cps-ir: Optimize identical used with constants.

pkg/compiler/lib/src/cps_ir/constant_propagation.dart

 // Copyright (c) 2014, 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.
 
 part of dart2js.optimizers;
 
 /**
  * Propagates constants throughout the IR, and replaces branches with fixed
  * jumps as well as side-effect free expressions with known constant results.
  * Should be followed by the [ShrinkingReducer] pass.
@@ skipping 589 matching lines @@
   // Conditions.
 
   void visitIsTrue(IsTrue node) {
     Branch branch = node.parent;
     visitBranch(branch);
   }
 
   // JavaScript specific nodes.
 
   void visitIdentical(Identical node) {
-    setValue(node, _ConstnessLattice.NonConst);
+    _ConstnessLattice leftConst = getValue(node.left.definition);

[karlklose, 2014/11/26 08:16:00]

Indentation is correct, the highlighting hides the '_'.

+    _ConstnessLattice rightConst = getValue(node.left.definition);
+    ConstantValue leftValue = leftConst.constant;
+    ConstantValue rightValue = rightConst.constant;
+    if (leftConst.isUnknown || rightConst.isUnknown) {
+      // Come back later.
+      return;
+    } else if (!leftConst.isConstant || !rightConst.isConstant) {
+      setValue(node, _ConstnessLattice.NonConst);
+    } else if (leftValue.isPrimitive && rightValue.isPrimitive) {
+      assert(leftConst.isConstant && rightConst.isConstant);
+      PrimitiveConstantValue left = leftValue;
+      PrimitiveConstantValue right = rightValue;
+      ConstantValue result =
+          new BoolConstantValue(left.primitiveValue == right.primitiveValue);
+      setValue(node, new _ConstnessLattice(result));
+    }
   }
 }
 
 /// Represents the constant-state of a variable at some point in the program.
 /// UNKNOWN: may be some as yet undetermined constant.
 /// CONSTANT: is a constant as stored in the local field.
 /// NONCONST: not a constant.
 class _ConstnessLattice {
   static const int UNKNOWN  = 0;
   static const int CONSTANT = 1;
@@ skipping 42 matching lines @@
       return that;
     }
 
     if (this.constant == that.constant) {
       return this;
     }
 
     return NonConst;
   }
 }