[Bug c/21159] New: "no effect" warning despite cast to void*

[Bug c/21159] New: "no effect" warning despite cast to void*

[bruno at clisp dot org]

The gcc-4.0 manual says 
 
        * An expression-statement or the left-hand side of a comma 
          expression contains no side effects.  To suppress the 
          warning, cast the unused expression to void.  For example, an 
          expression such as `x[i,j]' will cause a warning, but 
          `x[(void)i,j]' will not. 
 
This worked for earlier releases of gcc, but in gcc-4.0 the cast to void 
doesn't avoid the warning. 
 
$ gcc -v 
Using built-in specs. 
Target: powerpc-apple-darwin7.8.0 
Configured with: /Users/bruno/data/work/gcc-4.0.0-20050410/configure 
--prefix=/Volumes/UserData/experimental-macos --enable-shared 
--enable-version-specific-runtime-libs --enable-languages=c,c++ 
Thread model: posix 
gcc version 4.0.0 20050410 (prerelease) 
$ gcc -W -c foo.c 
foo.c: In function 'foo': 
foo.c:4: warning: left-hand operand of comma expression has no effect 
$ gcc -W -c bug.c  
bug.c: In function 'copy_string': 
bug.c:169: warning: left-hand operand of comma expression has no effect

-- 
           Summary: "no effect" warning despite cast to void*
           Product: gcc
           Version: 4.0.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P2
         Component: c
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: bruno at clisp dot org
                CC: gcc-bugs at gcc dot gnu dot org
 GCC build triplet: powerpc-apple-darwin7.8.0
  GCC host triplet: powerpc-apple-darwin7.8.0
GCC target triplet: powerpc-apple-darwin7.8.0


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=21159

[Bug c/21159] "no effect" warning despite cast to void*

[bruno at clisp dot org]

------- Additional Comments From bruno at clisp dot org  2005-04-22 11:01 -------
Created an attachment (id=8706)
 --> (http://gcc.gnu.org/bugzilla/attachment.cgi?id=8706&action=view)
source file foo.c


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=21159

[Bug c/21159] "no effect" warning despite cast to void*

[bruno at clisp dot org]

------- Additional Comments From bruno at clisp dot org  2005-04-22 11:01 -------
Created an attachment (id=8707)
 --> (http://gcc.gnu.org/bugzilla/attachment.cgi?id=8707&action=view)
source file bug.c


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=21159

[Bug c/21159] [4.0/4.1 Regression] "no effect" warning despite cast to void*

[pinskia at gcc dot gnu dot org]

-- 
           What    |Removed                     |Added
----------------------------------------------------------------------------
           Severity|normal                      |minor
           Keywords|                            |diagnostic
            Summary|"no effect" warning despite |[4.0/4.1 Regression] "no
                   |cast to void*               |effect" warning despite cast
                   |                            |to void*
   Target Milestone|---                         |4.0.1


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=21159

[Bug c/21159] [4.0/4.1 Regression] "no effect" warning despite cast to void*

[pinskia at gcc dot gnu dot org]

------- Additional Comments From pinskia at gcc dot gnu dot org  2005-04-22 11:23 -------
Confirmed.

-- 
           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |NEW
     Ever Confirmed|                            |1
      Known to fail|                            |4.0.0 4.1.0
      Known to work|                            |3.4.0
   Last reconfirmed|0000-00-00 00:00:00         |2005-04-22 11:23:13
               date|                            |


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=21159

[Bug c/21159] [4.0/4.1 Regression] "no effect" warning despite cast to void*

[jsm28 at gcc dot gnu dot org]

------- Additional Comments From jsm28 at gcc dot gnu dot org  2005-04-26 21:55 -------
What's actually happening is that GCC 4 is building trees for comma expressions
in accordance with how the C standard says they are parsed, where previous
versions were not.

(void)a, (void)b, c

is parsed as ((void)a, (void)b), c rather than as (void)a, ((void)b, c).  The
choice of internal representation should make no difference to the code
generated but as here it can affect diagnostics.  The diagnostic does seem
useless here where the left-hand side of the expression is a comma expression
with the right-hand side cast to void, so I'll add that as a case for which the
diagnostic is disabled.


