VM: Improve phi-elimination to improve code inside of try-catch.

runtime/vm/intermediate_language.h

Index: runtime/vm/intermediate_language.h
diff --git a/runtime/vm/intermediate_language.h b/runtime/vm/intermediate_language.h
index 1536cf4cde887b45c60fe15c6f489d48fa7873f6..a6e391bbdcc10734de77295899029f822dd8eeb2 100644
--- a/runtime/vm/intermediate_language.h
+++ b/runtime/vm/intermediate_language.h
@@ -1984,6 +1984,8 @@ class PhiInstr : public Definition {
   // A phi is redundant if all input operands are the same.
   bool IsRedundant() const;
 
+  bool HasReplacement(Definition** replacement) const;
+
   void set_induction_variable_info(InductionVariableInfo* info) {
     loop_variable_info_ = info;
   }