[Bug fortran/31016] New: Use __buildin_memcpy and __memcpy for array assignment

["burnus at gcc dot gnu dot org" <gcc-bugzilla@gcc.gnu.org>]

For the most common array assignments where the size is known at compile-time,
we already use __buildin_memcpy; but the following cases were missed:

subroutine bar(a)
 implicit none
 real :: a(*),b(12)
 b = a(1:12)
end subroutine


subroutine bar(a,b)
 implicit none
 real :: a(*),b(*)
 a(1:12) = b(2:13)
end subroutine


And __buildin_memset can be used for:

subroutine bar(a)
 implicit none
 real :: a(*),b(12)
 a(1:12) = 12
end subroutine


For the following examples, the __buildin_* function can not be used as the
size is not known at compile time, but the memory should be contiguous and thus
__memcpy can be used:

subroutine bar(a,n)
 implicit none
 integer :: n
 real :: a(n), b(n)
 a = b
end subroutine


For the following case, one could use memset, but I'm not sure whether it will
be on average be faster than a normal do loop. (Overhead of function call
versus the optimization of memset using e.g. copy-on-write.)

subroutine bar(a,n)
 implicit none
 integer :: n
 real :: a(n)
 a = 5
end subroutine


-- 
           Summary: Use __buildin_memcpy and __memcpy for array assignment
           Product: gcc
           Version: 4.3.0
            Status: UNCONFIRMED
          Keywords: missed-optimization
          Severity: enhancement
          Priority: P3
         Component: fortran
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: burnus at gcc dot gnu dot org


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=31016