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From: "Joost.VandeVondele at pci dot uzh.ch" <gcc-bugzilla@gcc.gnu.org>
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Subject: [Bug middle-end/47341] New: unnecessary versioning in the vectorizer.
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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=47341

           Summary: unnecessary versioning in the vectorizer.
           Product: gcc
           Version: 4.6.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: middle-end
        AssignedTo: unassigned@gcc.gnu.org
        ReportedBy: Joost.VandeVondele@pci.uzh.ch


with current trunk:

> cat test.f90
   SUBROUTINE HARD_NN_4_4_4_5_1_2_4(C,A,B)
      REAL(KIND=8) :: C(4,*)
      REAL(KIND=8) :: B(4,*), A(4,*)
      INTEGER ::i,j,l
      l=           1
      DO j=           1 ,           4 ,           2
      DO i=           1 ,           4 ,           1
        C(i+0,j+0)=C(i+0,j+0)+A(i+0,l+0)*B(l+0,j+0)
        C(i+0,j+0)=C(i+0,j+0)+A(i+0,l+1)*B(l+1,j+0)
        C(i+0,j+0)=C(i+0,j+0)+A(i+0,l+2)*B(l+2,j+0)
        C(i+0,j+0)=C(i+0,j+0)+A(i+0,l+3)*B(l+3,j+0)
        C(i+0,j+1)=C(i+0,j+1)+A(i+0,l+0)*B(l+0,j+1)
        C(i+0,j+1)=C(i+0,j+1)+A(i+0,l+1)*B(l+1,j+1)
        C(i+0,j+1)=C(i+0,j+1)+A(i+0,l+2)*B(l+2,j+1)
        C(i+0,j+1)=C(i+0,j+1)+A(i+0,l+3)*B(l+3,j+1)
      ENDDO
      ENDDO
    END SUBROUTINE

> gfortran-trunk -c -O2 -fno-unroll-loops -ftree-vectorize -ftree-vectorizer-verbose=1 -march=core2 -msse4.2 test.f90

test.f90:7: note: created 1 versioning for alias checks.

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

The compiler should not need to generate various version of these loops. With
the bounds info provided, nothing can alias (I think).