Ensure that all phis inserted by load optimizer have consistent representation.

runtime/vm/compiler.cc

Index: runtime/vm/compiler.cc
diff --git a/runtime/vm/compiler.cc b/runtime/vm/compiler.cc
index 05e4b783dc5e830d1ad5a407e15d58d8da84c500..a2f37fbee1f48dac0ba89cee21b0c7ffb976c457 100644
--- a/runtime/vm/compiler.cc
+++ b/runtime/vm/compiler.cc
@@ -445,6 +445,10 @@ static bool CompileParsedFunctionHelper(ParsedFunction* parsed_function,
         sinking->Optimize();
       }
 
+      // Ensure that all phis inserted by optimization passes have consistent
+      // representations.
+      optimizer.UnboxPhis();
+
       if (optimizer.Canonicalize()) {
         // To fully remove redundant boxing (e.g. BoxDouble used only in
         // environments and UnboxDouble instructions) instruction we