Diagnostic 15521: Loop was not vectorized: compile time constraints prevent loop optimization.

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 -traceback -check:bounds -check:nostack) states that loop was not vectorized due to compile time constraints.

Example:

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

subroutine foo (a,n)

 implicit none

interface
   function bar(n)
     integer :: bar
     integer, intent(in) :: n
   end function bar
end interface

    integer, intent(in) :: n
    real,intent(inout) :: a(n)
    integer :: i

  do i=1, bar(i)
     a(i) = 0
  end do

end  subroutine foo 

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

LOOP BEGIN f15521.f90(16,3)
   remark #15532: loop was not vectorized: compile time constraints prevent loop optimization. Consider using -O3.
LOOP END

Resolution:

Setting check:nobounds will vectorize the loop. Resulting optimization report will include the following remarks:

   remark #25084: Preprocess Loopnests: Moving Out Store   
   remark #15399: vectorization support: unroll factor set to 2
   remark #15300: LOOP WAS VECTORIZED

See also:

Requirements for Vectorizable Loops

Vectorization Essentials

Vectorization and Optimization Reports

Back to the list of vectorization diagnostics for Intel Fortran