Fold equals and not equals comparisons for constant strings.

runtime/vm/flow_graph_optimizer.cc

 // Copyright (c) 2013, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 #include "vm/flow_graph_optimizer.h"
 
 #include "vm/bit_vector.h"
 #include "vm/cha.h"
 #include "vm/dart_entry.h"
 #include "vm/flow_graph_builder.h"
@@ skipping 6033 matching lines @@
   const Object& left = instr->left()->definition()->constant_value();
   const Object& right = instr->right()->definition()->constant_value();
 
   if (instr->left()->definition() == instr->right()->definition()) {
     // Fold x == x, and x != x to true/false for numbers and checked strict
     // comparisons.
     if (instr->IsCheckedStrictEqual() ||
         RawObject::IsIntegerClassId(instr->operation_cid())) {
       return SetValue(instr,
                       (instr->kind() == Token::kEQ)
-                        ? Bool::True()
-                        : Bool::False());
+                          ? Bool::True()
+                          : Bool::False());
     }
   }
 
   if (IsNonConstant(left) || IsNonConstant(right)) {
     SetValue(instr, non_constant_);
   } else if (IsConstant(left) && IsConstant(right)) {
     if (left.IsInteger() && right.IsInteger()) {
       const bool result = CompareIntegers(instr->kind(),
                                           Integer::Cast(left),
                                           Integer::Cast(right));
       SetValue(instr, result ? Bool::True() : Bool::False());
+    } else if (left.IsString() && right.IsString()) {

[srdjan, 2013/08/26 16:00:39]

I believe all constant strings must be canonicalized, i.e., raw pointer
comparison should be enough.

+      const bool result = String::Cast(left).Equals(String::Cast(right));
+      SetValue(instr,
+               ((instr->kind() == Token::kEQ) == result)
+                   ? Bool::True()
+                   : Bool::False());
     } else {
       SetValue(instr, non_constant_);
     }
   }
 }
 
 
 void ConstantPropagator::VisitRelationalOp(RelationalOpInstr* instr) {
   const Object& left = instr->left()->definition()->constant_value();
   const Object& right = instr->right()->definition()->constant_value();
@@ skipping 1458 matching lines @@
   }
 
   // Insert materializations at environment uses.
   for (intptr_t i = 0; i < exits.length(); i++) {
     CreateMaterializationAt(exits[i], alloc, alloc->cls(), *fields);
   }
 }
 
 
 }  // namespace dart