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From:	Hans Horn <hannes AT 2horns DOT com>
Subject:	Re: status of gcc4 -ffast-math
Date:	Thu, 05 Nov 2009 14:57:53 -0800
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Dave Korn wrote:
> Hans Horn wrote:
>> Folks,
>>
>> what is the current status of -ffast-math for gcc4 under cygwin.
>>
>> I tried to use it for some numerical C code and get the following link
>> errors:
>>
>> eval.o:eval.c:(.text+0x79c): undefined reference to `_f_pow'
>> eval.o:eval.c:(.text+0x7d8): undefined reference to `_f_log'
>> eval.o:eval.c:(.text+0x7f0): undefined reference to `_f_exp'
> 
>   WJFFM:
> 
>> $ cat math.c
>>
>> #include <math.h>
>>
>> int main (int argc, const char **argv)
>> {
>>
>>   float f = atof (argv[1]);
>>   double d = log (f);
>>   return exp (f);
>> }
>>
>>
>> admin AT ubik /tmp/math
>> $ gcc-4 math.c -o math
>>
>> admin AT ubik /tmp/math
>> $ gcc-4 math.c -o math -ffast-math
>>
>> admin AT ubik /tmp/math
>> $ gcc-4 math.c -o math -ffast-math -O2
>>
>> admin AT ubik /tmp/math
>> $ gcc-4 math.c -o math -ffast-math -O3
>>
>> admin AT ubik /tmp/math
>> $
> 
>   Perhaps a few more details about what you're doing, a simple reproducible
> testcase, what kind of command-lines you're using, etc. etc... might help.
> 
>     cheers,
>       DaveK

Dave,

I was just shooting into the dark expecting more like a yes/no wrt use 
of -ffast-math. Thx for responding!

I'm linking with gfortran (v4.5 or v4.3.4) (because the C code calls a 
lot of fortran under the hood).

This is how I compile & link:

gcc-4 -c -D_XOPEN_SOURCE_EXTENDED=1 -D_ALL_SOURCE -D_POSIX_SOURCE \ 
-std=c99 -Wall -Wshadow -Wreturn-type -Wunused \
-Wuninitialized -Wformat -Wunused-function -Wunused-macros 
-Wunused-label -Wredundant-decls -fno-leading-underscore -O3 \
-fno-strict-aliasing -Winline -fexpensive-optimizations \ 
-finline-functions -finline-limit=500000 -fstrength-reduce -fgcse \
-fgcse-lm -fgcse-sm -funroll-loops -fforce-addr -fomit-frame-pointer \
-ftree-vectorize -mfpmath=sse -msse3 -ffast-math \
-march=pentium4 -pipe -fbounds-check -Wextra -Winit-self  \
-DYY_NO_UNISTD_H -o math.o math.c

gfortran -O3 -fno-strict-aliasing -Winline -fexpensive-optimizations \
-finline-functions -finline-limit=500000 \
-fstrength-reduce -fgcse -fgcse-lm -fgcse-sm -funroll-loops -fforce-addr 
-fomit-frame-pointer -ftree-vectorize -mfpmath=sse \
-msse3 -ffast-math -march=pentium4 -pipe -L. -o math.exe math.o -Xlinker 
-\( -O3 -fno-strict-aliasing -Winline -fexpensive-optimizations \
  -finline-functions -finline-limit=500000 -fstrength-reduce -fgcse 
-fgcse-lm -fgcse-sm -funroll-loops -fforce-addr -fomit-frame-pointer \
  -ftree-vectorize -mfpmath=sse -msse3 -ffast-math -march=pentium4 -pipe 
-lm -lgsl -ly -lfl --enable-auto-import -Xlinker -\)

Compiling/linking your example gives:

math.c: In function ‘main’:
math.c:4: warning: implicit declaration of function ‘atof’
math.c:5: warning: unused variable ‘d’
math.c:3: warning: unused parameter ‘argc’
math.o:math.c:(.text+0x30): undefined reference to `_f_exp'
collect2: ld returned 1 exit status

Do you where this gobble stuff ‘ comes from, btw?

H.


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