Make CTX allocatable by the register allocator.

runtime/vm/flow_graph.h

Index: runtime/vm/flow_graph.h
===================================================================
--- runtime/vm/flow_graph.h	(revision 41279)
+++ runtime/vm/flow_graph.h	(working copy)
@@ -111,6 +111,15 @@
     return num_non_copied_params_;
   }
 
+  LocalVariable* CurrentContextVar() const {
+    return parsed_function().saved_current_context_var();
+  }
+
+  intptr_t CurrentContextEnvIndex() const {
+    return parsed_function().saved_current_context_var()->BitIndexIn(
+        num_non_copied_params_);
+  }
+
   // Flow graph orders.
   const GrowableArray<BlockEntryInstr*>& preorder() const {
     return preorder_;
@@ -159,6 +168,15 @@
     return constant_dead_;
   }
 
+  ConstantInstr* constant_empty_context() const {
+    return constant_empty_context_;
+  }
+
+  Definition* CurrentContext(Environment* env) const {
+    while (env->outer() != NULL) env = env->outer();

[Vyacheslav Egorov (Google), 2014/10/28 13:44:58]

Kill this function. It's also a bit suspicious.

[Florian Schneider, 2014/10/28 19:04:31]

Done.

+    return env->ValueAt(CurrentContextEnvIndex())->definition();
+  }
+
   intptr_t alloc_ssa_temp_index() { return current_ssa_temp_index_++; }
 
   void AllocateSSAIndexes(Definition* def) {
@@ -333,6 +351,8 @@
   GrowableArray<BlockEntryInstr*> optimized_block_order_;
   ConstantInstr* constant_null_;
   ConstantInstr* constant_dead_;
+  ConstantInstr* constant_empty_context_;
+  Definition* current_context_;

[Vyacheslav Egorov (Google), 2014/10/28 13:44:58]

Kill this with fire.

[Florian Schneider, 2014/10/28 19:04:31]

Done.

 
   BlockEffects* block_effects_;
   bool licm_allowed_;