Diagnostic 15331: Using FP model: precise prevents vectorization

Product Version: Intel® Fortran Compiler 15.0 and above 


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  /Qopt-report:2 /Qopt-report-phase:vec includes non-vectorized loop instance. 


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
ifort -c /fp:precise /O2 /Qopt-report:2 /Qopt-report-phase:vec /Qopt-report-file:stdout f15331.f90
Begin optimization report for: FOO
    Report from: Vector optimizations [vec]
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 [f15331.f90(10,4)]


Using fast FP model (Windows OS: /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

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