c++: Redetermine whether to write vtables on stream-in [PR114229]

We currently always stream DECL_INTERFACE_KNOWN, which is needed since
many kinds of declarations already have their interface determined at
parse time.  But for vtables and type-info declarations we need to
re-evaluate on stream-in as whether they need to be emitted or not
changes in each TU, so this patch clears DECL_INTERFACE_KNOWN on these
kinds of declarations so that they can go through 'import_export_decl'
again.

Note that the precise details of the virt-2 tests will need to change
when we implement the resolution of [1], for now I just updated the test
to not fail with the new (current) semantics.

[1]: itanium-cxx-abi/cxx-abi#171

	PR c++/114229

gcc/cp/ChangeLog:

	* module.cc (trees_out::core_bools): Redetermine
	DECL_INTERFACE_KNOWN on stream-in for vtables and tinfo.
	* decl2.cc (import_export_decl): Add fixme for ABI changes with
	module vtables and tinfo.

gcc/testsuite/ChangeLog:

	* g++.dg/modules/virt-2_b.C: Update test to acknowledge that we
	now emit vtables here too.
	* g++.dg/modules/virt-3_a.C: New test.
	* g++.dg/modules/virt-3_b.C: New test.
	* g++.dg/modules/virt-3_c.C: New test.
	* g++.dg/modules/virt-3_d.C: New test.

Signed-off-by: Nathaniel Shead <nathanieloshead@gmail.com>

gcc/cp/decl2.cc

@@ -3398,6 +3398,10 @@ import_export_decl (tree decl)
      unit.  */
   import_p = false;
 
+  /* FIXME: Since https://github.com/itanium-cxx-abi/cxx-abi/pull/171,
+     the ABI specifies that classes attached to named modules should
+     have their vtables uniquely emitted in the object for the module
+     unit in which it is defined.  And similarly for RTTI structures.  */
   if (VAR_P (decl) && DECL_VTABLE_OR_VTT_P (decl))
     {
       class_type = DECL_CONTEXT (decl);

gcc/cp/module.cc

@@ -5376,7 +5376,17 @@ trees_out::core_bools (tree t)
       WB (t->decl_common.lang_flag_2);
       WB (t->decl_common.lang_flag_3);
       WB (t->decl_common.lang_flag_4);
-      WB (t->decl_common.lang_flag_5);
+
+      {
+	/* This is DECL_INTERFACE_KNOWN: We should redetermine whether
+	   we need to import or export any vtables or typeinfo objects
+	   on stream-in.  */
+	bool interface_known = t->decl_common.lang_flag_5;
+	if (VAR_P (t) && (DECL_VTABLE_OR_VTT_P (t) || DECL_TINFO_P (t)))
+	  interface_known = false;
+	WB (interface_known);
+      }
+
       WB (t->decl_common.lang_flag_6);
       WB (t->decl_common.lang_flag_7);
       WB (t->decl_common.lang_flag_8);

gcc/testsuite/g++.dg/modules/virt-2_b.C

@@ -21,8 +21,7 @@ int main ()
   return !(Visit (&me) == 1);
 }
 
-// We do not emit Visitor vtable
-// but we do emit rtti here
-// { dg-final { scan-assembler-not {_ZTVW3foo7Visitor:} } }
+// Again, we emit Visitor vtable and rtti here
+// { dg-final { scan-assembler {_ZTVW3foo7Visitor:} } }
 // { dg-final { scan-assembler {_ZTIW3foo7Visitor:} } }
 // { dg-final { scan-assembler {_ZTSW3foo7Visitor:} } }

gcc/testsuite/g++.dg/modules/virt-3_a.C

@@ -0,0 +1,9 @@
+// PR c++/114229
+// { dg-additional-options "-fmodules-ts -Wno-global-module" }
+// { dg-module-cmi modA }
+
+module;
+template<class> struct basic_streambuf { virtual void overflow() { } };
+extern template struct basic_streambuf<long>;
+export module modA;
+export basic_streambuf<long> *p;

gcc/testsuite/g++.dg/modules/virt-3_b.C

@@ -0,0 +1,6 @@
+// PR c++/114229
+// { dg-additional-options "-fmodules-ts -fno-module-lazy" }
+// { dg-module-cmi modB }
+
+export module modB;
+import modA;

gcc/testsuite/g++.dg/modules/virt-3_c.C

@@ -0,0 +1,3 @@
+// PR c++/114229
+template<class> struct basic_streambuf { virtual void overflow() { } };
+template struct basic_streambuf<long>;

gcc/testsuite/g++.dg/modules/virt-3_d.C

@@ -0,0 +1,7 @@
+// PR c++/114229
+// { dg-module-do link }
+// { dg-additional-options "-fmodules-ts -fno-module-lazy" }
+
+import modA;
+import modB;
+int main() { }