[cfe-dev] RFC: ODR checker for Clang and LLD

[Peter Collingbourne via cfe-dev]

On Wed, Jun 14, 2017 at 12:47 PM, David Blaikie <dblaikie at gmail.com> wrote:

>
>
> On Tue, Jun 13, 2017, 11:30 PM Peter Collingbourne <peter at pcc.me.uk>
> wrote:
>
>> On Tue, Jun 13, 2017 at 11:06 PM, David Blaikie <dblaikie at gmail.com>
>> wrote:
>>
>>>
>>>
>>> On Tue, Jun 13, 2017 at 10:05 PM Peter Collingbourne <peter at pcc.me.uk>
>>> wrote:
>>>
>>>> On Tue, Jun 13, 2017 at 8:48 PM, David Blaikie <dblaikie at gmail.com>
>>>> wrote:
>>>>
>>>>>
>>>>>
>>>>> On Tue, Jun 13, 2017 at 8:43 PM Peter Collingbourne <peter at pcc.me.uk>
>>>>> wrote:
>>>>>
>>>>>> On Tue, Jun 13, 2017 at 7:54 PM, David Blaikie <dblaikie at gmail.com>
>>>>>> wrote:
>>>>>>
>>>>>>>
>>>>>>>
>>>>>>> On Tue, Jun 13, 2017 at 6:34 PM Peter Collingbourne via cfe-dev <
>>>>>>> cfe-dev at lists.llvm.org> wrote:
>>>>>>>
>>>>>>>> On Wed, Jun 7, 2017 at 11:28 PM, Peter Collingbourne <
>>>>>>>> peter at pcc.me.uk> wrote:
>>>>>>>>
>>>>>>>>> On Wed, Jun 7, 2017 at 8:06 PM, Sean Silva <chisophugis at gmail.com>
>>>>>>>>> wrote:
>>>>>>>>>
>>>>>>>>>>
>>>>>>>>>>
>>>>>>>>>> On Wed, Jun 7, 2017 at 4:31 PM, Peter Collingbourne <
>>>>>>>>>> peter at pcc.me.uk> wrote:
>>>>>>>>>>
>>>>>>>>>>> On Wed, Jun 7, 2017 at 12:17 AM, Sean Silva <
>>>>>>>>>>> chisophugis at gmail.com> wrote:
>>>>>>>>>>>
>>>>>>>>>>>> Very nice and simple implementation!
>>>>>>>>>>>>
>>>>>>>>>>>> Do you have any statistics on how large these odr tables are
>>>>>>>>>>>> compared to other object file data? I assume that if these tables contain
>>>>>>>>>>>> full mangled symbol names, they could end up being very large and may want
>>>>>>>>>>>> to share the symbol name strings with the overall string table in the .o
>>>>>>>>>>>>
>>>>>>>>>>>
>>>>>>>>>>> Looking at Chromium's object files it looks like the total size
>>>>>>>>>>> of the odrtabs is about 50% of the total size of the object files, which
>>>>>>>>>>> isn't great. The current implementation only looks at records, so I imagine
>>>>>>>>>>> that it would be hard to share any of the strings that I'm currently
>>>>>>>>>>> creating. (I guess it's possible that some types will have a mangled vtable
>>>>>>>>>>> name in the string table, so we may be able to share a little that way.)
>>>>>>>>>>> Note however that this was without debug info.
>>>>>>>>>>>
>>>>>>>>>>> One option for reducing size would be to
>>>>>>>>>>> 1) store hashes of ODR names in ODR tables, per Rui's suggestion
>>>>>>>>>>> (alongside a reference to the name itself in the string table)
>>>>>>>>>>> 2) compress the string table for the ODR names with a standard
>>>>>>>>>>> compression algorithm like gzip.
>>>>>>>>>>> This wouldn't seem to affect link time performance much because
>>>>>>>>>>> I think we should only need to look at the strings if we see a ODR name
>>>>>>>>>>> hash match together with an ODR hash mismatch, which would mean an ODR
>>>>>>>>>>> violation with a high probability (i.e. unless there was an ODR name hash
>>>>>>>>>>> collision, we have found an ODR violation). If we don't expect a lot of
>>>>>>>>>>> sharing with regular string tables (see below), it seems even more
>>>>>>>>>>> reasonable.
>>>>>>>>>>>
>>>>>>>>>>
>>>>>>>>>> Neat observation!
