[Bug fortran/52861] New: (missed optimisation) missed transformation to memset with -O3

["arnaud02 at users dot sourceforge.net" <gcc-bugzilla at gcc dot gnu dot org>]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=52861

             Bug #: 52861
           Summary: (missed optimisation) missed transformation to memset
                    with -O3
    Classification: Unclassified
           Product: gcc
           Version: 4.7.0
            Status: UNCONFIRMED
          Severity: minor
          Priority: P3
         Component: fortran
        AssignedTo: unassigned@gcc.gnu.org
        ReportedBy: arnaud02@users.sourceforge.net


This is a minor missed-optimisation noticed as follow up to PR52835.
This is not a regression.

>cat qq1.f
      SUBROUTINE QQ2( ISU, ZSPM, RSV, MS )
      INTEGER :: ISU(MS)
      CHARACTER(8) :: ZSPM(MS)
      REAL :: RSV(MS)

      DO IS=1,MS
         ISU(IS)=0
         ZSPM(IS)=' '
         RSV(IS) =0.0
      ENDDO
      END subroutine qq2
>cat qq2.f
      SUBROUTINE QQ2( ISU, ZSPM, RSV, MS )
      INTEGER :: ISU(MS)
      CHARACTER(8) :: ZSPM(MS)
      REAL :: RSV(MS)

      DO IS=1,MS
         ISU(IS)=0
         RSV(IS) =0.0
      ENDDO
      DO IS=1,MS
         ZSPM(IS)=' '
      ENDDO
      END subroutine qq2
>gfortran470 -O3 -c qq1.f ; gfortran470 -O3 -c qq2.f
>nm qq1.o qq2.o

qq1.o:
0000000000000000 T qq2_

qq2.o:
                 U memset
0000000000000000 T qq2_

The compiler has not be able to transform the assignments to ISU and RSV as
calls to memset when the loop contains an assignment to a CHARACTER variable.
This suggests that the dependency generator can be improved or that the Fortran
front-end could pass a better representation to the middle-end.

Additionally, it should be possible to transform 
      DO IS=1,MS
         ZSPM(IS)=' '
      ENDDO
as a call to memset. gcc 4.7.0 cannot:

>cat qq3.f
      SUBROUTINE QQ2( ZSPM, MS )
      CHARACTER(8) :: ZSPM(MS)
      DO IS=1,MS
         ZSPM(IS)=' '
      ENDDO
      END subroutine qq2
>/usr/local/gcc/gfortran470 -O3 -c qq3.f
>nm qq3
qq3.f  qq3.o
>nm qq3.o
0000000000000000 T qq2_