Re: [PATCH] Fix PR68067

[Alan Lawrence <alan.lawrence@arm.com>]

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"? :)

--Alan