>>>>>>>>>>
>>>>>>>>>> FWIW, it is a birthday problem type situation though, so for a
>>>>>>>>>> 32-bit hash, we would expect a collision in about 1 in 2^16 distinct hashes
>>>>>>>>>> (and 2^16 seems pretty easy to hit in a large project). So 64-bit hashes
>>>>>>>>>> might be preferable.
>>>>>>>>>>
>>>>>>>>>
>>>>>>>>> Oh right, good point, using a 64-bit hash does seem like a good
>>>>>>>>> idea here.
>>>>>>>>>
>>>>>>>>>
>>>>>>>>>>
>>>>>>>>>>> Also, do you have any numbers on the performance of your initial
>>>>>>>>>>>> implementation?
>>>>>>>>>>>>
>>>>>>>>>>>
>>>>>>>>>>> I measured the link time for chromium's unit_tests (the largest
>>>>>>>>>>> single binary in chromium) at 5.05s without ODR checks and 6.61s with ODR
>>>>>>>>>>> checks. So about 30% overhead, but in absolute terms it doesn't seem too
>>>>>>>>>>> bad. So I think this may be acceptable for an initial implementation, but
>>>>>>>>>>> it certainly seems worth trying to do better.
>>>>>>>>>>>
>>>>>>>>>>
>>>>>>>>>> I know that things aren't currently apples-to-apples, but how
>>>>>>>>>> does that compare to gold?
>>>>>>>>>>
>>>>>>>>>
>>>>>>>>> I will measure it.
>>>>>>>>>
>>>>>>>>
>>>>>>>> For that unit_tests binary I measured the overhead at about 5
>>>>>>>> seconds (average of 10 runs). That is with debug info, of course.
>>>>>>>>
>>>>>>>> W.r.t. LLD and having it always on by default (and hence making it
>>>>>>>>>>>> as fast as possible), it seems like right now you are implementing the
>>>>>>>>>>>> checking process with a hash table. That's simple and fine for a first
>>>>>>>>>>>> implementation, but it's probably worth mentioning in a comment the problem
>>>>>>>>>>>> of checking the tables, at least from the linker's perspective, does fit
>>>>>>>>>>>> into a map-reduce pattern and could be easily parallelized if needed. E.g.
>>>>>>>>>>>> a parallel sort to coalesce all entries for symbols of the same name
>>>>>>>>>>>> followed by a parallel forEach to check each bucket with the same symbol
>>>>>>>>>>>> name (roughly speaking).
>>>>>>>>>>>>
>>>>>>>>>>>
>>>>>>>>>>> Right, that's one approach. I was thinking of a simpler approach
>>>>>>>>>>> where at compile time we sort ODR names by hash and partition them using
>>>>>>>>>>> (say) the upper bits of the hash, so that at link time we can have N
>>>>>>>>>>> threads each building a hash table for a specific partition.
>>>>>>>>>>>
>>>>>>>>>>> And of course this work can be started right after symbol
>>>>>>>>>>> resolution finishes and parallelised with the rest of the work done by the
>>>>>>>>>>> linker.
>>>>>>>>>>>
>>>>>>>>>>> Even better than doing it faster is just doing less work.
>>>>>>>>>>>> There's a lot of work that the linker is already doing that may be reusable
>>>>>>>>>>>> for the ODR checking.
>>>>>>>>>>>> E.g.
>>>>>>>>>>>> - maybe we could get the coalescing step as a byproduct of our
>>>>>>>>>>>> existing string deduping, which we are generally doing anyway.
>>>>>>>>>>>> - we are already coalescing symbol names for the symbol table.
>>>>>>>>>>>> If the ODR table is keyed off of symbols in the binary that we are
>>>>>>>>>>>> inserting into the symbol table, then I think we could do the entire ODR
>>>>>>>>>>>> check with no extra "string" work on LLD's part.
>>>>>>>>>>>>
>>>>>>>>>>>> I see Rui already mentioned some of this in
>>>>>>>>>>>> https://bugs.chromium.org/p/chromium/issues/detail?id=726071#c4
>>>>>>>>>>>> .
>>>>>>>>>>>> You mentioned that not everything is necessarily directly keyed
>>>>>>>>>>>> on a symbol (such as types), but I think that it would really simplify
>>>>>>>>>>>> things if the check was done as such. Do you have any idea exactly how much
>>>>>>>>>>>> of the things that we want to check are not keyed on symbols? If most
>>>>>>>>>>>> things are keyed on symbols, for the things we are not we can just emit
>>>>>>>>>>>> extra symbols prefixed by __clang_odr_check_ or whatever.
