Vectorize a loop in Fortran with vector processor

Question

I'm trying to vectorize the loops in a Fortran program with gfortran and the Intel Xeon CPU.

Previously, the vectorization was implemented by constating

!VOCL LOOP,NOVREC
!DIR$ IVDEP

which could have worked on a Fujitsu before the loop. But these don't work anymore.

Does anyone have ideas how to vectorize the loop.

Since I'm a newbie for this, it would be perfect if you can show an example to test the result

Here's the code I use to test if it works

        PROGRAM VECT_TEST
        IMPLICIT NONE

        INTEGER :: L(10)
        INTEGER :: I

        DO I = 1, 10
          L(I) = I
        END DO

!VOCL LOOP,NOVREC
!DIR$ IVDEP
        DO I = 1, 10
          L(I)=L(I) + 1
        END DO

        END PROGRAM

With a test command

gfortran vect_test.f -fopt-info-all -O3

I got the error output like this

vect_test.f:18:0: note: ===vect_slp_analyze_bb=== vect_test.f:18:0: note: === vect_analyze_data_refs === vect_test.f:18:0: note: not vectorized: not enough data-refs in basic block.

You can start here software.intel.com/en-us/articles/… software.intel.com/sites/default/files/article/301483/… — Vladimir F Героям слава
– Vladimir F Героям слава, Commented Jul 13, 2015 at 8:59
Yeah I did. Actually I also tried !DIR$ SMID that didn't work either. I'll show the code. Maybe I test it in a wrong way — Shiyu
– Shiyu, Commented Jul 13, 2015 at 9:07
Thanks Vladimir, I got your idea, I've just updated the post — Shiyu
– Shiyu, Commented Jul 13, 2015 at 9:52

Vladimir F Героям слава · Accepted Answer · 2015-07-13 10:57:35Z

3

Your program is useless, the compiler optimizes everything away. If you print the content of the array at the end and make the array larger, it will actually vectorize the loop:

PROGRAM VECT_TEST
IMPLICIT NONE

INTEGER :: L(1024)
INTEGER :: I

DO I = 1, 1024
  L(I) = I
END DO

DO I = 1, 1024
  L(I)=L(I) + 1
END DO

PRINT *, L

END PROGRAM

compile:

gfortran vec.f90 -ftree-vectorizer-verbose=1  -O3

Analyzing loop at vec.f90:13


Vectorizing loop at vec.f90:13

vec.f90:13: note: LOOP VECTORIZED.
Analyzing loop at vec.f90:7


Vectorizing loop at vec.f90:7

vec.f90:7: note: LOOP VECTORIZED.
vec.f90:1: note: vectorized 2 loops in function.

edited Jul 13, 2015 at 10:57

answered Jul 13, 2015 at 10:52

Vladimir F Героям слава

60.7k4 gold badges82 silver badges131 bronze badges

Sign up to request clarification or add additional context in comments.

1 Comment

Shiyu Over a year ago

Well okay. This command doesn't print any message on my computer but I got the same result with -fopt-info -O3. Thanks a lot

Collectives™ on Stack Overflow

Vectorize a loop in Fortran with vector processor

1 Answer 1

1 Comment

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

1 Comment

Your Answer

Sign up or log in

Post as a guest

Related