Diagnostic 15319: Using NOVECTOR directive

Product Version: Intel(R) Visual Fortran Compiler XE 15.0.0.070 

Cause:

When using NOVECTOR directive in code, the vectorization report generated using Visual Fortran Compiler's optimization and vectorization report options ( -O2 -Qopt-report:2) includes non-vectorized loop instance. 

Example:

An example below will generate the following remark in optimization report:

subroutine foo(a, b, n)
	implicit none
	integer, intent(in) :: n
	real, intent(inout) :: a(n)
	real, intent(in)    :: b(n)

    integer :: i

!DEC$ NOVECTOR

       do i=1,n
		     a(i)= b(i)+1
       end do

end subroutine foo 

Report from: Vector & Auto-parallelization optimizations [vec, par]

LOOP BEGIN at f15319.f90(11,8)

 remark #15319: loop was not vectorized: novector directive used

LOOP END

Resolution:

There may be cases where you want to explicitly avoid vectorization of a loop; for example, if vectorization would result in a performance regression rather than an improvement. In these cases, you can use the NOVECTOR directive to disable vectorization of the loop. 

See also:   

VECTOR and NOVECTOR

Requirements for Vectorizable Loops

Vectorization Essentials

Vectorization and Optimization Reports

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