Diagnostic 15331: Using FP model: precise prevents vectorization

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

Cause:

When using Intel Fortran Compiler's option -fp:precise (Linux OS and OS X syntax: -fp-model precise) the vectorization report generated using Visual Fortran Compiler's optimization and vectorization report options ( -O2 - Qvec-report2 - Qopt-report:2) includes non-vectorized loop instance. 

Example:

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

subroutine foo(a, b, n)
	implicit none
    integer, intent(in) :: n
	real, intent(inout) :: a(n)
	real, intent(out) :: b
	real :: x = 0
	integer :: i

	do i=1,n
			x = x + a(i)
	end do

	b = x

end subroutine foo

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

LOOP BEGIN at f15331.f90(9,2)

remark #15331: loop was not vectorized: precise FP model implied by the command line or a directive prevents vectorization. Consider using fast FP model 

LOOP END

Resolution:

Using fast FP model (Win: -fp:fast , Linux and OS X syntax: -fp-model fast) option which allows more aggressive optimizations on floating-point data will get this loop vectorized.

See also:

fp-model, fp

Vectorization Essentials

Vectorization and Optimization Reports

Back to the list of vectorization diagnostics for Intel Fortran