Make CTX allocatable by the register allocator.

runtime/vm/flow_graph_inliner.cc

Index: runtime/vm/flow_graph_inliner.cc
===================================================================
--- runtime/vm/flow_graph_inliner.cc	(revision 41279)
+++ runtime/vm/flow_graph_inliner.cc	(working copy)
@@ -926,6 +926,15 @@
         constant->ReplaceUsesWith(
             caller_graph_->GetConstant(constant->value()));
       }
+      CurrentContextInstr* context = (*defns)[i]->AsCurrentContext();
+      if ((context != NULL) && context->HasUses()) {
+        if (call->IsClosureCall()) {
+          context->ReplaceUsesWith(
+              call->AsClosureCall()->context()->definition());
+        } else {
+          context->ReplaceUsesWith(caller_graph_->CurrentContext(call->env()));

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

Just use the empty one here. If it's not a closure call it does not need no
context.

Potentially this is even dead code because in the flow graph construction for
non-closures we already put empty context into this slot and not
CurrentContextInstr.

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

Done.

+        }
+      }
     }
 
     // Check that inlining maintains use lists.
@@ -1335,6 +1344,16 @@
       constant->ReplaceUsesWith(
           owner_->caller_graph()->GetConstant(constant->value()));
     }
+    CurrentContextInstr* context = (*defns)[i]->AsCurrentContext();
+    if ((context != NULL) && context->HasUses()) {
+      if (call_data.call->IsClosureCall()) {
+        context->ReplaceUsesWith(
+            call_data.call->AsClosureCall()->context()->definition());
+      } else {
+        context->ReplaceUsesWith(
+            owner_->caller_graph()->CurrentContext(call_data.call->env()));

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

Ditto.

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

Done.

+      }
+    }
   }
   return true;
 }