When BRANCH is a tag --incremental does not work

Here we go:

$ ./scripts/build_tc-build.sh
projects...... clang;lld
targets....... X86
branch........ llvmorg-9.0.0-rc1
stage1-opts... --build-stage1-only --install-stage1-only
misc-opts..... --incremental
build-dir..... /home/sdi/src/llvm-toolchain/build
install-dir... /home/sdi/src/llvm-toolchain/install

========================
== Checking CC and LD ==
========================

CC: /usr/lib/llvm-9/bin/clang
CXX: /usr/lib/llvm-9/bin/clang++
LD: /usr/bin/ld.lld-9

===========================
== Checking dependencies ==
===========================

/usr/bin/cmake
/usr/bin/curl
/usr/bin/git
/usr/bin/ninja

===================
== Updating LLVM ==
===================

Note: checking out 'llvmorg-9.0.0-rc1'.

You are in 'detached HEAD' state. You can look around, make experimental
changes and commit them, and you can discard any commits you make in this
state without impacting any branches by performing another checkout.

If you want to create a new branch to retain commits you create, you may
do so (now or later) by using -b with the checkout command again. Example:

  git checkout -b <new-branch-name>

HEAD is now at 6aa75a25bdee Merging r367215: ------------------------------------------------------------------------ r367215 | hans | 2019-07-29 11:49:04 +0200 (Mon, 29 Jul 2019) | 66 lines

$ cd tc-build/llvm-project
$ git branch
* (HEAD detached at llvmorg-9.0.0-rc1)
  release/9.x

UPDATE: Add correct log in Updating LLVM section

[nathanchance]

Yes, we run git fetch origin which will fetch both new tags and branches. It looks like your example properly checked out. llvmorg-9.0.0-rc1?

[nathanchance]

Re-reading this, I think there is some confusion over the meaning of --incremental. --incremental deals with not removing the build artifacts from a previous compile, not incrementally updating the repo. There is no bug here.