How to get GCC on par with ICC?

[Steve Ellcey]

On Wed, 2018-06-20 at 17:11 -0400, NightStrike wrote:
>Â 
> If I could perhaps jump in here for a moment...  Just today I hit upon
> a series of small (in lines of code) loops that gcc can't vectorize,
> and intel vectorizes like a madman.  They all involve a lot of heavy
> use of std::vector<std::vector<float>>.  Comparisons were with gcc
> 8.1, intel 2018.u1, an AMD Opteron 6386 SE, with the program running
> as sched_FIFO, mlockall, affinity set to its own core, and all
> interrupts vectored off that core.  So, as close to not-noisy as
> possible.

There are a quite a number of bugzilla reports with examples where GCC
does not vectorize a loop. Â I wonder if this example is related to PR
61247.

Steve Ellcey