Re: [PATCH][RFC] Instrument function exit with __builtin_unreachable in C++.

[Martin Liška <mliska at suse dot cz>]

On 11/15/2017 10:42 AM, Eric Botcazou wrote:
>> But we don't.  Wonder if in addition to your patch or instead of it it
>> wouldn't be safer (especially for FEs added in the future) to:
>>
>>    /* If we see "return;" in some basic block, then we do reach the end
>>       without returning a value.  */
>> -  else if (warn_return_type
>> +  else if (warn_return_type > 0
>>             && !TREE_NO_WARNING (fun->decl)
>>             && EDGE_COUNT (EXIT_BLOCK_PTR_FOR_FN (fun)->preds) > 0
>>             && !VOID_TYPE_P (TREE_TYPE (TREE_TYPE (fun->decl))))
>>
>> in tree-cfg.c.  That change is preapproved if it works, and your
>> patch if you want in addition to that is ok too.
> 
> That's the first thing I tried and it indeed works.
> 

Hi.

Following patch survives regression tests and bootstraps.
There are multiple places where warn_return_type should be compared
to zero.

Ready for trunk?
Thanks,
Martin

>From 5f8daccc584c7ae749d25d59526e0173aa4334f7 Mon Sep 17 00:00:00 2001
From: marxin <mliska@suse.cz>
Date: Wed, 15 Nov 2017 09:16:23 +0100
Subject: [PATCH] Disable -Wreturn-type by default in all languages other from
 C++.

gcc/ChangeLog:

2017-11-15  Martin Liska  <mliska@suse.cz>

	* tree-cfg.c (pass_warn_function_return::execute):
	Compare warn_return_type for greater than zero.

gcc/ada/ChangeLog:

2017-11-15  Martin Liska  <mliska@suse.cz>

	* gcc-interface/misc.c (gnat_post_options):
	Do not set default value of warn_return_type.

gcc/c/ChangeLog:

2017-11-15  Martin Liska  <mliska@suse.cz>

	* c-decl.c (grokdeclarator):
	Compare warn_return_type for greater than zero.
	(start_function): Likewise.
	(finish_function): Likewise.
	* c-typeck.c (c_finish_return): Likewise.

gcc/cp/ChangeLog:

2017-11-15  Martin Liska  <mliska@suse.cz>

	* decl.c (finish_function):
	Compare warn_return_type for greater than zero.
	* semantics.c (finish_return_stmt): Likewise.

gcc/fortran/ChangeLog:

2017-11-15  Martin Liska  <mliska@suse.cz>

	* options.c (gfc_post_options):
	Do not set default value of warn_return_type.
	* trans-decl.c (gfc_trans_deferred_vars):
	Compare warn_return_type for greater than zero.
	(generate_local_decl): Likewise
	(gfc_generate_function_code): Likewise.
---
 gcc/ada/gcc-interface/misc.c | 3 ---
 gcc/c/c-decl.c               | 6 +++---
 gcc/c/c-typeck.c             | 2 +-
 gcc/cp/decl.c                | 2 +-
 gcc/cp/semantics.c           | 2 +-
 gcc/fortran/options.c        | 3 ---
 gcc/fortran/trans-decl.c     | 8 ++++----
 gcc/tree-cfg.c               | 2 +-
 8 files changed, 11 insertions(+), 17 deletions(-)

diff --git a/gcc/ada/gcc-interface/misc.c b/gcc/ada/gcc-interface/misc.c
index 9a4a48fba42..7bdb3803c13 100644
--- a/gcc/ada/gcc-interface/misc.c
+++ b/gcc/ada/gcc-interface/misc.c
@@ -262,9 +262,6 @@ gnat_post_options (const char **pfilename ATTRIBUTE_UNUSED)
   /* No psABI change warnings for Ada.  */
   warn_psabi = 0;
 
-  /* No return type warnings for Ada.  */
-  warn_return_type = 0;
-
   /* No caret by default for Ada.  */
   if (!global_options_set.x_flag_diagnostics_show_caret)
     global_dc->show_caret = false;
diff --git a/gcc/c/c-decl.c b/gcc/c/c-decl.c
index d95a2b6ea4f..7120420f2df 100644
--- a/gcc/c/c-decl.c
+++ b/gcc/c/c-decl.c
@@ -5689,7 +5689,7 @@ grokdeclarator (const struct c_declarator *declarator,
       /* Issue a warning if this is an ISO C 99 program or if
 	 -Wreturn-type and this is a function, or if -Wimplicit;
 	 prefer the former warning since it is more explicit.  */
-      if ((warn_implicit_int || warn_return_type || flag_isoc99)
+      if ((warn_implicit_int || warn_return_type > 0 || flag_isoc99)
 	  && funcdef_flag)
 	warn_about_return_type = 1;
       else
@@ -8655,7 +8655,7 @@ start_function (struct c_declspecs *declspecs, struct c_declarator *declarator,
 
   if (warn_about_return_type)
     warn_defaults_to (loc, flag_isoc99 ? OPT_Wimplicit_int
-			   : (warn_return_type ? OPT_Wreturn_type
+			   : (warn_return_type > 0 ? OPT_Wreturn_type
 			      : OPT_Wimplicit_int),
 		      "return type defaults to %<int%>");
 
@@ -9373,7 +9373,7 @@ finish_function (void)
   finish_fname_decls ();
 
