We can throw an exception but we cannot deoptimize at a runtime call.

runtime/vm/flow_graph_compiler_ia32.h

Index: runtime/vm/flow_graph_compiler_ia32.h
===================================================================
--- runtime/vm/flow_graph_compiler_ia32.h	(revision 11688)
+++ runtime/vm/flow_graph_compiler_ia32.h	(working copy)
@@ -77,8 +77,7 @@
   // no fall-through to regular code is needed.
   bool TryIntrinsify();
 
-  void GenerateCallRuntime(intptr_t deopt_id,
-                           intptr_t token_pos,
+  void GenerateCallRuntime(intptr_t token_pos,
                            const RuntimeEntry& entry,
                            LocationSummary* locs);
 
@@ -93,14 +92,12 @@
                         PcDescriptors::Kind kind,
                         LocationSummary* locs);
 
-  void GenerateAssertAssignable(intptr_t deopt_id,
-                                intptr_t token_pos,
+  void GenerateAssertAssignable(intptr_t token_pos,
                                 const AbstractType& dst_type,
                                 const String& dst_name,
                                 LocationSummary* locs);
 
-  void GenerateInstanceOf(intptr_t deopt_id,
-                          intptr_t token_pos,
+  void GenerateInstanceOf(intptr_t token_pos,
                           const AbstractType& type,
                           bool negate_result,
                           LocationSummary* locs);