On Thu, 24 Apr 2025 at 15:48, Jonathan Wakely <[email protected]> wrote:
>
> On Fri, 18 Apr 2025 at 23:08, Jason Merrill <[email protected]> wrote:
> >
> > limit_bad_template_recursion currently avoids immediate instantiation of
> > templates from uses in an already ill-formed instantiation, but we still can
> > get unnecessary recursive instantiation in pending_templates if the
> > instantiation was queued before the error.
> >
> > Currently this regresses several libstdc++ tests which seem to rely on a
> > static_assert in a function called from another that is separately
> > ill-formed.
> > For instance, in the 48101_neg.cc tests, we first get an error in find(),
> > then
> > later instantiate _S_key() (called from find) and get the static_assert
> > error
> > from there.
> >
> > Thoughts? Is this a desirable change, or is the fact that the use precedes
> > the
> > error reason to go ahead with the instantiation?
> >
> > > FAIL: 23_containers/map/48101_neg.cc -std=gnu++17 (test for errors,
> > > line )
> > > FAIL: 23_containers/multimap/48101_neg.cc -std=gnu++17 (test for
> > > errors, line )
> > > FAIL: 23_containers/multiset/48101_neg.cc -std=gnu++17 (test for
> > > errors, line )
> > > FAIL: 23_containers/set/48101_neg.cc -std=gnu++17 (test for errors,
> > > line )
>
> As discussed the other day, I will tweak the diagnostics for the
> associative containers so that these tests don't regress. I'll post
> that for review shortly.
>
> > > FAIL: 30_threads/packaged_task/cons/dangling_ref.cc -std=gnu++17 (test
> > > for errors, line )
> > > FAIL: 30_threads/packaged_task/cons/lwg4154_neg.cc -std=gnu++17 (test
> > > for errors, line )
>
> These two don't strictly need to use dg-error for the messages that
> disappear with your patch, they could have used dg-prune-output
> instead. What the test intends to check is that we get a failed
> static_assert for std::is_invocable_r_v, and that's still the case.
> The other errors are collateral damage, and your patch prevents that.
> Which is a good thing. So we can just remove the failing dg-error
> lines.
>
> I'll finish testing my associative container changes, then push your
> patch after mine lands.
The front end patch has been pushed as r16-133-g8acea9ffa82ed8
>
> >
> >
> > gcc/cp/ChangeLog:
> >
> > * cp-tree.h (struct tinst_level): Add had_errors bit.
> > * pt.cc (push_tinst_level_loc): Clear it.
> > (pop_tinst_level): Set it.
> > (reopen_tinst_level): Check it.
> > (instantiate_pending_templates): Call limit_bad_template_recursion.
> >
> > gcc/testsuite/ChangeLog:
> >
> > * g++.dg/template/recurse5.C: New test.
> > ---
> > gcc/cp/cp-tree.h | 10 ++++++++--
> > gcc/cp/pt.cc | 10 ++++++++--
> > gcc/testsuite/g++.dg/template/recurse5.C | 17 +++++++++++++++++
> > 3 files changed, 33 insertions(+), 4 deletions(-)
> > create mode 100644 gcc/testsuite/g++.dg/template/recurse5.C
> >
> > diff --git a/gcc/cp/cp-tree.h b/gcc/cp/cp-tree.h
> > index 7798efba3db..856202c65dd 100644
> > --- a/gcc/cp/cp-tree.h
> > +++ b/gcc/cp/cp-tree.h
> > @@ -6755,8 +6755,14 @@ struct GTY((chain_next ("%h.next"))) tinst_level {
> > /* The location where the template is instantiated. */
> > location_t locus;
> >
> > - /* errorcount + sorrycount when we pushed this level. */
> > - unsigned short errors;
> > + /* errorcount + sorrycount when we pushed this level. If the value
> > + overflows, it will always seem like we currently have more errors, so
> > we
> > + will limit template recursion even from non-erroneous templates. In
> > a TU
> > + with over 32k errors, that's fine. */
> > + unsigned short errors : 15;
> > +
> > + /* set in pop_tinst_level if there have been errors since we pushed. */
> > + bool had_errors : 1;
> >
> > /* Count references to this object. If refcount reaches
> > refcount_infinity value, we don't increment or decrement the
> > diff --git a/gcc/cp/pt.cc b/gcc/cp/pt.cc
> > index a71705fd085..e8d342f99f6 100644
> > --- a/gcc/cp/pt.cc
> > +++ b/gcc/cp/pt.cc
> > @@ -11418,6 +11418,7 @@ push_tinst_level_loc (tree tldcl, tree targs,
> > location_t loc)
> > new_level->targs = targs;
> > new_level->locus = loc;
> > new_level->errors = errorcount + sorrycount;
> > + new_level->had_errors = false;
> > new_level->next = NULL;
> > new_level->refcount = 0;
> > new_level->path = new_level->visible = nullptr;
> > @@ -11468,6 +11469,9 @@ pop_tinst_level (void)
> > /* Restore the filename and line number stashed away when we started
> > this instantiation. */
> > input_location = current_tinst_level->locus;
> > + if (unsigned errs = errorcount + sorrycount)
> > + if (errs > current_tinst_level->errors)
> > + current_tinst_level->had_errors = true;
> > set_refcount_ptr (current_tinst_level, current_tinst_level->next);
> > --tinst_depth;
> > }
> > @@ -11487,7 +11491,7 @@ reopen_tinst_level (struct tinst_level *level)
> >
> > set_refcount_ptr (current_tinst_level, level);
> > pop_tinst_level ();
> > - if (current_tinst_level)
> > + if (current_tinst_level && !current_tinst_level->had_errors)
> > current_tinst_level->errors = errorcount+sorrycount;
> >
> > tree decl = level->maybe_get_node ();
> > @@ -28072,7 +28076,9 @@ instantiate_pending_templates (int retries)
> > tree instantiation = reopen_tinst_level ((*t)->tinst);
> > bool complete = false;
> >
> > - if (TYPE_P (instantiation))
> > + if (limit_bad_template_recursion (instantiation))
> > + /* Do nothing. */;
> > + else if (TYPE_P (instantiation))
> > {
> > if (!COMPLETE_TYPE_P (instantiation))
> > {
> > diff --git a/gcc/testsuite/g++.dg/template/recurse5.C
> > b/gcc/testsuite/g++.dg/template/recurse5.C
> > new file mode 100644
> > index 00000000000..7bfe5239f0a
> > --- /dev/null
> > +++ b/gcc/testsuite/g++.dg/template/recurse5.C
> > @@ -0,0 +1,17 @@
> > +// Test that we don't bother to instantiate add since there were errors in
> > +// checked_add.
> > +
> > +template <class T> T add (T t) { return t+1; } // { dg-bogus "no match" }
> > +
> > +template <class T> T checked_add (T t)
> > +{
> > + add (t);
> > + return t+1; // { dg-error "no match" }
> > +}
> > +
> > +struct A { };
> > +
> > +int main()
> > +{
> > + checked_add (A());
> > +}
> >
> > base-commit: 6808f74b4f07decb3727624f0e62e7c57ae87022
> > --
> > 2.49.0
> >
