Diagnostic 15542: Loop was not vectorized: inner loop was already vectorized.

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

Cause:

The vectorization report generated when using Visual Fortran Compiler's optimization options ( -O2  -Qopt-report:2 ) states that loop was not vectorized since the inner loop was vectorized.

Example:

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

subroutine foo(a, n1, n)
    implicit none
    integer, intent(in) :: n, n1
    real, intent(inout) :: a(n1,n1)
    integer :: i, j

        do i=1,n
            do j=1,n
                a(j,i) = a(j,i) + 1
            end do
        end do
end subroutine foo

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

LOOP BEGIN at  f15542.f90(7,9)
remark #15542: loop was not vectorized: inner loop was already vectorized

LOOP BEGIN at  f15542.f90(8,13)
Peeled
LOOP END

LOOP BEGIN at  f15542.f90(8,13)
remark #15399: vectorization support: unroll factor set to 2
remark #15300: LOOP WAS VECTORIZED
LOOP END

LOOP END

See also:

Requirements for Vectorizable Loops

Vectorization Essentials

Vectorization and Optimization Reports

Back to the list of vectorization diagnostics for Intel Fortran