[Bug tree-optimization/56541] New: vectorizaton fails in conditional assignment of a constant

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

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=56541

             Bug #: 56541
           Summary: vectorizaton fails in conditional assignment of a
                    constant
    Classification: Unclassified
           Product: gcc
           Version: 4.8.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: tree-optimization
        AssignedTo: unassigned@gcc.gnu.org
        ReportedBy: vincenzo.innocente@cern.ch


this loop does not vectorize

#include<cmath>
float a,b,c,d;

float z[1024]; bool ok[1024];
constexpr float rBig = 150.;

void foo() {
  for (int i=0;i!=1024;++i) {
    float rR = a*z[i];
    float rL = b*z[i];
    float rMin = (rR<rL) ? rR : rL;  
    float rMax = (rR<rL) ? rL : rR;  
    //rMin = (rMax>0) ? rMin : rBig+std::abs(z[i]); // this vectorize (sic...)
    rMin = (rMax>0) ? rMin : rBig; // comment to vectorize
    rMin = (rMin>0) ? rMin : rMax; 
    ok[i] = rMin-c<rMax+d;
  }

}

c++ -std=c++11 -Ofast -march=corei7 -c range.cc -ftree-vectorizer-verbose=1

Analyzing loop at range.cc:8
range.cc:7: note: vectorized 0 loops in function.
range.cc:16: note: vect_recog_bool_pattern: detected: 
range.cc:16: note: pattern recognized: VIEW_CONVERT_EXPR<unsigned
char>(ok[i_22]) = patt_15;
range.cc:16: note: additional pattern stmt: patt_13 = _14 < _16 ? 1 : 0;

adding to "rBig" std::abs(z[i]) it does
c++ -std=c++11 -Ofast -march=corei7 -c range.cc -ftree-vectorizer-verbose=1

Analyzing loop at range.cc:8

range.cc:8: note: vect_recog_bool_pattern: detected: 
range.cc:8: note: pattern recognized: VIEW_CONVERT_EXPR<unsigned
char>(ok[i_24]) = patt_16;

range.cc:8: note: additional pattern stmt: patt_14 = _15 < _17 ? 1 : 0;


Vectorizing loop at range.cc:8

range.cc:8: note: LOOP VECTORIZED.
range.cc:7: note: vectorized 1 loops in function.