c++/modules: purview of explicit instantiations [PR114630]

When calling instantiate_pending_templates at end of parsing, any new
functions that are instantiated from this point have their module
purview set based on the current value of module_kind.

This is unideal, however, as the modules code will then treat these
instantiations as reachable and cause large swathes of the GMF to be
emitted into the module CMI, despite no code in the actual module
purview referencing it.

This patch fixes this by setting DECL_MODULE_PURVIEW_P as appropriate when
we see an explicit instantiation, and adjusting module_kind accordingly
during deferred instantiation, meaning that GMF entities won't be counted
as reachable unless referenced by an actually reachable entity.

Note that purviewness and attachment etc. is generally only determined
by the base template: this is purely for determining whether an
explicit instantiation is in the module purview and hence whether it
should be streamed out.  See the comment on 'set_instantiating_module'.

Incidentally, since the "xtreme" testcases are deliberately large (and this
commit adds another one), let's make sure we only run them once.

	PR c++/114630
	PR c++/114795

gcc/cp/ChangeLog:

	* pt.cc (reopen_tinst_level): Set or clear MK_PURVIEW.
	(mark_decl_instantiated): Call set_instantiating_module.
	(instantiate_pending_templates): Save and restore module_kind so
	it isn't affected by reopen_tinst_level.

gcc/testsuite/ChangeLog:

	* g++.dg/modules/modules.exp: Run xtreme tests once.
	* g++.dg/modules/gmf-3.C: New test.
	* g++.dg/modules/gmf-4.C: New test.
	* g++.dg/modules/gmf-xtreme.C: New test.

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

gcc/cp/pt.cc

@@ -11476,7 +11476,19 @@ reopen_tinst_level (struct tinst_level *level)
   pop_tinst_level ();
   if (current_tinst_level)
     current_tinst_level->errors = errorcount+sorrycount;
-  return level->maybe_get_node ();
+
+  tree decl = level->maybe_get_node ();
+  if (decl && modules_p ())
+    {
+      /* An instantiation is in module purview only if it had an explicit
+	 instantiation definition in module purview; mark_decl_instantiated uses
+	 set_instantiating_module to set the flag in that case.  */
+      if (DECL_MODULE_PURVIEW_P (decl))
+	module_kind |= MK_PURVIEW;
+      else
+	module_kind &= ~MK_PURVIEW;
+    }
+  return decl;
 }
 
 /* Returns the TINST_LEVEL which gives the original instantiation
@@ -25969,6 +25981,7 @@ mark_decl_instantiated (tree result, int extern_p)
     {
       mark_definable (result);
       mark_needed (result);
+      set_instantiating_module (result);
       /* Always make artificials weak.  */
       if (DECL_ARTIFICIAL (result) && flag_weak)
 	comdat_linkage (result);
@@ -27930,6 +27943,7 @@ instantiate_pending_templates (int retries)
 {
   int reconsider;
   location_t saved_loc = input_location;
+  unsigned saved_module_kind = module_kind;
 
   /* Instantiating templates may trigger vtable generation.  This in turn
      may require further template instantiations.  We place a limit here
@@ -28020,6 +28034,7 @@ instantiate_pending_templates (int retries)
   while (reconsider);
 
   input_location = saved_loc;
+  module_kind = saved_module_kind;
 }
 
 /* Substitute ARGVEC into T, which is a list of initializers for

gcc/testsuite/g++.dg/modules/gmf-3.C

@@ -0,0 +1,29 @@
+// PR c++/114630
+// { dg-additional-options "-fmodules-ts -Wno-global-module -fdump-lang-module" }
+// { dg-module-cmi M }
+
+module;
+template <typename> struct allocator {
+  allocator() {}
+};
+template class allocator<wchar_t>;
+
+// Deferred instantiation of GM virtual functions or friend functions
+// should not place newly discovered declarations in the module purview.
+template <typename T>
+void go() {
+  extern T fn_decl();
+}
+template <typename T>
+struct S {
+  friend void x() {}
+  virtual void f() {
+    go<char>();
+  }
+};
+inline S<int> s;
+
+export module M;
+
+// The whole GMF should be discarded here
+// { dg-final { scan-lang-dump "Wrote 0 clusters" module } }

gcc/testsuite/g++.dg/modules/gmf-4.C

@@ -0,0 +1,13 @@
+// PR c++/114630
+// { dg-additional-options "-fmodules-ts -Wno-global-module -fdump-lang-module" }
+// { dg-module-cmi M }
+
+module;
+template <typename> struct allocator {
+  allocator() {}
+};
+export module M;
+template class allocator<wchar_t>;
+
+// allocator is reachable because the explicit instantiation is in purview.
+// { dg-final { scan-lang-dump {Wrote declaration[^\n]*allocator} module } }

gcc/testsuite/g++.dg/modules/gmf-xtreme.C

@@ -0,0 +1,10 @@
+// PR c++/114630
+// { dg-additional-options "-fmodules-ts -fdump-lang-module" }
+// { dg-module-cmi empty }
+
+module;
+#include "xtreme-header.h"
+export module empty;
+
+// The whole GMF should be discarded here
+// { dg-final { scan-lang-dump "Wrote 0 clusters" module } }

gcc/testsuite/g++.dg/modules/modules.exp

@@ -269,6 +269,7 @@ proc module-init { src } {
     set std_prefix "-std=c++"
     global extra_tool_flags
     set extra_tool_flags {}
+    global MOD_STD_LIST
 
     foreach op $tmp {
 	switch [lindex $op 0] {
@@ -288,13 +289,16 @@ proc module-init { src } {
 	}
     }
 
-    if { !$have_std } {
-	global MOD_STD_LIST
+    if { $have_std } {
+	lappend option_list ""
+    } elseif { [string match "*xtreme*" $src] } {
+	# Only run the xtreme tests once.
+	set x [lindex $MOD_STD_LIST end]
+	lappend option_list "${std_prefix}$x"
+    } else {
 	foreach x $MOD_STD_LIST {
 	    lappend option_list "${std_prefix}$x"
 	}
-    } else {
-	lappend option_list ""
     }
 
     return $option_list