message: [XLA:GPU] Share the output buffer of cholesky calls with the input
  I didn't manage to come up with a small test case for this, it requires the
  surroundings to be just right, making integration testing fragile.
diff: @@ -491,13 +491,18 @@ StatusOr<std::unique_ptr<HloModule>> NVPTXCompiler::RunHloPasses(
  static absl::optional<bool> CanShareBufferHint(const HloInstruction* user,
  const HloInstruction* operand,
  - const ShapeIndex&) {
  + const ShapeIndex& user_index) {
  // Share the bias buffer with the parent instruction.
  if (IsCublasGemm(*user)) {
  if (user->operand_count() == 3 && user->operand(2) == operand) {
  return true;
  }
  }
  + // The operand of cholesky can be shared with the first output.
  + if (user->opcode() == HloOpcode::kCustomCall &&
  + user->custom_call_target() == kCusolverCholeskyCallTarget) {
  + return user_index.size() == 1 && user_index[0] == 0;
  + }
  return absl::nullopt;
  }
  