something is weird about llvm submodule handling

I just observed the following:
I did a git pull and it downloaded a bunch of llvm submodule data.
Afterwards, I did an x.py install, I'm not sure what happened with the llvm submodule but llvm did NOT get rebuilt, so probably nothing touched it?
Then, I did another x.py install afterwards, without touching anything on the repo and THAT did start rebuilding llvm again.

I'm having a gut feeling that we should have had rebuilt llvm already on the first x.py install but I don't know what the underlying issue is.

cfg:

[llvm]
download-ci-llvm = false
assertions = true
ninja = true
targets = "X86"
link-jobs = 16
cflags = "-march=native" # -D_GLIBCXX_DEBUG
cxxflags = "-march=native" # -D_GLIBCXX_DEBUG
ldflags = "-march=native" # -D_GLIBCXX_DEBUG
polly = false
[build]
dist-stage = 2
install-stage = 2
extended = true
tools = ["cargo", "clippy", "rustfmt", "analysis", "src", "miri"] # + "rust-demangler" if `profiler`
low-priority = true
[install]
prefix = "/home/gh-matthiaskrgr/.rustup/toolchains/local-debug-assertions"
sysconfdir = "etc"
[rust]
debug = true
debug-assertions = true
debug-assertions-std = true
overflow-checks = true
overflow-checks-std = true
debuginfo-level = 1
codegen-backends = ["llvm", "cranelift"]
backtrace-on-ice = true
verify-llvm-ir = true
lto = "thin"
[target.x86_64-unknown-linux-gnu]
[dist]
compression-formats = ["xz"]
```

Reproduce the two successive x.py install runs using the reported LLVM and build configuration, and compare the LLVM submodule and rebuild state after each run. Determine whether the first install should rebuild LLVM and document or correct the submodule handling so repeated installs behave consistently.