http://gcc.gnu.org/bugzilla/show_bug.cgi?id=58821
Bug ID: 58821 Summary: conditional reduction does not vectorize Product: gcc Version: 4.9.0 Status: UNCONFIRMED Severity: normal Priority: P3 Component: tree-optimization Assignee: unassigned at gcc dot gnu.org Reporter: vincenzo.innocente at cern dot ch in the following foo vectorize bar does not (bar does not vectorize even for if (x[i]>0) s+=x[i]; ) compiled as c++ -Ofast -fopt-info-loop -S condRed.cc -fopenmp -ftree-loop-if-convert-stores -march=core-avx2 gcc version 4.9.0 20131011 (experimental) [trunk revision 203426] (GCC) neither #pragma omp simd reduction(+:s) nor #pragma ivdep helps const int N=1024; float x[N], y[N]; float bar() { float s=0; for (int i=0; i<N; ++i) if (x[i]>0) s+=y[i]; return s; } float foo() { float s=0; for (int i=0; i<N; ++i) s+= (x[i]>0) ?y[i] : 0; return s; } float barOMP() { float s=0; #pragma omp simd reduction(+:s) for (int i=0; i<N; ++i) if (x[i]>0) s+=y[i]; return s; } float fooOMP() { float s=0; #pragma omp simd reduction(+:s) for (int i=0; i<N; ++i) s+= (x[i]>0) ?y[i] : 0; return s; } float barIVDEP() { float s=0; #pragma ivdep for (int i=0; i<N; ++i) if (x[i]>0) s+=y[i]; return s; }