On 02/21/2017 11:08 AM, Jason Merrill wrote:
On 02/17/2017 05:07 PM, Martin Sebor wrote:
* decl.c (poplevel): Avoid diagnosing entities declared with
attribute unused.
This change is OK.
(initialize_local_var): Do not consider the type of a variable
when determining whether or not it's used.
This is not; the documentation for attribute unused says,
When attached to a type (including a @code{union} or a @code{struct}),
this attribute means that variables of that type are meant to appear
possibly unused. GCC does not produce a warning for any variables of
that type, even if the variable appears to do nothing. This is often
the case with lock or thread classes, which are usually defined and then
not referenced, but contain constructors and destructors that have
nontrivial bookkeeping functions.
So a TREE_USED type should imply TREE_USED on variables of that type.
Yes, I'm familiar with the effect of the attribute on types but
in my testing this change doesn't affect how it works (i.e., it
passes a full bootstrap and regression tests and I haven't been
able to construct a failing test case.) It looks like that's
because TREE_USED(decl) is already set here for a decl whose
type is declared attribute used.
While trying to come up with a test case to exercise the scenario
you describe I see that current trunk doesn't handle it correctly
but the patch just happens to fix that too. For example:
template <class T>
void f ()
{
T t; // trunk warns for f<int> (good)
typedef T U;
U u; // trunk doesn't warn for f<int> (bug 79548)
}
template void f<int>();
struct __attribute__ ((unused)) S { };
template void f<S>(); // no warnings here (good)
void g ()
{
S s;
typedef S T;
T t; // trunk warns here (new bug), doesn't with the patch
}
In the test case above, TREE_USED (TREE_TYPE (decl)) is set for
t in g() so trunk sets it on t too and warbs. The patch doesn't
and so it doesn't warn as expected.
But it's entirely possible I'm missing a case. Do you have
a suggestion for a test that trunk handles correctly but that
fails with the patch?
Thanks
Martin
