Bug in polymake 2.10

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Max
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Joined: 19 Dec 2010, 19:47

Bug in polymake 2.10

Postby Max » 28 Oct 2011, 14:42

Hi there,
since I couldn't find any public bug tracker for polymake, nor any other information as to how to report bugs, except for a pointer to the forum in the "AQ" section, I am reporting this here now:

In polymake 2.10, file include/core/polymake/internal/sparse2d_ruler.h:151 says the following:

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if (diff<=0 ? -diff>m : (n_alloc=r->_alloc_size+std::max(diff, m)), true) {
I was compiling polymake using clang, which tends to give better diagnostics than GCC. It warned about the expression "-diff>m" being unused. Indeed, this code looks incorrect to me. I guess this was meant instead:

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if (diff<=0 ? -diff>m : ((n_alloc=r->_alloc_size+std::max(diff, m)), true)) {
Personally, I would avoid such needlessly "clever" code and just write

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if (diff<=0 ? -diff>m : true) { if (diff > 0) n_alloc=r->_alloc_size+std::max(diff, m);
which is clear and not as prone to hard-to-spot errors.

Max
Posts: 10
Joined: 19 Dec 2010, 19:47

Re: Bug in polymake 2.10

Postby Max » 28 Oct 2011, 17:21

Here is another bug uncovered by clang: In include/core/polymake/internal/constant_containers.h:80:

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bool operator< (const single_value_iterator& it) const { return !at_end && it.at_end; }
This will *always* return false, as at_end is a pointer to a member method -- while _at_end is the value that is really needed in this text. So this is the correct code:

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bool operator< (const single_value_iterator& it) const { return !_at_end && it._at_end; }
The same mistake is repeated in line 88.

Max
Posts: 10
Joined: 19 Dec 2010, 19:47

Re: Bug in polymake 2.10

Postby Max » 28 Oct 2011, 17:28

A third bug in include/core/polymake/Set.h:110

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return iterator(get_set().find_nearest(limit, polymake::operations::gt()), get_set.end());
should be

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return iterator(get_set().find_nearest(limit, polymake::operations::gt()), get_set().end());

Max
Posts: 10
Joined: 19 Dec 2010, 19:47

Re: Bug in polymake 2.10

Postby Max » 29 Oct 2011, 11:21

Another compiler error one gets with clang is in lib/core/include/internal/type_manip.h:1827

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template <typename Result, typename Source, typename _Generic>
Here _Generic is a reserved identifier, used for some C1X extensions. A simple workaround is to change this to Generic_.

Note: According to the C++03 standard (and the ISO C99 standard it is based on), all identifiers beginning with an underscore followed by an upper-case letter or another underscore are always reserved, in all namespace. Some references for this: <http://c-faq.com/decl/namespace.html> and <http://stackoverflow.com/questions/2287 ... identifier>

Polymake makes liberal use of such identifiers (for things like _Set, _Iterator, _Operation, _Matrix, _Vector etc.), which is bound to cause issues with more C++ compilers sooner or later. E.g. GCC will likely implement the "generic selections" extensions one day, too.

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gawrilow
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Joined: 25 Dec 2010, 17:40

Re: Bug in polymake 2.10

Postby gawrilow » 30 Oct 2011, 23:34

Thanks a lot for pointing to all these bugs! Indeed, they remained undiscovered by gcc, because they sat in a code written "for the stock", which was never instantiated so far. The fixes will appear in the next release. All identifiers starting with an underscore and a capital letter have gone as well.

Max
Posts: 10
Joined: 19 Dec 2010, 19:47

Re: Bug in polymake 2.10

Postby Max » 31 Oct 2011, 13:20

Glad to hear you could fix all of this. :)

There are more changes that are necessary for to make clang happy, though, and more warnings that are not critical but look as if it would be nice to fix them. E.g. polymake mixes "class" and "struct" when referring to a type. Harmless but trivial to fix.

Another problem is that sparse_proxy(_it)_base::iterator is protected in both types, which GCC accepts but triggers an error in clang. Looking at the code, I believe clang is right to complain.

