Re: [PATCH] Fix ICE with __builtin_unreachable() as only statement in a function.

[David Daney <ddaney at caviumnetworks dot com>]

H.J. Lu wrote:
> On Tue, Jun 16, 2009 at 11:18 AM, David Daney<ddaney@caviumnetworks.com> wrote:
> > This patch fixed an ICE I found doing additional __builtin_unreachable()
> >  testing.
> >
> > If __builtin_unreachable() is the only statement in a function, the
> > resulting barrier will be the first non-note insn when doing barrier
> > cleanup.  This causes SIGSEGV in cleanup_barriers.  The fix is to check for
> > NULL before dereferencing.
> >
> > Tested on x86_64-pc-linux-gnu all default languages.  No regressions found.
>
> Is this the same as
>
> http://gcc.gnu.org/bugzilla/show_bug.cgi?id=40445
>
> If yes, you should include PR in ChangeLog.

I think it is a different issue.  It would appear to only affect g++ and 
the ICE is at a different point.  I will however look at it.

David Daney


> H.J.
> > OK to commit?
> >
> > gcc/
> > 2009-06-16  David Daney  <ddaney@caviumnetworks.com>
> >
> >        * jump.c (cleanup_barriers): Handle case of no insns before a
> >        barrier.
> >
> > gcc/testsuite/
> > 2009-06-16  David Daney  <ddaney@caviumnetworks.com>
> >
> >        * gcc.dg/builtin-unreachable-3.c: New test.
> >
> > Index: gcc/testsuite/gcc.dg/builtin-unreachable-3.c
> > ===================================================================
> > --- gcc/testsuite/gcc.dg/builtin-unreachable-3.c        (revision 0)
> > +++ gcc/testsuite/gcc.dg/builtin-unreachable-3.c        (revision 0)
> > @@ -0,0 +1,9 @@
> > +/* Check that a function containing only __builtin_unreachable()
> > +   doesn't ICE.  */
> > +/* { dg-do compile } */
> > +/* { dg-options "-O2" } */
> > +const char *
> > +f (void)
> > +{
> > +  __builtin_unreachable ();
> > +}
> > Index: gcc/jump.c
> > ===================================================================
> > --- gcc/jump.c  (revision 148409)
> > +++ gcc/jump.c  (working copy)
> > @@ -113,6 +113,11 @@ cleanup_barriers (void)
> >       if (BARRIER_P (insn))
> >        {
> >          prev = prev_nonnote_insn (insn);
> > +         /* A function that contains only __builtin_unreachable() may
> > +            start with a barrier.  In this case PREV will be
> > +            NULL.  */
> > +         if (!prev)
> > +           continue;
> >          if (BARRIER_P (prev))
> >            delete_insn (insn);
> >          else if (prev != PREV_INSN (insn))