The heap control switches – `-H32' and `-H64' – determine whether dynamic allocation uses 32-bit or 64-bit memory. They only affect compiler-generated allocations via __gnat_malloc; explicit calls to malloc and related functions from the C run-time library are unaffected.
Allocate memory on 32-bit heap
Allocate memory on 64-bit heap. This is the default unless explicitly overridden by a ’Size clause on the access type.
These switches are only effective on VMS platforms.