bdiff stack overflow patch

[Benoit Boissinot]

On Tue, Dec 08, 2009 at 10:42:34PM +0100, Martin Geisler wrote:
> Benoit Boissinot <bboissin at gmail.com> writes:
> 
> > On Tue, Dec 8, 2009 at 8:23 PM, Alistair Bell <alistair at bellsonline.com> wrote:
> >> Hi all,
> >>
> >> As mentioned in http://mercurial.selenic.com/bts/issue1940 I found
> >> that I was getting a stack overflow in bdiff. You could possibly blame
> >> GCC 3.4.6 for not recognizing that it should optimize the code as tail
> >> recursion, but I converted the tail recursion to iteration and the
> >> problems went away.
> >
> > Really gcc 3.4.6? Could you check if using the 4.x series has better results?
> >
> > Gcc 3.4 is really old, I'm not sure we should take the patch,
> > especially given the code isn't tail-recursive, so it will stay
> > recursive anyway.
> 
> You're saying that GCC 4.x would also have to output recursive code. Is
> that not a good argument for why we *should* take the patch?

No. It only removes one call, so the patch doesn't change the worst case
recursion depth.

Was the code compiled with gcc 3.4 with -O2 (or with the flag
-foptimize-sibling-calls)?

On which OS was it?

regards,

Benoit

-- 
:wq