[cfe-dev] [llvm-dev] Testing Best Practices/Goals (in the context of compiler-rt)

[David Blaikie via cfe-dev]

On Mon, Feb 29, 2016 at 10:26 AM, Anna Zaks <ganna at apple.com> wrote:

>
> On Feb 28, 2016, at 7:57 AM, David Blaikie <dblaikie at gmail.com> wrote:
>
>
>
> On Sat, Feb 27, 2016 at 3:13 PM, Anna Zaks <ganna at apple.com> wrote:
>
>>
>> On Feb 26, 2016, at 2:10 PM, Alexey Samsonov via llvm-dev <
>> llvm-dev at lists.llvm.org> wrote:
>>
>>
>> On Fri, Feb 26, 2016 at 1:34 PM, David Blaikie <dblaikie at gmail.com>
>> wrote:
>>
>>>
>>>
>>> On Fri, Feb 26, 2016 at 1:31 PM, Sean Silva <chisophugis at gmail.com>
>>> wrote:
>>>
>>>>
>>>>
>>>> On Fri, Feb 26, 2016 at 1:11 PM, David Blaikie <dblaikie at gmail.com>
>>>> wrote:
>>>>
>>>>>
>>>>>
>>>>> On Fri, Feb 26, 2016 at 1:07 PM, Sean Silva <chisophugis at gmail.com>
>>>>> wrote:
>>>>>
>>>>>>
>>>>>>
>>>>>> On Wed, Feb 17, 2016 at 8:45 AM, David Blaikie via cfe-dev <
>>>>>> cfe-dev at lists.llvm.org> wrote:
>>>>>>
>>>>>>>
>>>>>>>
>>>>>>> On Fri, Feb 12, 2016 at 5:43 PM, Alexey Samsonov <vonosmas at gmail.com
>>>>>>> > wrote:
>>>>>>>
>>>>>>>>
>>>>>>>>
>>>>>>>> On Thu, Feb 11, 2016 at 1:50 PM, David Blaikie <dblaikie at gmail.com>
>>>>>>>>  wrote:
>>>>>>>>
>>>>>>>>>
>>>>>>>>>
>>>>>>>>> On Wed, Feb 10, 2016 at 3:55 PM, Alexey Samsonov via cfe-dev <
>>>>>>>>> cfe-dev at lists.llvm.org> wrote:
>>>>>>>>>
>>>>>>>>>> I mostly agree with what Richard and Justin said. Adding a few
>>>>>>>>>> notes about the general strategy we use:
>>>>>>>>>>
>>>>>>>>>> (1) lit tests which look "end-to-end" proved to be way more
>>>>>>>>>> convenient for testing runtime libraries than unit tests.
>>>>>>>>>>
>>>>>>>>> We do have
>>>>>>>>>> the latter, and use them to provide test coverage for utility
>>>>>>>>>> functions, but we quite often accompany fix to the runtime library with
>>>>>>>>>> "end-to-end" small reproducer extracted from the real-world code
>>>>>>>>>> that exposed the issue.
>>>>>>>>>> Incidentally, this tests a whole lot of other functionality:
>>>>>>>>>> Clang driver, frontend, LLVM passes, etc, but it's not the intent of the
>>>>>>>>>> test.
>>>>>>>>>>
>>>>>>>>>
>>>>>>>>> Indeed - this is analogous to the tests for, say, LLD that use
>>>>>>>>> llvm-mc to produce the inputs rather than checking in object files. That
>>>>>>>>> area is open to some discussion as to just how many tools we should rope
>>>>>>>>> in/how isolated we should make tests (eg: maybe building the json object
>>>>>>>>> file format was going too far towards isolation? Not clear - opinions
>>>>>>>>> differ). But the point of the test is to test the compiler-rt functionality
>>>>>>>>> that was added/removed/modified.
>>>>>>>>>
>>>>>>>>> I think most people are in agreement with that, while
>>>>>>>>> acknowledging the fuzzy line about how isolated we might be.
>>>>>>>>>
>>>>>>>>
>>>>>>>> Yes.
>>>>>>>>
>>>>>>>>
>>>>>>>>>
>>>>>>>>>
>>>>>>>>>> These tests are sometimes platform-specific and poorly portable,
>>>>>>>>>> but they are more reliable (we make the same steps as the
>>>>>>>>>> user of the compiler), and serve the purpose of documentation.
>>>>>>>>>>
>>>>>>>>>> (2) If we change LLVM instrumentation - we add a test to LLVM. If
>>>>>>>>>> we change Clang code generation or driver behavior - we add
>>>>>>>>>> a test to Clang. No excuses here.
>>>>>>>>>>
>>>>>>>>>> (3) Sometimes we still add a compiler-rt test for the change in
>>>>>>>>>> LLVM or Clang: e.g. if we enhance Clang frontend to teach UBSan
>>>>>>>>>> to detecting yet another kind of overflow, it makes sense to add
>>>>>>>>>> a test to UBSan test-suite that demonstrates it, in addition to
>>>>>>>>>> Clang test verifying that we emit a call to UBSan runtime. Also,
>>>>>>>>>> compiler-rt test would allow us to verify that the actual error report
>>>>>>>>>> we present to the user is sane.
>>>>>>>>>>
>>>>>>>>>
>>>>>>>>> This bit ^ is a bit unclear to me. If there was no change to the
>>>>>>>>> UBSan runtime, and the code generated by Clang is equivalent/similar to an
>>>>>>>>> existing use of the UBSan runtime - what is it that the new compiler-rt
>>>>>>>>> test is providing? (perhaps you could give a concrete example you had in
>>>>>>>>> mind to look at?)
>>>>>>>>>
>>>>>>>>
>>>>>>>> See r235568 (change to Clang) followed by r235569 (change to
>>>>>>>> compiler-rt test). Now, it's a cheat because I'm fixing test, not adding
>>>>>>>> it. However, I would have definitely added it, if it was missing.
>>>>>>>>
>>>>>>>
>>>>>>> Right, I think the difference here is "if it was missing" - the test
>>>>>>> case itself seems like it could be a reasonable one (are there other tests
>>>>>>> of the same compiler-rt functionality? (I assume the compiler-rt
>>>>>>> functionality is the implementation of sadd/ssub?))
>>>>>>>
>>>>>>>
>>>>>>>> In this case, a change to Clang
>>>>>>>> instrumentation (arguments passed to UBSan runtime callbacks)
>>>>>>>> improved the user-facing part of the tool, and compiler-rt test suite is a
