Re: [PATCH] Fix PR68067

[Richard Biener <rguenther@suse.de>]

On Fri, 20 Nov 2015, Alan Lawrence wrote:

> On 6 November 2015 at 10:39, Richard Biener <rguenther@suse.de> wrote:
> >> ../spec2000/benchspec/CINT2000/254.gap/src/polynom.c:358:11: error: location
> >> references block not in block tree
> >> l1_279 = PHI <1(28), l1_299(33)>
> >
> > ^^^
> >
> > this is the error to look at!  It means that the GC heap will be corrupted
> > quite easily.
> >
> 
> This looked very similar to PR68117 - the invalid phi arg, and block
> not in  block-tree, even if not the invalid tree code - and as the
> posters there were having success with valgrind, whereas I wasn't, I
> watched and waited. First observation is that it triggers the asserts
> you suggested in comment 27
> (https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D68117#c27). Indeed, it
> fails those asserts, even after the patch in comment 25 (committed as
> r230594) to tree-ssa.c (delete_tree_ssa), and the patch in comment#35
> to function.c (set_cfun), and the patch in comment#30 (committed as
> r230424) to cfgexpand.c (pass_expand::execute).
> 
> The patch in comment#29 (which replaces the asserts in comment#27 with
> empties), however, fixes the problem - although I can't rule out, that
> that's just by changing the memory allocation pattern.
> 
> Moreover, if I take those patches and rebase onto a recent trunk (onto
> which the delete_tree_ssa and pass_expand::execute patches have
> already been committed), i.e. just adding the assertions from
> comment#27 and the call in function.c (set_cfun) - the assertions are
> still failing on my testcase, whereas the original (assertionless)
> failure was very erratic, and had since disappeared/been hidden on
> trunk. Indeed those same assertions break in a few other places (even
> in a --disable-bootstrap build after gcc/xgcc is built), so I feel I
> have a good chance of producing a reasonable assertion-breaking
> testcase.
> 
> So I have to ask, how sure are you that those assertions are(/should
> be!) "correct"? :)

Ideally they should be correct but they happen to be not (and I think
the intent was that this should be harmless).  Basically I tried
to assert that nobody creates stale edge redirect data that is not
later consumed or cleared.  Happens to be too optimistic :/

Richard.