[clang][ci] Improves buildkite artifacts.

[Mordante]

Summary

The financial cost of the network I/O for the Clang install artifacts is
quite significant. afd3478f37c8 improved this by creating tarballs. This
commit improves the tarball by using xz compression instead of gzip. This
option is the slowest, but gives the smallest size.

size  time           time
      (compression)  (decompression)

gzip 51 M 7 s 1.2 s
bz2 44 M 17 s 5.8 s
xz 33 M 76 s 3.1 s

[Mordante]

CI fixes.

[Mordante]

libcxx/utils/ci/buildkite-pipeline-clang.yml

28

I used this build https://buildkite.com/llvm-project/libcxx-ci/builds/23579 to test the changes with Clang.
This is build https://buildkite.com/llvm-project/libcxx-ci/builds/23567 of Clang before the changes.

Unsurprisingly, here the timings are closer than locally. I haven't checked what the noise on the timings is for Clang builds.

[philnik]

Are you sure that it's worth it? Adding a minute of compression time for a decrease of 20MB seems like it's the wrong call to me. Without this change we already shaved off ~4Gigs/clang pipeline.

[Mordante]

In D150062#4325290, @philnik wrote:

Are you sure that it's worth it? Adding a minute of compression time for a decrease of 20MB seems like it's the wrong call to me. Without this change we already shaved off ~4Gigs/clang pipeline.

That was on my system. Looking at the CI the difference is much smaller. It seems our CI has a beefier machine than I do ;-)

[ldionne]

The difference is like 15 seconds (and that might be due to normal variance in the CI), but we're reducing the size by 40% so IMO this is worth it. Not like a *must*, but interesting savings nonetheless. Let's do it!

libcxx/utils/ci/buildkite-pipeline-clang.yml

steps:
   - label: "Building clang"
     commands:
       - "mkdir install"
       # We use Release here to avoid including debug information. Otherwise, the clang binary is very large, which
       # is problematic because we need to upload the artifacts for other jobs to use. This may seem like nothing,
       # but with the number of jobs we run daily, this can result in thousands of GB of network I/O.
       - "cmake -S llvm -B build -G Ninja -DCMAKE_BUILD_TYPE=Release -DCMAKE_INSTALL_PREFIX=install -DLLVM_ENABLE_PROJECTS=\"clang;compiler-rt\""
       - "ninja -C build install-clang install-clang-resource-headers"
-      - "tar -czvf install.tar.gz install/"
-      - "buildkite-agent artifact upload --debug install.tar.gz"
+      - "tar -cJvf install.tar.xz install/"
+      - "buildkite-agent artifact upload --debug install.tar.xz"
     env:
         CC: "clang-${LLVM_HEAD_VERSION}"
         CXX: "clang++-${LLVM_HEAD_VERSION}"
     agents:
       queue: "libcxx-builders"
       os: "linux"
     retry:
       automatic:
         - exit_status: -1  # Agent was lost
           limit: 2
     timeout_in_minutes: 120
 
   - wait
 
   - label: "C++03"
     commands:
-      - "buildkite-agent artifact download install.tar.gz ."
-      - "tar -xzvf install.tar.gz"
+      - "buildkite-agent artifact download install.tar.xz ."
+      - "tar -xvf install.tar.xz"
       - "export CC=$(pwd)/install/bin/clang"
       - "export CXX=$(pwd)/install/bin/clang++"
       - "chmod +x install/bin/clang install/bin/clang++"
       - "libcxx/utils/ci/run-buildbot generic-cxx03"
     artifact_paths:
       - "**/test-results.xml"
       - "**/crash_diagnostics/*"
     env:
         LLVM_SYMBOLIZER_PATH: "/usr/bin/llvm-symbolizer-${LLVM_HEAD_VERSION}" # TODO: Should we build that from scratch?
         CLANG_CRASH_DIAGNOSTICS_DIR: "crash_diagnostics"
     agents:
       queue: "libcxx-builders"
       os: "linux"
     retry:
       automatic:
         - exit_status: -1  # Agent was lost
           limit: 2
     timeout_in_minutes: 120
 
   - label: "C++2b"
     commands:
-      - "buildkite-agent artifact download install.tar.gz ."
-      - "tar -xzvf install.tar.gz"
+      - "buildkite-agent artifact download install.tar.xz ."
+      - "tar -xvf install.tar.xz"
       - "export CC=$(pwd)/install/bin/clang"
       - "export CXX=$(pwd)/install/bin/clang++"
       - "chmod +x install/bin/clang install/bin/clang++"
       - "libcxx/utils/ci/run-buildbot generic-cxx2b"
     artifact_paths:
       - "**/test-results.xml"
       - "**/crash_diagnostics/*"
     env:
         LLVM_SYMBOLIZER_PATH: "/usr/bin/llvm-symbolizer-${LLVM_HEAD_VERSION}" # TODO: Should we build that from scratch?
         CLANG_CRASH_DIAGNOSTICS_DIR: "crash_diagnostics"
     agents:
       queue: "libcxx-builders"
       os: "linux"
     retry:
       automatic:
         - exit_status: -1  # Agent was lost
           limit: 2
     timeout_in_minutes: 120
 
   - label: "Modules"
     commands:
-      - "buildkite-agent artifact download install.tar.gz ."
-      - "tar -xzvf install.tar.gz"
+      - "buildkite-agent artifact download install.tar.xz ."
+      - "tar -xvf install.tar.xz"
       - "export CC=$(pwd)/install/bin/clang"
       - "export CXX=$(pwd)/install/bin/clang++"
       - "chmod +x install/bin/clang install/bin/clang++"
       - "libcxx/utils/ci/run-buildbot generic-modules"
     artifact_paths:
       - "**/test-results.xml"
       - "**/crash_diagnostics/*"
     env: