------- Additional Comments From wilson at gcc dot gnu dot org  2004-01-29 
21:41 -------
This is a known interaction problem with cselib/sched-ebb.  I have never seen a
report of it resulting in an ICE or incorrect code.  It only results in code
that is scheduled differently, and hence this can cause the gcc compare test to
fail.

The oversimplified description of the problem is that memory is being accessed
after it has been freed.

This problem is difficult to reproduce.  It is known to be sensitive to the
environment size.  Small changes to the environment size can cause the problem
to appear or disappear.  This is because environment size changes cause pointers
to have different values resulting in different behaviour in the presense of the
bug.

The problem is difficult to fix.  Andrew Pinksi suggested a patch, but it is one
patch is a long sequence of patches that have been directed at this problem, and
the problem is still not fully fixed on mainline.  I do not recommend taking
this approach for gcc-3.3.

It is safe to ignore the problem if you can.  If you can't ignore the problem
then I would suggest changing sched-ebb.c to stop using cselib.  This will
result in some performance loss, though I don't know how much.  There is a minor
chance of exposing latent bugs with this change, but I think the chance is
acceptably small.

I will put my suggested patch in an attachment.  If this patch does not fix the
problem, then there must be something else wrong that needs to be investigated.

-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=13918

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