[Bug tree-optimization/91425] Ordered compares aren't optimised

[segher at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=91425

--- Comment #4 from Segher Boessenkool <segher at gcc dot gnu.org> ---
(In reply to Richard Biener from comment #1)
> where we end up with
> 
>   <bb 2> [local count: 1073741824]:
>   if (a_3(D) < b_4(D))
>     goto <bb 4>; [50.00%]
>   else
>     goto <bb 3>; [50.00%]
> 
>   <bb 3> [local count: 536870913]:
>   _6 = a_3(D) > b_4(D);
> 
>   <bb 4> [local count: 1073741824]:
>   # prephitmp_8 = PHI <_6(3), 1(2)>
> 
> instead of != compares.

instead of <> compares (LTGT).  With -ffast-math we should get the NE as
you say, and that works fine.