Diagnostic 15414: Loop was not vectorized: loop body became empty after optimizations

Product Version: Intel® Fortran Compiler 15.0 and above

Cause:

The vectorization report generated when using Intel® Fortran Compiler's optimization options (/O2 /Qopt-report:2) states that loop was not vectorized since loop body became empty after optimizations.

Example:

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

integer function foo(a, b, n) 
    implicit none
    integer, intent(in) :: n
    real, intent(inout) :: a
    real, intent (in)   :: b
    integer :: i
    
    do i=1,n
           a = b + 1
    end do
    
    foo = a
    
end function 

Resolution:

In the example above, there is only one expression inside the loop. When moved outside the loop as a result of the compiler's optimization process there is nothing else left inside the loop to vectorize. 

See also:

Requirements for Vectorizable Loops

Vectorization Essentials

Vectorization and Optimization Reports

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