[Bug c/67730] New: [5.2 Regression] No warning when returning NULL in void function

[Bug c/67730] New: [5.2 Regression] No warning when returning NULL in void function

[damwdan at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=67730

            Bug ID: 67730
           Summary: [5.2 Regression] No warning when returning NULL in
                    void function
           Product: gcc
           Version: 5.2.0
            Status: UNCONFIRMED
          Severity: major
          Priority: P3
         Component: c
          Assignee: unassigned at gcc dot gnu.org
          Reporter: damwdan at gmail dot com
  Target Milestone: ---

Created attachment 36401
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=36401&action=edit
preprocessed source file

Following up on this Stackoverflow post:
http://stackoverflow.com/q/32732281/5366270

There seems to be a regression in gcc 5.2.0. When returning NULL in a void
function, gcc *does not* warn or error. gcc 4.9.2 (and some other previous
versions, as mentioned in the post) warns. clang 3.7 errors. As noted by "Marc
Glisse", using -Wsystem-headers does the trick and generates a warning. Though,
the preprocessed output (attached) is exactly the same.

$ cat c.c
#include <stddef.h>

void procedure(void)
{
    return NULL;
}
$ gcc -Wall -Wextra -std=c99 -pedantic -c c.c
$ gcc -Wall -Wextra -std=c99 -pedantic -Wsystem-headers -c c.c
In file included from c.c:1:0:
c.c: In function ‘procedure’:
c.c:5:12: warning: ‘return’ with a value, in function returning void
     return NULL;
            ^
$ gcc -v
Using built-in specs.
COLLECT_GCC=gcc
COLLECT_LTO_WRAPPER=/usr/lib/gcc/x86_64-unknown-linux-gnu/5.2.0/lto-wrapper
Target: x86_64-unknown-linux-gnu
Configured with: /build/gcc-multilib/src/gcc-5.2.0/configure --prefix=/usr
--libdir=/usr/lib --libexecdir=/usr/lib --mandir=/usr/share/man
--infodir=/usr/share/info --with-bugurl=https://bugs.archlinux.org/
--enable-languages=c,c++,ada,fortran,go,lto,objc,obj-c++ --enable-shared
--enable-threads=posix --enable-libmpx --with-system-zlib --with-isl
--enable-__cxa_atexit --disable-libunwind-exceptions --enable-clocale=gnu
--disable-libstdcxx-pch --disable-libssp --enable-gnu-unique-object
--enable-linker-build-id --enable-lto --enable-plugin
--enable-install-libiberty --with-linker-hash-style=gnu
--enable-gnu-indirect-function --enable-multilib --disable-werror
--enable-checking=release --with-default-libstdcxx-abi=gcc4-compatible
Thread model: posix
gcc version 5.2.0 (GCC) 

Note that the bug also appears when returning NULL in an int or char function,
but not double (an error is generated).
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Subject: [Bug target/67391] [SH] Convert clrt addc to normal add insn
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https://gcc.gnu.org/bugzilla/show_bug.cgi?idg391

--- Comment #25 from Kazumoto Kojima <kkojima at gcc dot gnu.org> ---
(In reply to Oleg Endo from comment #24)
> Could you please re-run that test with attachment 36400 [details]?

Yes, 36400 fixes that failure:
PASS: gcc.c-torture/compile/sync-3.c   -O1   (test for warnings, line )

[Bug c/67730] [5/6 Regression] No warning when returning NULL in void function

[rguenth at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=67730

Richard Biener <rguenth at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
   Target Milestone|---                         |5.3
            Summary|[5.2 Regression] No warning |[5/6 Regression] No warning
                   |when returning NULL in void |when returning NULL in void
                   |function                    |function

[Bug c/67730] [5/6 Regression] No warning when returning NULL in void function

[joseph at codesourcery dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=67730

--- Comment #1 from joseph at codesourcery dot com <joseph at codesourcery dot com> ---
Probably caused by:

r211978 | mpolacek | 2014-06-25 12:43:05 +0000 (Wed, 25 Jun 2014) | 7 
lines

        PR c/61162
        * c-parser.c (c_parser_statement_after_labels): Pass the location of
        the return expression to c_finish_return.

        * gcc.dg/pr61162.c: Adjust dg-warning.
        * gcc.dg/pr61162-2.c: New test.

For this warning, either it should use the location of the return keyword, 
or (maybe better) it should use the location of the return value before 
macro expansion - not the location of the macro definition - since this 
diagnostic is about the context in which the expression is used, not the 
contents of that expression.

[Bug c/67730] [5/6 Regression] No warning when returning NULL in void function

[manu at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=67730

Manuel López-Ibáñez <manu at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |manu at gcc dot gnu.org

--- Comment #2 from Manuel López-Ibáñez <manu at gcc dot gnu.org> ---
I think this is covered by:

https://gcc.gnu.org/wiki/DiagnosticsGuidelines#warn_on_NULL

no?
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Subject: [Bug c++/67737] ICE in make_decl_rtl, at varasm.c:1299
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https://gcc.gnu.org/bugzilla/show_bug.cgi?idg737

ryan.burn at gmail dot com changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|RESOLVED                    |UNCONFIRMED
         Resolution|DUPLICATE                   |---

