use TypingEnv when no infcx is available

the behavior of the type system not only depends on the current
assumptions, but also the currentnphase of the compiler. This is
mostly necessary as we need to decide whether and how to reveal
opaque types. We track this via the `TypingMode`.

compiler/rustc_mir_transform/src/jump_threading.rs

@@ -77,13 +77,12 @@ impl<'tcx> crate::MirPass<'tcx> for JumpThreading {
             return;
         }
 
-        let param_env = tcx.param_env_reveal_all_normalized(def_id);
-
+        let typing_env = body.typing_env(tcx);
         let arena = &DroplessArena::default();
         let mut finder = TOFinder {
             tcx,
-            param_env,
-            ecx: InterpCx::new(tcx, DUMMY_SP, param_env, DummyMachine),
+            typing_env,
+            ecx: InterpCx::new(tcx, DUMMY_SP, typing_env.param_env, DummyMachine),
             body,
             arena,
             map: Map::new(tcx, body, Some(MAX_PLACES)),
@@ -119,7 +118,7 @@ struct ThreadingOpportunity {
 
 struct TOFinder<'a, 'tcx> {
     tcx: TyCtxt<'tcx>,
-    param_env: ty::ParamEnv<'tcx>,
+    typing_env: ty::TypingEnv<'tcx>,
     ecx: InterpCx<'tcx, DummyMachine>,
     body: &'a Body<'tcx>,
     map: Map<'tcx>,
@@ -207,7 +206,7 @@ impl<'a, 'tcx> TOFinder<'a, 'tcx> {
         let Some(discr) = self.map.find(discr.as_ref()) else { return };
         debug!(?discr);
 
-        let cost = CostChecker::new(self.tcx, self.param_env, None, self.body);
+        let cost = CostChecker::new(self.tcx, self.typing_env, None, self.body);
         let mut state = State::new_reachable();
 
         let conds = if let Some((value, then, else_)) = targets.as_static_if() {
@@ -528,7 +527,8 @@ impl<'a, 'tcx> TOFinder<'a, 'tcx> {
                     // Avoid handling them, though this could be extended in the future.
                     return;
                 }
-                let Some(value) = value.const_.try_eval_scalar_int(self.tcx, self.param_env) else {
+                let Some(value) = value.const_.try_eval_scalar_int(self.tcx, self.typing_env)
+                else {
                     return;
                 };
                 let conds = conditions.map(self.arena, |c| Condition {