Cannot get autocomplete from the plugin

[lulitao1997]

cannot get autocomplete from the plugin when editing a cpp file

my operating system is Manjaro Linux, and package clang is already installed.
my vimrc file can be seen here, https://pastebin.com/qRd2P1QU
my nvim :checkhealth result can be seen here, https://pastebin.com/0ULJhfsR

run nvim --version in the terminal give me the following result:

NVIM v0.2.2
Build type: Release
LuaJIT 2.0.5
Compilation: /usr/bin/cc -march=x86-64 -mtune=generic -O2 -pipe -fstack-protector-strong -fno-plt -Wconversion -DNVIM_MSGPACK_HAS_FLOAT32 -DNVIM_UNIBI_HAS_VAR_FROM -O2 -DNDEBUG -DMIN_LOG_LEVEL=3 -Wall -Wextra -pedantic -Wno-unused-parameter -Wstrict-prototypes -std=gnu99 -Wimplicit-fallthrough -Wvla -fstack-protector-strong -fdiagnostics-color=auto -DINCLUDE_GENERATED_DECLARATIONS -D_GNU_SOURCE -I/build/neovim/src/build/config -I/build/neovim/src/neovim-0.2.2/src -I/usr/include -I/usr/include -I/usr/include -I/usr/include -I/usr/include -I/usr/include -I/usr/include -I/build/neovim/src/build/src/nvim/auto -I/build/neovim/src/build/include
Compiled by builduser

Features: +acl +iconv +jemalloc +tui 
See ":help feature-compile"

   system vimrc file: "$VIM/sysinit.vim"
  fall-back for $VIM: "/usr/share/nvim"

Run :checkhealth for more info

also, when typing #include < I noticed my cpu usage surge to 100% for about 4 seconds before falling back.