Expand use and support for LTO and FDO builds

Adds LTO to the CI build for Linux, which bring it as close as possible
to the planned formal release, which will additionally use FDO.

Adds some helper scripts to work with FDO files.

Improves the build notes for how to create and use FDO files.

scripts/automator/build/clang-defaults

@@ -3,10 +3,10 @@ cc="${ccache}clang${postfix}"
 cxx="${ccache}clang++${postfix}"
 
 # Flag additions
-TYPES+=(debug warnmore profile)
-cflags_release=("${cflags[@]}" -Os)
+TYPES+=(debug warnmore pgotrain)
+cflags_release=("${cflags[@]}" -O3)
 cflags_debug=("${cflags[@]}" -g -fno-omit-frame-pointer)
-cflags_profile=("${cflags_debug[@]}" -fprofile-instr-generate -fcoverage-mapping)
+cflags_pgotrain=("${cflags_debug[@]}" -fprofile-instr-generate -fcoverage-mapping)
 cflags_warnmore=("${cflags_debug[@]}" -Wextra -Wshadow -Wcast-align -Wunused
                  -Woverloaded-virtual -Wpedantic -Wconversion -Wsign-conversion
                  -Wdouble-promotion -Wformat=2)
@@ -19,5 +19,4 @@ fi
 
 # Modifier additions
 MODIFIERS=(fdo)
-ldflags_fdo=(-fprofile-instr-generate)
-cflags_fdo=("-fprofile-sample-use=${FDO_FILE:-}")
+cflags_fdo=("-fprofile-sample-use=${FDO_FILE:-${repo_root}/current.afdo}")

scripts/automator/build/gcc-defaults

@@ -6,18 +6,20 @@ ld="gcc${postfix}"
 ranlib="gcc-ranlib${postfix}"
 
 # Flag additions
-TYPES+=(debug warnmore profile)
+TYPES+=(debug warnmore pgotrain fdotrain)
 
 cflags+=(-fstack-protector -fdiagnostics-color=auto)
 cflags_debug=("${cflags[@]}" -g -fno-omit-frame-pointer)
-cflags_release=("${cflags[@]}" -Ofast -ffunction-sections -fdata-sections)
-cflags_profile=("${cflags_debug[@]}" -pg)
+cflags_release=("${cflags[@]}" -DNDEBUG -O3 -ffunction-sections -fdata-sections)
+cflags_pgotrain=("${cflags_debug[@]}" -pg)
 cflags_warnmore=("${cflags_debug[@]}" -pedantic -Wcast-align -Wdouble-promotion
                  -Wduplicated-branches -Wduplicated-cond -Wextra -Wformat=2
                  -Wlogical-op -Wmisleading-indentation -Wnull-dereference
                  -Wshadow -Wunused)
 cxxonly_warnmore=(-Weffc++ -Wnon-virtual-dtor -Woverloaded-virtual -Wuseless-cast)
+cflags_fdotrain=("${cflags[@]}" -DNDEBUG -g1 -fno-omit-frame-pointer)
 
 # Modifier additions
 MODIFIERS=(fdo)
-cflags_fdo=("-fauto-profile=${FDO_FILE:-}")
+# Override the prior optimization flag because O2 does better w/ feedback 
+cflags_fdo=("-O2 -fauto-profile=${FDO_FILE:-${repo_root}/current.afdo}")

scripts/automator/main.sh

@@ -109,7 +109,10 @@ function perform_steps() {
 }
 
 function main() {
-	cd "$(dirname "$0")/automator"
+	cd "$(dirname "$0")"/..
+	export repo_root
+	repo_root="$PWD"
+	cd scripts/automator
 	if [[ -z "${data_dir:-}" ]]; then data_dir="$(basename "$0" '.sh')"; fi
 	parse_args "$@"
 	construct_environment