>>>>>>>>>>>>
>>>>>>>>>>>
>>>>>>>>>>> Since the current implementation only works with records there
>>>>>>>>>>> is basically zero overlap right now between ODR names and symbols. I
>>>>>>>>>>> suppose that I could estimate the amount of function overlap in a
>>>>>>>>>>> hypothetical implementation that computes ODR hashes of functions by
>>>>>>>>>>> comparing the number of *_odr functions after clang has finished IRgen with
>>>>>>>>>>> the number after optimization finishes. This of course would be strictly
>>>>>>>>>>> more than functions + types.
>>>>>>>>>>>
>>>>>>>>>>
>>>>>>>>>> Wouldn't any function or symbol using the record type have the
>>>>>>>>>> type name somewhere in it? If we used an offset+length encoding (instead of
>>>>>>>>>> offset + NUL termination) we might be able to reuse it then (at some cost
>>>>>>>>>> in finding the reference).
>>>>>>>>>>
>>>>>>>>>
>>>>>>>>> That may be possible with some work in the string table builder.
>>>>>>>>> But at that point of course we're not dealing with regular symbols any
>>>>>>>>> more. I guess we could have two ODR tables per object file: an array of
>>>>>>>>> (ODR hash, location) tuples for ODR names that correspond to symbol table
>>>>>>>>> symbols (i.e. Rui's proposal on the chromium bug), and an array of (ODR
>>>>>>>>> name, ODR hash, location) tuples for all other ODR names. I guess if we
>>>>>>>>> wanted a "low overhead" mode we could just omit the second table or put
>>>>>>>>> fewer symbols in it.
>>>>>>>>>
>>>>>>>>> With debug info surely there is some sort of string representing
>>>>>>>>>> the record name or something like that, no?
>>>>>>>>>>
>>>>>>>>>
>>>>>>>>> Not the record name on its own (they do appear but a bit awkwardly
>>>>>>>>> -- each namespace component is stored in a separate string), but if the
>>>>>>>>> record has at least one member function the mangled type name will appear
>>>>>>>>> somewhere in .debug_str, so we could in principle reuse that with the
>>>>>>>>> offset/length trick.
>>>>>>>>>
>>>>>>>>> I guess we may have to have our "low-overhead" user-facing
>>>>>>>>>> behavior be a bit more nuanced. E.g.:
>>>>>>>>>> 1. does this feature bloat object files significantly
>>>>>>>>>> 2. does this feature slow down link times significantly
>>>>>>>>>>
>>>>>>>>>> Intuitively, it seems like we should be able to get 1. when debug
>>>>>>>>>> info happens to be enabled (not sure about split dwarf?) and possibly in
>>>>>>>>>> all cases at the cost of complexity. We may be able to get 2. in all cases
>>>>>>>>>> with proper design.
>>>>>>>>>>
>>>>>>>>>
>>>>>>>>> I think that would be my rough assessment as well. I think we have
>>>>>>>>> a good shot at 1 for all cases with some of the ideas that have been
>>>>>>>>> mentioned already. If we can avoid creating dependencies on DWARF I think
>>>>>>>>> that would be ideal -- I'd ideally like this to work for COFF as well,
>>>>>>>>> where you'd typically expect to find CodeView in object files. If I were to
>>>>>>>>> try this I think the first thing that I would try is hash/compression
>>>>>>>>> combined with the two ODR tables (no reuse for non-symbol ODR names to
>>>>>>>>> start with, as compression may be enough on its own).
>>>>>>>>>
>>>>>>>>
>>>>>>>> I developed a second prototype which uses hash/compression with no
>>>>>>>> attempt to reuse. It is available here: https://github.com/pcc/
>>>>>>>> llvm-project/tree/odr-checker2
>>>>>>>>
>>>>>>>> For Chromium the object file size overhead was 536566007 bytes, or
>>>>>>>> in relative terms about 25%, or about 4% with debug info. I measured perf
>>>>>>>> overhead for unit_tests at about 6%, but after I moved the checker onto
>>>>>>>> another thread, the overhead disappeared into the noise.
>>>>>>>>
>>>>>>>
>>>>>>> Still seems like quite a big increase.
>>>>>>>
>>>>>>> Any chance of compression?
>>>>>>>
>>>>>>
>>>>>> That was with compression -- the implementation compresses the parts
>>>>>> of the ODR table that aren't hashes (aside from the header and the Clang
>>>>>> version, which is a small fixed cost), as well as the string table. The
>>>>>> hashes were left uncompressed because they are in the critical path of the
>>>>>> linker and because I imagine that they wouldn't really be that compressible.
