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Re: make bootstrap segfaults on current cvs head (i686-pc-linux-gnu)
- To: Mike Coleman <mcoleman2 at kc dot rr dot com>
- Subject: Re: make bootstrap segfaults on current cvs head (i686-pc-linux-gnu)
- From: Alan Modra <alan at linuxcare dot com dot au>
- Date: Sat, 14 Oct 2000 12:48:10 +1100 (EST)
- cc: "Joseph S. Myers" <jsm28 at cam dot ac dot uk>, gcc-bugs at gcc dot gnu dot org, jh at suse dot cz
On 13 Oct 2000, Mike Coleman wrote:
> "Joseph S. Myers" <jsm28@cam.ac.uk> writes:
> > On Fri, 13 Oct 2000, Alan Modra wrote:
> >
> > > On Fri, 13 Oct 2000, Mike Coleman wrote:
> > >
> > > > I get a segfault when trying to build gcc from the current cvs head. I tried
> > >
> > > So do I. This might help.
> > >
> > > gcc/ChangeLog
> > > * emit_rtl.c (init_emit_once): Create const_int_htab before using.
> >
> > I think there's more to the problem than this. ...
Indeed.
> FWIW, I tried Alan's patch and it didn't affect the segfault for me. (Thanks,
> though, Alan.)
Well, it did affect the segfault. You just got a different one. :-(
All due to wrong comparisons or conditional jumps being generated.
For this comparison in emit-rtl.c:gen_rtx_CONST_INT
if (arg >= - MAX_SAVED_CONST_INT && arg <= MAX_SAVED_CONST_INT)
return const_int_rtx[arg + MAX_SAVED_CONST_INT];
I see
lea 0x40(%edx),%eax ; add MAX_SAVED_CONST_INT
add $0xffffff80,%eax ; add -2*MAX_SAVED_CONST_INT
ja
<return const_int_rtx[] code>
"ja" branches if CF=0 and ZF=0, which is quite wrong. Correct in this
case would be "jbe"
The patch I submitted fixes a real bug (gen_rtx_CONST_INT called in
init_emit_once before the CONST_INT hash has been created), which happened
to be exposed by one of these bad comparison bugs.
Alan
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