[llvm] add logging to pipeline generation (PR #68983)

[Mikhail Goncharov via llvm-commits]

https://github.com/metaflow updated https://github.com/llvm/llvm-project/pull/68983

>From 05be74af61226909c21b74ae9069fe8ae5367690 Mon Sep 17 00:00:00 2001
From: Mikhail Goncharov <goncharov.mikhail at gmail.com>
Date: Mon, 16 Oct 2023 11:09:10 +0200
Subject: [PATCH] add logging to pipeline generation

we tried to generate a full diff against main in
ec9d80ec43f5761a34c4a785c67d9e7d21ec8bda but it resulted in wrong diffs
[citation needed]. It seems that the issue was that 'main' reference is
not updated after agent restart and diff main...HEAD keep increasing.
---
 .ci/generate-buildkite-pipeline-premerge | 10 ++++++++++
 1 file changed, 10 insertions(+)

diff --git a/.ci/generate-buildkite-pipeline-premerge b/.ci/generate-buildkite-pipeline-premerge
index e389df431505bd1..d00762a615c2659 100755
--- a/.ci/generate-buildkite-pipeline-premerge
+++ b/.ci/generate-buildkite-pipeline-premerge
@@ -23,6 +23,16 @@ set -o pipefail
 # Environment variables script works with:
 # List of files affected by this commit
 : ${MODIFIED_FILES:=$(git diff --name-only HEAD~1)}
+# Fetch origin/main to have an up to date merge base for main..HEAD diff.
+git fetch origin main:main
+echo "files modified HEAD~1" >&2
+git --no-pager diff --name-only HEAD~1 >&2
+echo "files modified main...HEAD" >&2
+git --no-pager diff --name-only main...HEAD | head -n 10 >&2
+merge_base=$(git merge-base main HEAD)
+echo "merge base with main $merge_base" >&2
+echo "git log" >&2
+git --no-pager log --oneline --abbrev-commit -n 5 >&2
 # Filter rules for generic windows tests
 : ${WINDOWS_AGENTS:='{"queue": "windows"}'}
 # Filter rules for generic linux tests