Cause:
This vectorization diagnostic is emitted starting from Intel(R) C++ Compiler 15.0. This diagnostic message is emitted when -ffreestanding compiler option is used. Generally the vectorizer uses SVML ldivide ibrary call to vectorize this loop. Using -ffreestanding compiler option will not use the SVML library and that's when this diagnostic message is emitted.
Examples:
void foo(int *a, int *b, int n){
int i;
for (i=0;i<n;i++){
a[i] /= b[i];
}
}
$ icpc -c test41.cc -qopt-report2 -qopt-report-phase=vec -qopt-report-file=stderr -ffreestanding
Begin optimization report for: foo(int *, int *, int)
Report from: Vector optimizations [vec]
LOOP BEGIN at test41.cc(3,3)
<Multiversioned v1>
remark #15378: loop was not vectorized: -ffreestanding flag prevents vectorization of integer divide/remainder [ test41.cc(4,5) ]
LOOP END
LOOP BEGIN at test41.cc(3,3)
<Multiversioned v2>
remark #15304: loop was not vectorized: non-vectorizable loop instance from multiversioning
LOOP END