>>>>>>>> good place to verify that.
>>>>>>>>
>>>>>>>
>>>>>>> This seems like the problematic part - changes to LLVM improve the
>>>>>>> user-facing part of Clang, but we don't add end-to-end tests of that, as a
>>>>>>> general rule. I'm trying to understand why the difference between that and
>>>>>>> compiler-rt
>>>>>>>
>>>>>>
>>>>>> In what way do changes in LLVM change the user-facing part of Clang?
>>>>>> It obviously depends on how broadly one defines user-facing. Is a 1%
>>>>>> performance improvement from a particular optimization user-facing? Is
>>>>>> better debug info accuracy user-facing? I'm not sure. But it seems clear
>>>>>> that "the user sees a diagnostic or not" definitely is.
>>>>>>
>>>>>
>>>>> There's more than just performance in LLVM - ABI features, and yes,
>>>>> I'd argue some pieces of debug info are pretty user facing (as are some
>>>>> optimizations). We also have the remarks system in place now. (also the
>>>>> compiler crashing (or not) is pretty user facing).
>>>>>
>>>>
>>>> I'd argue that we probably should have some sort of integration tests
>>>> for ABI features. I think at the moment we're getting by thanks to
>>>> self-hosting and regularly building lots of real-world programs with
>>>> ToT-ish compilers.
>>>>
>>>
>>> Perhaps so, but I'd argue that they shouldn't be run as part of "make
>>> check" & should be in a separate test grouping (probably mostly run by
>>> buildbots) for the purpose of integration testing.
>>>
>>
>> If you have llvm/clang/compiler-rt/libc++/libc++abi checkout, they are
>> not run as a part of "make check", only "make check-all", which kind of
>> makes sense (run *all* the tests!). You're free to run "make check-clang",
>> "make check-asan" etc.
>> if you're sure your changes are limited in scope. Just to be clear - do
>> you suggest that compiler-rt tests are too heavy for this configuration,
>> and want to introduce extra level - i.e. extract "make check-compiler-rt"
>> out of "make check-all", and introduce "make check-absolutely-everything",
>> that would encompass them?
>>
>>
>>> We've made a pretty conscious, deliberate, and consistent effort to not
>>> do integration testing across the LLVM projects in "make check"-like
>>> testing, and to fix it where we do find it. It seems to me that compiler-rt
>>> diverged from that approach and I'm not really in favor of that divergence.
>>>
>>
>> I don't see why consistency by itself is a good thing. As a sanitizer
>> developer, current situation is convenient for me, but if it harms / slows
>> down / complicates workflow for other developers or LLVM as a whole - sure,
>> let's fix it.
>>
>>
>> +1
>>
>> I find the end-to-end compiler-rt tests very useful and easy to write.
>> They run much faster on my machine than the Unit tests. The LLVM modular
>> test policy does not apply as well to compiler-rt.
>>
>
> Sorry this all seems to have become a bit confused. I am not generally
> objecting to end-to-end tests in compiler-rt or elsewhere. I'm trying to
> understand why, beyond that, in compiler-rt those tests seem to be being
> used to exercise code and fixes in LLVM and Clang. Generally across the
> LLVM project when we fix something in LLVM we test it there, when we fix
> something in Clang we test it there. We don't add a Clang test for every
> codegen/optimization fix we add in LLVM (even putting aside the question of
> the observability of optimizations that Sean raised - consider debug info,
> or correctness issues like noinline/alwaysinline, etc). So I'm trying to
> understand why compiler-rt is being treated differently in this regard.
>
>
>> (David, maybe following up with some specifics such as this test is
>> redundant or we should rewrite these tests in a certain way would help to
>> convey your point across.)
>>
>
> Thanks for chiming in, Anna (I'd really like some more voices on this
> thread - it seems like a pretty fundamental issue about LLVM's project
> philosophy and I'm really confused). I started this conversation in such an
> example (
> http://lists.llvm.org/pipermail/llvm-commits/Week-of-Mon-20160208/330759.html
> ) and that's how I ended up here. A more recent example would be
> r262161/r262157.
>
>
> Whenever someone changes clang/llvm, a modular clang/llvm test should be
> added. We want to make sure people do not rely solely on end-to-end tests
> to test modifications to clang/llvm. From what I understand, everyone on
> this thread agrees with that.
>
> So the question is if the end-to-end tests are redundant or not.
> Sanitizers and the rest of compiler-rt builds on a complex interplay of
> many players: the compiler, the runtime, symbolicator, the linker...
> End-to-end tests are an effective way of testing that all these pieces
> align and we get the expected behavior. One way to explain this particular
> commit is that this test is not testing the specific clang change, but was
> added because constructors were not tested sufficiently before.
>

