Revert "dart2js cps: Add logical rewriter rules to favor null-aware operators."

pkg/compiler/lib/src/tree_ir/optimization/logical_rewriter.dart

Index: pkg/compiler/lib/src/tree_ir/optimization/logical_rewriter.dart
diff --git a/pkg/compiler/lib/src/tree_ir/optimization/logical_rewriter.dart b/pkg/compiler/lib/src/tree_ir/optimization/logical_rewriter.dart
index 605d5e23a0da249fefb37aec7a00ca4f817e3ba9..0bb70ed14ee9d9695136c159c23ebb4e491f5126 100644
--- a/pkg/compiler/lib/src/tree_ir/optimization/logical_rewriter.dart
+++ b/pkg/compiler/lib/src/tree_ir/optimization/logical_rewriter.dart
@@ -306,15 +306,6 @@ class LogicalRewriter extends RecursiveTransformer
       node.elseExpression = tmp;
     }
 
-    // x ? y : x ==> x && y
-    if (isSameVariable(node.condition, node.elseExpression)) {
-      return new LogicalOperator.and(node.condition, node.thenExpression);
-    }
-    // x ? x : y ==> x || y
-    if (isSameVariable(node.condition, node.thenExpression)) {
-      return new LogicalOperator.or(node.condition, node.elseExpression);
-    }
-
     return node;
   }
 
@@ -477,16 +468,6 @@ class LogicalRewriter extends RecursiveTransformer
         e.elseExpression = (e.elseExpression as Not).operand;
         return new Not(e);
       }
-
-      // x ? y : x ==> x && y
-      if (isSameVariable(e.condition, e.elseExpression)) {
-        return new LogicalOperator.and(e.condition, e.thenExpression);
-      }
-      // x ? x : y ==> x || y
-      if (isSameVariable(e.condition, e.thenExpression)) {
-        return new LogicalOperator.or(e.condition, e.elseExpression);
-      }
-
       return e;
     }
     if (e is Constant && e.value.isBool) {
@@ -528,19 +509,5 @@ class LogicalRewriter extends RecursiveTransformer
       return new LogicalOperator.or(e1, e2);
     }
   }
-
-  /// True if [e2] is known to return the same value as [e1] 
-  /// (with no additional side effects) if evaluated immediately after [e1].
-  /// 
-  /// Concretely, this is true if [e1] and [e2] are uses of the same variable,
-  /// or if [e2] is a use of a variable assigned by [e1].
-  bool isSameVariable(Expression e1, Expression e2) {
-    if (e1 is VariableUse) {
-      return e2 is VariableUse && e1.variable == e2.variable;
-    } else if (e1 is Assign) {
-      return e2 is VariableUse && e1.variable == e2.variable;
-    }
-    return false;
-  }
 }