c++: Better module initializer code

c++: Better module initializer code

[Nathan Sidwell]

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Every module interface needs to emit a global initializer, but it
might have nothing to init.  In those cases, there's no need for any
idempotency boolean to be emitted.

nathan

-- 
Nathan Sidwell

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From 227ffed7dbbdffeeb5bc013852d61a97aa468c62 Mon Sep 17 00:00:00 2001
From: Nathan Sidwell <nathan@acm.org>
Date: Wed, 8 Jun 2022 11:25:14 -0700
Subject: [PATCH] c++: Better module initializer code

Every module interface needs to emit a global initializer, but it
might have nothing to init.  In those cases, there's no need for any
idempotency boolean to be emitted.

	gcc/cp
	* cp-tree.h (module_initializer_kind): Replace with ...
	(module_global_init_needed, module_has_import_inits): ...
	these.
	* decl2.cc (start_objects): Add has_body parm.  Reorganize
	module initializer creation.
	(generate_ctor_or_dtor_function): Adjust.
	(c_parse_final_cleanups): Adjust.
	(vtv_start_verification_constructor_init_function): Adjust.
	* module.cc (module_initializer_kind): Replace with ...
	(module_global_init_needed, module_has_import_inits): ...
	these.

	gcc/testsuite/
	* g++.dg/modules/init-2_a.C: Check no idempotency.
	* g++.dg/modules/init-2_b.C: Check idempotency.
---
 gcc/cp/cp-tree.h                        |  3 ++-
 gcc/cp/decl2.cc                         | 32 +++++++++++++------------
 gcc/cp/module.cc                        | 23 +++++++++---------
 gcc/testsuite/g++.dg/modules/init-2_a.C |  2 ++
 gcc/testsuite/g++.dg/modules/init-2_b.C |  2 ++
 5 files changed, 34 insertions(+), 28 deletions(-)

diff --git a/gcc/cp/cp-tree.h b/gcc/cp/cp-tree.h
index 3d8a08b8dd7..a5d93282167 100644
--- a/gcc/cp/cp-tree.h
+++ b/gcc/cp/cp-tree.h
@@ -7179,7 +7179,8 @@ extern module_state *get_module (tree name, module_state *parent = NULL,
 				 bool partition = false);
 extern bool module_may_redeclare (tree decl);
 
-extern int module_initializer_kind ();
+extern bool module_global_init_needed ();
+extern bool module_has_import_inits ();
 extern void module_add_import_initializers ();
 
 /* Where the namespace-scope decl was originally declared.  */
diff --git a/gcc/cp/decl2.cc b/gcc/cp/decl2.cc
index bfb6a32e3b6..9de9a7a4f8a 100644
--- a/gcc/cp/decl2.cc
+++ b/gcc/cp/decl2.cc
@@ -55,7 +55,7 @@ int raw_dump_id;
  
 extern cpp_reader *parse_in;
 
-static tree start_objects (bool, unsigned);
+static tree start_objects (bool, unsigned, bool);
 static tree finish_objects (bool, unsigned, tree);
 static tree start_partial_init_fini_fn (bool, unsigned, unsigned);
 static void finish_partial_init_fini_fn (tree);
@@ -3848,15 +3848,13 @@ generate_tls_wrapper (tree fn)
 /* Start a global constructor or destructor function.  */
 
 static tree
-start_objects (bool initp, unsigned priority)
+start_objects (bool initp, unsigned priority, bool has_body)
 {
-  int module_init = 0;
-
-  if (priority == DEFAULT_INIT_PRIORITY && initp)
-    module_init = module_initializer_kind ();
-
+  bool default_init = initp && priority == DEFAULT_INIT_PRIORITY;
+  bool is_module_init = default_init && module_global_init_needed ();
   tree name = NULL_TREE;
-  if (module_init > 0)
+
+  if (is_module_init)
     name = mangle_module_global_init (0);
   else
     {
@@ -3880,7 +3878,7 @@ start_objects (bool initp, unsigned priority)
   tree fntype =	build_function_type (void_type_node, void_list_node);
   tree fndecl = build_lang_decl (FUNCTION_DECL, name, fntype);
   DECL_CONTEXT (fndecl) = FROB_CONTEXT (global_namespace);
-  if (module_init > 0)
+  if (is_module_init)
     {
       SET_DECL_ASSEMBLER_NAME (fndecl, name);
       TREE_PUBLIC (fndecl) = true;
@@ -3905,8 +3903,10 @@ start_objects (bool initp, unsigned priority)
 
   tree body = begin_compound_stmt (BCS_FN_BODY);
 
