Cursed gvn type_id test

Author: oli-obk

tests/mir-opt/gvn_type_id_polymorphic.rs

@@ -6,7 +6,20 @@
 fn generic<T>() {}
 
 const fn type_id_of_val<T: 'static>(_: &T) -> u128 {
-    std::intrinsics::type_id::<T>()
+    let name = std::intrinsics::type_name::<T>();
+    let len = name.len() as u64;
+    let len = u64::to_be_bytes(len);
+    let mut ret = [0; 16];
+    let mut i = 0;
+    while i < 8 {
+        ret[i] = len[i];
+        i += 1;
+    }
+    while i < 16 {
+        ret[i] = name.as_bytes()[i - 8];
+        i += 1;
+    }
+    u128::from_be_bytes(ret)
 }
 
 // EMIT_MIR gvn_type_id_polymorphic.cursed_is_i32.GVN.diff