> HMm, i'd just record it for all of them, since the [fields] are accessible
> through a pointer to the structure.
They are indeed accessible this way...
> Just because you can't directly take the address of a bitfield doesn't
> mean you can't access one through a pointer, which is the entire
> purpose of knowing alias sets (knowing what a pointer dereference
> could affect).
...but DECL_NONADDRESSABLE_P precisely means that the alias set used for
accessing these fields at the RTL level is that of the containing structure:
/* Return true if all nested component references handled by
get_inner_reference in T are such that we should use the alias set
provided by the object at the heart of T.
This is true for non-addressable components (which don't have their
own alias set), as well as components of objects in alias set zero.
This later point is a special case wherein we wish to override the
alias set used by the component, but we don't have per-FIELD_DECL
assignable alias sets. */
bool
component_uses_parent_alias_set (tree t)
{
while (1)
{
/* If we're at the end, it vacuously uses its own alias set. */
if (!handled_component_p (t))
return false;
switch (TREE_CODE (t))
{
case COMPONENT_REF:
if (DECL_NONADDRESSABLE_P (TREE_OPERAND (t, 1)))
return true;
break;
so the code in record_component_aliases is consistent with that.
Adam has simply run with C into another form of the same discrepancy we have
run into when we tried to enable struct aliasing with Ada, see PR 25737.
--
Eric Botcazou
