c++/modules: Handle gnu_inline attribute, cleanup linkage determination [PR119154]

Currently, note_vague_linkage_fn is called on all definitions imported
from modules.  This is not correct, however; among other things, a
gnu_inline function does not have vague linkage, and causes an ICE if
its treated as such.

There are other things that we seem to potentially miss (e.g. dllexport
handling), so it seems sensible to stop trying to manage linkage in such
an ad-hoc manner but to use the normal interfaces more often.  While
looking at this I also found that we seem to miss marking vague linkage
variables as COMDAT, so this patch fixes that as well.

The change to use expand_or_defer_fn exposes a checking-only ICE in
trees_in::assert_definition, where we forget that we already installed a
definition for a function.  We work around this by instead of clearing
DECL_SAVED_TREE entirely in expand_or_defer_fn_1, we instead set it to a
dummy value.  This way we can also avoid the check for !TREE_ASM_WRITTEN
beforehand.

	PR c++/119154

gcc/cp/ChangeLog:

	* decl2.cc (vague_linkage_p): Don't treat gnu_inline functions
	as having vague linkage.
	* module.cc (trees_out::core_bools): Clear DECL_INTERFACE_KNOWN
	for vague-linkage entities.
	(read_var_def): Maybe set comdat linkage for imported var
	definitions.
	(module_state::read_cluster): Use expand_or_defer_fn instead of
	ad-hoc linkage management.
	(post_load_processing): Likewise.
	* semantics.cc (expand_or_defer_fn_1): Don't forget that we had
	a definition at all.

gcc/testsuite/ChangeLog:

	* g++.dg/modules/linkage-3_a.C: New test.
	* g++.dg/modules/linkage-3_b.C: New test.
	* g++.dg/modules/pr119154_a.C: New test.
	* g++.dg/modules/pr119154_b.C: New test.

Signed-off-by: Nathaniel Shead <nathanieloshead@gmail.com>
Reviewed-by: Jason Merrill <jason@redhat.com>

gcc/cp/decl2.cc

@@ -2482,7 +2482,9 @@ vague_linkage_p (tree decl)
      DECL_COMDAT.  */
   if (DECL_COMDAT (decl)
       || (TREE_CODE (decl) == FUNCTION_DECL
-	  && DECL_DECLARED_INLINE_P (decl))
+	  && DECL_DECLARED_INLINE_P (decl)
+	  /* But gnu_inline functions are always external.  */
+	  && !lookup_attribute ("gnu_inline", DECL_ATTRIBUTES (decl)))
       || (DECL_LANG_SPECIFIC (decl)
 	  && DECL_TEMPLATE_INSTANTIATION (decl))
       || (VAR_P (decl) && DECL_INLINE_VAR_P (decl)))

gcc/cp/module.cc

@@ -5657,10 +5657,10 @@ trees_out::core_bools (tree t, bits_out& bits)
 
       {
 	/* This is DECL_INTERFACE_KNOWN: We should redetermine whether
-	   we need to import or export any vtables or typeinfo objects
-	   on stream-in.  */
+	   we need to import or export any vague-linkage entities 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)))
+	if (interface_known && vague_linkage_p (t))
 	  interface_known = false;
 	WB (interface_known);
       }
@@ -12616,6 +12616,7 @@ trees_in::read_var_def (tree decl, tree maybe_template)
   bool installing = maybe_dup && !initialized;
   if (installing)
     {
+      DECL_INITIAL (decl) = init;
       if (DECL_EXTERNAL (decl))
 	DECL_NOT_REALLY_EXTERN (decl) = true;
       if (VAR_P (decl))
@@ -12623,13 +12624,13 @@ trees_in::read_var_def (tree decl, tree maybe_template)
 	  DECL_INITIALIZED_P (decl) = true;
 	  if (maybe_dup && DECL_INITIALIZED_BY_CONSTANT_EXPRESSION_P (maybe_dup))
 	    DECL_INITIALIZED_BY_CONSTANT_EXPRESSION_P (decl) = true;
+	  tentative_decl_linkage (decl);
 	  if (DECL_IMPLICIT_INSTANTIATION (decl)
 	      || (DECL_CLASS_SCOPE_P (decl)
 		  && !DECL_VTABLE_OR_VTT_P (decl)
 		  && !DECL_TEMPLATE_INFO (decl)))
 	    note_vague_linkage_variable (decl);
 	}
-      DECL_INITIAL (decl) = init;
       if (!dyn_init)
 	;
       else if (CP_DECL_THREAD_LOCAL_P (decl))
@@ -16534,12 +16535,7 @@ module_state::read_cluster (unsigned snum)
 	  cfun->returns_pcc_struct = aggr;
 #endif
 	  cfun->returns_struct = aggr;
-
-	  if (DECL_COMDAT (decl))
-	    // FIXME: Comdat grouping?
-	    comdat_linkage (decl);
-	  note_vague_linkage_fn (decl);
-	  cgraph_node::finalize_function (decl, true);
+	  expand_or_defer_fn (decl);
 	}
 
     }
@@ -19018,22 +19014,7 @@ post_load_processing ()
       dump () && dump ("Post-load processing of %N", decl);
 
       gcc_checking_assert (DECL_MAYBE_IN_CHARGE_CDTOR_P (decl));
-
-      if (DECL_COMDAT (decl))
-	comdat_linkage (decl);
-      if (!TREE_ASM_WRITTEN (decl))
-	{
-	  /* Cloning can cause loading -- specifically operator delete for
-	     the deleting dtor.  */
-	  if (maybe_clone_body (decl))
-	    TREE_ASM_WRITTEN (decl) = 1;
-	  else
-	    {
-	      /* We didn't clone the cdtor, make sure we emit it.  */
-	      note_vague_linkage_fn (decl);
-	      cgraph_node::finalize_function (decl, true);
-	    }
-	}
+      expand_or_defer_fn (decl);
     }
 
   cfun = old_cfun;

gcc/cp/semantics.cc

@@ -5502,7 +5502,7 @@ expand_or_defer_fn_1 (tree fn)
 	 need it anymore.  */
       if (!DECL_DECLARED_CONSTEXPR_P (fn)
 	  && !(module_maybe_has_cmi_p () && vague_linkage_p (fn)))
-	DECL_SAVED_TREE (fn) = NULL_TREE;
+	DECL_SAVED_TREE (fn) = void_node;
       return false;
     }
 

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

@@ -0,0 +1,5 @@
+// { dg-do compile { target *-*-*gnu* } }
+// { dg-additional-options "-fmodules" }
+
+export module M;
+export inline int x = 0;

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

@@ -0,0 +1,9 @@
+// { dg-do compile { target *-*-*gnu* } }
+// { dg-additional-options "-fmodules" }
+// { dg-final { scan-assembler "_ZW1M1x,comdat" } }
+
+import M;
+
+int main() {
+  return x;
+}

gcc/testsuite/g++.dg/modules/pr119154_a.C

@@ -0,0 +1,6 @@
+// PR c++/119154
+// { dg-additional-options "-fmodules" }
+// { dg-module-cmi foo }
+
+export module foo;
+extern "C++" inline __attribute__((__gnu_inline__)) void bar() {}

gcc/testsuite/g++.dg/modules/pr119154_b.C

@@ -0,0 +1,10 @@
+// PR c++/119154
+// { dg-module-do link }
+// { dg-additional-options "-fmodules" }
+
+void bar();
+import foo;
+
+int main() {
+  bar();
+}