2020-07-30  Richard Biener  <rguenther@suse.de>

	PR debug/96383
	* langhooks-def.h (lhd_finalize_early_debug): Declare.
	(LANG_HOOKS_FINALIZE_EARLY_DEBUG): Define.
	(LANG_HOOKS_INITIALIZER): Amend.
	* langhooks.c: Include cgraph.h and debug.h.
	(lhd_finalize_early_debug): Default implementation from
	former code in finalize_compilation_unit.
	* langhooks.h (lang_hooks::finalize_early_debug): Add.
	* cgraphunit.c (symbol_table::finalize_compilation_unit):
	Call the finalize_early_debug langhook.

gcc/c-family/
	* c-common.h (c_common_finalize_early_debug): Declare.
	* c-common.c: Include debug.h.
	(c_common_finalize_early_debug): finalize_early_debug langhook
	implementation generating debug for extern declarations.

gcc/c/
	* c-objc-common.h (LANG_HOOKS_FINALIZE_EARLY_DEBUG):
	Define to c_common_finalize_early_debug.

gcc/cp/
	* cp-objcp-common.h (LANG_HOOKS_FINALIZE_EARLY_DEBUG):
	Define to c_common_finalize_early_debug.

gcc/testsuite/
	* gcc.dg/debug/dwarf2/pr96383-1.c: New testcase.
	* gcc.dg/debug/dwarf2/pr96383-2.c: Likewise.

libstdc++-v3/
	* testsuite/20_util/assume_aligned/3.cc: Use -g0.

--- gcc/c-family/c-common.c
+++ gcc/c-family/c-common.c
@@ -50,6 +50,7 @@ along with GCC; see the file COPYING3.  If not see
 #include "spellcheck.h"
 #include "c-spellcheck.h"
 #include "selftest.h"
+#include "debug.h"
 
 cpp_reader *parse_in;		/* Declared in c-pragma.h.  */
 
@@ -9086,4 +9087,20 @@ braced_lists_to_strings (tree type, tree ctor)
   return braced_lists_to_strings (type, ctor, false);
 }
 
+
+/* Emit debug for functions before finalizing early debug.  */
+
+void
+c_common_finalize_early_debug (void)
+{
+  /* Emit early debug for reachable functions, and by consequence,
+     locally scoped symbols.  Also emit debug for extern declared
+     functions that are still reachable at this point.  */
+  struct cgraph_node *cnode;
+  FOR_EACH_FUNCTION (cnode)
+    if (!cnode->alias && !cnode->thunk.thunk_p
+	&& (cnode->has_gimple_body_p () || !DECL_IS_BUILTIN (cnode->decl)))
+      (*debug_hooks->early_global_decl) (cnode->decl);
+}
+
 #include "gt-c-family-c-common.h"
--- gcc/c-family/c-common.h
+++ gcc/c-family/c-common.h
@@ -885,6 +885,8 @@ extern bool bool_promoted_to_int_p (tree);
 extern tree fold_for_warn (tree);
 extern tree c_common_get_narrower (tree, int *);
 extern bool get_attribute_operand (tree, unsigned HOST_WIDE_INT *);
+extern void c_common_finalize_early_debug (void);
+
 
 #define c_sizeof(LOC, T)  c_sizeof_or_alignof_type (LOC, T, true, false, 1)
 #define c_alignof(LOC, T) c_sizeof_or_alignof_type (LOC, T, false, false, 1)
--- gcc/c/c-objc-common.h
+++ gcc/c/c-objc-common.h
@@ -65,6 +65,8 @@ along with GCC; see the file COPYING3.  If not see
   c_simulate_builtin_function_decl
 #undef LANG_HOOKS_EMITS_BEGIN_STMT
 #define LANG_HOOKS_EMITS_BEGIN_STMT true
+#undef LANG_HOOKS_FINALIZE_EARLY_DEBUG
+#define LANG_HOOKS_FINALIZE_EARLY_DEBUG c_common_finalize_early_debug
 
 /* Attribute hooks.  */
 #undef LANG_HOOKS_COMMON_ATTRIBUTE_TABLE
--- gcc/cgraphunit.c
+++ gcc/cgraphunit.c
@@ -2998,11 +2998,9 @@ symbol_table::finalize_compilation_unit (void)
 
   if (!seen_error ())
     {
-      /* Emit early debug for reachable functions, and by consequence,
-	 locally scoped symbols.  */
-      struct cgraph_node *cnode;
-      FOR_EACH_FUNCTION_WITH_GIMPLE_BODY (cnode)
-	(*debug_hooks->early_global_decl) (cnode->decl);
+      /* Give the frontends the chance to emit early debug based on
+	 what is still reachable in the TU.  */
+      (*lang_hooks.finalize_early_debug) ();
 
       /* Clean up anything that needs cleaning up after initial debug
 	 generation.  */
--- gcc/cp/cp-objcp-common.h
+++ gcc/cp/cp-objcp-common.h
@@ -115,6 +115,8 @@ extern tree cxx_simulate_enum_decl (location_t, const char *,
 #define LANG_HOOKS_BLOCK_MAY_FALLTHRU cxx_block_may_fallthru
 #undef LANG_HOOKS_EMITS_BEGIN_STMT
 #define LANG_HOOKS_EMITS_BEGIN_STMT true
+#undef LANG_HOOKS_FINALIZE_EARLY_DEBUG
+#define LANG_HOOKS_FINALIZE_EARLY_DEBUG c_common_finalize_early_debug
 
