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

runtime/vm/intermediate_language.h

Index: runtime/vm/intermediate_language.h
===================================================================
--- runtime/vm/intermediate_language.h	(revision 11688)
+++ runtime/vm/intermediate_language.h	(working copy)
@@ -502,7 +502,7 @@
 
   virtual void PrintOperandsTo(BufferFormatter* f) const;
 
-  virtual bool CanDeoptimize() const { return true; }
+  virtual bool CanDeoptimize() const { return false; }
   virtual intptr_t ResultCid() const { return kDynamicCid; }
 
  private:
@@ -540,7 +540,7 @@
 
   virtual void PrintOperandsTo(BufferFormatter* f) const;
 
-  virtual bool CanDeoptimize() const { return true; }
+  virtual bool CanDeoptimize() const { return false; }
   virtual intptr_t ResultCid() const { return kBoolCid; }
 
  private:
@@ -573,7 +573,7 @@
 
   virtual void PrintOperandsTo(BufferFormatter* f) const;
 
-  virtual bool CanDeoptimize() const { return true; }
+  virtual bool CanDeoptimize() const { return false; }
   virtual intptr_t ResultCid() const { return kBoolCid; }
 
  private:
@@ -1235,7 +1235,7 @@
 
   virtual void PrintOperandsTo(BufferFormatter* f) const;
 
-  virtual bool CanDeoptimize() const { return true; }
+  virtual bool CanDeoptimize() const { return false; }
   virtual intptr_t ResultCid() const { return kBoolCid; }
 
  private:
@@ -1301,7 +1301,7 @@
 
   virtual void PrintOperandsTo(BufferFormatter* f) const;
 
-  virtual bool CanDeoptimize() const { return true; }
+  virtual bool CanDeoptimize() const { return false; }
   virtual intptr_t ResultCid() const { return kDynamicCid; }
 
  private:
@@ -1475,7 +1475,7 @@
 
   virtual void PrintOperandsTo(BufferFormatter* f) const;
 
-  virtual bool CanDeoptimize() const { return true; }
+  virtual bool CanDeoptimize() const { return false; }
   virtual intptr_t ResultCid() const { return kDynamicCid; }
 
  private:
@@ -1605,7 +1605,7 @@
 
   DECLARE_COMPUTATION(CloneContext)
 
-  virtual bool CanDeoptimize() const { return true; }
+  virtual bool CanDeoptimize() const { return false; }
   virtual intptr_t ResultCid() const { return kIllegalCid; }
 
  private:
@@ -1956,7 +1956,7 @@
 
   DECLARE_COMPUTATION(CheckStackOverflow)
 
-  virtual bool CanDeoptimize() const { return true; }
+  virtual bool CanDeoptimize() const { return false; }
   virtual intptr_t ResultCid() const { return kIllegalCid; }
 
  private:
@@ -3064,15 +3064,12 @@
 
 class ThrowInstr : public TemplateInstruction<0> {
  public:
-  explicit ThrowInstr(intptr_t token_pos)
-      : deopt_id_(Isolate::Current()->GetNextDeoptId()),
-        token_pos_(token_pos) { }
+  explicit ThrowInstr(intptr_t token_pos) : token_pos_(token_pos) { }
 
   DECLARE_INSTRUCTION(Throw)
 
   virtual intptr_t ArgumentCount() const { return 1; }
 
-  intptr_t deopt_id() const { return deopt_id_; }
   intptr_t token_pos() const { return token_pos_; }
 
   virtual LocationSummary* MakeLocationSummary() const;
@@ -3082,7 +3079,6 @@
   virtual bool CanDeoptimize() const { return false; }
 
  private:
-  const intptr_t deopt_id_;
   const intptr_t token_pos_;
 
   DISALLOW_COPY_AND_ASSIGN(ThrowInstr);
@@ -3091,15 +3087,12 @@
 
 class ReThrowInstr : public TemplateInstruction<0> {
  public:
-  explicit ReThrowInstr(intptr_t token_pos)
-      : deopt_id_(Isolate::Current()->GetNextDeoptId()),
-        token_pos_(token_pos) { }
+  explicit ReThrowInstr(intptr_t token_pos) : token_pos_(token_pos) { }
 
   DECLARE_INSTRUCTION(ReThrow)
 
   virtual intptr_t ArgumentCount() const { return 2; }
 
-  intptr_t deopt_id() const { return deopt_id_; }
   intptr_t token_pos() const { return token_pos_; }
 
   virtual LocationSummary* MakeLocationSummary() const;
@@ -3109,7 +3102,6 @@
   virtual bool CanDeoptimize() const { return false; }
 
  private:
-  const intptr_t deopt_id_;
   const intptr_t token_pos_;
 
   DISALLOW_COPY_AND_ASSIGN(ReThrowInstr);