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Re: Urgent: bug fixes needed for GCC 3.0.2
- To: "law at redhat dot com" <law at redhat dot com>
- Subject: Re: Urgent: bug fixes needed for GCC 3.0.2
- From: Mark Mitchell <mark at codesourcery dot com>
- Date: Thu, 04 Oct 2001 08:57:13 -0700
- cc: "gcc at gcc dot gnu dot org" <gcc at gcc dot gnu dot org>, "wilson at redhat dot com" <wilson at redhat dot com>, "jh at suse dot cz" <jh at suse dot cz>
> > I'm not sure. This is a MEM on the stack, and one that is not
> > necessarily going to be around for the entire function -- witness
> > the fact that we are going to overwrite it. Perhaps I misunderstand
> > a subtlety of RTX_UNCHANGING_P (quite likely, in fact!) but to me
> > it doesn't make sense to set it for this MEM; the value there is
> > likely to change.
> > Am I speaking nonsense?
> Well, if it wasn't for the sibcall optimization the stack slot would be
> unchanging. That's the crux of the issue.
Yes. Perhaps a good fix, in the 3.0.2 time frame, is to turn off
RTX_UNCHANGING_P if flag_sibling_calls is on.
> If we believe that without the sibcall that having RTX_UNCHANGING_P set is
> correct and desirable, then we need to clear the bit if we have a sibcall
> since the sibcall sequence will overwrite the incoming stack slots. This
> may (or may not) be a difficult thing to do.
It sounds difficult to me. Especially to get right the first time.
Mark Mitchell email@example.com
CodeSourcery, LLC http://www.codesourcery.com