c/3074: Statement with no effect not flagged with -Wall

c/3074: Statement with no effect not flagged with -Wall

[fritz]

>Number:         3074
>Category:       c
>Synopsis:       Statement with no effect not flagged with -Wall
>Confidential:   no
>Severity:       non-critical
>Priority:       medium
>Responsible:    unassigned
>State:          open
>Class:          accepts-illegal
>Submitter-Id:   net
>Arrival-Date:   Thu Jun 07 07:56:01 PDT 2001
>Closed-Date:
>Last-Modified:
>Originator:     Fritz Boehm
>Release:        gcc version 2.96 20000731 (Red Hat Linux 7.1 2.96-81)
>Organization:
>Environment:
Red Hat Linux 7.1
>Description:
This bug has to do with some statements with no effect going undetected
by gcc.  The line on line 4 of bug.c should (I believe) be flagged as
a statement with no effect when run with -Wall.  I munged the statement
in two different ways (lines 5 and 6) which are correctly reported as 
statements with no effect.

I have access to two linux boxes with different revisions of g++.  Both
yield the same results:



<fritz @ schrems.eng.evsx.com> 1491% gcc -v
Reading specs from /usr/lib/gcc-lib/i386-redhat-linux/egcs-2.91.66/specs
gcc version egcs-2.91.66 19990314/Linux (egcs-1.1.2 release)

<fritz @ schrems.eng.evsx.com> 1492% gcc -c bug.c -Wall
bug.c: In function `main':
bug.c:5: warning: statement with no effect
bug.c:6: warning: statement with no effect




<fritz @ lott.eng.evsx.com> 10% gcc -v
Reading specs from /usr/lib/gcc-lib/i386-redhat-linux/2.96/specs
gcc version 2.96 20000731 (Red Hat Linux 7.1 2.96-81)

<fritz @ lott.eng.evsx.com> 11% gcc -c -Wall bug.c 
bug.c: In function `main':
bug.c:5: warning: statement with no effect
bug.c:6: warning: statement with no effect



Another aspect that you might find interesting - there is assembly
code generated for the apparently dead code at line 4.  I'm not an
x86 assembly wizard so I can't tell you what the code does, but there
is extra code generated.

I hope this helps.  Feel free to email me with any questions.  This is
the first bug I've submitted for GNU tools (which I make use of extensively)
so I hope I'm providing good feedback.
>How-To-Repeat:
gcc -c -Wall bug.c
>Fix:
Don't enter statements that have no effect  :-D
>Release-Note:
>Audit-Trail:
>Unformatted:
 
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Re: c/3074: Statement with no effect not flagged with -Wall

[Dara Hazeghi]

The following reply was made to PR c/3074; it has been noted by GNATS.

From: Dara Hazeghi <dhazeghi@yahoo.com>
To: gcc-gnats@gcc.gnu.org
Cc:  
Subject: Re: c/3074: Statement with no effect not flagged with -Wall
Date: Thu, 8 May 2003 01:39:44 -0700

 http://gcc.gnu.org/cgi-bin/gnatsweb.pl?cmd=view%20audit- 
 trail&database=gcc&pr=3074
 
 Confirmed with mainline 20030507
 
 Dara