round-robin.sh: Add ${rr[update_baseline]} "rebase" capability

When initial results of CI jobs are not ideal we may be interested
in exporing whether earlier versions of components gave better results.
This is useful for general book-keeping, and as basis for manual
bisections.  E.g., for code-size benchmarking we have started with
gcc-8 branches, but, ideally, also want to check whether gcc-7, gcc-6,
and earlier branches might have provided smaller binaries.

For this we add "rebase" mode for update_baseline parameter.  This
mode is intended to be manually selected in jenkins web-UI, along
with component versions pre-dating earliest result recorded in
base-artifacts.git repo.  The essence of this mode is to push results
to the bottom of base-artifacts.git history, rather than the top.

For code-size example we would trigger builds for gcc versions from
latest to earliest: gcc-7, gcc-6, gcc-5, and so on.

Note that "rebase" builds don't change apparent baseline viewed by
normal builds.

Change-Id: I0b0590a90460a1cd273165c0bf270a4cb227515a

1 files changed, 57 insertions, 26 deletions

diff --git a/round-robin.sh b/round-robin.sh
index a0c15aa2..a62bf98c 100644
--- a/round-robin.sh
+++ b/round-robin.sh
@@ -32,7 +32,9 @@
 #          build successful.  Push our artifacts to the top of base-artifacts/.
 # - init:  use "empty" results for base-artifacts, which will make current
 #          build successful.  Push our artifacts as the one and only entry.
-#rr[update_baseline]=update/reset/init
+# - rebase: treat results of this build as historically eldest, and
+#           rebase base-artifacts commits on top of this build's artifacts.
+#rr[update_baseline]=update/reset/init/rebase
 
 # Target architecture to build for: arm or aarch64.
 #rr[target]="$target"
@@ -380,7 +382,8 @@ check_regression ()
     (
     set -euf -o pipefail
 
-    if [ x"${rr[update_baseline]}" = x"update" ] && ! no_regression_p; then
+    if [ x"${rr[update_baseline]}" = x"update" ] \
+	   && ! no_regression_p base-artifacts ${rr[top_artifacts]}; then
 	local single_component=$(print_single_updated_component)
 
 	if [ x"$single_component" = x"" -o x"${rr[mode]}" = x"bisect" ]; then
@@ -409,6 +412,19 @@ EOF
 
 	# Fail.
 	false
+    elif [ x"${rr[update_baseline]}" = x"rebase" ]; then
+	local base_artifacts_head base_artifacts_tail
+	base_artifacts_head=$(git -C base-artifacts rev-parse HEAD)
+	base_artifacts_tail=$(git -C base-artifacts rev-list --max-parents=0 HEAD)
+	git -C base-artifacts reset --hard $base_artifacts_tail
+
+	if no_regression_p ${rr[top_artifacts]} base-artifacts; then
+	    # Current results are no better then the all-time-best results.
+	    # No reason to rebase base-artifacts.
+	    false
+	fi
+
+	git -C base-artifacts reset --hard $base_artifacts_head
     fi
     )
 }
@@ -420,32 +436,39 @@ update_baseline ()
     set -euf -o pipefail
 
     local amend=""
-    local prev_head=""
-
-    # We discard baseline entries for results worse or same than
-    # the current one, but keep entries for results that are better
-    # (so that we have a record of pending regressions).
-    while no_regression_p; do
-	prev_head=""
-	if git -C base-artifacts rev-parse HEAD^ >/dev/null 2>&1; then
-	    # For every regression we want to keep artifacts for the first-bad
-	    # build, so reset to the most relevant regression (marked by reset-baseline).
-	    if [ -f base-artifacts/reset-baseline ] \
-		   && [ x"${rr[update_baseline]}" = x"update" ]; then
-		prev_head=$(git -C base-artifacts rev-parse HEAD)
+    local rebase_head
+    if [ x"${rr[update_baseline]}" != x"rebase" ]; then
+	local prev_head=""
+
+	# We discard baseline entries for results worse or same than
+	# the current one, but keep entries for results that are better
+	# (so that we have a record of pending regressions).
+	while no_regression_p base-artifacts ${rr[top_artifacts]}; do
+	    prev_head=""
+	    if git -C base-artifacts rev-parse HEAD^ >/dev/null 2>&1; then
+		# For every regression we want to keep artifacts for the first-bad
+		# build, so reset to the most relevant regression (marked by reset-baseline).
+		if [ -f base-artifacts/reset-baseline ] \
+		       && [ x"${rr[update_baseline]}" = x"update" ]; then
+		    prev_head=$(git -C base-artifacts rev-parse HEAD)
+		fi
+		git -C base-artifacts reset --hard HEAD^
+	    else
+		# We got to the beginning of git history, so amend the current
+		# commit.  The initial state of baseline is "empty" branch,
+		# which we treat as worst possible in no_regression_p().
+		amend="--amend"
+		break
 	    fi
-	    git -C base-artifacts reset --hard HEAD^
-	else
-	    # We got to the beginning of git history, so amend the current
-	    # commit.  The initial state of baseline is "empty" branch,
-	    # which we treat as worst possible in no_regression_p().
-	    amend="--amend"
-	    break
-	fi
-    done
+	done
 
-    if [ x"$prev_head" != x"" ]; then
-	git -C base-artifacts reset --hard $prev_head
+	if [ x"$prev_head" != x"" ]; then
+	    git -C base-artifacts reset --hard $prev_head
+	fi
+    else
+	rebase_head=$(git -C base-artifacts rev-parse HEAD)
+	git -C base-artifacts reset --hard refs/remotes/origin/empty
+	amend="--amend"
     fi
 
     # Rsync current artifacts.  Make sure to use -I rsync option since
@@ -486,6 +509,10 @@ update_baseline ()
     git -C base-artifacts commit $amend -m "$msg_title
 
 $(cat ${rr[top_artifacts]}/results)"
+
+    if [ x"${rr[update_baseline]}" = x"rebase" ]; then
+	git -C base-artifacts rebase -X theirs HEAD $rebase_head
+    fi
     )
 }
 
@@ -498,6 +525,10 @@ push_baseline ()
     git_init_linaro_local_remote base-artifacts baseline false
     git_push base-artifacts baseline ${rr[baseline_branch]}
 
+    if [ x"${rr[update_baseline]}" = x"rebase" ]; then
+	return
+    fi
+
     local c
     for c in $(print_updated_components); do
 	git_push $c baseline ${rr[baseline_branch]}