-- 
           What    |Removed                     |Added
----------------------------------------------------------------------------
         AssignedTo|unassigned at gcc dot gnu   |jsm28 at gcc dot gnu dot org
                   |dot org                     |
             Status|NEW                         |ASSIGNED
   Last reconfirmed|2005-04-22 11:23:13         |2005-04-26 21:55:59
               date|                            |


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=21159

[Bug c/21159] [4.0/4.1 Regression] "no effect" warning despite cast to void*

[cvs-commit at gcc dot gnu dot org]

------- Additional Comments From cvs-commit at gcc dot gnu dot org  2005-04-27 21:41 -------
Subject: Bug 21159

CVSROOT:	/cvs/gcc
Module name:	gcc
Changes by:	jsm28@gcc.gnu.org	2005-04-27 21:41:15

Modified files:
	gcc            : ChangeLog c-typeck.c 
	gcc/testsuite  : ChangeLog 
Added files:
	gcc/testsuite/gcc.dg: void-cast-1.c 

Log message:
	PR c/21159
	* c-typeck.c (build_compound_expr): Don't warn for left-hand side
	being a compound expression whose right-hand side is cast to void.
	
	testsuite:
	* gcc.dg/void-cast-1.c: New test.

Patches:
http://gcc.gnu.org/cgi-bin/cvsweb.cgi/gcc/gcc/ChangeLog.diff?cvsroot=gcc&r1=2.8501&r2=2.8502
http://gcc.gnu.org/cgi-bin/cvsweb.cgi/gcc/gcc/c-typeck.c.diff?cvsroot=gcc&r1=1.436&r2=1.437
http://gcc.gnu.org/cgi-bin/cvsweb.cgi/gcc/gcc/testsuite/ChangeLog.diff?cvsroot=gcc&r1=1.5407&r2=1.5408
http://gcc.gnu.org/cgi-bin/cvsweb.cgi/gcc/gcc/testsuite/gcc.dg/void-cast-1.c.diff?cvsroot=gcc&r1=NONE&r2=1.1



-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=21159

[Bug c/21159] [4.0/4.1 Regression] "no effect" warning despite cast to void*

[cvs-commit at gcc dot gnu dot org]

------- Additional Comments From cvs-commit at gcc dot gnu dot org  2005-04-27 21:47 -------
Subject: Bug 21159

CVSROOT:	/cvs/gcc
Module name:	gcc
Branch: 	gcc-4_0-branch
Changes by:	jsm28@gcc.gnu.org	2005-04-27 21:47:31

Modified files:
	gcc            : ChangeLog c-typeck.c 
	gcc/testsuite  : ChangeLog 
Added files:
	gcc/testsuite/gcc.dg: void-cast-1.c 

Log message:
	PR c/21159
	* c-typeck.c (build_compound_expr): Don't warn for left-hand side
	being a compound expression whose right-hand side is cast to void.
	
	testsuite:
	* gcc.dg/void-cast-1.c: New test.

Patches:
http://gcc.gnu.org/cgi-bin/cvsweb.cgi/gcc/gcc/ChangeLog.diff?cvsroot=gcc&only_with_tag=gcc-4_0-branch&r1=2.7592.2.198&r2=2.7592.2.199
http://gcc.gnu.org/cgi-bin/cvsweb.cgi/gcc/gcc/c-typeck.c.diff?cvsroot=gcc&only_with_tag=gcc-4_0-branch&r1=1.419.2.2&r2=1.419.2.3
http://gcc.gnu.org/cgi-bin/cvsweb.cgi/gcc/gcc/testsuite/ChangeLog.diff?cvsroot=gcc&only_with_tag=gcc-4_0-branch&r1=1.5084.2.143&r2=1.5084.2.144
http://gcc.gnu.org/cgi-bin/cvsweb.cgi/gcc/gcc/testsuite/gcc.dg/void-cast-1.c.diff?cvsroot=gcc&only_with_tag=gcc-4_0-branch&r1=NONE&r2=1.1.2.1



-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=21159

[Bug c/21159] [4.0/4.1 Regression] "no effect" warning despite cast to void*

[pinskia at gcc dot gnu dot org]

------- Additional Comments From pinskia at gcc dot gnu dot org  2005-04-27 21:49 -------
Fixed.

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


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=21159