Re: [Mingw-users] Really slow executables generated by Msys/Mingw gcc

[Douglas V. <dou...@dy...>]

>Douglas Vechinski wrote:
>
>  
>
>>  1) gcc -o spdtst spdtst.c -lm
>>  2) gcc -O -o spdtst spdtst.c -lm
>>  3) gcc -O2 -o spdtst spdtst.c -lm
>>  4) gcc -O2 -ffast-math -o spdtst spdtst.c -lm
>>    
>>
>
>You didn't specify -march or -mtune anywhere.  Without those gcc is
>going to be rather conservative about the kind of code it generates, so
>it's probably not really a fair judge of its optimization capability
>verses other compilers.  Try giving -march to reflect the CPU of the
>system.  I'm not sure why the mingw and cygwin gcc doesn't line up
>against the linux compiled version of gcc very well, but it could be
>that those packages have different defaults "baked in" for -march and/or
>-mtune.
>
>gcc 4.2 will have -mtune=generic which does a somewhat better job of
>optimizing in a generic way for modern CPUs, but that is many versions
>removed from 3.3.
>
>Also, -lm is not necessary and does nothing under both mingw and Cygwin.
>
>Brian
>
>  
>
I tried what you suggested.  I added a -march=pentium4 to all the 
command lines and reran them. (I added the -mtune on the Msys/Mingw one 
also.  The cygwin one didn't recognize -mtune (maybe because of the 
version difference?) ) It did not make a difference worth mentioning.  
Resulted in similar run times for Cygwin, Cygwin -mno-cygwin, and 
Msys/Mingw as reported previously.

Douglas