message: [XLA:CPU] Run ScatterExpander much earlier in CPU pipeline.
  Before, the ScatterExpander was run after fusion (!), meaning that nothing it
  emitted would ever be fused.
  On my machine, this is good for a 3.2/2.6 = 1.2x speedup on the testcase from
diff: @@ -297,6 +297,7 @@ Status CpuCompiler::RunHloPassesThroughLayoutAssn(
  pass.AddInvariantChecker<HloVerifier>(/*layout_sensitive=*/false,
  /*allow_mixed_precision=*/false);
  + pass.AddPass<ScatterExpander>();
  pass.AddPass<BatchNormExpander>(
  /*rewrite_training_op=*/true,
  /*rewrite_inference_op=*/true,
  @@ -340,8 +341,6 @@ Status CpuCompiler::RunHloPassesThroughLayoutAssn(
  pipeline.AddPass<CpuInstructionFusion>();
  - pipeline.AddPass<ScatterExpander>();
  -
  ReducePrecisionInsertion::AddPasses(
  &pipeline, module->config().debug_options(),
  ReducePrecisionInsertion::PassTiming::AFTER_FUSION);
  