[Bug tree-optimization/123335] New: Missed vectorization for fortran deferred-shape array

[liuhongt at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=123335

            Bug ID: 123335
           Summary: Missed vectorization for fortran deferred-shape array
           Product: gcc
           Version: 16.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: tree-optimization
          Assignee: unassigned at gcc dot gnu.org
          Reporter: liuhongt at gcc dot gnu.org
  Target Milestone: ---

testcase: 

MODULE DDD
    REAL(8), DIMENSION(:,:,:), POINTER, CONTIGUOUS ::  u
    REAL(8), DIMENSION(:,:,:), POINTER, CONTIGUOUS ::  v
    REAL(8), DIMENSION(:), POINTER, CONTIGUOUS::  y 
END MODULE

MODULE KKK
USE DDD,    &
        ONLY: u,    &
              v,  &
              y

IMPLICIT NONE
PRIVATE
PUBLIC square
INTERFACE square
MODULE PROCEDURE square_ij
END INTERFACE square

CONTAINS
SUBROUTINE square_ij(i, j, x1, x2)


    implicit none
    integer, intent(in) :: x1
    integer, intent(in) :: x2
    INTEGER ::  i
    INTEGER ::  j
    INTEGER ::  k

    DO k = x1, x2
      y(k) = u(k,j, i) + v(k,j,i)
    ENDDO


 END SUBROUTINE  square_ij
 ENDMODULE KKK


link: https://godbolt.org/z/bvbn9h7oa

For deferred-shape array, compiler need to dynamically load element size so the
iv step is variable.

  _15 = u.span;

And GCC can't do vectorization for that, but LLVM can vectorize the loop, I
guess it supports dynamic versioning for the iv step.

It's probably similar issue as PR101450 which also need dynamic versioning but
for overflow not the size of iv step.