Performance problem with gcc 4.9.2-3 on 64 bit

Marco Atzeri marco.atzeri@gmail.com
Sat Feb 28 12:14:00 GMT 2015


On 2/27/2015 5:49 PM, Bengt Larsson wrote:
> Below are two benchmarks that explore maximum floating point
> performance. loopm6 is double precision floating point and loopm6fp is
> parallell single-precision. They are manually unrolled multiply-add
> loops.
>
> I used to reach 2.8 and 11 GFlops on these. Now I only get
> 2 and 6.
>
> If you explore the inner loop with gcc -O2 -S you can see that it seems
> to use few registers.
>
> If you run them, there is a parameter expected. I use 30000 - 50000.
>
> gcc 4.9.2-3 on 64-bit. I use gcc -O2.
>

May be
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=53967


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