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
