Updating clang

1. Sync your Chromium tree to the latest revision to pick up any plugin changes

2. Run python tools/clang/scripts/upload_revision.py NNNN with the target LLVM SVN revision number. This creates a roll CL on a new branch, uploads it and starts tryjobs that build the compiler binaries into a staging bucket on Google Cloud Storage (GCS).

3. If the clang upload try bots succeed, copy the binaries from the staging bucket to the production one. For example:

   $ export rev=123456-1
   $ for x in Linux_x64 Mac Win ; do \
       gsutil.py cp -n -a public-read gs://chromium-browser-clang-staging/$x/clang-$rev.tgz \
           gs://chromium-browser-clang/$x/clang-$rev.tgz ; \
       gsutil.py cp -n -a public-read gs://chromium-browser-clang-staging/$x/llvmobjdump-$rev.tgz \
           gs://chromium-browser-clang/$x/llvmobjdump-$rev.tgz ; \
       gsutil.py cp -n -a public-read gs://chromium-browser-clang-staging/$x/llvmcfiverify-$rev.tgz \
           gs://chromium-browser-clang/$x/llvmcfiverify-$rev.tgz ; \
       gsutil.py cp -n -a public-read gs://chromium-browser-clang-staging/$x/translation_unit-$rev.tgz \
           gs://chromium-browser-clang/$x/translation_unit-$rev.tgz ; \
       gsutil.py cp -n -a public-read gs://chromium-browser-clang-staging/$x/llvm-code-coverage-$rev.tgz \
           gs://chromium-browser-clang/$x/llvm-code-coverage-$rev.tgz ; \
       done
   $ gsutil.py cp -n -a public-read gs://chromium-browser-clang-staging/Mac/lld-$rev.tgz \
         gs://chromium-browser-clang/Mac/lld-$rev.tgz
   

4. Run the goma package update script to push these packages to goma. If you do not have the necessary credentials to do the upload, ask clang@chromium.org to find someone who does

5. Run an exhaustive set of try jobs to test the new compiler:

   git cl try &&
   git cl try -m tryserver.chromium.mac -b mac_chromium_asan_rel_ng &&
   git cl try -m tryserver.chromium.linux -b linux_chromium_cfi_rel_ng &&
   git cl try -m tryserver.blink -b linux_trusty_blink_rel &&
   git cl try -B luci.chromium.try -b ios-device \
     -b linux_chromium_chromeos_asan_rel_ng -b linux_chromium_msan_rel_ng \
     -b linux_chromium_chromeos_msan_rel_ng -b linux-chromeos-dbg
   

6. Start Pinpoint perf tryjobs. These are generally too noisy to catch minor regressions pre-commit, but make sure there are no large regressions.

   a. (Log in to store OAuth2 token in the depot_tools cache. Only needs to be run once:)

   ```shell
   $ PYTHONPATH=$(dirname $(which git-cl)) python -c"import auth;auth.OAUTH_CLIENT_ID='62121018386-h08uiaftreu4dr3c4alh3l7mogskvb7i.apps.googleusercontent.com';auth.OAUTH_CLIENT_SECRET='vc1fZfV1cZC6mgDSHV-KSPOz';print auth.get_authenticator_for_host('pinpoint',auth.make_auth_config()).login()"
   ```
   

   a. Generate a fresh Oath2 token:

   ```shell
   $ TOKEN=$(PYTHONPATH=$(dirname $(which git-cl)) python -c"import auth;print auth.get_authenticator_for_host('pinpoint',auth.make_auth_config()).get_access_token().token")
   ```
   

   a. Launch Pinpoint job:

   ```shell
   $ curl -H"Authorization: Bearer $TOKEN" -F configuration=chromium-rel-win7-gpu-nvidia \
       -F target=telemetry_perf_tests -F benchmark=speedometer2 \
       -F patch=https://chromium-review.googlesource.com/c/chromium/src/+/$(git cl issue | cut -d' ' -f3) \
       -F start_git_hash=HEAD -F end_git_hash=HEAD https://pinpoint-dot-chromeperf.appspot.com/api/new
   ```
   

   a. Use the URL returned by the command above to see the progress and result of the tryjob, checking that it doesn't regress significantly (> 10%). Post the URL to the codereview.

7. Commit roll CL from the first step

8. The bots will now pull the prebuilt binary, and goma will have a matching binary, too.