[Bug c/49859] New: gcc could warn about statements between "switch" and first "case"

[Bug c/49859] New: gcc could warn about statements between "switch" and first "case"

[wkoszek at gmail dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=49859

           Summary: gcc could warn about statements between "switch" and
                    first "case"
           Product: gcc
           Version: 4.5.2
            Status: UNCONFIRMED
          Severity: minor
          Priority: P3
         Component: c
        AssignedTo: unassigned@gcc.gnu.org
        ReportedBy: wkoszek@gmail.com


Created attachment 24838
  --> http://gcc.gnu.org/bugzilla/attachment.cgi?id=24838
Sample source code.

wkoszek@wkoszek:~/p/switch$ cat switch.c 
#include <stdio.h>

int
main(int argc, char **argv)
{
    int    type;

    type = 123;
    switch (type) {
        printf("SOMETHING\n");
    case 1:
        printf("1\n");
        break;
    case 2:
        printf("2\n");
        break;
    default:
        printf("default\n");
        return 1;
    }
    return 0;
}
wkoszek@wkoszek:~/p/switch$ gcc -pedantic -Wall -Wunused -Wunreachable-code -c
switch.c
wkoszek@wkoszek:~/p/switch$ clang -pedantic -Wall -Wunused -Wunreachable-code
-c switch.c
switch.c:10:3: warning: will never be executed [-Wunreachable-code]
                printf("SOMETHING\n");
                ^~~~~~~~~~~~~~~~~~~~~
1 warning generated.


wkoszek@wkoszek:~/p/switch$ gcc -v
Using built-in specs.
COLLECT_GCC=gcc
COLLECT_LTO_WRAPPER=/usr/lib/i386-linux-gnu/gcc/i686-linux-gnu/4.5.2/lto-wrapper
Target: i686-linux-gnu
Configured with: ../src/configure -v --with-pkgversion='Ubuntu/Linaro
4.5.2-8ubuntu4' --with-bugurl=file:///usr/share/doc/gcc-4.5/README.Bugs
--enable-languages=c,c++,fortran,objc,obj-c++ --prefix=/usr
--program-suffix=-4.5 --enable-shared --enable-multiarch
--with-multiarch-defaults=i386-linux-gnu --enable-linker-build-id
--with-system-zlib --libexecdir=/usr/lib/i386-linux-gnu
--without-included-gettext --enable-threads=posix
--with-gxx-include-dir=/usr/include/c++/4.5 --libdir=/usr/lib/i386-linux-gnu
--enable-nls --with-sysroot=/ --enable-clocale=gnu --enable-libstdcxx-debug
--enable-libstdcxx-time=yes --enable-plugin --enable-gold --enable-ld=default
--with-plugin-ld=ld.gold --enable-objc-gc --enable-targets=all --disable-werror
--with-arch-32=i686 --with-tune=generic --enable-checking=release
--build=i686-linux-gnu --host=i686-linux-gnu --target=i686-linux-gnu
Thread model: posix
gcc version 4.5.2 (Ubuntu/Linaro 4.5.2-8ubuntu4)

[Bug c/49859] gcc could warn about statements between "switch" and first "case"

[wkoszek at gmail dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=49859

--- Comment #1 from Wojciech Koszek <wkoszek at gmail dot com> 2011-07-27 01:16:25 UTC ---
I'd expect GCC to warn me about this case, since it's very likely an error.

[Bug c/49859] gcc could warn about statements between "switch" and first "case"

[pinskia at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=49859

--- Comment #2 from Andrew Pinski <pinskia at gcc dot gnu.org> 2011-07-27 01:22:05 UTC ---
-Wunreachable-code support was removed because it dependent on optimization and
caused some "false positives" (well they are not false positives in the sense
they were unreachable code but rather the code compiled with some optimization
was a truly unreachable but only with inlining and such).

Also does clang warn about Duff's loops?

[Bug c/49859] gcc could warn about statements between "switch" and first "case"

[wkoszek at gmail dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=49859

--- Comment #3 from Wojciech Koszek <wkoszek at gmail dot com> 2011-07-27 01:28:28 UTC ---
Looks like GCC and Clang both agree on Duff's stuff:

wkoszek@wkoszek:~/p/duff$ cat duff.c
#include <stdio.h>

void
duff(to, from, count)
register short *to, *from;
register int count;
{
        register int n=(count+7)/8;
        switch(count%8){
        case 0:      do{      *to = *from++;
        case 7:              *to = *from++;
        case 6:              *to = *from++;
        case 5:              *to = *from++;
        case 4:              *to = *from++;
        case 3:              *to = *from++;
        case 2:              *to = *from++;
        case 1:              *to = *from++;
                }while(--n>0);
        }
}

int
main(int argc, char **argv)
{
    short    *dummy = NULL;

    (void)argc;
    (void)argv;

    duff(dummy, dummy, 123);
    return 0;
}
wkoszek@wkoszek:~/p/duff$ gcc -Wall -pedantic -Wunreachable-code -c duff.c
wkoszek@wkoszek:~/p/duff$ clang -Wall -pedantic -Wunreachable-code -c duff.c

[Bug c/49859] gcc could warn about statements between "switch" and first "case"

[rguenth at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=49859

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |NEW
   Last reconfirmed|                            |2011.07.27 10:07:14
     Ever Confirmed|0                           |1
           Severity|minor                       |enhancement

--- Comment #4 from Richard Guenther <rguenth at gcc dot gnu.org> 2011-07-27 10:07:14 UTC ---
Confirmed.

[Bug c/49859] gcc could warn about statements between "switch" and first "case"

[manu at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=49859

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

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

--- Comment #5 from Manuel López-Ibáñez <manu at gcc dot gnu.org> ---
For sure we do not need the old -Wunreachable here. Just when parsing a switch
block, anything found before the first case is basically unreachable, no?

(Why the standard does not consider this an error?)
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Subject: [Bug fortran/63331] Fortran -fcompare-debug issues
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https://gcc.gnu.org/bugzilla/show_bug.cgi?idc331

--- Comment #3 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
Author: jakub
Date: Tue Sep 23 15:25:55 2014
New Revision: 215516

URL: https://gcc.gnu.org/viewcvs?rev!5516&root=gcc&view=rev
Log:
    PR fortran/63331
    * trans-types.c (gfc_get_array_descr_info): Build DEBUG_EXPR_DECL
    instead of VAR_DECL for base_decl.

    * gfortran.dg/pr63331.f90: New test.

Added:
    trunk/gcc/testsuite/gfortran.dg/pr63331.f90
Modified:
    trunk/gcc/fortran/ChangeLog
    trunk/gcc/fortran/trans-types.c
    trunk/gcc/testsuite/ChangeLog