Call special VM interpolate for single element interpolation.

runtime/vm/flow_graph_builder.cc

Index: runtime/vm/flow_graph_builder.cc
diff --git a/runtime/vm/flow_graph_builder.cc b/runtime/vm/flow_graph_builder.cc
index 0f4966f9e9a7fb40b00ea7f8c943e9eb12ab3069..143ef664b79347ce89b45a2e678c8e0480c1a85e 100644
--- a/runtime/vm/flow_graph_builder.cc
+++ b/runtime/vm/flow_graph_builder.cc
@@ -2386,10 +2386,19 @@ void EffectGraphVisitor::VisitArrayNode(ArrayNode* node) {
 void EffectGraphVisitor::VisitStringInterpolateNode(
     StringInterpolateNode* node) {
   ValueGraphVisitor for_argument(owner());
-  node->value()->Visit(&for_argument);
+  ArrayNode* arguments = node->value();
+  intptr_t length = arguments->length();
+  bool singleton = false;
+  if (length == 1) {

[Florian Schneider, 2014/09/12 10:33:37]

Drop length and replace with just arguments->length() here.

[Lasse Reichstein Nielsen, 2014/09/12 12:49:39]

Done.

+    arguments->ElementAt(0)->Visit(&for_argument);
+    singleton = true;
+  } else {
+    arguments->Visit(&for_argument);
+  }
   Append(for_argument);
   StringInterpolateInstr* instr =
-      new(I) StringInterpolateInstr(for_argument.value(), node->token_pos());
+      new(I) StringInterpolateInstr(for_argument.value(), node->token_pos(),
+                                    singleton);
   ReturnDefinition(instr);
 }