GenerateNot was not respecting "generateAtUseSite".

sdk/lib/_internal/compiler/implementation/ssa/codegen.dart

 // Copyright (c) 2012, 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 ssa;
 
 class SsaCodeGeneratorTask extends CompilerTask {
 
   final JavaScriptBackend backend;
 
@@ skipping 1799 matching lines @@
       // This optimization doesn't work for NaN, so we only do it if the
       // type is known to be an integer.
       return left.isInteger(compiler) && right.isInteger(compiler);
     }
 
     bool handledBySpecialCase = false;
     if (isGenerateAtUseSite(input)) {
       handledBySpecialCase = true;
       if (input is HIs) {
         emitIs(input, '!==');
+      } else if (input is HNot) {
+        use(input.inputs[0]);
       } else if (input is HIdentity) {
         HIdentity identity = input;
         emitIdentityComparison(identity.left, identity.right, true);
       } else if (input is HBoolify) {
         use(input.inputs[0]);
         push(new js.Binary("!==", pop(), newLiteralBool(true)), input);
       } else if (canGenerateOptimizedComparison(input)) {
         HRelational relational = input;
         BinaryOperation operation =
             relational.operation(backend.constantSystem);
@@ skipping 29 matching lines @@
     HBasicBlock ifBlock = node.block.dominator;
     assert(controlFlowOperators.contains(ifBlock.last));
     HInstruction input = ifBlock.last.inputs[0];
     if (input.isConstantFalse()) {
       use(node.inputs[1]);
     } else if (input.isConstantTrue()) {
       use(node.inputs[0]);
     } else if (node.inputs[1].isConstantBoolean()) {
       String operation = node.inputs[1].isConstantFalse() ? '&&' : '||';
       if (operation == '||') {
-        if (input is HNot) {
-          use(input.inputs[0]);
-        } else {
-          generateNot(input);
-        }
+        generateNot(input);
       } else {
         use(input);
       }
       js.Expression left = pop();
       use(node.inputs[0]);
       push(new js.Binary(operation, left, pop()));
     } else {
       use(input);
       js.Expression test = pop();
       use(node.inputs[0]);
@@ skipping 786 matching lines @@
     if (left.isConstantNull() || right.isConstantNull() ||
         (left.isPrimitive(compiler) &&
          left.instructionType == right.instructionType)) {
       return '==';
     }
     return null;
   } else {
     return '===';
   }
 }