message: [XLA] Make the inner block kernel of CholeskyExpander override-able.
  Add a special case for the degenerate n=1 case of Cholesky decomposition.
diff: @@ -17,6 +17,7 @@ limitations under the License.
  #define TENSORFLOW_COMPILER_XLA_SERVICE_CHOLESKY_EXPANDER_H_
  #include "absl/container/flat_hash_map.h"
  +#include "tensorflow/compiler/xla/client/xla_builder.h"
  #include "tensorflow/compiler/xla/service/op_expander_pass.h"
  namespace xla {
  @@ -31,7 +32,13 @@ class CholeskyExpander : public OpExpanderPass {
  StatusOr<HloInstruction*> ExpandInstruction(
  HloInstruction* instruction) override;
  + virtual StatusOr<std::pair<XlaOp, XlaOp>> CholeskyUnblocked(
  + XlaOp a, PrecisionConfig::Precision precision);
  +
  private:
  + XlaOp BuildCholesky(XlaOp a, int64 block_size,
  + PrecisionConfig::Precision precision);
  +
  // Mapping from op signatures to existing computations.
  absl::flat_hash_map<string, HloComputation*> computation_cache_;
  };
  