Add script for performing compilation size regression investigations. (#15303)

* Add script for performing compilation size regression investigations.

* Print deltas

* Correct scoping.

* Concurrency control

* Job count control, skip zeros (unless no build output), fix usage.

* Add usage under -h arg.

* Updated usage output.

* Copyright header.

util/size_regression.sh

@@ -0,0 +1,79 @@
+#!/bin/bash
+
+# Copyright 2021 Nick Brassel (@tzarc)
+# SPDX-License-Identifier: GPL-2.0-or-later
+
+set -eEuo pipefail
+
+job_count=$(getconf _NPROCESSORS_ONLN 2>/dev/null || sysctl -n hw.ncpu 2>/dev/null || echo 2)
+source_ref="0.11.0"
+dest_ref="develop"
+ignore_ref="master"
+unset skip_zero
+
+function usage() {
+    echo "Usage: $(basename "$0") [-h] [-j <jobs>] [-s <source>] [-d <dest>] [-n] planck/rev6:default"
+    echo "    -h           : Shows this usage page."
+    echo "    -j <threads> : Change the number of threads to execute with. Defaults to \`$job_count\`."
+    echo "    -s <source>  : Use source commit, branch, tag, or sha1 to start the search. Defaults to \`$source_ref\`."
+    echo "    -d <dest>    : Use destination commit, branch, tag, or sha1 to end the search. Defaults to \`$dest_ref\`."
+    echo "    -i <ignore>  : The branch to ignore refs from. Defaults to \`$ignore_ref\`."
+    echo "    -n           : Skips printing changes if the delta is zero."
+    exit 1
+}
+
+if [[ ${#} -eq 0 ]]; then
+   usage
+fi
+
+while getopts "hj:s:d:i:n" opt "$@" ; do
+    case "$opt" in
+        h) usage; exit 0;;
+        j) job_count="${OPTARG:-}";;
+        s) source_ref="${OPTARG:-}";;
+        d) dest_ref="${OPTARG:-}";;
+        i) ignore_ref="${OPTARG:-}";;
+        n) skip_zero=1;;
+        \?) usage >&2; exit 1;;
+    esac
+done
+
+# Work out the target board
+shift $((OPTIND-1))
+keyboard_target=$1
+
+last_size=0
+last_line=""
+function build_executor() {
+    git rev-list --oneline --no-merges ${source_ref}...${dest_ref} ^${ignore_ref} | while IFS= read -r line ; do
+        revision=$(echo $line | cut -d' ' -f1)
+
+        make distclean >/dev/null 2>&1
+        git checkout $revision >/dev/null 2>&1 || { echo "Failed to check out revision ${revision}" >&2 ; exit 1 ; }
+        make -j${job_count} $keyboard_target >/dev/null 2>&1 || true
+        file_size=$(arm-none-eabi-size .build/*.elf 2>/dev/null | awk '/elf/ {print $1}' 2>/dev/null || true)
+
+        if [[ "$last_size" == 0 ]] ; then last_size=$file_size ; fi
+        if [[ -z "$file_size" ]] ; then file_size=0 ; fi
+
+        if [[ -n "$last_line" ]] ; then
+            size_delta=$(( $last_size - $file_size ))
+            if { [[ -n "${skip_zero:-}" ]] && [[ $size_delta -ne 0 ]] ; } || [[ $file_size -eq 0 ]] ; then
+                printf "Size: %8d, delta: %+6d -- %s\n" "$last_size" "$size_delta" "$last_line"
+            fi
+        fi
+
+        last_size=$file_size
+        last_line=$line
+    done
+
+    if [ -n "$last_line" ] ; then
+        size_delta=0
+        printf "Size: %8d, delta: %+6d -- %s\n" "$last_size" "$size_delta" "$last_line"
+    fi
+}
+
+# The actual execution of all the builds needs to be the last command in the entire script
+# - During builds, this script file will disappear, so we need the entire script to be
+#   loaded into the script interpreter at the time of execution. Do not refactor.
+build_executor