Re: [PATCH] c++ modules: ICE with class NTTP argument [PR100616]

[Patrick Palka <ppalka@redhat.com>]

On Thu, 22 Sep 2022, Nathan Sidwell wrote:

> On 9/22/22 14:25, Patrick Palka wrote:
> 
> > index 80467c19254..722b64793ed 100644
> > --- a/gcc/cp/decl.cc
> > +++ b/gcc/cp/decl.cc
> > @@ -18235,9 +18235,11 @@ maybe_register_incomplete_var (tree var)
> >   	{
> >   	  /* When the outermost open class is complete we can resolve any
> >   	     pointers-to-members.  */
> > -	  tree context = outermost_open_class ();
> > -	  incomplete_var iv = {var, context};
> > -	  vec_safe_push (incomplete_vars, iv);
> > +	  if (tree context = outermost_open_class ())
> > +	    {
> > +	      incomplete_var iv = {var, context};
> > +	      vec_safe_push (incomplete_vars, iv);
> > +	    }
> 
> My immediate thought here is eek!  during stream in, the outermost_open_class
> could be anything -- to do with the context that wanted to lookup of the thing
> being streamed in, right?  So, the above change is I think just papering over
> a problem in this case.

D'oh, makes sense.  I suppose this second branch of
maybe_register_incomplete_var shouldn't ever be taken during stream-in.

> 
> not sure how to approach this.

Judging by the two commits that introduced/modified this part of
maybe_register_incomplete_var, r196852 and r214333, ISTM the code
is really only concerned with constexpr static data members (whose
initializer may contain a pointer-to-member for a currently open class).
So maybe we ought to restrict the branch like so, which effectively
disables this part of maybe_register_incomplete_var during stream-in, and
guarantees that outermost_open_class doesn't return NULL if the branch is
taken?

Bootstrapped and regtested on x86_64-pc-linux-gnu.


-- >8 --

Subject: [PATCH] c++ modules: ICE with class NTTP argument [PR100616]

	PR c++/100616

gcc/cp/ChangeLog:

	* decl.cc (maybe_register_incomplete_var): Restrict second branch
	to static data members from a currently open class.

gcc/testsuite/ChangeLog:

	* g++.dg/modules/pr100616_a.C: New test.
	* g++.dg/modules/pr100616_b.C: New test.
---
 gcc/cp/decl.cc                            |  2 ++
 gcc/testsuite/g++.dg/modules/pr100616_a.C |  8 ++++++++
 gcc/testsuite/g++.dg/modules/pr100616_b.C | 10 ++++++++++
 3 files changed, 20 insertions(+)
 create mode 100644 gcc/testsuite/g++.dg/modules/pr100616_a.C
 create mode 100644 gcc/testsuite/g++.dg/modules/pr100616_b.C

diff --git a/gcc/cp/decl.cc b/gcc/cp/decl.cc
index 80467c19254..ea616f0e686 100644
--- a/gcc/cp/decl.cc
+++ b/gcc/cp/decl.cc
@@ -18230,6 +18230,8 @@ maybe_register_incomplete_var (tree var)
 	  vec_safe_push (incomplete_vars, iv);
 	}
       else if (!(DECL_LANG_SPECIFIC (var) && DECL_TEMPLATE_INFO (var))
+	       && DECL_CLASS_SCOPE_P (var)
+	       && currently_open_class (DECL_CONTEXT (var))
 	       && decl_constant_var_p (var)
 	       && (TYPE_PTRMEM_P (inner_type) || CLASS_TYPE_P (inner_type)))
 	{
diff --git a/gcc/testsuite/g++.dg/modules/pr100616_a.C b/gcc/testsuite/g++.dg/modules/pr100616_a.C
new file mode 100644
index 00000000000..788af2eb533
--- /dev/null
+++ b/gcc/testsuite/g++.dg/modules/pr100616_a.C
@@ -0,0 +1,8 @@
+// PR c++/100616
+// { dg-additional-options "-std=c++20 -fmodules-ts" }
+// { dg-module-cmi pr100616 }
+export module pr100616;
+
+template<auto> struct C { };
+struct A { };
+C<A{}> c1;
diff --git a/gcc/testsuite/g++.dg/modules/pr100616_b.C b/gcc/testsuite/g++.dg/modules/pr100616_b.C
new file mode 100644
index 00000000000..a37eb08131b
--- /dev/null
+++ b/gcc/testsuite/g++.dg/modules/pr100616_b.C
@@ -0,0 +1,10 @@
+// PR c++/100616
+// { dg-additional-options "-std=c++20 -fmodules-ts" }
+module pr100616;
+
+C<A{}> c2;
+
+// FIXME: We don't reuse the artificial VAR_DECL for the class NTTP argument A{}
+// from the other translation unit, which causes these types to be different.
+using type = decltype(c1);
+using type = decltype(c2); // { dg-bogus "conflicting" "" { xfail *-*-* } }
-- 
2.38.0.rc1.2.g4b79ee4b0c