Diagnostic 15523: Loop was not vectorized: cannot compute loop iteration count before executing the loop.

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 ( -O3  -Qopt-report:2 ) states that loop was not vectorized since loop iteration count cannot be computed.

Example:

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

subroutine foo(a, n)

       implicit none
       integer, intent(in) :: n
       double precision, intent(inout) :: a(n)
       integer :: bar
       integer :: i

       i=0
 100   CONTINUE
       a(i)=0
       i=i+1
       if (i .lt. bar()) goto 100

  end subroutine foo

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

  LOOP BEGIN  
      remark #15523: loop was not vectorized: cannot compute loop iteration count before executing the loop.
 
  LOOP END

Resolution:

 -goto statements prevent vectorization, rewriting the code will get this loop vectorized.

See also:

Requirements for Vectorizable Loops

Vectorization Essentials

Vectorization and Optimization Reports

Back to the list of vectorization diagnostics for Intel Fortran