Re: [AMBER-Developers] RHEL 4's gcc does not like -mtune=generic

From: Mark Williamson <>
Date: Mon, 02 Nov 2009 15:40:00 -0800

MengJuei Hsieh wrote:
> Hi,
> Here I have a slightly off-topic remark on the gfortran flags: If you see a
> warning on some certain version of gfortran (that happened to me on gcc
> version 4.3.0 20080428 (Red Hat 4.3.0-8) (GCC)), like this:
> gfortran -c -O3 -mtune=generic -mfpmath=sse -ffree-form -o foo.o _foo.f
> f951: warning: SSE instruction set disabled, using 387 arithmetics
> Just add a -msse before the -mfpmath=sse and the warnings will go away.
> Best,

As you justed stated off list to me, this is a i386 machine and from the
gfortran 4.4.2 man page:

        Use scalar floating point instructions present in the SSE instruction
set. This instruction set is supported by Pentium3 and newer chips, in
the AMD line by Athlon-4, Athlon-xp and Athlon-mp chips. The earlier
version of SSE instruction set supports only single precision
arithmetics, thus the double and extended precision arithmetics is still
done using 387. Later version, present only in Pentium4 and the future
AMD x86-64 chips supports double precision arithmetics too.
                For the i386 compiler, you need to use -march=cpu-type,
-msse or -msse2 switches to enable SSE extensions and make this option
effective. For the x86-64 compiler, these extensions are enabled by


I've justed updated the tree's configure file to deal with the i386
situation. Thanks for the report.



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Received on Mon Nov 02 2009 - 16:00:07 PST
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