Re: c/4210: bad warning with dead code

Re: c/4210: bad warning with dead code

[bangerth]

Synopsis: bad warning with dead code

State-Changed-From-To: open->analyzed
State-Changed-By: bangerth
State-Changed-When: Tue Nov  5 07:43:05 2002
State-Changed-Why:
    Confirmed. I may be wrong, but I believe Toon Moene has
    recently filed a similar bug (recently=it's number should be
    in the high 8000s) where the dead code was actually created
    by a template parameter, instead of a plain constant. Whoever
    looks at this one might want to look for the other report
    as well.

http://gcc.gnu.org/cgi-bin/gnatsweb.pl?cmd=view%20audit-trail&database=gcc&pr=4210

Re: c/4210: bad warning with dead code

[Wolfgang Bangerth]

The following reply was made to PR c/4210; it has been noted by GNATS.

From: Wolfgang Bangerth <bangerth@ticam.utexas.edu>
To: gcc-gnats@gcc.gnu.org
Cc:  
Subject: Re: c/4210: bad warning with dead code
Date: Wed, 6 Nov 2002 16:12:43 -0600 (CST)

 I was wrong on the name of the originator, the range of numbers, and maybe 
 more of the duplicate I suspected. It had templates in it, though :-)
 
 In any case, the duplicate was c++/8419, which I closed because it is 
 almost an exact duplicate.
 
 W.
 
 -------------------------------------------------------------------------
 Wolfgang Bangerth              email:           bangerth@ticam.utexas.edu
                                www: http://www.ticam.utexas.edu/~bangerth
 
 

c/4210: bad warning with dead code

[gustav]

>Number:         4210
>Category:       c
>Synopsis:       bad warning with dead code
>Confidential:   no
>Severity:       non-critical
>Priority:       medium
>Responsible:    unassigned
>State:          open
>Class:          sw-bug
>Submitter-Id:   net
>Arrival-Date:   Mon Sep 03 11:36:00 PDT 2001
>Closed-Date:
>Last-Modified:
>Originator:     gustav@virtutech.se
>Release:        GNU C version 3.0.1 20010626 (prerelease) (i386-pc-linux-gnu)
>Organization:
>Environment:

>Description:
gcc outputs a warning about shifts >= width of type inside
dead code when that code is dead because of a const
variable. This can easily happen in autogenerated code, or
when you do operations on preprocessor defines.
>How-To-Repeat:
Compile the following with -Wall -O2:

int rol0(int a)
{
        const int b = 0;
	if (b) {
		a = (a << b) | (a >> (8 * sizeof a - b));
        }
	return a;
}
>Fix:

>Release-Note:
>Audit-Trail:
>Unformatted: