[Bug fortran/41137] New: inefficient zeroing of an array

[jv244 at cam dot ac dot uk]

triggered by some discussion in PR41113

SUBROUTINE S(a,n)
INTEGER :: n
REAL :: a(n,n,n,n)
a(:,:,:,:)=0.0
END SUBROUTINE

generates a four-fold look to do the zeroing, while it would be more efficient
to zero n**4 elements starting from a(1,1,1,1). I.e. since a is contiguous in
memory a memset or similar can be done (properly guarded for zero-sized
arrays).

Note that the case with compile time constant bounds is already captured i.e. 

.LFB2:
        movl    $40000, %edx
        xorl    %esi, %esi
        jmp     memset
.LFE2:

is generated for 

SUBROUTINE S(a)
REAL :: a(10,10,10,10)
a(:,:,:,:)=0.0
END SUBROUTINE


-- 
           Summary: inefficient zeroing of an array
           Product: gcc
           Version: 4.5.0
            Status: UNCONFIRMED
          Keywords: missed-optimization
          Severity: normal
          Priority: P3
         Component: fortran
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: jv244 at cam dot ac dot uk


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=41137