Diagnostic 15532: Loop Was Not Vectorized: Compile Time Constraints Prevent Loop Optimization

Product Version: Intel® Visual Fortran Compiler XE 15.0 or a later version 

Cause:

The vectorization report generated when using Visual Fortran Compiler's optimization options ( /O2  /Qopt-report:2 ) states that compile time constraints prevent optimization.

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 #15532: loop was not vectorized: compile time constraints prevent loop optimization. Consider using -O3.
 
  LOOP END

Resolution:

GOTO statements prevent vectorization since loop iteration count cannot be computed.

See also:

Requirements for Vectorizable Loops

Vectorization Essentials

Vectorization and Optimization Reports

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