Implement "one-shot" interceptors.

sdk/lib/_internal/compiler/implementation/ssa/codegen_helpers.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;
 
 /**
  * Instead of emitting each SSA instruction with a temporary variable
  * mark instructions that can be emitted at their use-site.
  * For example, in:
@@ skipping 22 matching lines @@
     assert(!instruction.isJsStatement());
     generateAtUseSite.add(instruction);
   }
 
   SsaInstructionMerger(this.types, this.generateAtUseSite);
 
   void visitGraph(HGraph graph) {
     visitDominatorTree(graph);
   }
 
-  /**
-   * Return whether the instructions do not belong to a loop or
-   * belong to the same loop.
-   */
-  bool notInLoopOrInSameLoop(HInstruction one, HInstruction two) {
-    return one.block.enclosingLoopHeader == two.block.enclosingLoopHeader;
-  }
-
   void analyzeInputs(HInstruction user, int start) {
     List<HInstruction> inputs = user.inputs;
     for (int i = start; i < inputs.length; i++) {
       HInstruction input = inputs[i];
       if (!generateAtUseSite.contains(input)
           && !input.isCodeMotionInvariant()
           && input.usedBy.length == 1
           && input is !HPhi
           && input is !HLocalValue
           && !input.isJsStatement()) {
         if (input.isPure()) {
           // Only consider a pure input if it is in the same loop.
           // Otherwise, we might move GVN'ed instruction back into the
           // loop.
-          if (notInLoopOrInSameLoop(user, input)) {
+          if (user.hasSameLoopHeaderAs(input)) {
             // Move it closer to [user], so that instructions in
             // between do not prevent making it generate at use site.
             input.moveBefore(user);
             pureInputs.add(input);
             // Visit the pure input now so that the expected inputs
             // are after the expected inputs of [user].
             input.accept(this);
           }
         } else {
           expectedInputs.add(input);
@@ skipping 303 matching lines @@
     }
 
     // If [thenInput] is defined in the first predecessor, then it is only used
     // by [phi] and can be generated at use site.
     if (identical(thenInput.block, end.predecessors[0])) {
       assert(thenInput.usedBy.length == 1);
       markAsGenerateAtUseSite(thenInput);
     }
   }
 }