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AX_CC_MAXOPT
Try to turn on "good" C optimization flags for various compilers and architectures, for some definition of "good". (In our case, good for FFTW and hopefully for other scientific codes. Modify as needed.)
The user can override the flags by setting the CFLAGS environment variable. The user can also specify --enable-portable-binary in order to disable any optimization flags that might result in a binary that only runs on the host architecture.
Note also that the flags assume that ANSI C aliasing rules are followed by the code (e.g. for gcc's -fstrict-aliasing), and that floating-point computations can be re-ordered as needed.
Requires macros: AX_CHECK_COMPILER_FLAGS, AX_COMPILER_VENDOR, AX_GCC_ARCHFLAG, AX_GCC_X86_CPUID.
Steven G. Johnson <stevenj@alum.mit.edu> and Matteo Frigo.
2005-05-30
AC_DEFUN([AX_CC_MAXOPT], [ AC_REQUIRE([AC_PROG_CC]) AC_REQUIRE([AX_COMPILER_VENDOR]) AC_REQUIRE([AC_CANONICAL_HOST]) AC_ARG_ENABLE(portable-binary, [AC_HELP_STRING([--enable-portable-binary], [disable compiler optimizations that would produce unportable binaries])], acx_maxopt_portable=$withval, acx_maxopt_portable=no) # Try to determine "good" native compiler flags if none specified via CFLAGS if test "$ac_test_CFLAGS" != "set"; then CFLAGS="" case $ax_cv_c_compiler_vendor in dec) CFLAGS="-newc -w0 -O5 -ansi_alias -ansi_args -fp_reorder -tune host" if test "x$acx_maxopt_portable" = xno; then CFLAGS="$CFLAGS -arch host" fi;; sun) CFLAGS="-native -fast -xO5 -dalign" if test "x$acx_maxopt_portable" = xyes; then CFLAGS="$CFLAGS -xarch=generic" fi;; hp) CFLAGS="+Oall +Optrs_ansi +DSnative" if test "x$acx_maxopt_portable" = xyes; then CFLAGS="$CFLAGS +DAportable" fi;; ibm) if test "x$acx_maxopt_portable" = xno; then xlc_opt="-qarch=auto -qtune=auto" else xlc_opt="-qtune=auto" fi AX_CHECK_COMPILER_FLAGS($xlc_opt, CFLAGS="-O3 -qansialias -w $xlc_opt", [CFLAGS="-O3 -qansialias -w" echo "******************************************************" echo "* You seem to have the IBM C compiler. It is *" echo "* recommended for best performance that you use: *" echo "* *" echo "* CFLAGS=-O3 -qarch=xxx -qtune=xxx -qansialias -w *" echo "* ^^^ ^^^ *" echo "* where xxx is pwr2, pwr3, 604, or whatever kind of *" echo "* CPU you have. (Set the CFLAGS environment var. *" echo "* and re-run configure.) For more info, man cc. *" echo "******************************************************"]) ;; intel) CFLAGS="-O3 -ansi_alias" if test "x$acx_maxopt_portable" = xno; then icc_archflag=unknown icc_flags="" case $host_cpu in i686*|x86_64*) # icc accepts gcc assembly syntax, so these should work: AX_GCC_X86_CPUID(0) AX_GCC_X86_CPUID(1) case $ax_cv_gcc_x86_cpuid_0 in # see AX_GCC_ARCHFLAG *:756e6547:*:*) # Intel case $ax_cv_gcc_x86_cpuid_1 in *6a?:*[[234]]:*:*|*6[[789b]]?:*:*:*) icc_flags="-xK";; *f3[[347]]:*:*:*|*f4[1347]:*:*:*) icc_flags="-xP -xN -xW -xK";; *f??:*:*:*) icc_flags="-xN -xW -xK";; esac ;; esac ;; esac if test "x$icc_flags" != x; then for flag in $icc_flags; do AX_CHECK_COMPILER_FLAGS($flag, [icc_archflag=$flag; break]) done fi AC_MSG_CHECKING([for icc architecture flag]) AC_MSG_RESULT($icc_archflag) if test "x$icc_archflag" != xunknown; then CFLAGS="$CFLAGS $icc_archflag" fi fi ;; gnu) # default optimization flags for gcc on all systems CFLAGS="-O3 -fomit-frame-pointer" # -malign-double for x86 systems AX_CHECK_COMPILER_FLAGS(-malign-double, CFLAGS="$CFLAGS -malign-double") # -fstrict-aliasing for gcc-2.95+ AX_CHECK_COMPILER_FLAGS(-fstrict-aliasing, CFLAGS="$CFLAGS -fstrict-aliasing") # note that we enable "unsafe" fp optimization with other compilers, too AX_CHECK_COMPILER_FLAGS(-ffast-math, CFLAGS="$CFLAGS -ffast-math") AX_GCC_ARCHFLAG($acx_maxopt_portable) ;; esac if test -z "$CFLAGS"; then echo "" echo "********************************************************" echo "* WARNING: Don't know the best CFLAGS for this system *" echo "* Use ./configure CFLAGS=... to specify your own flags *" echo "* (otherwise, a default of CFLAGS=-O3 will be used) *" echo "********************************************************" echo "" CFLAGS="-O3" fi AX_CHECK_COMPILER_FLAGS($CFLAGS, [], [ echo "" echo "********************************************************" echo "* WARNING: The guessed CFLAGS don't seem to work with *" echo "* your compiler. *" echo "* Use ./configure CFLAGS=... to specify your own flags *" echo "********************************************************" echo "" CFLAGS="" ]) fi ])