The way I think about this, much like the comment I made to David (email I
just sent) is that these things still seem to be fairly orthogonal - in
Clang we don't test template type diffing in every diagnostic that could
trigger it. We test the diagnostics and we test a sample of the type
diffing, and we know/rely on them being essentially orthogonal. We have to
do this in any testing strategy or we'd be testing the possible combination
of every feature of C++, which is intractable.

It seems like compiler-rt is orthogonal to constructors, it just profiles
whatever it profiles - Clang decides not to profile ctors, so as long as we
have a test of compiler-rt of a function with a counter and a function
without a counter, I'm not sure why we'd want another test of a different
way to produce a function without a counter.


> I believe the LLVM policy was designed for testing the compiler
> infrastructure and does not apply to features that heavily depend on
> runtime libraries as much.
>

I'm really not understanding the large difference here, though. What I'm
picturing is, if the runtime were built into Clang (& we just generated
gobs of static LLVM IR each time we compiled and needed the runtime
support) we wouldn't be compelled to test every way we call into that
library I don't think - we'd test representative cases in each of the
otherwise independent pieces.


> The libc++ repo is another example of an LLVM project with a runtime
> library and it does utilize end-to-end tests.
>

I haven't looked closely at libc++'s testing strategy, but I would
hope/imagine/expect that it would treat it's runtime library in the same
way. Test its features, but not test every possible combination of ways
that might exercise those features.

