> > Here's some questions I need to figure out: > (1) Why do I have to throw the -funsafe-math-optimizations flag to > enable this? > -- I see where the .vect file warns of it, but it refers to an SSA line, > so I'm not sure what's going on.
This flag is needed in order to allow vectorization of reduction (summation in your case) of floating-point data. This is because vectorization of reduction changes the order of the computation, which may result in different behavior (instead of summing this way: ((((((a0+a1)+a2)+a3)+a4)+a5)+a6)+a7, we sum this way (((a0+a2)+a4)+a6)+(((a1+a3)+a5)+a7) > (2) Is there any pragma or assertion, etc, that I can put in the code to > notify the compiler that certain pointers point to 16-byte aligned data? > -- Only the output array (C) is possibly misaligned in ATLAS > Not really, I'm afraid - there is something that's not entirely supported in gcc yet - see details in PR20794. dorit > Thanks, > Clint > > > -- > > > http://gcc.gnu.org/bugzilla/show_bug.cgi?id=27827 >
