Re: [naviserver-devel] strict aliasing?

[Vlad S. <vl...@cr...>]

I went through google about this and found out that many projects like 
Linux, PostgreSQL and others use -fno-strict-aliasing. And nobody could 
determine if this affects optimnization, so we can use that flag as well 
and in the meantime slowly change the code.

Zoran Vasiljevic wrote:
> Hi
> 
> When you compile w/o debugging (i.e. with optimisation)
> the GCC spits whole-lotta stuff like that:
> 
> tclthread.c:401: warning: dereferencing type-punned pointer will  break 
> strict-aliasing rules
> tclthread.c:401: warning: dereferencing type-punned pointer will  break 
> strict-aliasing rules
> 
> The warning sems to trigger when a pointer is casted like this:
> 
>     enum {
>         EAbsWaitIdx, EBroadcastIdx, ECreateIdx, EDestroyIdx, ESetIdx,
>         ESignalIdx, ETimedWaitIdx, EWaitIdx
>     } opt;
> 
>     if (!GetArgs(interp, objc, objv, opts, 'e', ECreateIdx,
>                   (int *) &opt, (void **) &condPtr)) {
>         return TCL_ERROR;
> 
> The "opt" and "condPtr" in GetArgs() are casted and it barks
> at them. I cannot possibly imagine changing all code to
> something like:
> 
>     enum {
>         EAbsWaitIdx, EBroadcastIdx, ECreateIdx, EDestroyIdx, ESetIdx,
>         ESignalIdx, ETimedWaitIdx, EWaitIdx
>     } opt;
>     int myOpt = (int)opt;
> 
>     if (!GetArgs(interp, objc, objv, opts, 'e', ECreateIdx,
>                   &myOpt, (void **) &condPtr)) {
>         return TCL_ERROR;
> 
> This would mean lots of work and may introduce errors.
> 
> I've read that you can use (starting with gcc 3.3) -fno-strict-aliasing
> which would remove those warnings. But also, somebody said that the
> effect of the "-O2" is gone in such cases (haven't be able to verify)
> 
> What to do?
> Any ideas?
> 
> Zoran
> 
> 
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-- 
Vlad Seryakov
571 262-8608 office
vl...@cr...
http://www.crystalballinc.com/vlad/