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Re: [patch, fortran] Warn about suspicious assignment to contiguous pointers
Hi Janus,
I think an unconditional warning is OK
in this case because
- Assigning to a pointer from an obvious non-contiguous target
is not useful at all, that I can see
I guess you're talking about a *contiguous* pointer here,
Correct.
and in that
case I would argue that, beyond being "not useful", it's even illegal,
so why not throw a hard error, if we can infer at compile-time that
the target is non-contiguous?
Problem is, we cannot infer this from the tests done.
We would also have to add a test if the array is empty
or that it contains only a single element, and that (I think)
is a) impossible in the general case, and b) not worth the bother.
I'm not sure I understand which cases you're worried about here. Maybe
you can give an example?
real, dimension(5,5), target :: a
real, dimension(:,:), pointer, contiguous :: ap
ap => a(4::2,4::2)
points to a single element, which is (by definition) contiguous.
In any case, I think your test case is a bit short, so I extended it
somewhat (see attachment) and found two cases along the way where your
patch throws a warning but shouldn't:
r => x(::-1)
This one is _not_ contiguous; contiguos implies stride==1.
r => x2(2:3,1)
Correct, I will correct that one.
Apart from the two mishandled cases above, one other thing comes to my
mind: It might be a good idea to apply your checks not only to pointer
assignments, but also to dummy arguments (passing a non-contiguous
array to a contiguous dummy pointer), where the same rules should
apply.
This is true.
There are also a few other checks that I missed, for
example
subroutine foo(a)
real, dimension(:), target, intent(inout) :: a
real, dimension(:), contiguous :: ap
ap => a
I will also address this in a future version of the patch. This will
take a bit of time, though.
Regards
Thomas