message: [XLA:GPU] Make sure the input for ThenMemcpy stays alive when it executes
  asynchronously
  By the time memcpy actually executes the source on stack would've gone out of
  scope. Also drop an unneeded BlockHostUntilDone from the autotune code.
diff: @@ -240,7 +240,7 @@ CudnnConvolutionAlgorithmPicker::PickBestAlgorithm(
  CHECK_EQ(0, left_over_bytes % 2);
  constexpr float kBroadcastedConstant = 0.1f;
  - Eigen::half halfs[2] = {Eigen::half(kBroadcastedConstant),
  + static const Eigen::half halfs[2] = {Eigen::half(kBroadcastedConstant),
  Eigen::half(kBroadcastedConstant)};
  uint32 bits;
  static_assert(sizeof(bits) == sizeof(halfs), "");
  @@ -265,7 +265,6 @@ CudnnConvolutionAlgorithmPicker::PickBestAlgorithm(
  .ThenMemZero(&filter_buf, filter_buf.size())
  .ThenMemZero(&output_buf, output_buf.size());
  }
  - TF_RETURN_IF_ERROR(stream.BlockHostUntilDone());
  DeviceMemoryBase* result_buf = [&] {
  switch (kind) {
  