   /* Complain if there's just no return statement.  */
-  if (warn_return_type
+  if (warn_return_type > 0
       && TREE_CODE (TREE_TYPE (TREE_TYPE (fndecl))) != VOID_TYPE
       && !current_function_returns_value && !current_function_returns_null
       /* Don't complain if we are no-return.  */
diff --git a/gcc/c/c-typeck.c b/gcc/c/c-typeck.c
index 4bdc48a9ea3..492a245d296 100644
--- a/gcc/c/c-typeck.c
+++ b/gcc/c/c-typeck.c
@@ -10091,7 +10091,7 @@ c_finish_return (location_t loc, tree retval, tree origtype)
   if (!retval)
     {
       current_function_returns_null = 1;
-      if ((warn_return_type || flag_isoc99)
+      if ((warn_return_type > 0 || flag_isoc99)
 	  && valtype != NULL_TREE && TREE_CODE (valtype) != VOID_TYPE)
 	{
 	  bool warned_here;
diff --git a/gcc/cp/decl.c b/gcc/cp/decl.c
index 041893db937..96bbff6c1f9 100644
--- a/gcc/cp/decl.c
+++ b/gcc/cp/decl.c
@@ -15583,7 +15583,7 @@ finish_function (bool inline_p)
     save_function_data (fndecl);
 
   /* Complain if there's just no return statement.  */
-  if (warn_return_type
+  if (warn_return_type > 0
       && !VOID_TYPE_P (TREE_TYPE (fntype))
       && !dependent_type_p (TREE_TYPE (fntype))
       && !current_function_returns_value && !current_function_returns_null
diff --git a/gcc/cp/semantics.c b/gcc/cp/semantics.c
index 51489d17ad5..cbb395e3f61 100644
--- a/gcc/cp/semantics.c
+++ b/gcc/cp/semantics.c
@@ -890,7 +890,7 @@ finish_return_stmt (tree expr)
       || (flag_openmp && !check_omp_return ()))
     {
       /* Suppress -Wreturn-type for this function.  */
-      if (warn_return_type)
+      if (warn_return_type > 0)
 	TREE_NO_WARNING (current_function_decl) = true;
       return error_mark_node;
     }
diff --git a/gcc/fortran/options.c b/gcc/fortran/options.c
index c584a19e559..0ee6b7808d9 100644
--- a/gcc/fortran/options.c
+++ b/gcc/fortran/options.c
@@ -435,9 +435,6 @@ gfc_post_options (const char **pfilename)
     gfc_fatal_error ("Maximum subrecord length cannot exceed %d",
 		     MAX_SUBRECORD_LENGTH);
 
-  if (warn_return_type == -1)
-    warn_return_type = 0;
-
   gfc_cpp_post_options ();
 
   if (gfc_option.allow_std & GFC_STD_F2008)
diff --git a/gcc/fortran/trans-decl.c b/gcc/fortran/trans-decl.c
index 8efaae79ebc..60e7d8f79ee 100644
--- a/gcc/fortran/trans-decl.c
+++ b/gcc/fortran/trans-decl.c
@@ -4198,7 +4198,7 @@ gfc_trans_deferred_vars (gfc_symbol * proc_sym, gfc_wrapped_block * block)
 		  break;
 	    }
 	  /* TODO: move to the appropriate place in resolve.c.  */
-	  if (warn_return_type && el == NULL)
+	  if (warn_return_type > 0 && el == NULL)
 	    gfc_warning (OPT_Wreturn_type,
 			 "Return value of function %qs at %L not set",
 			 proc_sym->name, &proc_sym->declared_at);
@@ -5619,7 +5619,7 @@ generate_local_decl (gfc_symbol * sym)
   else if (sym->attr.flavor == FL_PROCEDURE)
     {
       /* TODO: move to the appropriate place in resolve.c.  */
-      if (warn_return_type
+      if (warn_return_type > 0
 	  && sym->attr.function
 	  && sym->result
 	  && sym != sym->result
@@ -6494,11 +6494,11 @@ gfc_generate_function_code (gfc_namespace * ns)
       if (result == NULL_TREE || artificial_result_decl)
 	{
 	  /* TODO: move to the appropriate place in resolve.c.  */
-	  if (warn_return_type && sym == sym->result)
+	  if (warn_return_type > 0 && sym == sym->result)
 	    gfc_warning (OPT_Wreturn_type,
 			 "Return value of function %qs at %L not set",
 			 sym->name, &sym->declared_at);
-	  if (warn_return_type)
+	  if (warn_return_type > 0)
 	    TREE_NO_WARNING(sym->backend_decl) = 1;
 	}
       if (result != NULL_TREE)
diff --git a/gcc/tree-cfg.c b/gcc/tree-cfg.c
index 9a2fa1d98ca..f08a0547f0f 100644
--- a/gcc/tree-cfg.c
+++ b/gcc/tree-cfg.c
@@ -9071,7 +9071,7 @@ pass_warn_function_return::execute (function *fun)
 
   /* If we see "return;" in some basic block, then we do reach the end
      without returning a value.  */
-  else if (warn_return_type
+  else if (warn_return_type > 0
 	   && !TREE_NO_WARNING (fun->decl)
 	   && EDGE_COUNT (EXIT_BLOCK_PTR_FOR_FN (fun)->preds) > 0
 	   && !VOID_TYPE_P (TREE_TYPE (TREE_TYPE (fun->decl))))
-- 
2.14.3