[Bug tree-optimization/77859] New: Ofast needed in presence of conditional code

["vincenzo.innocente at cern dot ch" <gcc-bugzilla at gcc dot gnu dot org>]

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

            Bug ID: 77859
           Summary: Ofast needed in presence of conditional code
           Product: gcc
           Version: 7.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: tree-optimization
          Assignee: unassigned at gcc dot gnu.org
          Reporter: vincenzo.innocente at cern dot ch
  Target Milestone: ---

It looks to me that to vectorize this code "relaxed floating point math" is not
a requirement

currently gcc version 7.0.0 20161004 (experimental) [trunk revision 240754]
(GCC) 
requires Ofast and not O3 to vectorize it

#include <cmath>

float x[1024];
float y[1024];

void needOfast() {
  for (int i=0; i<1024; ++i) {
   constexpr float pi4 = M_PI/4.;
   constexpr float pi2 = M_PI/2.;
   auto g1 = x[i] > pi4;
   auto xx = x[i];
   xx = g1 ? xx-pi2 : xx;
   auto g2 = xx > pi4;
   xx = g2 ? xx-pi2 : xx;
   y[i] = xx;
  }
}

in case anyone wonder this alternative formulation needs Ofast as well
void needOfastAsWell() {
  for (int i=0; i<1024; ++i) {
   constexpr float pi  = M_PI;
   constexpr float pi4 = M_PI/4.;
   constexpr float pi34 = 3.*M_PI/4.;
   constexpr float pi2 = M_PI/2.;
   auto g1 = x[i] > pi4;
   auto xx = x[i];
   xx = g1 ? xx-pi2 : xx;
   auto g2 = x[i] > pi34;
   xx = g2 ? x[i]-pi : xx;
   y[i] = xx;
  }
}