add test for #107228

Fixes #107228

tests/ui/specialization/broken-mir-drop-glue-107228.rs

@@ -0,0 +1,28 @@
+// issue: rust-lang/rust#107228
+// ICE broken MIR in DropGlue
+//@ compile-flags: -Zvalidate-mir
+//@ check-pass
+
+#![feature(specialization)]
+#![crate_type="lib"]
+#![allow(incomplete_features)]
+
+pub(crate) trait SpecTrait {
+    type Assoc;
+}
+
+impl<C> SpecTrait for C {
+    default type Assoc = Vec<Self>;
+}
+
+pub(crate) struct AssocWrap<C: SpecTrait> {
+    _assoc: C::Assoc,
+}
+
+fn instantiate<C: SpecTrait>() -> AssocWrap<C> {
+    loop {}
+}
+
+pub fn main() {
+    instantiate::<()>();
+}