 /* Attribute hooks.  */
 #undef LANG_HOOKS_COMMON_ATTRIBUTE_TABLE
--- gcc/langhooks-def.h
+++ gcc/langhooks-def.h
@@ -92,6 +92,7 @@ extern const char *lhd_get_substring_location (const substring_loc &,
 					       location_t *out_loc);
 extern int lhd_decl_dwarf_attribute (const_tree, int);
 extern int lhd_type_dwarf_attribute (const_tree, int);
+extern void lhd_finalize_early_debug (void);
 
 #define LANG_HOOKS_NAME			"GNU unknown"
 #define LANG_HOOKS_IDENTIFIER_SIZE	sizeof (struct lang_identifier)
@@ -139,6 +140,7 @@ extern int lhd_type_dwarf_attribute (const_tree, int);
 #define LANG_HOOKS_EMITS_BEGIN_STMT	false
 #define LANG_HOOKS_RUN_LANG_SELFTESTS   lhd_do_nothing
 #define LANG_HOOKS_GET_SUBSTRING_LOCATION lhd_get_substring_location
+#define LANG_HOOKS_FINALIZE_EARLY_DEBUG lhd_finalize_early_debug
 
 /* Attribute hooks.  */
 #define LANG_HOOKS_ATTRIBUTE_TABLE		NULL
@@ -364,7 +366,8 @@ extern void lhd_end_section (void);
   LANG_HOOKS_CUSTOM_FUNCTION_DESCRIPTORS, \
   LANG_HOOKS_EMITS_BEGIN_STMT, \
   LANG_HOOKS_RUN_LANG_SELFTESTS, \
-  LANG_HOOKS_GET_SUBSTRING_LOCATION \
+  LANG_HOOKS_GET_SUBSTRING_LOCATION, \
+  LANG_HOOKS_FINALIZE_EARLY_DEBUG \
 }
 
 #endif /* GCC_LANG_HOOKS_DEF_H */
--- gcc/langhooks.c
+++ gcc/langhooks.c
@@ -36,6 +36,8 @@ along with GCC; see the file COPYING3.  If not see
 #include "output.h"
 #include "timevar.h"
 #include "stor-layout.h"
+#include "cgraph.h"
+#include "debug.h"
 
 /* Do nothing; in many cases the default hook.  */
 
@@ -866,6 +868,18 @@ lhd_unit_size_without_reusable_padding (tree t)
   return TYPE_SIZE_UNIT (t);
 }
 
+/* Default implementation for the finalize_early_debug hook.  */
+
+void
+lhd_finalize_early_debug (void)
+{
+  /* Emit early debug for reachable functions, and by consequence,
+     locally scoped symbols.  */
+  struct cgraph_node *cnode;
+  FOR_EACH_FUNCTION_WITH_GIMPLE_BODY (cnode)
+    (*debug_hooks->early_global_decl) (cnode->decl);
+}
+
 /* Returns true if the current lang_hooks represents the GNU C frontend.  */
 
 bool
--- gcc/langhooks.h
+++ gcc/langhooks.h
@@ -580,6 +580,9 @@ struct lang_hooks
   const char *(*get_substring_location) (const substring_loc &,
 					 location_t *out_loc);
 
+  /* Invoked before the early_finish debug hook is invoked.  */
+  void (*finalize_early_debug) (void);
+
   /* Whenever you add entries here, make sure you adjust langhooks-def.h
      and langhooks.c accordingly.  */
 };
--- gcc/testsuite/gcc.dg/debug/dwarf2/pr96383-1.c
+++ gcc/testsuite/gcc.dg/debug/dwarf2/pr96383-1.c
@@ -0,0 +1,17 @@
+/* { dg-do compile } */
+/* { dg-options "-g -gdwarf -dA" } */
+
+extern void foo (int);
+extern void unusedbar (int);
+
+int main()
+{
+  foo (1);
+}
+
+/* We want subprogram DIEs for both foo and main and a DIE for
+   the formal parameter of foo.  We do not want a DIE for
+   unusedbar.  */
+/* { dg-final { scan-assembler-times "DW_TAG_subprogram" 4 } } */
+/* { dg-final { scan-assembler-times "DW_TAG_formal_parameter" 2 } } */
+/* { dg-final { scan-assembler-not "unusedbar" } } */
--- gcc/testsuite/gcc.dg/debug/dwarf2/pr96383-2.c
+++ gcc/testsuite/gcc.dg/debug/dwarf2/pr96383-2.c
@@ -0,0 +1,17 @@
+/* { dg-do compile } */
+/* { dg-options "-g -O2 -gdwarf -dA" } */
+
+extern void foo (int);
+extern void unusedbar (int);
+
+int main()
+{
+  foo (1);
+}
+
+/* We want subprogram DIEs for both foo and main and a DIE for
+   the formal parameter of foo.  We do not want a DIE for
+   unusedbar.  */
+/* { dg-final { scan-assembler-times "DW_TAG_subprogram" 4 } } */
+/* { dg-final { scan-assembler-times "DW_TAG_formal_parameter" 2 } } */
+/* { dg-final { scan-assembler-not "unusedbar" } } */
--- libstdc++-v3/testsuite/20_util/assume_aligned/3.cc
+++ libstdc++-v3/testsuite/20_util/assume_aligned/3.cc
@@ -15,7 +15,7 @@
 // with this library; see the file COPYING3.  If not see
 // <http://www.gnu.org/licenses/>.
 
-// { dg-options "-std=gnu++2a -O2" }
+// { dg-options "-std=gnu++2a -O2 -g0" }
 // { dg-do compile { target c++2a } }
 // { dg-final { scan-assembler-not "undefined" } }