Detect leaf optimized methods and skip stack check overflow test in those, unless it is in a loop (…

runtime/vm/flow_graph_compiler.cc

Index: runtime/vm/flow_graph_compiler.cc
===================================================================
--- runtime/vm/flow_graph_compiler.cc	(revision 21574)
+++ runtime/vm/flow_graph_compiler.cc	(working copy)
@@ -160,6 +160,8 @@
   pc_descriptors_list_ = new DescriptorList(64);
   exception_handlers_list_ = new ExceptionHandlerList();
   block_info_.Clear();
+  bool is_leaf = !parsed_function().function().IsClosureFunction() &&
+                 is_optimizing();
   for (int i = 0; i < block_order_.length(); ++i) {
     block_info_.Add(new BlockInfo());
     if (is_optimizing()) {
@@ -185,9 +187,24 @@
           may_reoptimize_ = true;
           break;
         }
+        if (is_leaf && !current->IsCheckStackOverflow()) {
+          // Note that we do no care if the code contains instructions that
+          // can deoptimize.
+          LocationSummary* locs = current->locs();
+          if (locs != NULL && locs->can_call()) {
+            is_leaf = false;
+          }
+        }
       }
     }
   }
+  if (is_leaf) {
+    BlockEntryInstr* entry = block_order_[1];

[Kevin Millikin (Google), 2013/04/18 10:05:28]

I don't think we should rely on properties of the block order here (i.e., we
might want to reorder blocks).

The simplest way to avoid it is to have the FlowGraphCompiler hold onto the flow
graph so you can write

Instruction* entry = flow_graph_->normal_entry();

[srdjan, 2013/04/18 18:15:57]

Yes, using: flow_graph_.graph_entry()->normal_entry()->next()

+    ASSERT(entry != NULL);
+    CheckStackOverflowInstr* check = entry->next()->AsCheckStackOverflow();
+    ASSERT(check != NULL);
+    check->RemoveFromGraph();
+  }
 }