[Bug c/21322] O2 and O3 memory access error - compiled program - incorrect debug output

["fastsnip-bcard1 at yahoo dot com" <gcc-bugzilla@gcc.gnu.org>]

------- Additional Comments From fastsnip-bcard1 at yahoo dot com  2005-05-01 20:24 -------
Subject: Re:  O2 and O3 memory access error - compiled program - incorrect debug output

On Sunday 01 May 2005 15:40, you wrote:
> ------- Additional Comments From pinskia at gcc dot gnu dot org  2005-05-01
> 19:40 ------- (In reply to comment #5)
>
> > Subject: Re:  O2 and O3 memory access error - compiled program -
> > incorrect debug output
> >
> > On Sunday 01 May 2005 15:19, you wrote:
> > > ------- Additional Comments From pinskia at gcc dot gnu dot org 
> > > 2005-05-01 19:19 ------- Also can you look to see you have any warnings
> > > with -W -Wall? The warnings about unsigned vs signed were there before
> > > just enabled with -pedantic.
> > >
> > > Also does -fno-strict-aliasing help if so this might not be a bug in
> > > GCC but your code.
> >
> > Compiled with the above flag as you suggested - no change - I still get a
> > memory access error using "-O3" optiomization.
> >
> > Will try the "-W -Wall" flags top see what that produces and let you
> > know.
> >
> > Terry
>
> Hmm, try -O1 -funit-at-a-time also make sure that you are not going past an
> array bounds. Also make sure that you are not invoking undefined behavior.

Okay I tried the following optimizing options:

-O1 -funit-at-a-time ==== program ran fine
-O1                       ==== program ran fine
-O2 -funit-at-a-time ==== memory access error
-O3 -funit-at-a-time ==== memory access error

It seems that O2 and O3 only trigger the memory access error.


Do not know exactly what you mean by "Also make sure that you are not invoking 
undefined behavior." Exactly how do I do this. Is there something in 4.0.0 
that wasn't in 2.95 through 3.4.3 that would trigger this? The program 
compiled and ran fine under previous versions with the same compilation 
optimization options.



>
> I get a lot of warnings about uninitialized variables like so:
> awkpcmp.c: In function 'c_pop':
> awkpcmp.c:57: warning: 'R_Token' may be used uninitialized in this function
> awkpcmp.c: In function 'c_primary_expr':
> awkpcmp.c:159: warning: 'arg2' may be used uninitialized in this function
> awkpcmp.c:158: warning: 'arg1' may be used uninitialized in this function
> awkpcmp.c: In function 'c_statement':
> awkpcmp.c:1122: warning: 'Last_Token' may be used uninitialized in this
> function awkpcmp.c: In function 'set_user_fun':
> awkpcmp.c:1789: warning: 'name' may be used uninitialized in this function
>
> so you might just be invoking undefined.



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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=21322