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.
Download the latest version of ax_cc_maxopt.m4 or browse the macro’s revision history.
Copyright © 2008 Steven G. Johnson email@example.com
Copyright © 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 <http://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.