Re: [Lzip-bug] Speedup by including intrinsics for vectorization

[Antonio Diaz Diaz]

Hello Erick,

Erick Couts II wrote:
> I wanted to point out that no SSE intrinsics were included in the source
> code in order to vectorize the encoding process.  I've found that a small
> but decent speed gain can be achieved by including the immintrin.h header
> and then compiling with auto-vectorization enabled in GCC and LTO for
> linktime.  I also profiled the program after running with the --best option
> in order to further optimize the program.

What program? There are several programs in the lzip family.

I have tried your suggestion and I haven't noticed any increase in speed 
for '-9' in lzip-1.18 after including 'immintrin.h' (or 'ammintrin.h') 
and compiling with '-O3 -flto' on an AMD Athlon64 X2.


> I know that you like to keep code simple, but just adding in the #include
> immintrin.h to the headers will allow for auto-vectorization without
> requiring further changes to any of the existing code.

I like to keep code simple and portable. For example, 'immintrin.h' does 
not exist in the computer from which I'm writing this.

But the problem with these optimization hacks is that they tend to not 
being reproducible in other environments. As seems to be the case for 
this one.


Best regards,
Antonio.