- David


>
> - Dave
>
>
>>
>>
>>> - David
>>>
>>>
>>>>
>>>> -- Sean Silva
>>>>
>>>>
>>>>>
>>>>>
>>>>>> Also, I think part of this is that in compiler-rt there are usually
>>>>>> more moving parts we don't control. E.g. it isn't just the interface
>>>>>> between LLVM and clang. The information needs to pass through archivers,
>>>>>> linkers, runtime loaders, etc. that all may have issues that affect whether
>>>>>> the user sees the final result. In general the interface between LLVM and
>>>>>> clang has no middlemen so there really isn't anything to check.
>>>>>>
>>>>>
>>>>> Correctness/behavior of the compiler depends on those things too
>>>>> (linkers, loaders, etc) to produce the final working product the user
>>>>> requested. If we emitted symbols with the wrong linkage we could produce
>>>>> linker errors, drop important entities, etc. But we don't generally test
>>>>> that the output of LLVM/Clang produces the right binary when linked, we
>>>>> test that it produces the right linkages on the resulting entities.
>>>>>
>>>>> - David
>>>>>
>>>>>
>>>>>>
>>>>>> -- Sean Silva
>>>>>>
>>>>>>
>>>>>>>
>>>>>>>
>>>>>>>>
>>>>>>>>
>>>>>>>
>>>>>>>> You may argue that Clang test would have been enough (I disagree
>>>>>>>> with that), or that it qualifies as "adding coverage" (maybe).
>>>>>>>>
>>>>>>>>
>>>>>>>>>
>>>>>>>>>
>>>>>>>>>> (4) True, we're intimidated by test-suite :) I feel that current
>>>>>>>>>> use of compiler-rt test suite to check compiler-rt libs better follows
>>>>>>>>>> the doctrine described by David.
>>>>>>>>>>
>>>>>>>>>
>>>>>>>>> Which David? ;) (I guess David Li, not me)
>>>>>>>>>
>>>>>>>>
>>>>>>>> Nope, paragraph 2 from your original email.
>>>>>>>>
>>>>>>>>
>>>>>>>>> I think maybe what could be worth doing would be separating out
>>>>>>>>> the broader/intentionally "end to end" sort of tests from the ones intended
>>>>>>>>> to test compiler-rt in relative isolation.
>>>>>>>>>
>>>>>>>>
>>>>>>>> It's really hard to draw the line here, even some of compiler-rt
>>>>>>>> unit tests require instrumentation, therefore depend on new features of
>>>>>>>> Clang/LLVM. Unlike builtins, which are
>>>>>>>> trivial to test in isolation, testing sanitizer runtimes in
>>>>>>>> isolation (w/o compiler) is often hard to implement (we tried to do so for
>>>>>>>> TSan, but found unit tests extremely hard to write),
>>>>>>>> and is barely useful - compiler-rt runtimes don't consist of
>>>>>>>> modules (like LLVMCodeGen and LLVMMC for instance), and are never used w/o
>>>>>>>> the compiler anyway.
>>>>>>>>
>>>>>>>>
>>>>>>>>>
>>>>>>>>> Most importantly, I'd expect only the latter to run in a "make
>>>>>>>>> check-all" run, as we do for Clang/LLVM, etc.
>>>>>>>>>
>>>>>>>>
>>>>>>>> And now we're getting to the goals :) Why would such a change be
>>>>>>>> good? Do you worry about the time it takes to execute the test suite?
>>>>>>>>
>>>>>>>>
>>>>>>>>>
>>>>>>>>>
>>>>>>>>>> Also, there's significant complexity in compiler-rt test suite
>>>>>>>>>> that narrows the tests executed
>>>>>>>>>> to those supported by current host.
>>>>>>>>>>
>>>>>>>>>
>>>>>>>>>
>>>>>>>>>
>>>>>>>>>
>>>>>>>>>>
>>>>>>>>>> On Wed, Feb 10, 2016 at 2:33 PM, Xinliang David Li via cfe-dev <
>>>>>>>>>> cfe-dev at lists.llvm.org> wrote:
>>>>>>>>>>
>>>>>>>>>>>
>>>>>>>>>>>
>>>>>>>>>>> On Wed, Feb 10, 2016 at 2:11 PM, Justin Bogner via llvm-dev <
