Re: c/9944: gcc does not warn for always-false "if (!a & 0x4)" bitwise and on boolean value

Re: c/9944: gcc does not warn for always-false "if (!a & 0x4)" bitwise and on boolean value

[bangerth]

Synopsis: gcc does not warn for always-false "if (!a & 0x4)" bitwise and on boolean value

State-Changed-From-To: open->analyzed
State-Changed-By: bangerth
State-Changed-When: Sat Mar 22 04:31:36 2003
State-Changed-Why:
    Patches already floating around

http://gcc.gnu.org/cgi-bin/gnatsweb.pl?cmd=view%20audit-trail&database=gcc&pr=9944

Re: c/9944: gcc does not warn for always-false "if (!a & 0x4)" bitwise and on boolean value

[John Levon]

The following reply was made to PR c/9944; it has been noted by GNATS.

From: John Levon <levon@movementarian.org>
To: gcc-gnats@gcc.gnu.org
Cc:  
Subject: Re: c/9944: gcc does not warn for always-false "if (!a & 0x4)" bitwise and on boolean value
Date: Fri, 21 Mar 2003 01:42:56 +0000

 On Tue, Mar 04, 2003 at 07:44:31PM -0000, levon@movementarian.org wrote:
 
 >      if (!a & 0x4)  // really meant if (!(a & 0x4))
 
 Patch:
 
 http://gcc.gnu.org/ml/gcc-patches/2003-03/msg01856.html
 
 john

c/9944: gcc does not warn for always-false "if (!a & 0x4)" bitwise and on boolean value

[levon]

>Number:         9944
>Category:       c
>Synopsis:       gcc does not warn for always-false "if (!a & 0x4)" bitwise and on boolean value
>Confidential:   no
>Severity:       non-critical
>Priority:       low
>Responsible:    unassigned
>State:          open
>Class:          change-request
>Submitter-Id:   net
>Arrival-Date:   Tue Mar 04 19:46:01 UTC 2003
>Closed-Date:
>Last-Modified:
>Originator:     levon@movementarian.org
>Release:        gcc 3.4 CVS and earlier
>Organization:
>Environment:
Linux i386
>Description:
GCC does not warn for expressions that are always false,
such as the following :

     if (!a & 0x4)  // really meant if (!(a & 0x4))

I thought this might be easy to fix but its beyond
my admittedly meagre capabilities. Apparently I should
be doing it in GIMPLE according to dnovillo.

I'll attach my part-working patch here anyway in the
hope it inspires somebody with more nous (I'd also like to know the answer to "is there a simple way to find out if a tree is constrained to boolean, i.e. 0|1, result", but only
academically).
>How-To-Repeat:

>Fix:

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