[Bug tree-optimization/58359] New: __builtin_unreachable prevents vectorization

[glisse at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=58359

            Bug ID: 58359
           Summary: __builtin_unreachable prevents vectorization
           Product: gcc
           Version: 4.9.0
            Status: UNCONFIRMED
          Keywords: missed-optimization
          Severity: normal
          Priority: P3
         Component: tree-optimization
          Assignee: unassigned at gcc dot gnu.org
          Reporter: glisse at gcc dot gnu.org

void f(int*q){
  int*p=(int*)__builtin_assume_aligned(q,32);
  for(int i=0;i<(1<<20);++i){
    if(p+i==0)__builtin_unreachable();
    p[i]=i;
  }
}

If I remove the line with __builtin_unreachable, this is vectorized at -O3. But
as is, we have control flow in the loop and the vectorizer won't even try.