>>>>>>
>>>>>
>>>>> I'd be a bit surprised if they weren't especially compressible -
>>>>>
>>>>
>>>> Maybe I'm wrong, but my intuition about compression is that it works
>>>> best when the data contains repeated patterns. If we use a hash function
>>>> with good dispersion then I'd expect each hash to have little in common
>>>> with other hashes.
>>>>
>>>>
>>>>> and how much of the size increase is the compressed data V the
>>>>> uncompressed data?
>>>>>
>>>>
>>>> The ratio was roughly 60% compressed data to 40% uncompressed data.
>>>>
>>>>
>>>>> Is it still in the hot path when parallelized?
>>>>>
>>>>
>>>> Not right now according to my benchmarking, but decompression could
>>>> push it into the critical path if it ends up taking longer than the rest of
>>>> the work done by the linker after symbol resolution. On the same machine
>>>> that I used for benchmarking, gunzip'ing 200MB of /dev/urandom (which is
>>>> roughly what I'd expect the hashes to look like) takes around 1.1s, i.e. a
>>>> not insignificant fraction of lld's runtime.
>>>>
>>>>
>>>>> So I think the remaining gains would either be through limiting the
>>>>>> number of ODR table entries, or through reuse of data.
>>>>>>
>>>>>> Limiting might be something to explore -- one possibility is that we
>>>>>> could limit the ODR table entries to the declarations that are "used" by a
>>>>>> particular translation unit (it appears that Clang tracks something like
>>>>>> that in Decl::Used/Decl::Referenced, but I'm not sure if that is exactly
>>>>>> what we need -- I think we would basically need to test for reference
>>>>>> reachability from the functions/globals that are IRgen'd).
>>>>>>
>>>>>
>>>>> Currently it has every type and function that is in the AST? Yeah,
>>>>> that's a lot - perhaps it should be more like the things that go in the
>>>>> DWARF? (though would need to add some cases there - since the DWARF logic
>>>>> already relies on the ODR to not emit duplicates in some cases)
>>>>>
>>>>
>>>> Just every record declaration -- Clang only supports ODR hashes for
>>>> record declarations right now. I understand that function declarations
>>>> (including function bodies) are still works in progress.
>>>>
>>>> I think it should indeed just be roughly the things that go in the
>>>> DWARF. I think that at one point I observed that every record declaration,
>>>> even unused ones, were going into the DWARF, but I might have been mistaken
>>>> because I can no longer reproduce that. I'll take a closer look to see if I
>>>> can reuse what logic presumably already exists for DWARF.
>>>>
>>>> In terms of reuse, it seems that of the 536566007 bytes of
>>>>>> overhead, 319309579 were the compressed part of the ODR tables. So even if
>>>>>> we achieved 100% sharing,
>>>>>>
>>>>>
>>>>> 100% sharing? You mean if all the data were compressed, and assuming
>>>>> the hashes were compressible at the same ratio as the other data?
>>>>>
>>>>
>>>> Sorry, I mean if 100% of the data in the compressed part of the ODR
>>>> table could be eliminated by reusing data stored elsewhere (e.g. in the
>>>> object file string table or in the DWARF).
>>>>
>>>> with the current scheme I think that our minimum achievable overhead
>>>>>> would be ~15% (no debug info) or ~2% (with debug info).
>>>>>>
>>>>>>
>>>>>>> Could this go into .dwo files with Fission and be checked by dwp
>>>>>>> instead, perhaps?
>>>>>>>
>>>>>>
>>>>>> I think it could also work that way, yes.
>>>>>>
>>>>>> I'm reasonably happy with these figures, at least for a first
>>>>>>>> implementation. We may be able to do even better for file size with reuse,
>>>>>>>> but I'd leave that for version 2.
>>>>>>>>
>>>>>>>
>>>>>>> What's the story with compatibility between versions, then? Is there
>>>>>>> a version header?
>>>>>>>
>>>>>>
>>>>>> Yes, the header contains a version number.
>>>>>>
>>>>>>
>>>>>>> Will old formats be supported by lld indefinitely? Not at all?
>>>>>>>
>>>>>>
>>>>>> I think we should drop support for old formats when we introduce a
>>>>>> new format. My understanding is that the ODR hash can change whenever Clang
>>>>>> changes (the implementation only performs ODR checking if all ODR tables
>>>>>> were produced by the same revision of Clang), so there wouldn't seem to be
>>>>>> a huge benefit in keeping support for old formats around.
