Re: gcc 2.95 optimizer bug?

[Mumit Khan <khan at xraylith dot wisc dot EDU>]

Joe Ramey <ramey@csc.ti.com> writes:
> 
> Ok, here's a fixed version of the program that no longer has these
> illegal accesses, but still dumps core with a Bus Error.  I took your
> suggestion and ran the code under a memory debugger (Purify).  It
> found 6 problems with the version of the code that I sent in before,
> but this version comes through cleanly.  Again, the program gets a Bus
> Error if I compile with -O2, but with -O1 it runs with no error, and
> compiling with gcc 2.8.1 -O2 also produces code that runs with no
> error.
> 
> FYI I also compiled with -O2 -g and then ran the program under gdb.
> It dies here:
> 
> Program received signal SIGBUS, Bus error.
> 0x10c98 in inittab () at trybug.c:120
> 120       hashused = 9757 ;
> (gdb) 
> 
> That was my first clue that something very strange is going on, since
> it's not dying on a line that looks like the typical bus error point
> (dereference a null pointer, divide by zero maybe, stuff like that).
> 
> So again here's the C code (the fixed version) that seems to
> demonstrate the problem.

Thanks. I can reproduce it on a sparc-sun-solaris2.5.1, but not on
a i686-pc-linux-gnu. Perhaps a platform specific bug? I'll take a
look at the assembly later to see if I can spot anything.

The only workaround I see is to use -fno-gcse.

Regards,
Mumit