Then there are some constructs GCC accepts but clang rejects -- and clang is right according to the C++ standard, so it's likely future GCC versions will eventually reject the code, too. Example: the definition of the ListValueOutput& operator<< (const X& x) method uses class Value before it is defined; in GCC this may be accepted, perhaps because the method is only instantiated *after* class Value has been declared, but this is a bug in GCC.

There are various more errors and warnings, which I recorded in a local git repository I made out of polymake 2.10. This also includes a patch which makes configure.pl a bit more clever about detecting compilers. I.e. it does not anymore assume that every compiler is either Intel C++, or else an (possible outdated) GCC version... ;). But I am not sure whether these changes are still relevant / applicable for your secret development version of the code.

Max
Posts: 10
Joined: 19 Dec 2010, 19:47

Re: Bug in polymake 2.10

Postby Max » 31 Oct 2011, 16:21

Oh, and lest I be misunderstood: I think polymake is doing exceedingly well when compiled with clang; all "issues" it found are very minor ones, which is very good for a project of this size which makes so heavy use of template techniques. It also uncovered at least one compiler bug in clang itself ;). So, please don't read this all as a complaint, it's just a factual list of minor issues you may want to correct.

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gawrilow
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Joined: 25 Dec 2010, 17:40

Re: Bug in polymake 2.10

Postby gawrilow » 01 Nov 2011, 00:02

You are absolutely right regarding ListValueOutput::operator<<, its definition is indeed misplaced.
But I couldn't localize any references to the protected iterators of sparse_proxy outside of these classes. Could you please point me to them?

Regarding "secret" code repository: if you are going to contribute any useful fixes or new functionality, you are welcome! You do know very well, whom to ask for an access :-)

Max
Posts: 10
Joined: 19 Dec 2010, 19:47

Re: Bug in polymake 2.10

Postby Max » 01 Nov 2011, 12:11

The "iterator" error seems to be triggered by e.g. the DeclTypedefCHECK(iterator) in core/polymake/internal/iterators.h:700.
Attached to this post is a .zip file with a text file iterator-clang-err.txt that contains one set of these warnings. Unfortunately I don't know how to copy the nice coloring of the output clang++ produces (copy&paste into TextEdit.app didn't work). But I hope the output is readable enough.

The .zip file also includes some of my less-hackish patches, maybe some of them will be useful to you. Since clang is not yet supported, you may want to modify the configure.pl patch to error out when clang is detected; but I think having clean detection of GCC and ICC will be helpful regardless of this.

Regarding the "secret" code repository: That was a tongue-in-cheek comment, sorry :). Calling it "internal" is better. The GAP CVS repository is currently "internal only", too. I am not happy with that, and hope it'll change when the project switches to Mercurial (and I gave a talk on the subject, trying to sway my fellow developers), but for now this is the same situation in any case.
Attachments
polymake-patches.tar.bz2
clang error message and some patches
(6.23 KiB) Downloaded 315 times

Max
Posts: 10
Joined: 19 Dec 2010, 19:47

Re: Bug in polymake 2.10

Postby Max » 01 Nov 2011, 16:38

There is another error which I can't figure out (present with Apple clang 2.0 and 3.0 and also the latest development version of clang). In particular, I am not sure whether this a problem in Polymake, or one in clang. Basically, it appears as if some code is to be compiled that is meant to multiply a (diagonal) matrix by an integer. But there is no operator* doing that, and so it errors out. And indeed, I can't find such an operator. But that just proves that I am insufficient and don't know the polymake codebase well enough -- in fact I am not even sure whether my interpretation of what is going on is correct :).

So it's best if somebody who actually knows polymake well could take a look and see if they can spot where the issues is. If it is definitely not a problem in polymake, then I'll try to narrow it down to a reproducible test case for the clang folks. For this, I'd appreciate if somebody could adjust my interpretation of what is going on accordingly (unless you want to file a bug report yourself, of course).

The error message is in the attached file.
Attachments
polymake-mul-err.log.bz2
clang 3.1 (trunk 143371) error message
(1.53 KiB) Downloaded 336 times


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