>>>>>>
>>>>>
>>>>> I imagine it's possible people aren't necessarily going to rev lld in
>>>>> exact lock-step with clang, but I could be wrong. (certainly binutils ld or
>>>>> gold aren't released/kept in lock-step with GCC, for example)
>>>>>
>>>>
>>>> That's certainly possible, but I'd say that the bar for dropping
>>>> backwards compatibility is lower because ODR tables are not required for
>>>> correctness. We could keep compatibility with the last version or so if it
>>>> isn't too burdensome, or otherwise print a warning.
>>>>
>>>
>>> They aren't required for correctness, but upgrading your compiler or
>>> linker then silently losing ODR checking would be bad (or even not silently
>>> losing it, but having no choice but to rev both to keep the functionality &
>>> hold the ODR-cleanliness bar) - it's the sort of thing where if you lost
>>> the checking, then gained it back again later, the regression cleanup would
>>> be annoying/an impediment to using the feature.
>>>
>>
>> Makes sense I guess. I'd be fine with a policy where the Nth open source
>> release should be able to read ODR tables produced by the N-1th and
>> possibly the N-2th release.
>>
>
> Still strikes me as a bit awkward - wonder how that compared to other
> (similar or different) linker features.
>

I think the most similar existing feature is .gdb_index. They have already
gone through a few format revisions:
https://sourceware.org/gdb/onlinedocs/gdb/Index-Section-Format.html
and have deprecated/removed support for older formats.

Because the requirements for ODR tables are simpler than those for
.gdb_index, I'd expect us to converge on a final format sooner, so in
practice the window of compatibility would end up being longer than a year.

Peter


>
>> Any idea what Daniel Jasper & co have been working on WRT ODR checking &
>>> how this feature integrates or doesn't with their work? I imagine they
>>> might be working on something more like a Clang Tooling style approach, but
>>> I'm not sure.
>>>
>>
>> I'm not aware of any work like that, only of Richard Trieu's efforts for
>> modules that I'm piggybacking on.
>>
>
> +Djasper - perhaps you could provide some context on other odr detection
> efforts?
>
>
>> Peter
>>
>>>
>>> - Dave
>>>
>>>
>>>>
>>>> Peter
>>>>
>>>>>
>>>>>
>>>>>>
>>>>>> Peter
>>>>>>
>>>>>>>
>>>>>>> - Dave
>>>>>>>
>>>>>>>
>>>>>>>>
>>>>>>>> Peter
>>>>>>>>
>>>>>>>>>
>>>>>>>>> Peter
>>>>>>>>>
>>>>>>>>>
>>>>>>>>>>
>>>>>>>>>> -- Sean Silva
>>>>>>>>>>
>>>>>>>>>>
>>>>>>>>>>>
>>>>>>>>>>>
>>>>>>>>>>>> The issue of retaining the ODR check for functions even if they
>>>>>>>>>>>> get inlined may inherently pose an extra cost that can't be folded into
>>>>>>>>>>>> existing work the linker is doing, so there might be a reason for clang to
>>>>>>>>>>>> have a default mode that has practically no linking overhead and one that
>>>>>>>>>>>> does more thorough checking but imposes extra linking overhead. Think
>>>>>>>>>>>> something like a crazy boost library with thousands of functions that get
>>>>>>>>>>>> inlined away, but have gigantic mangled names and so precisely are the ones
>>>>>>>>>>>> that are going to impose extra cost on the linker. Simply due to the extra
>>>>>>>>>>>> volume of strings that the linker would need to look at, I don't think
>>>>>>>>>>>> there's a way to include checking of all inlined function "for free" at the
>>>>>>>>>>>> linker level using the symbol approach.
>>>>>>>>>>>>
>>>>>>>>>>>
>>>>>>>>>>>>
>>>>>>>>>>> I guess those inlined functions would still have those symbol
>>>>>>>>>>>> names in debug info (I think?), so piggybacking on the string deduplication
>>>>>>>>>>>> we're already doing might make it possible to fold away the work in that
>>>>>>>>>>>> case (but then again, would still impose extra cost with split dwarf...).
>>>>>>>>>>>>
>>>>>>>>>>>> Anyway, let's wait to see what the actual performance numbers
>>>>>>>>>>>> are.
