[Bug rtl-optimization/78200] [7 Regression] 429.mcf of cpu2006 regresses in GCC trunk for avx2 target.

[rguenther at suse dot de]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=78200

--- Comment #18 from rguenther at suse dot de <rguenther at suse dot de> ---
On Tue, 15 Nov 2016, venkataramanan.kumar at amd dot com wrote:

> https://gcc.gnu.org/bugzilla/show_bug.cgi?id=78200
> 
> --- Comment #17 from Venkataramanan <venkataramanan.kumar at amd dot com> ---
> Looking at the check 
>                red_cost < 0 && arc->ident == AT_LOWER)
>             || (red_cost > 0 && arc->ident == AT_UPPER
> 
> The order if-combine created seem to be the best.
> 
> if (red_cost_86 < 0)
>     goto <bb 17>;
>   else
>     goto <bb 18>;
> 
>   <bb 17>:
>   if (_23 == 1)
>     goto <bb 19>;
>   else
>     goto <bb 20>;
> 
>   <bb 18>:
>   _340 = _23 == 2;
>   _341 = red_cost_86 > 0;
>   _338 = _340 & _341;
>   if (_338 != 0)
>     goto <bb 19>;
>   else
>     goto <bb 20>;
> 
>   <bb 19>:
>   basket_size.5_30 = basket_size;
>   _31 = basket_size.5_30 + 1;
>   basket_size = _31;
>   _32 = perm[_31];
>   _32->a = arc_47;
>   _32->cost = red_cost_86;
>   _33 = ABS_EXPR <red_cost_86>;
>   _32->abs_cost = _33;
> 
> If red_cost < 0  is false then checking for arc->ident == AT_UPPER first. This
> is better, since we know red_cost >0 will always be true.

red_cost can be zero.  The "bad" order is best (just slower for some
still unknown reason).