--- Comment #5 from ryan.burn at gmail dot com ---
replaced with correct file

[Bug c/67730] [5/6 Regression] No warning when returning NULL in void function

[manu at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=67730

--- Comment #3 from Manuel López-Ibáñez <manu at gcc dot gnu.org> ---
Or perhaps we need to a new function (and a new entry in the guidelines) for
the case that we always want the expansion point.
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https://gcc.gnu.org/bugzilla/show_bug.cgi?idg726

Jonathan Wakely <redi at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|ASSIGNED                    |RESOLVED
         Resolution|---                         |FIXED
   Target Milestone|---                         |6.0

--- Comment #3 from Jonathan Wakely <redi at gcc dot gnu.org> ---
Fixed on trunk

[Bug c/67730] [5/6 Regression] No warning when returning NULL in void function

[mpolacek at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=67730

Marek Polacek <mpolacek at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |ASSIGNED
   Last reconfirmed|                            |2015-09-29
                 CC|                            |mpolacek at gcc dot gnu.org
           Assignee|unassigned at gcc dot gnu.org      |mpolacek at gcc dot gnu.org
     Ever confirmed|0                           |1
           Severity|major                       |normal

--- Comment #4 from Marek Polacek <mpolacek at gcc dot gnu.org> ---
Mine then.

[Bug c/67730] [5/6 Regression] No warning when returning NULL in void function

[mpolacek at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=67730

--- Comment #5 from Marek Polacek <mpolacek at gcc dot gnu.org> ---
Author: mpolacek
Date: Wed Sep 30 11:26:44 2015
New Revision: 228286

URL: https://gcc.gnu.org/viewcvs?rev=228286&root=gcc&view=rev
Log:
        PR c/67730
        * c-typeck.c (c_finish_return): Use the expansion point location for
        certain "return with value" warnings.

        * gcc.dg/pr67730.c: New test.

Added:
    trunk/gcc/testsuite/gcc.dg/pr67730.c
Modified:
    trunk/gcc/c/ChangeLog
    trunk/gcc/c/c-typeck.c
    trunk/gcc/testsuite/ChangeLog

[Bug c/67730] [5/6 Regression] No warning when returning NULL in void function

[mpolacek at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=67730

--- Comment #6 from Marek Polacek <mpolacek at gcc dot gnu.org> ---
Author: mpolacek
Date: Wed Sep 30 12:21:03 2015
New Revision: 228288

URL: https://gcc.gnu.org/viewcvs?rev=228288&root=gcc&view=rev
Log:
        PR c/67730
        * c-typeck.c (c_finish_return): Use the expansion point location for
        certain "return with value" warnings.

        * gcc.dg/pr67730.c: New test.

Added:
    branches/gcc-5-branch/gcc/testsuite/gcc.dg/pr67730.c
Modified:
    branches/gcc-5-branch/gcc/c/ChangeLog
    branches/gcc-5-branch/gcc/c/c-typeck.c
    branches/gcc-5-branch/gcc/testsuite/ChangeLog

[Bug c/67730] [5/6 Regression] No warning when returning NULL in void function

[mpolacek at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=67730

--- Comment #7 from Marek Polacek <mpolacek at gcc dot gnu.org> ---
Author: mpolacek
Date: Fri Oct  2 18:01:50 2015
New Revision: 228408

URL: https://gcc.gnu.org/viewcvs?rev=228408&root=gcc&view=rev
Log:
        PR c/67730
        * c-typeck.c (convert_for_assignment): Use the expansion point
        location throughout.

        * gcc.dg/pr67730-1.c: New test.
        * gcc.dg/pr67730-2.c: New test.
        * gcc.dg/pr67730.h: New test.

Added:
    trunk/gcc/testsuite/gcc.dg/pr67730-1.c
    trunk/gcc/testsuite/gcc.dg/pr67730-2.c
    trunk/gcc/testsuite/gcc.dg/pr67730.h
Modified:
    trunk/gcc/c/ChangeLog
    trunk/gcc/c/c-typeck.c
    trunk/gcc/testsuite/ChangeLog

[Bug c/67730] [5 Regression] No warning when returning NULL in void function

[mpolacek at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=67730

--- Comment #8 from Marek Polacek <mpolacek at gcc dot gnu.org> ---
Author: mpolacek
Date: Mon Oct  5 12:35:20 2015
New Revision: 228480

URL: https://gcc.gnu.org/viewcvs?rev=228480&root=gcc&view=rev
Log:
        PR c/67730
        * c-typeck.c (convert_for_assignment): Use the expansion point
        location throughout.

        * gcc.dg/pr67730-1.c: New test.
        * gcc.dg/pr67730-2.c: New test.
        * gcc.dg/pr67730.h: New test.

Added:
    branches/gcc-5-branch/gcc/testsuite/gcc.dg/pr67730-1.c
    branches/gcc-5-branch/gcc/testsuite/gcc.dg/pr67730-2.c
    branches/gcc-5-branch/gcc/testsuite/gcc.dg/pr67730.h
Modified:
    branches/gcc-5-branch/gcc/c/ChangeLog
    branches/gcc-5-branch/gcc/c/c-typeck.c
    branches/gcc-5-branch/gcc/testsuite/ChangeLog

[Bug c/67730] [5 Regression] No warning when returning NULL in void function

[mpolacek at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=67730

Marek Polacek <mpolacek at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|ASSIGNED                    |RESOLVED
         Resolution|---                         |FIXED

--- Comment #9 from Marek Polacek <mpolacek at gcc dot gnu.org> ---
Should be fixed (both GCC 5 and trunk).