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+# ===========================================================================
+# https://www.gnu.org/software/autoconf-archive/ax_cc_maxopt.html
+# ===========================================================================
+#
+# SYNOPSIS
+#
+# AX_CC_MAXOPT
+#
+# DESCRIPTION
+#
+# 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_COMPILE_FLAG, AX_COMPILER_VENDOR,
+# AX_GCC_ARCHFLAG, AX_GCC_X86_CPUID.
+#
+# LICENSE
+#
+# Copyright (c) 2008 Steven G. Johnson <stevenj@alum.mit.edu>
+# Copyright (c) 2008 Matteo Frigo
+#
+# This program is free software: you can redistribute it and/or modify it
+# under the terms of the GNU General Public License as published by the
+# Free Software Foundation, either version 3 of the License, or (at your
+# option) any later version.
+#
+# This program is distributed in the hope that it will be useful, but
+# WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General
+# Public License for more details.
+#
+# You should have received a copy of the GNU General Public License along
+# with this program. If not, see <https://www.gnu.org/licenses/>.
+#
+# As a special exception, the respective Autoconf Macro's copyright owner
+# gives unlimited permission to copy, distribute and modify the configure
+# scripts that are the output of Autoconf when processing the Macro. You
+# need not follow the terms of the GNU General Public License when using
+# or distributing such scripts, even though portions of the text of the
+# Macro appear in them. The GNU General Public License (GPL) does govern
+# all other use of the material that constitutes the Autoconf Macro.
+#
+# This special exception to the GPL applies to versions of the Autoconf
+# Macro released by the Autoconf Archive. When you make and distribute a
+# modified version of the Autoconf Macro, you may extend this special
+# exception to the GPL to apply to your modified version as well.
+
+#serial 18
+
+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, [AS_HELP_STRING([--enable-portable-binary], [disable compiler optimizations that would produce unportable binaries])],
+ acx_maxopt_portable=$enableval, acx_maxopt_portable=no)
+
+# Try to determine "good" native compiler flags if none specified via CFLAGS
+if test "$ac_test_CFLAGS" != "set"; then
+ case $ax_cv_c_compiler_vendor in
+ dec) CFLAGS="$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="$CFLAGS -native -fast -xO5 -dalign"
+ if test "x$acx_maxopt_portable" = xyes; then
+ CFLAGS="$CFLAGS -xarch=generic"
+ fi;;
+
+ hp) CFLAGS="$CFLAGS +Oall +Optrs_ansi +DSnative"
+ if test "x$acx_maxopt_portable" = xyes; then
+ CFLAGS="$CFLAGS +DAportable"
+ fi;;
+
+ ibm) if test "x$acx_maxopt_portable" = xno; then
+ xlc_opt="-qarch=auto -qtune=auto"
+ else
+ xlc_opt="-qtune=auto"
+ fi
+ AX_CHECK_COMPILE_FLAG($xlc_opt,
+ CFLAGS="$CFLAGS -O3 -qansialias -w $xlc_opt",
+ [CFLAGS="$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="$CFLAGS -O3 -ansi_alias"
+ if test "x$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
+ *:756e6547:6c65746e:49656e69) # Intel
+ case $ax_cv_gcc_x86_cpuid_1 in
+ *0?6[[78ab]]?:*:*:*|?6[[78ab]]?:*:*:*|6[[78ab]]?:*:*:*) icc_flags="-xK" ;;
+ *0?6[[9d]]?:*:*:*|?6[[9d]]?:*:*:*|6[[9d]]?:*:*:*|*1?65?:*:*:*) icc_flags="-xSSE2 -xB -xK" ;;
+ *0?6e?:*:*:*|?6e?:*:*:*|6e?:*:*:*) icc_flags="-xSSE3 -xP -xO -xB -xK" ;;
+ *0?6f?:*:*:*|?6f?:*:*:*|6f?:*:*:*|*1?66?:*:*:*) icc_flags="-xSSSE3 -xT -xB -xK" ;;
+ *1?6[[7d]]?:*:*:*) icc_flags="-xSSE4.1 -xS -xT -xB -xK" ;;
+ *1?6[[aef]]?:*:*:*|*2?6[[5cef]]?:*:*:*) icc_flags="-xSSE4.2 -xS -xT -xB -xK" ;;
+ *2?6[[ad]]?:*:*:*) icc_flags="-xAVX -SSE4.2 -xS -xT -xB -xK" ;;
+ *3?6[[ae]]?:*:*:*) icc_flags="-xCORE-AVX-I -xAVX -SSE4.2 -xS -xT -xB -xK" ;;
+ *3?6[[cf]]?:*:*:*|*4?6[[56]]?:*:*:*) icc_flags="-xCORE-AVX2 -xCORE-AVX-I -xAVX -SSE4.2 -xS -xT -xB -xK" ;;
+ *000?f[[346]]?:*:*:*|?f[[346]]?:*:*:*|f[[346]]?:*:*:*) icc_flags="-xSSE3 -xP -xO -xN -xW -xK" ;;
+ *00??f??:*:*:*|??f??:*:*:*|?f??:*:*:*|f??:*:*:*) icc_flags="-xSSE2 -xN -xW -xK" ;;
+ esac ;;
+ esac ;;
+ esac
+ if test "x$icc_flags" != x; then
+ for flag in $icc_flags; do
+ AX_CHECK_COMPILE_FLAG($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 $icc_archflag"
+ fi
+ fi
+ ;;
+
+ gnu)
+ # default optimization flags for gcc on all systems
+ CFLAGS="$CFLAGS -O3 -fomit-frame-pointer"
+
+ # -malign-double for x86 systems
+ AX_CHECK_COMPILE_FLAG(-malign-double, CFLAGS="$CFLAGS -malign-double")
+
+ # -fstrict-aliasing for gcc-2.95+
+ AX_CHECK_COMPILE_FLAG(-fstrict-aliasing,
+ CFLAGS="$CFLAGS -fstrict-aliasing")
+
+ # note that we enable "unsafe" fp optimization with other compilers, too
+ AX_CHECK_COMPILE_FLAG(-ffast-math, CFLAGS="$CFLAGS -ffast-math")
+
+ AX_GCC_ARCHFLAG($acx_maxopt_portable)
+ ;;
+
+ microsoft)
+ # default optimization flags for MSVC opt builds
+ CFLAGS="$CFLAGS -O2"
+ ;;
+ esac
+
+ if test -z "$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="$CFLAGS -O3"
+ fi
+
+ AX_CHECK_COMPILE_FLAG($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 ""
+ ])
+
+fi
+])