-  if (module_init > 0)
+  bool has_import_inits = default_init && module_has_import_inits ();
+  if (is_module_init && (has_import_inits || has_body))
     {
+      // If the function is going to be empty, don't emit idempotency.
       // 'static bool __in_chrg = false;
       // if (__inchrg) return;
       // __inchrg = true
@@ -3930,7 +3930,7 @@ start_objects (bool initp, unsigned priority)
       finish_expr_stmt (assign);
     }
 
-  if (module_init)
+  if (has_import_inits)
     module_add_import_initializers ();
 
   return body;
@@ -4321,7 +4321,7 @@ generate_ctor_or_dtor_function (bool initp, unsigned priority,
 {
   input_location = locus;
 
-  tree body = start_objects (initp, priority);
+  tree body = start_objects (initp, priority, bool (fns));
 
   /* To make sure dynamic construction doesn't access globals from other
      compilation units where they might not be yet constructed, for
@@ -4359,7 +4359,9 @@ generate_ctor_or_dtor_function (bool initp, unsigned priority,
   if (initp && (flag_sanitize & SANITIZE_ADDRESS))
     finish_expr_stmt (asan_dynamic_init_call (/*after_p=*/true));
 
-  /* Close out the function.  */
+  /* Close out the function, and arrange for it to be called at init
+     or fini time.  (Even module initializer functions need this, as
+     we cannot guarantee the module is imported somewhere in the programq.)  */
   expand_or_defer_fn (finish_objects (initp, priority, body));
 }
 
@@ -5205,7 +5207,7 @@ c_parse_final_cleanups (void)
   push_lang_context (lang_name_c);
 
   if ((c_dialect_objc () && objc_static_init_needed_p ())
-      || module_initializer_kind ())
+      || module_global_init_needed () || module_has_import_inits ())
     {
       // Make sure there's a default priority entry.
       if (!static_init_fini_fns[true])
@@ -5871,7 +5873,7 @@ mark_used (tree decl)
 tree
 vtv_start_verification_constructor_init_function (void)
 {
-  return start_objects (/*initp=*/true, MAX_RESERVED_INIT_PRIORITY - 1);
+  return start_objects (/*initp=*/true, MAX_RESERVED_INIT_PRIORITY - 1, true);
 }
 
 tree
diff --git a/gcc/cp/module.cc b/gcc/cp/module.cc
index d1dc73724d1..7e36996c0fc 100644
--- a/gcc/cp/module.cc
+++ b/gcc/cp/module.cc
@@ -19026,22 +19026,21 @@ declare_module (module_state *module, location_t from_loc, bool exporting_p,
     }
 }
 
-/* +1, we're the primary or a partition.  Therefore emitting a
-   globally-callable idemportent initializer function.
-   -1, we have direct imports.  Therefore emitting calls to their
-   initializers.  */
+/* Return true IFF we must emit a module global initializer function
+   (which will be called by importers' init code).  */
 
-int
-module_initializer_kind ()
+bool
+module_global_init_needed ()
 {
-  int result = 0;
+  return module_has_cmi_p () && !header_module_p ();
+}
 
-  if (module_has_cmi_p () && !header_module_p ())
-    result = +1;
-  else if (num_init_calls_needed)
-    result = -1;
+/* Return true IFF we have import global inits to call.  */
 
-  return result;
+bool
+module_has_import_inits ()
+{
+  return bool (num_init_calls_needed);
 }
 
 /* Emit calls to each direct import's global initializer.  Including
diff --git a/gcc/testsuite/g++.dg/modules/init-2_a.C b/gcc/testsuite/g++.dg/modules/init-2_a.C
index c0390a1b56e..4174cf53911 100644
--- a/gcc/testsuite/g++.dg/modules/init-2_a.C
+++ b/gcc/testsuite/g++.dg/modules/init-2_a.C
@@ -3,3 +3,5 @@ export module Foo;
 // { dg-module-cmi Foo }
 
 // { dg-final { scan-assembler {_ZGIW3Foo:} } }
+// But it is empty, and so no idempotency bool
+// { dg-final { scan-assembler-not {_ZZ9_ZGIW3FooE9__in_chrg} } }
diff --git a/gcc/testsuite/g++.dg/modules/init-2_b.C b/gcc/testsuite/g++.dg/modules/init-2_b.C
index 912ee406931..4350944139f 100644
--- a/gcc/testsuite/g++.dg/modules/init-2_b.C
+++ b/gcc/testsuite/g++.dg/modules/init-2_b.C
@@ -5,4 +5,6 @@ export module Bar;
 import Foo;
 
 // { dg-final { scan-assembler {_?_ZGIW3Bar:} } }
+// There should be an idempotency check
+// { dg-final { scan-assembler {_ZZ9_ZGIW3BarE9__in_chrg} } }
 // { dg-final { scan-assembler {call[ \t]+_?_ZGIW3Foo} { target i?86-*-* x86_64-*-* } } }
-- 
2.30.2