enhance build process to allow selective -O3 optimization
the motivation for this patch is that the vast majority of libc is
code that does not benefit at all from optimizations, but that certain
components like string/memory operations can be major performance
bottlenecks.
at the same time, the old -falign-*=1 options are removed, since they
were only beneficial for avoiding bloat when global -O3 was used, and
in that case, they may have prevented some of the performance gains.
to be the most useful, this patch will need further tuning. in
particular, research is needed to determine which components should be
built with -O3 by default, and it may be desirable to remove the
hard-coded -O3 and instead allow more customization of the
optimization level used for selected modules.
diff --git a/configure b/configure
index b679986..327863c 100755
--- a/configure
+++ b/configure
@@ -24,6 +24,7 @@
--host=HOST same as --target
Optional features:
+ --enable-optimize=... optimize listed components for speed over size [auto]
--enable-debug build with debugging information [disabled]
--enable-warnings build with recommended warnings flags [disabled]
--enable-gcc-wrapper build musl-gcc toolchain wrapper [auto]
@@ -104,6 +105,7 @@
CFLAGS_C99FSE=
CFLAGS_AUTO=
LDFLAGS_AUTO=
+OPTIMIZE_GLOBS=
prefix=/usr/local/musl
exec_prefix='$(prefix)'
bindir='$(exec_prefix)/bin'
@@ -111,6 +113,7 @@
includedir='$(prefix)/include'
syslibdir='/lib'
target=
+optimize=auto
debug=no
warnings=no
shared=yes
@@ -129,6 +132,9 @@
--disable-shared|--enable-shared=no) shared=no ;;
--enable-static|--enable-static=yes) static=yes ;;
--disable-static|--enable-static=no) static=no ;;
+--enable-optimize) optimize=yes ;;
+--enable-optimize=*) optimize=${arg#*=} ;;
+--disable-optimize) optimize=no ;;
--enable-debug|--enable-debug=yes) debug=yes ;;
--disable-debug|--enable-debug=no) debug=no ;;
--enable-warnings|--enable-warnings=yes) warnings=yes ;;
@@ -230,14 +236,57 @@
|| { test "$ARCH" = i386 && tryflag CFLAGS_C99FSE -ffloat-store ; }
tryflag CFLAGS_C99FSE -frounding-math
+
#
-# Setup basic default CFLAGS: debug, optimization, and -pipe
+# If debugging is explicitly enabled, don't auto-enable optimizations
#
-if fnmatch '-O*|*\ -O*' "$CFLAGS_AUTO $CFLAGS" ; then :
-else
-tryflag CFLAGS_AUTO -Os || tryflag CFLAGS_AUTO -O2
+if test "$debug" = yes ; then
+CFLAGS_AUTO=-g
+test "$optimize" = auto && optimize=no
fi
-test "x$debug" = xyes && CFLAGS_AUTO="-g"
+
+#
+# Possibly add a -O option to CFLAGS and select modules to optimize with
+# -O3 based on the status of --enable-optimize and provided CFLAGS.
+#
+printf "checking for optimization settings... "
+case "x$optimize" in
+xauto)
+if fnmatch '-O*|*\ -O*' "$CFLAGS_AUTO $CFLAGS" ; then
+printf "using provided CFLAGS\n" ;optimize=no
+else
+printf "using defaults\n" ; optimize=yes
+fi
+;;
+xsize|xnone) printf "minimize size\n" ; optimize=size ;;
+xno|x) printf "disabled\n" ; optimize=no ;;
+*) printf "custom\n" ;;
+esac
+
+test "$optimize" = no || tryflag CFLAGS_AUTO -Os || tryflag CFLAGS_AUTO -O2
+test "$optimize" = yes && optimize="internal,malloc,math,string"
+
+if fnmatch 'no|size' "$optimize" ; then :
+else
+printf "components to be optimized for speed:"
+while test "$optimize" ; do
+case "$optimize" in
+*,*) this=${optimize%%,*} optimize=${optimize#*,} ;;
+*) this=$optimize optimize=
+esac
+printf " $this"
+case "$this" in
+*/*.c) ;;
+*/*) this=$this*.c ;;
+*) this=$this/*.c ;;
+esac
+OPTIMIZE_GLOBS="$OPTIMIZE_GLOBS $this"
+done
+OPTIMIZE_GLOBS=${OPTIMIZE_GLOBS# }
+printf "\n"
+fi
+
+# Always try -pipe
tryflag CFLAGS_AUTO -pipe
#
@@ -267,14 +316,6 @@
tryflag CFLAGS_AUTO -Wa,--noexecstack
#
-# Some optimization levels add bloated alignment that hurt performance
-#
-tryflag CFLAGS_AUTO -falign-functions=1
-tryflag CFLAGS_AUTO -falign-labels=1
-tryflag CFLAGS_AUTO -falign-loops=1
-tryflag CFLAGS_AUTO -falign-jumps=1
-
-#
# On x86, make sure we don't have incompatible instruction set
# extensions enabled by default. This is bad for making static binaries.
# We cheat and use i486 rather than i386 because i386 really does not
@@ -366,6 +407,7 @@
LDFLAGS = $LDFLAGS_AUTO $LDFLAGS
CROSS_COMPILE = $CROSS_COMPILE
LIBCC = $LIBCC
+OPTIMIZE_GLOBS = $OPTIMIZE_GLOBS
EOF
test "x$static" = xno && echo "STATIC_LIBS ="
test "x$shared" = xno && echo "SHARED_LIBS ="