>>>>>>>>>>> llvm-dev at lists.llvm.org> wrote:
>>>>>>>>>>>
>>>>>>>>>>>> David Blaikie via cfe-dev <cfe-dev at lists.llvm.org> writes:
>>>>>>>>>>>> > Recently had a bit of a digression in a review thread related
>>>>>>>>>>>> to some tests
>>>>>>>>>>>> > going in to compiler-rt (
>>>>>>>>>>>> >
>>>>>>>>>>>> http://lists.llvm.org/pipermail/llvm-commits/Week-of-Mon-20160208/330759.html
>>>>>>>>>>>> > ) and there seems to be some disconnect at least between my
>>>>>>>>>>>> expectations
>>>>>>>>>>>> > and reality. So I figured I'd have a bit of a discussion out
>>>>>>>>>>>> here on the
>>>>>>>>>>>> > dev lists where there's a bit more visibility.
>>>>>>>>>>>> >
>>>>>>>>>>>> > My basic expectation is that the lit tests in any LLVM
>>>>>>>>>>>> project except the
>>>>>>>>>>>> > test-suite are targeted tests intended to test only the
>>>>>>>>>>>> functionality in
>>>>>>>>>>>> > the project. This seems like a pretty well accepted doctrine
>>>>>>>>>>>> across most
>>>>>>>>>>>> > LLVM projects - most visibly in Clang, where we make a
>>>>>>>>>>>> concerted effort not
>>>>>>>>>>>> > to have tests that execute LLVM optimizations, etc.
>>>>>>>>>>>> >
>>>>>>>>>>>> > There are exceptions/middle ground to this - DIBuilder is in
>>>>>>>>>>>> LLVM, but
>>>>>>>>>>>> > essentially tested in Clang rather than writing LLVM unit
>>>>>>>>>>>> tests. It's
>>>>>>>>>>>> > somewhat unavoidable that any of the IR building code
>>>>>>>>>>>> (IRBuilder,
>>>>>>>>>>>> > DIBuilder, IR asm printing, etc) is 'tested' incidentally in
>>>>>>>>>>>> Clang in
>>>>>>>>>>>> > process of testing Clang's IR generation. But these are seen
>>>>>>>>>>>> as incidental,
>>>>>>>>>>>> > not intentionally trying to cover LLVM with Clang tests (we
>>>>>>>>>>>> don't add a
>>>>>>>>>>>> > Clang test if we add a new feature to IRBuilder just to test
>>>>>>>>>>>> the IRBuilder).
>>>>>>>>>>>> >
>>>>>>>>>>>> > Another case with some middle ground are things like linker
>>>>>>>>>>>> tests and
>>>>>>>>>>>> > objdump, dwarfdump, etc - in theory to isolate the test we
>>>>>>>>>>>> would checkin
>>>>>>>>>>>> > binaries (or the textual object representation lld had for a
>>>>>>>>>>>> while, etc) to
>>>>>>>>>>>> > test those tools. Some tests instead checkin assembly and
>>>>>>>>>>>> assemble it with
>>>>>>>>>>>> > llvm-mc. Again, not to cover llvm-mc, but on the assumption
>>>>>>>>>>>> that llvm-mc is
>>>>>>>>>>>> > tested, and just using it as a tool to make tests easier to
>>>>>>>>>>>> maintain.
>>>>>>>>>>>> >
>>>>>>>>>>>> > So I was surprised to find that the compiler-rt lit tests
>>>>>>>>>>>> seem to diverge
>>>>>>>>>>>> > from this philosophy & contain more intentional end-to-end
>>>>>>>>>>>> tests (eg:
>>>>>>>>>>>> > adding a test there when making a fix to Clang to add a
>>>>>>>>>>>> counter to a
>>>>>>>>>>>> > function that was otherwise missing a counter - I'd expect
>>>>>>>>>>>> that to be
>>>>>>>>>>>> > tested in Clang and that there would already be coverage in
>>>>>>>>>>>> compiler-rt for
>>>>>>>>>>>> > "if a function has a counter, does compiler-rt do the right
>>>>>>>>>>>> thing with that
>>>>>>>>>>>> > counter" (testing whatever code in compiler-rt needs to be
>>>>>>>>>>>> tested)).
>>>>>>>>>>>> >
>>>>>>>>>>>> > Am I off base here? Are compiler-rt's tests fundamentally
