Re: Enable -Wreturn-type by default ?

[Sylvestre Ledru <sylvestre at debian dot org>]

On 16/01/2014 03:45, Jonathan Wakely wrote:
> On 16 January 2014 11:11, Sylvestre Ledru wrote:
>> Hello,
>>
>> On 17/11/2013 17:47, Jonathan Wakely wrote:
>>> On 17 November 2013 15:40, Sylvestre Ledru wrote:
>>>> For "control reaches end of non-void function", I haven't activated by
>>>> default and I called the option -Wfalloff-nonvoid-function
>>>> Of course, that is just a proposal! :) Better names are welcome.
>>> It was nearly called -Wmissing-return a decade ago, but got bundled
>>> with -Wreturn-type, see
>>> http://gcc.gnu.org/ml/gcc-patches/2002-02/msg02002.html
>> As discussed on this mailing list, I proposed a patch on the gcc-patches
>> mailing list.
>> http://gcc.gnu.org/ml/gcc-patches/2014-01/msg00820.html
>>
>> Any chance one of you could review it?
> I like the change in principle, but it's not up to me, I can't approve
> front-end patches.  I can comment on the docs and ChangeLog but I'm
> not subscribed to gcc-patches so didn't get the mail. I'll send some
> comments, could you please reply to your gcc-patches mail and include
> my comments? Thanks.
Following the comments you sent me, here it is:

> Does -Wreturn-type enable -Wmissing-return?  If not, users who
> currently use -Werror=return-type might be surprised when "missing
> return" warnings are no longer errors., because they are controlled by
> a different option. That would require users to add
> -Werror=missing-return to their makefiles, which would not be
> compatible with older versions of GCC.

Actually, I wonder if -Wmissing-return should not be included by default ...
If you do not agree, could you tell me how I could enable
-Wmissing-return with both
-Wreturn-type and -Wall?

Now, the code (I haven't touched the testsuite, the archive remains the
same).

gcc/ChangeLog:

2014-01-23  Sylvestre Ledru  <sylvestre@debian.org>

    PR other/PR55189
        * doc/invoke.texi: Update of the documentation (-Wreturn-type
        -Wmissing-return enabled by default)
        * tree-cfg.c: Likewise
  
gcc/c-family/ChangeLog:

2014-01-23  Sylvestre Ledru  <sylvestre@debian.org>

    * c.opt: Extract -Wmissing-return from -Wreturn-type to return
        a warning when a return statement is missing.

gcc/fortran/ChangeLog:

2014-01-23  Sylvestre Ledru  <sylvestre@debian.org>

    * options.c: Extract -Wmissing-return from -Wreturn-type to return
        a warning when a return statement is missing.

Index: gcc/c-family/c.opt
===================================================================
--- gcc/c-family/c.opt    (révision 206953)
+++ gcc/c-family/c.opt    (copie de travail)
@@ -673,9 +673,13 @@
 Warn about returning a pointer/reference to a local or temporary variable.
 
 Wreturn-type
-C ObjC C++ ObjC++ Var(warn_return_type) Warning LangEnabledBy(C ObjC
C++ ObjC++,Wall)
+C ObjC C++ ObjC++ Var(warn_return_type) Init(1) Warning
 Warn whenever a function's return type defaults to \"int\" (C), or
about inconsistent return types (C++)
 
+Wmissing-return
+C ObjC C++ ObjC++ Var(warn_missing_return) Init(1) Warning
LangEnabledBy(C ObjC C++ ObjC++, Wreturn-type)
+Warn whenever control may reach end of non-void function
+
 Wselector
 ObjC ObjC++ Var(warn_selector) Warning
 Warn if a selector has multiple methods
Index: gcc/doc/invoke.texi
===================================================================
--- gcc/doc/invoke.texi    (révision 206953)
+++ gcc/doc/invoke.texi    (copie de travail)
@@ -255,7 +255,7 @@
 -Winvalid-pch -Wlarger-than=@var{len}  -Wunsafe-loop-optimizations @gol
 -Wlogical-op -Wlong-long @gol
 -Wmain -Wmaybe-uninitialized -Wmissing-braces 
-Wmissing-field-initializers @gol
--Wmissing-include-dirs @gol
+-Wmissing-include-dirs  -Wmissing-return @gol
 -Wno-multichar  -Wnonnull  -Wno-overflow -Wopenmp-simd @gol
 -Woverlength-strings  -Wpacked  -Wpacked-bitfield-compat  -Wpadded @gol
 -Wparentheses  -Wpedantic-ms-format -Wno-pedantic-ms-format @gol
@@ -3348,6 +3348,7 @@
 -Wmain @r{(only for C/ObjC and unless} @option{-ffreestanding}@r{)}  @gol
 -Wmaybe-uninitialized @gol
 -Wmissing-braces @r{(only for C/ObjC)} @gol
+-Wmissing-return  @gol
 -Wnonnull  @gol
 -Wopenmp-simd @gol
 -Wparentheses  @gol
@@ -3810,7 +3811,11 @@
 message, even when @option{-Wno-return-type} is specified.  The only
 exceptions are @samp{main} and functions defined in system headers.
 
-This warning is enabled by @option{-Wall}.
+@item -Wmissing-return
+@opindex Wmissing-return
+@opindex Wno-missing-return
+Warn whenever falling off the end of the function body (i.e. without
+a return statement).
 
 @item -Wswitch
 @opindex Wswitch
Index: gcc/fortran/options.c
===================================================================
--- gcc/fortran/options.c    (révision 206953)
+++ gcc/fortran/options.c    (copie de travail)
@@ -717,6 +717,10 @@
       warn_return_type = value;
       break;
 
+    case OPT_Wmissing_return:
+      warn_missing_return = value;
+      break;
+
     case OPT_Wsurprising:
       gfc_option.warn_surprising = value;
       break;
Index: gcc/tree-cfg.c
===================================================================
--- gcc/tree-cfg.c    (révision 206953)
+++ gcc/tree-cfg.c    (copie de travail)
@@ -8097,7 +8097,7 @@
 
   /* 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_missing_return
        && !TREE_NO_WARNING (cfun->decl)
        && EDGE_COUNT (EXIT_BLOCK_PTR_FOR_FN (cfun)->preds) > 0
        && !VOID_TYPE_P (TREE_TYPE (TREE_TYPE (cfun->decl))))
@@ -8112,7 +8112,7 @@
           location = gimple_location (last);
           if (location == UNKNOWN_LOCATION)
           location = cfun->function_end_locus;
-          warning_at (location, OPT_Wreturn_type, "control reaches end
of non-void function");
+          warning_at (location, OPT_Wmissing_return, "control reaches
end of non-void function");
           TREE_NO_WARNING (cfun->decl) = 1;
           break;
         }