Add nightly benchmark regression detection pipeline

libeigen/eigen!2349

Co-authored-by: Rasmus Munk Larsen <rmlarsen@gmail.com>

ci/scripts/push_perf_data.sh

@@ -0,0 +1,100 @@
+#!/bin/sh
+# Push benchmark results to the perf-data orphan branch.
+# POSIX sh compatible (runs under Alpine's busybox ash).
+#
+# Expected environment variables:
+#   EIGEN_CI_BUILDDIR       - build directory containing results/
+#   EIGEN_CI_GIT_PUSH_URL   - authenticated git push URL
+#   CI_COMMIT_SHORT_SHA     - short commit hash
+
+set -ex
+
+results_dir="$(pwd)/${EIGEN_CI_BUILDDIR:-.bench-build}/results"
+perf_branch="perf-data"
+clone_dir="/tmp/perf-data-push"
+push_url="${EIGEN_CI_GIT_PUSH_URL:?EIGEN_CI_GIT_PUSH_URL must be set}"
+
+rm -rf "${clone_dir}"
+
+# Clone perf-data branch, or create orphan if it doesn't exist.
+if git clone --depth=1 --single-branch --branch "${perf_branch}" \
+     "${push_url}" "${clone_dir}" 2>/dev/null; then
+  echo "Cloned existing ${perf_branch} branch."
+else
+  echo "${perf_branch} branch does not exist, creating orphan..."
+  mkdir -p "${clone_dir}"
+  cd "${clone_dir}"
+  git init
+  git checkout --orphan "${perf_branch}"
+  cat > README.md <<'EOF'
+# Benchmark Performance Data
+
+This branch stores nightly/weekly benchmark results as JSON files.
+It is maintained automatically by the CI benchmark pipeline.
+
+## Structure
+
+    <target>/
+      <date>_<commit>_<target>.json
+
+## Analysis
+
+See `ci/scripts/detect_regressions.py` on the main branch for the
+regression detection script that consumes this data.
+EOF
+  git add README.md
+  git -c user.name="CI Bot" -c user.email="ci@eigen.tuxfamily.org" \
+    commit -m "Initialize perf-data branch"
+  git remote add origin "${push_url}"
+  cd -
+fi
+
+cd "${clone_dir}"
+
+# Copy combined result files into target subdirectories.
+# Only match canonical combined formats:
+#   YYYY-MM-DDTHH-MM-SSZ_<hex>_<target>.json
+#   YYYY-MM-DD_<hex>_<target>.json
+# This avoids picking up raw per-benchmark files like bench_gemm_double.json.
+copied=0
+for combined_json in "${results_dir}"/*.json; do
+  [ -f "${combined_json}" ] || continue
+  filename=$(basename "${combined_json}")
+  # Must start with a UTC timestamp or date, followed by a hex commit hash.
+  case "${filename}" in
+    [0-9][0-9][0-9][0-9]-[0-9][0-9]-[0-9][0-9]T[0-9][0-9]-[0-9][0-9]-[0-9][0-9]Z_[0-9a-f]*_*.json) ;;
+    [0-9][0-9][0-9][0-9]-[0-9][0-9]-[0-9][0-9]_[0-9a-f]*_*.json) ;;
+    *) continue ;;
+  esac
+  # Extract target: strip timestamp/date + commit prefix and .json suffix.
+  target=$(echo "${filename}" | sed 's/^[^_]*_[a-f0-9]*_//' | sed 's/\.json$//')
+  mkdir -p "${target}"
+  cp "${combined_json}" "${target}/${filename}"
+  copied=$((copied + 1))
+done
+
+if [ "${copied}" -eq 0 ]; then
+  echo "No result files to store."
+  exit 0
+fi
+
+# Prune data older than 90 days to keep the branch manageable.
+# We parse the date from the filename since clone mtime is always "now".
+cutoff=$(date -u -d "@$(($(date +%s) - 90*86400))" +%Y-%m-%d)
+find . -name '*.json' -path './*/*.json' | while IFS= read -r f; do
+  file_date=$(basename "$f" | grep -oE '^[0-9]{4}-[0-9]{2}-[0-9]{2}')
+  if [ -n "$file_date" ] && [ "$file_date" \< "$cutoff" ]; then
+    rm -f "$f"
+  fi
+done
+
+# Commit and push.
+git add -A
+git -c user.name="CI Bot" -c user.email="ci@eigen.tuxfamily.org" \
+  commit -m "Add benchmark results for $(date -u +%Y-%m-%d) (${CI_COMMIT_SHORT_SHA:-unknown})" || {
+  echo "No changes to commit."
+  exit 0
+}
+git push origin "${perf_branch}"
+
+echo "Pushed ${copied} result file(s) to ${perf_branch} branch."