>>>>>>>>>>>>
>>>>>>>>>>>> -- Sean Silva
>>>>>>>>>>>>
>>>>>>>>>>>> On Tue, Jun 6, 2017 at 10:40 PM, Peter Collingbourne via
>>>>>>>>>>>> cfe-dev <cfe-dev at lists.llvm.org> wrote:
>>>>>>>>>>>>
>>>>>>>>>>>>> Hi all,
>>>>>>>>>>>>>
>>>>>>>>>>>>> I'd like to propose an ODR checker feature for Clang and LLD.
>>>>>>>>>>>>> The feature would be similar to gold's --detect-odr-violations feature, but
>>>>>>>>>>>>> better: we can rely on integration with clang to avoid relying on debug
>>>>>>>>>>>>> info and to perform more precise matching.
>>>>>>>>>>>>>
>>>>>>>>>>>>> The basic idea is that we use clang's ability to create ODR
>>>>>>>>>>>>> hashes for declarations. ODR hashes are computed using all information
>>>>>>>>>>>>> about a declaration that is ODR-relevant. If the flag
>>>>>>>>>>>>> -fdetect-odr-violations is passed, Clang will store the ODR hashes in a
>>>>>>>>>>>>> so-called ODR table in each object file. Each ODR table will contain a
>>>>>>>>>>>>> mapping from mangled declaration names to ODR hashes. At link time, the
>>>>>>>>>>>>> linker will read the ODR table and report any mismatches.
>>>>>>>>>>>>>
>>>>>>>>>>>>> To make this work:
>>>>>>>>>>>>> - LLVM will be extended with the ability to represent ODR
>>>>>>>>>>>>> tables in the IR and emit them to object files
>>>>>>>>>>>>> - Clang will be extended with the ability to emit ODR tables
>>>>>>>>>>>>> using ODR hashes
>>>>>>>>>>>>> - LLD will be extended to read ODR tables from object files
>>>>>>>>>>>>>
>>>>>>>>>>>>> I have implemented a prototype of this feature. It is
>>>>>>>>>>>>> available here: https://github.com/pcc/
>>>>>>>>>>>>> llvm-project/tree/odr-checker and some results from applying
>>>>>>>>>>>>> it to chromium are here: crbug.com/726071
>>>>>>>>>>>>> As you can see it did indeed find a number of real ODR
>>>>>>>>>>>>> violations in Chromium, including some that wouldn't be detectable using
>>>>>>>>>>>>> debug info.
>>>>>>>>>>>>>
>>>>>>>>>>>>> If you're interested in what the format of the ODR table would
>>>>>>>>>>>>> look like, that prototype shows pretty much what I had in mind, but I
>>>>>>>>>>>>> expect many other aspects of the implementation to change as it is
>>>>>>>>>>>>> upstreamed.
>>>>>>>>>>>>>
>>>>>>>>>>>>> Thanks,
>>>>>>>>>>>>> --
>>>>>>>>>>>>> --
>>>>>>>>>>>>> Peter
>>>>>>>>>>>>>
>>>>>>>>>>>>> _______________________________________________
>>>>>>>>>>>>> cfe-dev mailing list
>>>>>>>>>>>>> cfe-dev at lists.llvm.org
>>>>>>>>>>>>> http://lists.llvm.org/cgi-bin/mailman/listinfo/cfe-dev
>>>>>>>>>>>>>
>>>>>>>>>>>>>
>>>>>>>>>>>>
>>>>>>>>>>>
>>>>>>>>>>>
>>>>>>>>>>> --
>>>>>>>>>>> --
>>>>>>>>>>> Peter
>>>>>>>>>>>
>>>>>>>>>>
>>>>>>>>>>
>>>>>>>>>
>>>>>>>>>
>>>>>>>>> --
>>>>>>>>> --
>>>>>>>>> Peter
>>>>>>>>>
>>>>>>>>
>>>>>>>>
>>>>>>>>
>>>>>>>> --
>>>>>>>> --
>>>>>>>> Peter
>>>>>>>> _______________________________________________
>>>>>>>> cfe-dev mailing list
>>>>>>>> cfe-dev at lists.llvm.org
>>>>>>>> http://lists.llvm.org/cgi-bin/mailman/listinfo/cfe-dev
>>>>>>>>
>>>>>>>
>>>>>>
>>>>>>
>>>>>> --
>>>>>> --
>>>>>> Peter
>>>>>>
>>>>>
>>>>
>>>>
>>>> --
>>>> --
>>>> Peter
>>>>
>>>
>>
>>
>> --
>> --
>> Peter
>>
>


-- 
-- 
Peter
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