Get !nonnull metadata consistently in slice iterators, without needing assumes

tests/codegen/slice-iter-nonnull.rs

@@ -2,11 +2,16 @@
 // compile-flags: -O
 // ignore-debug (these add extra checks that make it hard to verify)
 #![crate_type = "lib"]
+#![feature(exact_size_is_empty)]
 
 // The slice iterator used to `assume` that the `start` pointer was non-null.
 // That ought to be unneeded, though, since the type is `NonNull`, so this test
 // confirms that the appropriate metadata is included to denote that.
 
+// It also used to `assume` the `end` pointer was non-null, but that's no longer
+// needed as the code changed to read it as a `NonNull`, and thus gets the
+// appropriate `!nonnull` annotations naturally.
+
 // CHECK-LABEL: @slice_iter_next(
 #[no_mangle]
 pub fn slice_iter_next<'a>(it: &mut std::slice::Iter<'a, u32>) -> Option<&'a u32> {
@@ -75,3 +80,37 @@ pub fn slice_iter_mut_new(slice: &mut [u32]) -> std::slice::IterMut<'_, u32> {
     // CHECK: }
     slice.iter_mut()
 }
+
+// CHECK-LABEL: @slice_iter_is_empty
+#[no_mangle]
+pub fn slice_iter_is_empty(it: &std::slice::Iter<'_, u32>) -> bool {
+    // CHECK: %[[ENDP:.+]] = getelementptr{{.+}}ptr %it,{{.+}} 1
+    // CHECK: %[[END:.+]] = load ptr, ptr %[[ENDP]]
+    // CHECK-SAME: !nonnull
+    // CHECK-SAME: !noundef
+    // CHECK: %[[START:.+]] = load ptr, ptr %it,
+    // CHECK-SAME: !nonnull
+    // CHECK-SAME: !noundef
+
+    // CHECK: %[[RET:.+]] = icmp eq ptr %[[START]], %[[END]]
+    // CHECK: ret i1 %[[RET]]
+    it.is_empty()
+}
+
+// CHECK-LABEL: @slice_iter_len
+#[no_mangle]
+pub fn slice_iter_len(it: &std::slice::Iter<'_, u32>) -> usize {
+    // CHECK: %[[START:.+]] = load ptr, ptr %it,
+    // CHECK-SAME: !nonnull
+    // CHECK-SAME: !noundef
+    // CHECK: %[[ENDP:.+]] = getelementptr{{.+}}ptr %it,{{.+}} 1
+    // CHECK: %[[END:.+]] = load ptr, ptr %[[ENDP]]
+    // CHECK-SAME: !nonnull
+    // CHECK-SAME: !noundef
+
+    // CHECK: ptrtoint
+    // CHECK: ptrtoint
+    // CHECK: sub nuw
+    // CHECK: lshr exact
+    it.len()
+}