pgo: replace meson-pgo.sh with several script primitives

All scripts are in the ‘pgo’ directory:

* options: command line options for generate-alt-random-writes.py,
  sourced by other scripts.

* pgo.sh: top-level script, generates a meson build directory, selects
  a PGO method, generates the profiling data, re-configures the meson
  build directory and does the final build.

  This script is intended to be used by end-users, and shows _how_ to
  integrate the script primitives.

  Build servers will most likely *not* want to use this script as-is.

* partial.sh: generates alt-random-write data and runs “foot{,client}
  --version”, and then feeds the alt-random data to the PGO helper
  binary. Does not require a running Wayland session. Touches
  $blddir/pgo-ok on success.

* full-inner.sh: runs “footclient --version”, and then a complex
  “foot” command that first generates alt-random-write data, and then
  “cat’s” it. Requires a running Wayland session, *but*, this script
  is usually not called directly (see below). Touches $blddir/pgo-ok
  onsucces..

* full-current-session.sh: runs full-inner.sh. That is, it runs foot
  in the currently running Wayland session. Note that this will pop up a
  foot window.

* full-headless-sway.sh: generates a custom Sway configuration that
  exec’s foot-headless-sway-inner.sh (see below), and then executes a
  headless Sway. In other words, this script does a *full* PGO build,
  but *without* requiring a running Wayland session. Requires Sway >=
  1.6.2.

* full-headless-sway.sh: runs full-inner.sh + “swaymsg exit”.

To do a custom PGO build, without using pgo.sh, you’d need to:

CFLAGS=”$CFLAGS -O3” meson --buildtype=release -Db_lto=true
meson configure -Db_pgo=generate
ninja
ninja test (only needed if tllist+fcft are built as subprojects)

Run *one* of:
  - partial.sh
  - full-current-session.sh
  - full-headless-sway.sh

meson configure -D b_pgo=use
ninja

pgo/pgo.sh

@@ -0,0 +1,101 @@
+#!/bin/sh
+
+set -eu
+
+usage_and_die() {
+    echo "Usage: ${0} none|partial|full-current-session|full-headless-sway|[auto] <source-dir> <build-dir> [meson options]"
+    exit 1
+}
+
+[ ${#} -ge 3 ] || usage_and_die
+
+mode=${1}
+srcdir=$(realpath "${2}")
+blddir=$(realpath "${3}")
+shift 3
+
+if [ -e "${blddir}" ]; then
+    echo "error: ${blddir}: build directory already exists"
+    exit 1
+fi
+
+compiler=other
+do_pgo=no
+
+CFLAGS="${CFLAGS-} -O3"
+
+case $(${CC-cc} --version) in
+    *GCC*)
+        compiler=gcc
+        do_pgo=yes
+        ;;
+
+    *clang*)
+        compiler=clang
+
+        if command -v llvm-profdata > /dev/null; then
+            do_pgo=yes
+            CFLAGS="${CFLAGS} -Wno-ignored-optimization-argument"
+        fi
+        ;;
+esac
+
+case ${mode} in
+    partial|full-current-session|full-headless-sway)
+    ;;
+
+    none)
+        do_pgo=no
+        ;;
+
+    auto)
+        # TODO: once Sway 1.6.2 has been released, prefer
+        # full-headless-sway
+
+        if [ -n "${WAYLAND_DISPLAY+x}" ]; then
+            mode=full-current-session
+        elif command -v sway > /dev/null; then
+            mode=full-headless-sway
+        else
+            mode=partial
+        fi
+        ;;
+
+    *)
+        usage_and_die
+        ;;
+esac
+
+# echo "source: ${srcdir}"
+# echo "build: ${blddir}"
+# echo "compiler: ${compiler}"
+# echo "mode: ${mode}"
+# echo "CFLAGS: ${CFLAGS}"
+
+export CFLAGS
+meson "${@}" "${blddir}" "${srcdir}" --buildtype=release -Db_lto=true
+
+if [ ${do_pgo} = yes ]; then
+    find . -name "*.gcda" -delete
+    meson configure "${blddir}" -Db_pgo=generate
+    ninja -C "${blddir}"
+
+    # If fcft/tllist are subprojects, we need to ensure their tests
+    # have been executed, or we’ll get “profile count data file not
+    # found” errors.
+    ninja -C "${blddir}" test
+
+    # Run mode-dependent script to generate profiling data
+    "${srcdir}"/pgo/${mode}.sh "${srcdir}" "${blddir}"
+
+    if [ ${compiler} = clang ]; then
+        llvm-profdata \
+            merge \
+            "${blddir}"/default_*.profraw \
+            --output="${blddir}"/default.profdata
+    fi
+
+    meson configure "${blddir}" -Db_pgo=use
+fi
+
+ninja -C "${blddir}"