On 2/9/21 3:11 PM, Jakub Jelinek wrote:
On Tue, Feb 09, 2021 at 03:00:20PM -0500, Jason Merrill wrote:
With -fno-delete-null-pointer-checks which is e.g. implied by
-fsanitize=undefined or default on some embedded targets, the middle-end
folder doesn't consider addresses of global VAR_DECLs to be non-NULL, as one
of them could have address 0.
Hmm, are these VAR_DECLs going into the symtab? That seems undesirable.
They are not in the symtab from the C++ FE. And we don't allow those VAR_DECLs
or their
addresses to leak into the IL anyway.
But, they are TREE_STATIC because pretending they are automatic didn't
really work (e.g. address of automatic variables is not a constant expression).
The generic folding code uses maybe_nonzero_address predicate which
apprently creates a symtab entry for them but as nothing uses them they
won't be emitted.
Ah.
If we wanted to avoid that, we'd need to either add some generic VAR_DECL
bit for those vars or add a target hook that would return true for them and
then handle them in the middle-end.
I'm surprised that nonzero_address has such a limited set of things it
will actually believe have non-zero addresses with
-fno-delete-null-pointer-checks. But it seems that we should be able to
arrange to satisfy
if (definition && !DECL_EXTERNAL (decl)
since these "variables" are indeed defined within the current
translation unit.
Jason
