zero.rs

@@ -253,7 +253,7 @@ fn check_trait_items(cx: &LateContext<'_>, visited_trait: &Item<'_>, trait_items
     // fill the set with current and super traits
     fn fill_trait_set(traitt: DefId, set: &mut DefIdSet, cx: &LateContext<'_>) {
         if set.insert(traitt) {
-            for supertrait in rustc_trait_selection::traits::supertrait_def_ids(cx.tcx, traitt) {
+            for supertrait in cx.tcx.supertrait_def_ids(traitt) {
                 fill_trait_set(supertrait, set, cx);
             }
         }