[Bug tree-optimization/77859] Ofast needed to vectorize loop in presence of conditional code

[rguenth at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=77859

Richard Biener <rguenth at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |NEW
   Last reconfirmed|                            |2016-10-05
     Ever confirmed|0                           |1

--- Comment #1 from Richard Biener <rguenth at gcc dot gnu.org> ---
The reason is that without -fno-trapping-math if-conversion fails as

iftmp.0_7 = _1 - 1.57079637050628662109375e+0;
tree could trap...

and we are gimplifying gi ? xx-pi2 : xx into control flow (I'm not 100% sure
what the standard says to the conditional operator and short-circuiting
of side-effects but I guess it is a short-circuite operation).

So, confirmed, but I don't see how we could fix this.  You might be able
to fix it by moving xx-pi2 compute to a separate statement.  OTOH sinking
may cause us ending up with exactly the same IL for if-conversion.