message: [XLA] Make utility functions anonymous
  Also, polish comments in instruction_fusion.cc.
diff: @@ -29,15 +29,19 @@ limitations under the License.
  namespace xla {
  namespace gpu {
  +namespace {
  bool ElementIsF32OrF16(const Shape& shape) {
  PrimitiveType type = shape.element_type();
  return type == F32 || type == F16;
  }
  +} // namespace
  /*static*/ bool GpuInstructionFusion::IsExpensive(
  const HloInstruction& instruction) {
  - // We say that some floating-point math ops are cheap on the GPU.
  + // We say that some floating-point math ops are cheap on the GPU. Unlike other
  + // intrinsics that can be expanded into many instructions, Div and Rsqrt are
  + // lowered into single hardware instructions.
  switch (instruction.opcode()) {
  case HloOpcode::kDivide:
  case HloOpcode::kRsqrt:
  