message: Simplify logic in XlaCompilationCache::CompileImpl
  As far as I can tell, `executable` is never nullptr.
diff: @@ -258,6 +258,7 @@ Status XlaCompilationCache::CompileImpl(
  xla::LocalExecutable** executable,
  const XlaCompiler::CompileOptions* compile_options,
  bool compile_single_op) {
  + CHECK_NE(executable, nullptr);
  VLOG(1) << "XlaCompilationCache::Compile " << DebugString();
  if (VLOG_IS_ON(2)) {
  @@ -329,18 +330,15 @@ Status XlaCompilationCache::CompileImpl(
  compile_options ? *compile_options : XlaCompiler::CompileOptions(),
  function, args, &entry->compilation_result);
  }
  + TF_RETURN_IF_ERROR(entry->compilation_status);
  + CHECK_EQ(entry->executable.get(), nullptr);
  + entry->compilation_status =
  + BuildExecutable(options, entry->compilation_result, &entry->executable);
  }
  + TF_RETURN_IF_ERROR(entry->compilation_status);
  *compilation_result = &entry->compilation_result;
  - if (entry->compilation_status.ok() && executable) {
  - if (entry->executable == nullptr) {
  - entry->compilation_status = BuildExecutable(
  - options, entry->compilation_result, &entry->executable);
  - }
  *executable = entry->executable.get();
  - }
  -
  - Status status = entry->compilation_status;
  - return status;
  + return Status::OK();
  }
  } // namespace tensorflow
  