[Vm-dev] [commit][3753] Do not use -O3 optimization, -O2 is safer and works well.

[David T. Lewis]

On Wed, Dec 21, 2016 at 10:40:32AM +0800, Ben Coman wrote:
>  
> On Wed, Dec 21, 2016 at 9:03 AM,  <commits at squeakvm.org> wrote:
> >
> > Revision: 3753
> > Author:   lewis
> > Date:     2016-12-20 17:03:04 -0800 (Tue, 20 Dec 2016)
> > Log Message:
> > -----------
> > Do not use -O3 optimization, -O2 is safer and works well.
> >
> > gcc 4.9.2 gives crashes and heisenbugs with OSPP compiled with -O3.
> >
> > Symptoms:
> > (1 to: 10) collect: [ :e | (CommandShell new pipeline: 'ps > /dev/null | cat') output]
> >   ==> segfaults in some of the spawned child processes
> >
> > This appears to be an actual compiler bug, although it goes away when print
> > statements are added, so I cannot say for sure (and it is difficult to attach
> > gdb to the newly spawned child process before it crashes). The bad behavior
> > happens only with -O3 and there are no real performance benefits compared
> > to -O2 (bytecodes faster, sends slower).
> 
> I'd be interested to know the reason sends get slower (if known).
> cheers -ben

No clue, I was just sanity checking to make sure that -O2 was not horribly
worse. It was not. But I suspect all of this is likely to vary depending on
gcc compiler version and phase of the moon.

Dave