Re: optimization/8302: Pointer casting causes ++ to be ignored when optimizing

Re: optimization/8302: Pointer casting causes ++ to be ignored when optimizing

[bangerth]

Synopsis: Pointer casting causes ++ to be ignored when optimizing

State-Changed-From-To: feedback->closed
State-Changed-By: bangerth
State-Changed-When: Tue Dec 10 08:34:27 2002
State-Changed-Why:
    Aliasing violation, as discussed in 
      http://gcc.gnu.org/ml/gcc-bugs/2002-10/msg00886.html 
    
    
      

http://gcc.gnu.org/cgi-bin/gnatsweb.pl?cmd=view%20audit-trail&database=gcc&pr=8302

Re: optimization/8302: Pointer casting causes ++ to be ignored when optimizing

[bangerth]

Synopsis: Pointer casting causes ++ to be ignored when optimizing

State-Changed-From-To: open->feedback
State-Changed-By: bangerth
State-Changed-When: Fri Dec  6 12:18:13 2002
State-Changed-Why:
    There is no self-contained testcase in this report. Do you
    still have it, so that we can take a look at it?
    
    Thanks
      Wolfgang

http://gcc.gnu.org/cgi-bin/gnatsweb.pl?cmd=view%20audit-trail&database=gcc&pr=8302

optimization/8302: Pointer casting causes ++ to be ignored when optimizing

[noaml]

>Number:         8302
>Category:       optimization
>Synopsis:       Pointer casting causes ++ to be ignored when optimizing
>Confidential:   no
>Severity:       critical
>Priority:       medium
>Responsible:    unassigned
>State:          open
>Class:          wrong-code
>Submitter-Id:   net
>Arrival-Date:   Mon Oct 21 09:46:01 PDT 2002
>Closed-Date:
>Last-Modified:
>Originator:     Noam Lampert
>Release:        gcc version 3.3 20021019 (experimental)
>Organization:
>Environment:
Intel 386. RH 7.3. kernel 2.4.18-3
>Description:
unsigned char *p;
unsigned char x;
....
*(*((unsigned char **)(&p)))++ = x;
as a side effect, p should be incremented. Sometimes, in optimized, it is not.
>How-To-Repeat:
gcc -O2 main.c
a.out
This source is in standard testcase format, and will call abort() upon failure.
>Fix:
Changing the code to 
*(*((unsigned char **)(&p))) = x;
p += sizeof(x);

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