>>>>>>>>>>>> different to the
>>>>>>>>>>>> > rest of the LLVM project? Why? Should they continue to be?
>>>>>>>>>>>>
>>>>>>>>>>>> I think there's a bit of grey area in terms testing the runtime
>>>>>>>>>>>> -
>>>>>>>>>>>> generally it's pretty hard to use the runtime without a fairly
>>>>>>>>>>>> end-to-end test, so tests of the runtime often end up looking
>>>>>>>>>>>> pretty
>>>>>>>>>>>> close to an end-to-end test.
>>>>>>>>>>>>
>>>>>>>>>>>> That said, I don't think that should be used as an excuse to
>>>>>>>>>>>> sneak
>>>>>>>>>>>> arbitrary end-to-end tests into compiler-rt. We should
>>>>>>>>>>>> absolutely write
>>>>>>>>>>>> tests in clang and llvm that we're inputting what we expect to
>>>>>>>>>>>> the
>>>>>>>>>>>> runtime and try to keep the tests in compiler-rt as focused on
>>>>>>>>>>>> just
>>>>>>>>>>>> exercising the runtime code as possible.
>>>>>>>>>>>>
>>>>>>>>>>>
>>>>>>>>>>> Yes, we should not use compiler-rt tests as an excuse of not
>>>>>>>>>>> adding clang/LLVM test. The latter should always be added if possible --
>>>>>>>>>>> they are platform independent and is the first level of defense.  runtime
>>>>>>>>>>> test's focus is also more on the runtime lib itself and interaction between
>>>>>>>>>>>  runtime, compiler, binutils and other tools.
>>>>>>>>>>>
>>>>>>>>>>> David
>>>>>>>>>>>
>>>>>>>>>>>>
>>>>>>>>>>>> IIUC, the correct place for integration tests in general is
>>>>>>>>>>>> somewhere
>>>>>>>>>>>> like test-suite, but I think it's a bit intimidating to some
>>>>>>>>>>>> people to
>>>>>>>>>>>> add new tests there (Are there docs on this?). I suspect some
>>>>>>>>>>>> of the
>>>>>>>>>>>> profiling related tests in compiler-rt are doing a bit much and
>>>>>>>>>>>> should
>>>>>>>>>>>> graduate to a spot in the test-suite (but I don't have time to
>>>>>>>>>>>> volunteer
>>>>>>>>>>>> to do the work, unfortunately).
>>>>>>>>>>>> _______________________________________________
>>>>>>>>>>>> LLVM Developers mailing list
>>>>>>>>>>>> llvm-dev at lists.llvm.org
>>>>>>>>>>>> http://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev
>>>>>>>>>>>>
>>>>>>>>>>>
>>>>>>>>>>>
>>>>>>>>>>> _______________________________________________
>>>>>>>>>>> cfe-dev mailing list
>>>>>>>>>>> cfe-dev at lists.llvm.org
>>>>>>>>>>> http://lists.llvm.org/cgi-bin/mailman/listinfo/cfe-dev
>>>>>>>>>>>
>>>>>>>>>>>
>>>>>>>>>>
>>>>>>>>>>
>>>>>>>>>> --
>>>>>>>>>> Alexey Samsonov
>>>>>>>>>> vonosmas at gmail.com
>>>>>>>>>>
>>>>>>>>>> _______________________________________________
>>>>>>>>>> cfe-dev mailing list
>>>>>>>>>> cfe-dev at lists.llvm.org
>>>>>>>>>> http://lists.llvm.org/cgi-bin/mailman/listinfo/cfe-dev
>>>>>>>>>>
>>>>>>>>>>
>>>>>>>>>
>>>>>>>>
>>>>>>>>
>>>>>>>> --
>>>>>>>> Alexey Samsonov
>>>>>>>> vonosmas at gmail.com
>>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>> _______________________________________________
>>>>>>> cfe-dev mailing list
>>>>>>> cfe-dev at lists.llvm.org
>>>>>>> http://lists.llvm.org/cgi-bin/mailman/listinfo/cfe-dev
>>>>>>>
>>>>>>>
>>>>>>
>>>>>
>>>>
>>>
>>
>>
>> --
>> Alexey Samsonov
>> vonosmas at gmail.com
>> _______________________________________________
>> LLVM Developers mailing list
>> llvm-dev at lists.llvm.org
>> http://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev
>>
>>
>
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