Improve compilation speed on a pathological case > 2x (7 sec -> 2.7 sec) by improving local lookups.

runtime/vm/scopes.cc

Index: runtime/vm/scopes.cc
===================================================================
--- runtime/vm/scopes.cc	(revision 17040)
+++ runtime/vm/scopes.cc	(working copy)
@@ -294,9 +294,11 @@
 
 
 LocalVariable* LocalScope::LocalLookupVariable(const String& name) const {
+  ASSERT(name.IsSymbol());
   for (intptr_t i = 0; i < variables_.length(); i++) {
     LocalVariable* var = variables_[i];
-    if (var->name().Equals(name) && !var->is_invisible_) {
+    ASSERT(var->name().IsSymbol());

[hausner, 2013/01/15 19:00:22]

Nit: instead of checking whether the names in a scope are symbols on every
lookup, we could assert that when the name is entered in the scope. We should
not make debug builds unnecessarily slow.

[srdjan, 2013/01/15 19:11:38]

I agree that we should keep an eye on not making debug build slow. In this case
I think is needed. Assuming that the right assert is done somewhere else would
weaken the check and add a non-obvious dependency, IMHO.

+    if ((var->name().raw() == name.raw()) && !var->is_invisible_) {
       return var;
     }
   }