[Vm-dev] Portability problems: compiler flags

Mariano Martinez Peck marianopeck at gmail.com
Sun Apr 10 19:17:59 UTC 2011


On Sun, Apr 10, 2011 at 9:08 PM, Andreas Raab <andreas.raab at gmx.de> wrote:

>
>  On 4/10/2011 18:35, Mariano Martinez Peck wrote:
>
> Sorry for arriving late to the thread. I have a simiar problem now trying
> to compile Cog in a Windows box with MinGW.
>
> The problem is described in another thread:
> http://forum.world.st/Cannot-generate-VM-in-Windows-with-CMake-and-Git-tp3434566p3434566.html
>
> So...if we remove "-mno-fused-madd"  from windows confs like
> CogMsWindowsConfig, then Corquet wouldn't behave correctly ?  but if we keep
> them, it is difficult to compile in some platforms. So...I wonder, I am the
> only one trying to compile this on Windows?  Who do the Croquet guys do to
> compile with this flag in Windows?
>
>
> gcc 3.x accepts -mno-fused-madd fine.
>

Weird...I have

$ gcc --version
gcc.exe (GCC) 3.4.5 (mingw-vista special r3)
Copyright (C) 2004 Free Software Foundation, Inc.
This is free software; see the source for copying conditions.  There is NO
warranty; not even fo

and I have the error:

Scanning dependencies of target FloatMathPlugin
[ 13%] Building C object
FloatMathPlugin/CMakeFiles/FloatMathPlugin.dir/C_/maria
no/squeak/vm/cogVM/blessed/src/plugins/FloatMathPlugin/FloatMathPlugin.c.obj
cc1.exe: error: invalid option `no-fused-madd'
make[2]: ***
[FloatMathPlugin/CMakeFiles/FloatMathPlugin.dir/C_/mariano/squeak/v
m/cogVM/blessed/src/plugins/FloatMathPlugin/FloatMathPlugin.c.obj] Error 1
make[1]: *** [FloatMathPlugin/CMakeFiles/FloatMathPlugin.dir/all] Error 2
make: *** [all] Error 2
r MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.


Cheers

mariano


> Cheers,
>   - Andreas
>
>
> Thanks
>
> Mariano
>
> On Tue, Jan 25, 2011 at 9:05 PM, Nicolas Cellier <
> nicolas.cellier.aka.nice at gmail.com> wrote:
>
>>
>> 2011/1/25 Andreas Raab <andreas.raab at gmx.de>:
>> >
>> > On 1/25/2011 11:38 AM, Igor Stasenko wrote:
>> >>>
>> >>> Squeak uses highly unportable flag "-mno-fused-madd".
>> >>> It isn't present in many systems, even those using GCC,
>> >>> since many systems use older compilers.
>> >>>
>> >>> Also, why do you build fdlibm? It is old stuff that works not so well,
>> >>> we have better libm. Is there a way to use our libm?
>> >>>
>> >> I asked  same question few weeks ago.
>> >> Check mailing list archive for discussion.
>> >> In short: differrent libm implementations work differently and some
>> >> have bad support of IEEE standard.
>> >
>> > Actually, that's not quite the point. The issue is that Croquet requires
>> > bit-identical computations including floating point. For FPU
>> computations,
>> > the use of -mno-fused-madd avoids the use of the fused multiply-add
>> > operation by compilers which support it which would generate different
>> > results from compilers not using fused madd.
>> >
>> > The usage of fdlibm is similar. As Nicolas has pointed out elsewhere,
>> fdlibm
>> > is in some cases actually inferior of the platform libms (one might say
>> > outright broken) but the requirement for the usage in Croquet isn't
>> really
>> > whether it's "correct" or "good". The requirement is bit-identical
>> results
>> > across all platforms. The results can be wrong as long as they are
>> > consistently wrong. But they mustn't be different.
>> >
>>
>>  Yes, I was disappointed by exp(1), but fdlibm sin(pi+epsilon) is far
>> far superior to i86 hardwired answer (i86 approximation of pi is well
>> known to be poor).
>>
>> Nicolas
>>
>> > Having said that, for your regular Squeak VM (i.e., not requiring
>> > bit-identical floating point results) there really isn't a requirement
>> to
>> > use either -mno-fused-madd or fdlibm.
>> >
>> > Cheers,
>> >  - Andreas
>> >
>>
>
>
>
> --
> Mariano
> http://marianopeck.wordpress.com
>
>
>


-- 
Mariano
http://marianopeck.wordpress.com
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