Use ensure for thir_abstract_const.

Author: cjgillot

compiler/rustc_mir_build/src/build/mod.rs

@@ -48,17 +48,14 @@ pub(crate) fn mir_built(
 /// Construct the MIR for a given `DefId`.
 fn mir_build(tcx: TyCtxt<'_>, def: ty::WithOptConstParam<LocalDefId>) -> Body<'_> {
     // Ensure unsafeck and abstract const building is ran before we steal the THIR.
-    // We can't use `ensure()` for `thir_abstract_const` as it doesn't compute the query
-    // if inputs are green. This can cause ICEs when calling `thir_abstract_const` after
-    // THIR has been stolen if we haven't computed this query yet.
     match def {
         ty::WithOptConstParam { did, const_param_did: Some(const_param_did) } => {
             tcx.ensure().thir_check_unsafety_for_const_arg((did, const_param_did));
-            drop(tcx.thir_abstract_const_of_const_arg((did, const_param_did)));
+            tcx.ensure().thir_abstract_const_of_const_arg((did, const_param_did));
         }
         ty::WithOptConstParam { did, const_param_did: None } => {
             tcx.ensure().thir_check_unsafety(did);
-            drop(tcx.thir_abstract_const(did));
+            tcx.ensure().thir_abstract_const(did);
         }
     }