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  1. JDK
  2. JDK-8261137

Optimization of Box nodes in uncommon_trap

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    • Subcomponent:
    • Resolved In Build:
      b17
    • CPU:
      generic
    • OS:
      generic
    • Verification:
      Fix failed

      Description

      JDK-8075052 has removed useless autobox. However, in some cases, the box is still saved. For instance:

      @Benchmark
      public void testMethod(Blackhole bh) {
        int sum = 0;
        for (int i = 0; i < data.length; i++) {
            Integer ii = Integer.valueOf(data[i]);
            if (i < data.length) {
                sum += ii.intValue();
            }
        }
        bh.consume(sum);
      }

      Although the variable ii is only used at ii.intValue(), it cannot be eliminated as a result of being used by a hidden uncommon_trap.
      The uncommon_trap is generated by the optimized "if", because its condition is always true.

      We can postpone box in uncommon_trap in this situation. We treat box as a scalarized object by adding a SafePointScalarObjectNode in the uncommon_trap node,
      and deleting the use of box:

      ```
      @@ -603,6 +603,51 @@ void CallGenerator::do_late_inline_helper() {
           C->remove_macro_node(call);
         }
       
      + if (callprojs.resproj != NULL && call->is_CallStaticJava() &&
      + call->as_CallStaticJava()->is_boxing_method()) {
      + GraphKit kit(call->jvms());
      + PhaseGVN& gvn = kit.gvn();
      +
      + Node_List delay_boxes;
      + bool no_use = true;
      + for (DUIterator_Fast imax, i = callprojs.resproj->fast_outs(imax); i < imax; i++) {
      + Node* m = callprojs.resproj->fast_out(i);
      + if (m->is_CallStaticJava() &&
      + m->as_CallStaticJava()->uncommon_trap_request() != 0) {
      + delay_boxes.push(m);
      + } else {
      + no_use = false;
      + break;
      + }
      + }
      +
      + if (no_use) {
      + // delay box node in uncommon_trap runtime, treat box as a scalarized object
      + while (delay_boxes.size() > 0) {
      + ProjNode* res = callprojs.resproj->as_Proj();
      + Node* uncommon_trap_node = delay_boxes.pop();
      + int in_edge = uncommon_trap_node->find_edge(res);
      + assert(in_edge > 0, "sanity");
      +
      + ciInstanceKlass* klass = call->as_CallStaticJava()->method()->holder();
      + int n_fields = klass->nof_nonstatic_fields();
      + assert(n_fields == 1, "sanity");
      +
      + uint first_ind = (uncommon_trap_node->req() - uncommon_trap_node->jvms()->scloff());
      + Node* sobj = new SafePointScalarObjectNode(gvn.type(res)->isa_oopptr(),
      +#ifdef ASSERT
      + NULL,
      +#endif // ASSERT
      + first_ind, n_fields);
      + sobj->init_req(0, C->root());
      + uncommon_trap_node->add_req(call->in(res->_con));
      + sobj = gvn.transform(sobj);
      + uncommon_trap_node->jvms()->set_endoff(uncommon_trap_node->req());
      + uncommon_trap_node->set_req(in_edge, sobj);
      + }
      + }
      + }
      +
      ```
      It is shown in the following table that the patch improves the performance on x64 and aarch64.
      The following table shows results of the performance test on x64 and aarch64:
      x64:
      base:
      Benchmark Mode Samples Score Score error Units
      o.s.MyBenchmark.testMethod avgt 30 50.374 3.927 us/op
      delay box in uncommon_trap:
      Benchmark Mode Samples Score Score error Units
      o.s.MyBenchmark.testMethod avgt 30 4.571 0.004 us/op
      aarch64:
      base:
      Benchmark Mode Samples Score Score error Units
      o.s.MyBenchmark.testMethod avgt 30 51.782 0.357 us/op
      delay box in uncommon_trap:
      Benchmark Mode Samples Score Score error Units
      o.s.MyBenchmark.testMethod avgt 30 3.876 0.002 us/op

      There is no additional fail/error(s) of jtreg after this patch.

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              Assignee:
              whuang Wang Huang
              Reporter:
              whuang Wang Huang
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                Created:
                Updated:
                Resolved: