Make CTX allocatable by the register allocator.

runtime/vm/intermediate_language.cc

Index: runtime/vm/intermediate_language.cc
===================================================================
--- runtime/vm/intermediate_language.cc	(revision 41279)
+++ runtime/vm/intermediate_language.cc	(working copy)
@@ -1066,7 +1066,9 @@
 }
 
 
-void JoinEntryInstr::InsertPhi(intptr_t var_index, intptr_t var_count) {
+void JoinEntryInstr::InsertPhi(intptr_t var_index,
+                               intptr_t var_count,
+                               bool always_alive) {
   // Lazily initialize the array of phis.
   // Currently, phis are stored in a sparse array that holds the phi
   // for variable with index i at position i.
@@ -1079,6 +1081,7 @@
   }
   ASSERT((*phis_)[var_index] == NULL);
   (*phis_)[var_index] = new PhiInstr(this, PredecessorCount());
+  if (always_alive) (*phis_)[var_index]->mark_alive();
 }
 
 
@@ -2740,7 +2743,7 @@
 
 LocationSummary* InstanceCallInstr::MakeLocationSummary(Isolate* isolate,
                                                         bool optimizing) const {
-  return MakeCallSummary();
+  return MakeCallSummary(isolate);
 }
 
 
@@ -2858,7 +2861,7 @@
 
 LocationSummary* StaticCallInstr::MakeLocationSummary(Isolate* isolate,
                                                       bool optimizing) const {
-  return MakeCallSummary();
+  return MakeCallSummary(isolate);
 }