c++/modules: Prevent maybe_clone_decl being called multiple times [PR115007]

The ICE in the linked PR is caused because maybe_clone_decl is not
prepared to be called on a declaration that has already had clones
created; what happens otherwise is that start_preparsed_function early
exits and never sets up cfun, causing a segfault later on.

To fix this we ensure that post_load_processing only calls
maybe_clone_decl if TREE_ASM_WRITTEN has not been marked on the
declaration yet, and (if maybe_clone_decls succeeds) marks this flag on
the decl so that it doesn't get called again later when finalising
deferred vague linkage declarations in c_parse_final_cleanups.

As a bonus this now allows us to only keep the DECL_SAVED_TREE around in
expand_or_defer_fn_1 for modules which have CMIs, which will have
benefits for LTO performance in non-interface TUs.

For clarity we also update the streaming code to do post_load_decls for
maybe in-charge cdtors rather than any DECL_ABSTRACT_P declaration, as
this is more accurate to the decls affected by maybe_clone_body.

	PR c++/115007

gcc/cp/ChangeLog:

	* module.cc (module_state::read_cluster): Replace
	DECL_ABSTRACT_P with DECL_MAYBE_IN_CHARGE_CDTOR_P.
	(post_load_processing): Check and mark TREE_ASM_WRITTEN.
	* semantics.cc (expand_or_defer_fn_1): Use the more specific
	module_maybe_has_cmi_p instead of modules_p.

gcc/testsuite/ChangeLog:

	* g++.dg/modules/virt-6_a.C: New test.
	* g++.dg/modules/virt-6_b.C: New test.

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

4 files changed, 24 insertions, 4 deletions

diff --git a/gcc/cp/module.cc b/gcc/cp/module.cc
index fd9b1d3..d7494cc 100644
--- a/gcc/cp/module.cc
+++ b/gcc/cp/module.cc
@@ -15539,7 +15539,7 @@ module_state::read_cluster (unsigned snum)
 
       if (abstract)
 	;
-      else if (DECL_ABSTRACT_P (decl))
+      else if (DECL_MAYBE_IN_CHARGE_CDTOR_P (decl))
 	vec_safe_push (post_load_decls, decl);
       else
 	{
@@ -17958,10 +17958,11 @@ post_load_processing ()
 
       dump () && dump ("Post-load processing of %N", decl);
 
-      gcc_checking_assert (DECL_ABSTRACT_P (decl));
+      gcc_checking_assert (DECL_MAYBE_IN_CHARGE_CDTOR_P (decl));
       /* Cloning can cause loading -- specifically operator delete for
 	 the deleting dtor.  */
-      maybe_clone_body (decl);
+      if (!TREE_ASM_WRITTEN (decl) && maybe_clone_body (decl))
+	TREE_ASM_WRITTEN (decl) = 1;
     }
 
   cfun = old_cfun;
diff --git a/gcc/cp/semantics.cc b/gcc/cp/semantics.cc
index 8c1a8b3..266fba1 100644
--- a/gcc/cp/semantics.cc
+++ b/gcc/cp/semantics.cc
@@ -5242,7 +5242,7 @@ expand_or_defer_fn_1 (tree fn)
 	 demand, so we also need to keep the body.  Otherwise we don't
 	 need it anymore.  */
       if (!DECL_DECLARED_CONSTEXPR_P (fn)
-	  && !(modules_p () && vague_linkage_p (fn)))
+	  && !(module_maybe_has_cmi_p () && vague_linkage_p (fn)))
 	DECL_SAVED_TREE (fn) = NULL_TREE;
       return false;
     }
diff --git a/gcc/testsuite/g++.dg/modules/virt-6_a.C b/gcc/testsuite/g++.dg/modules/virt-6_a.C
new file mode 100644
index 0000000..68e466a
--- /dev/null
+++ b/gcc/testsuite/g++.dg/modules/virt-6_a.C
@@ -0,0 +1,13 @@
+// PR c++/115007
+// { dg-additional-options "-fmodules-ts -Wno-global-module" }
+// { dg-module-cmi M:a }
+
+module;
+struct S {
+  virtual ~S() = default;
+  virtual void f() = 0;
+};
+module M:a;
+extern S* p;
+template <typename T> void format(T) { p->~S(); }
+template void format(int);
diff --git a/gcc/testsuite/g++.dg/modules/virt-6_b.C b/gcc/testsuite/g++.dg/modules/virt-6_b.C
new file mode 100644
index 0000000..c53f5fa
--- /dev/null
+++ b/gcc/testsuite/g++.dg/modules/virt-6_b.C
@@ -0,0 +1,6 @@
+// PR c++/115007
+// { dg-additional-options "-fmodules-ts" }
+// { dg-module-cmi M }
+
+export module M;
+import :a;