llvm dev - Jun 2014 - [LLVMdev] Issues with clang-llvm debug info validity

>> Without needing to change how namespaces are handled.
>>
>> Yes, using DIRefs for namespaces would cause the actual type nodes to
>> be deduplicated when they aren't even with the patch above, and
that
>> would help reduce debug info metadata further if that's
>> useful/necessary.
>
> Exactly. While the above patch will cover up the problem, we will still
have many duplicate type entries during LTO that will take up memory, even
though only the last one to be entered into DIRefMap will actually be used for
emitting DWARF. Since DIRefs are also more expensive in terms of lookup speed, I
think I’d prefer to only use them only where necessary (=as far down the MDNode
DAG as possible).
>
Right, though, to be fair, some numbers here might be nice. The
tradeoff of "extra lookup for ref" versus "extra memory
allocation for
larger debug info".

I also don't think it'll matter for speed :)

-eric
>>
>>>
>>> Question to the C++ experts: Is the name (“test” in this case) a
sufficient appropriate unique ID for a C++ namespace?
>>
>> Potentially - assuming you don't do this for anything in an
anonymous
>> namespace. I'd probably see about using the standard mangling
> Good point! We should avoid unifying the anonymous namespace :-)
>> machinery as we do for other things, though, if possible. Might keep
>> it more consistent.
>
> I will do some experiments with nested namespaces, but it seems as if name
mangling does not buy us much: this will merely turn into N4test.
>
> -- adrian
>
>>
>>>
>>> -- adrian
>>>
>>>
>>>> On Jun 24, 2014, at 1:49 PM, David Blaikie <dblaikie at
gmail.com> wrote:
>>>>
>>>> +Adrian & Manman,
>>>>
>>>> Looks like this is a case of non-DIRef references ending up in
the IR,
>>>> and thus the references not being deduplicated. This could lead
to
>>>> some of the IR bloat that you guys implemented the DIRef stuff
to
>>>> reduce/avoid.
>>>>
>>>> The specific issue is that the type is slightly different in
the two
>>>> TUs (since the namespace scope it's contained within is
different in
>>>> the two TUs - note the namespace preceeding the header include
in
>>>> test2.cpp) and the actual DIRef-usage failure is when building
>>>> subroutine types. The subroutine types are made with direct
references
>>>> to types, not with DIRef references to types. This means they
won't be
>>>> deduplicated/resolved to a single type during linking
correctly.
>>>>
>>>> It also leads to an assertion as per the original email.
Figured you
>>>> guys might want to look into/fix this (I assume the right fix
is to
>>>> use DIRef more pervasively in the frontend - I'm doing a
little
>>>> experimenting with clang now to see how that looks).
>>>>
>>>> - David
>>>>
>>>> On Fri, Jun 13, 2014 at 11:08 PM, David Blaikie <dblaikie at
gmail.com> wrote:
>>>>> Yep, looks like a legit bug to me. I'll try to
reproduce it and reduce
>>>>> a test case, etc.
>>>>>
>>>>> (the ODR doesn't require that the two copies of the
Test class
>>>>> template appear on the same line in the same file in two
distinct
>>>>> translation units, it only requires that the two copies
have the same
>>>>> sequence of tokens - which they do in your example)
>>>>>
>>>>> On Fri, Jun 13, 2014 at 5:33 PM, Kevin Modzelewski <kmod
at dropbox.com> wrote:
>>>>>> Hi all, sorry to post to both lists, but I'm
running into an issue where
>>>>>> clang-generated debug info is deemed to be invalid by
LLVM tools (throws an
>>>>>> assertion error in both llc and mcjit), and I'm not
sure what the proper
>>>>>> resolution is.
>>>>>>
>>>>>> Here's a test case; I last tested it on revision
r210953:
>>>>>>
>>>>>> $ cat test1.cpp
>>>>>> #include "test.h"
>>>>>> test::Test<int> foo1() {
>>>>>>   return test::Test<int>();
>>>>>> }
>>>>>>
>>>>>> $ cat test2.cpp
>>>>>> namespace test {
>>>>>> }
>>>>>> #include "test.h"
>>>>>> test::Test<int> foo2() {
>>>>>>   return test::Test<int>();
>>>>>> }
>>>>>>
>>>>>> $ cat test.h
>>>>>> namespace test {
>>>>>> template <class T>
>>>>>> class Test {
>>>>>> };
>>>>>> }
>>>>>>
>>>>>> $ clang++ -g -emit-llvm test1.cpp -S -o test1.ll
>>>>>> $ clang++ -g -emit-llvm test2.cpp -S -o test2.ll
>>>>>> $ llvm-link test1.ll test2.ll -S -o linked.ll
>>>>>> $ llc linked.ll
>>>>>>
>>>>>> The last step raises an assertion error, assuming you
have assertions
>>>>>> enabled:
>>>>>> llc: lib/CodeGen/AsmPrinter/DwarfUnit.cpp:953:
llvm::DIE*
>>>>>> llvm::DwarfUnit::getOrCreateTypeDIE(const
llvm::MDNode*): Assertion `Ty =>>>>>> resolve(Ty.getRef())
&& "type was not uniqued, possible ODR violation."'
>>>>>> failed
>>>>>>
>>>>>> The initial introduction of the "test"
namespace in test2.cpp seems to
>>>>>> confuse clang -- test1.cpp and test2.cpp have
non-compatible debug
>>>>>> information for the test::Test type.  test1.cpp says
that test::Test's
>>>>>> namespace is defined in test.h, and test2.cpp says that
test::Test's
>>>>>> namespace is defined in test2.cpp (they both say that
the class itself is
>>>>>> defined in test.h).  Regardless of whether LLVM tools
should allow this,
>>>>>> this seems like the wrong output for these files?
>>>>>>
>>>>>> Another related example, is if we simply defined the
test::Test template in
>>>>>> both files (ie, manually executed the #include
"test.h") and got rid of the
>>>>>> test2.cpp "namespace test {}" definition,
we'd run into the same assertion,
>>>>>> without hitting the weird clang behavior with the empty
namespace
>>>>>> pre-declaration.
>>>>>>
>>>>>> It's probably also worth noting that compiling
directly with clang, ie
>>>>>> adding a "int main() {}" function and then
doing
>>>>>> $ clang++ -g test1.cpp test2.cpp -o test
>>>>>> works fine.
>>>>>>
>>>>>> I'm not a C++ expert and I don't know if these
template issues really are
>>>>>> violations of the ODR, but it feels like this should be
allowed, and
>>>>>> somewhere in the llvm toolchain (llvm-link?
DwarfUnit.cpp?) this should be
>>>>>> handled.  What do people think?
>>>>>>
>>>>>> kmod
>>>
>
>
> _______________________________________________
> LLVM Developers mailing list
> LLVMdev at cs.uiuc.edu         http://llvm.cs.uiuc.edu
> http://lists.cs.uiuc.edu/mailman/listinfo/llvmdev

> On Jun 24, 2014, at 4:34 PM, Eric Christopher <echristo at gmail.com>
wrote:
> 
>>> Without needing to change how namespaces are handled.
>>> 
>>> Yes, using DIRefs for namespaces would cause the actual type nodes
to
>>> be deduplicated when they aren't even with the patch above, and
that
>>> would help reduce debug info metadata further if that's
>>> useful/necessary.
>> 
>> Exactly. While the above patch will cover up the problem, we will still
have many duplicate type entries during LTO that will take up memory, even
though only the last one to be entered into DIRefMap will actually be used for
emitting DWARF. Since DIRefs are also more expensive in terms of lookup speed, I
think I’d prefer to only use them only where necessary (=as far down the MDNode
DAG as possible).
>> 
> 
> Right, though, to be fair, some numbers here might be nice. The
> tradeoff of "extra lookup for ref" versus "extra memory
allocation for
> larger debug info”.
Then again, it’s not like the extra lookups introduced by David’s proposed patch
would get rid of those extra memory allocations. Granted, they do get rid of the
assertion, which obviously provides some value ;-)
> 
> I also don't think it'll matter for speed :)
> 
You’re probably right about the lookup, but depending on the project you’re
building the memory usage could matter.

-- adrian
> -eric
> 
>>> 
>>>> 
>>>> Question to the C++ experts: Is the name (“test” in this case)
a sufficient appropriate unique ID for a C++ namespace?
>>> 
>>> Potentially - assuming you don't do this for anything in an
anonymous
>>> namespace. I'd probably see about using the standard mangling
>> Good point! We should avoid unifying the anonymous namespace :-)
>>> machinery as we do for other things, though, if possible. Might
keep
>>> it more consistent.
>> 
>> I will do some experiments with nested namespaces, but it seems as if
name mangling does not buy us much: this will merely turn into N4test.
>> 
>> -- adrian
>> 
>>> 
>>>> 
>>>> -- adrian
>>>> 
>>>> 
>>>>> On Jun 24, 2014, at 1:49 PM, David Blaikie <dblaikie at
gmail.com> wrote:
>>>>> 
>>>>> +Adrian & Manman,
>>>>> 
>>>>> Looks like this is a case of non-DIRef references ending up
in the IR,
>>>>> and thus the references not being deduplicated. This could
lead to
>>>>> some of the IR bloat that you guys implemented the DIRef
stuff to
>>>>> reduce/avoid.
>>>>> 
>>>>> The specific issue is that the type is slightly different
in the two
>>>>> TUs (since the namespace scope it's contained within is
different in
>>>>> the two TUs - note the namespace preceeding the header
include in
>>>>> test2.cpp) and the actual DIRef-usage failure is when
building
>>>>> subroutine types. The subroutine types are made with direct
references
>>>>> to types, not with DIRef references to types. This means
they won't be
>>>>> deduplicated/resolved to a single type during linking
correctly.
>>>>> 
>>>>> It also leads to an assertion as per the original email.
Figured you
>>>>> guys might want to look into/fix this (I assume the right
fix is to
>>>>> use DIRef more pervasively in the frontend - I'm doing
a little
>>>>> experimenting with clang now to see how that looks).
>>>>> 
>>>>> - David
>>>>> 
>>>>> On Fri, Jun 13, 2014 at 11:08 PM, David Blaikie
<dblaikie at gmail.com> wrote:
>>>>>> Yep, looks like a legit bug to me. I'll try to
reproduce it and reduce
>>>>>> a test case, etc.
>>>>>> 
>>>>>> (the ODR doesn't require that the two copies of the
Test class
>>>>>> template appear on the same line in the same file in
two distinct
>>>>>> translation units, it only requires that the two copies
have the same
>>>>>> sequence of tokens - which they do in your example)
>>>>>> 
>>>>>> On Fri, Jun 13, 2014 at 5:33 PM, Kevin Modzelewski
<kmod at dropbox.com> wrote:
>>>>>>> Hi all, sorry to post to both lists, but I'm
running into an issue where
>>>>>>> clang-generated debug info is deemed to be invalid
by LLVM tools (throws an
>>>>>>> assertion error in both llc and mcjit), and I'm
not sure what the proper
>>>>>>> resolution is.
>>>>>>> 
>>>>>>> Here's a test case; I last tested it on
revision r210953:
>>>>>>> 
>>>>>>> $ cat test1.cpp
>>>>>>> #include "test.h"
>>>>>>> test::Test<int> foo1() {
>>>>>>>  return test::Test<int>();
>>>>>>> }
>>>>>>> 
>>>>>>> $ cat test2.cpp
>>>>>>> namespace test {
>>>>>>> }
>>>>>>> #include "test.h"
>>>>>>> test::Test<int> foo2() {
>>>>>>>  return test::Test<int>();
>>>>>>> }
>>>>>>> 
>>>>>>> $ cat test.h
>>>>>>> namespace test {
>>>>>>> template <class T>
>>>>>>> class Test {
>>>>>>> };
>>>>>>> }
>>>>>>> 
>>>>>>> $ clang++ -g -emit-llvm test1.cpp -S -o test1.ll
>>>>>>> $ clang++ -g -emit-llvm test2.cpp -S -o test2.ll
>>>>>>> $ llvm-link test1.ll test2.ll -S -o linked.ll
>>>>>>> $ llc linked.ll
>>>>>>> 
>>>>>>> The last step raises an assertion error, assuming
you have assertions
>>>>>>> enabled:
>>>>>>> llc: lib/CodeGen/AsmPrinter/DwarfUnit.cpp:953:
llvm::DIE*
>>>>>>> llvm::DwarfUnit::getOrCreateTypeDIE(const
llvm::MDNode*): Assertion `Ty =>>>>>>> resolve(Ty.getRef())
&& "type was not uniqued, possible ODR violation."'
>>>>>>> failed
>>>>>>> 
>>>>>>> The initial introduction of the "test"
namespace in test2.cpp seems to
>>>>>>> confuse clang -- test1.cpp and test2.cpp have
non-compatible debug
>>>>>>> information for the test::Test type.  test1.cpp
says that test::Test's
>>>>>>> namespace is defined in test.h, and test2.cpp says
that test::Test's
>>>>>>> namespace is defined in test2.cpp (they both say
that the class itself is
>>>>>>> defined in test.h).  Regardless of whether LLVM
tools should allow this,
>>>>>>> this seems like the wrong output for these files?
>>>>>>> 
>>>>>>> Another related example, is if we simply defined
the test::Test template in
>>>>>>> both files (ie, manually executed the #include
"test.h") and got rid of the
>>>>>>> test2.cpp "namespace test {}" definition,
we'd run into the same assertion,
>>>>>>> without hitting the weird clang behavior with the
empty namespace
>>>>>>> pre-declaration.
>>>>>>> 
>>>>>>> It's probably also worth noting that compiling
directly with clang, ie
>>>>>>> adding a "int main() {}" function and
then doing
>>>>>>> $ clang++ -g test1.cpp test2.cpp -o test
>>>>>>> works fine.
>>>>>>> 
>>>>>>> I'm not a C++ expert and I don't know if
these template issues really are
>>>>>>> violations of the ODR, but it feels like this
should be allowed, and
>>>>>>> somewhere in the llvm toolchain (llvm-link?
DwarfUnit.cpp?) this should be
>>>>>>> handled.  What do people think?
>>>>>>> 
>>>>>>> kmod
>>>> 
>> 
>> 
>> _______________________________________________
>> LLVM Developers mailing list
>> LLVMdev at cs.uiuc.edu         http://llvm.cs.uiuc.edu
>> http://lists.cs.uiuc.edu/mailman/listinfo/llvmdev

I looked into this a little. My proposal is this:

- extend DINamespace with an extra UniqueID filed (analogous to DICompositeType)
- add an extra case to DIScope::getRef()
- Let CGDebugInfo create a mangled name for each namespace to use as UID
  -> the UID of the anonymous namespace is null.

For example:

namespace a { namespace b {} } -> “_ZN1a", “_ZN1a1b"

!0 = [compile unit]
!1 = metadata !{i32 786489, metadata !0, metadata !”_ZN1a", metadata
!”b", i32 1, metadata !”_ZN1a1b"} ; [ DW_TAG_namespace ] [a]
!2 = metadata !{i32 786489, metadata !0, null, metadata !”a", i32 1,
metadata !”_ZN1a"} ; [ DW_TAG_namespace ] [a] [line 1]

namespace a1b {} -> “_ZN3a1b"
namespace {} -> null (!= “”) // Anonymous namespaces will remain
old-fashioned MDNode references to prevent uniquing.

With this change we will get the full type uniquing benefits. As a side effect,
definitions that are in the same namespace will be children of the same
DW_TAG_namespace in the debug info, which I’d argue is the expected behavior for
LTO anyway.

-- adrian
> On Jun 24, 2014, at 4:39 PM, Adrian Prantl <aprantl at apple.com>
wrote:
> 
> 
>> On Jun 24, 2014, at 4:34 PM, Eric Christopher <echristo at
gmail.com> wrote:
>> 
>>>> Without needing to change how namespaces are handled.
>>>> 
>>>> Yes, using DIRefs for namespaces would cause the actual type
nodes to
>>>> be deduplicated when they aren't even with the patch above,
and that
>>>> would help reduce debug info metadata further if that's
>>>> useful/necessary.
>>> 
>>> Exactly. While the above patch will cover up the problem, we will
still have many duplicate type entries during LTO that will take up memory, even
though only the last one to be entered into DIRefMap will actually be used for
emitting DWARF. Since DIRefs are also more expensive in terms of lookup speed, I
think I’d prefer to only use them only where necessary (=as far down the MDNode
DAG as possible).
>>> 
>> 
>> Right, though, to be fair, some numbers here might be nice. The
>> tradeoff of "extra lookup for ref" versus "extra memory
allocation for
>> larger debug info”.
> 
> Then again, it’s not like the extra lookups introduced by David’s proposed
patch would get rid of those extra memory allocations. Granted, they do get rid
of the assertion, which obviously provides some value ;-)
> 
>> 
>> I also don't think it'll matter for speed :)
>> 
> You’re probably right about the lookup, but depending on the project you’re
building the memory usage could matter.
> 
> -- adrian
> 
>> -eric
>> 
>>>> 
>>>>> 
>>>>> Question to the C++ experts: Is the name (“test” in this
case) a sufficient appropriate unique ID for a C++ namespace?
>>>> 
>>>> Potentially - assuming you don't do this for anything in an
anonymous
>>>> namespace. I'd probably see about using the standard
mangling
>>> Good point! We should avoid unifying the anonymous namespace :-)
>>>> machinery as we do for other things, though, if possible. Might
keep
>>>> it more consistent.
>>> 
>>> I will do some experiments with nested namespaces, but it seems as
if name mangling does not buy us much: this will merely turn into N4test.
>>> 
>>> -- adrian
>>> 
>>>> 
>>>>> 
>>>>> -- adrian
>>>>> 
>>>>> 
>>>>>> On Jun 24, 2014, at 1:49 PM, David Blaikie <dblaikie
at gmail.com> wrote:
>>>>>> 
>>>>>> +Adrian & Manman,
>>>>>> 
>>>>>> Looks like this is a case of non-DIRef references
ending up in the IR,
>>>>>> and thus the references not being deduplicated. This
could lead to
>>>>>> some of the IR bloat that you guys implemented the
DIRef stuff to
>>>>>> reduce/avoid.
>>>>>> 
>>>>>> The specific issue is that the type is slightly
different in the two
>>>>>> TUs (since the namespace scope it's contained
within is different in
>>>>>> the two TUs - note the namespace preceeding the header
include in
>>>>>> test2.cpp) and the actual DIRef-usage failure is when
building
>>>>>> subroutine types. The subroutine types are made with
direct references
>>>>>> to types, not with DIRef references to types. This
means they won't be
>>>>>> deduplicated/resolved to a single type during linking
correctly.
>>>>>> 
>>>>>> It also leads to an assertion as per the original
email. Figured you
>>>>>> guys might want to look into/fix this (I assume the
right fix is to
>>>>>> use DIRef more pervasively in the frontend - I'm
doing a little
>>>>>> experimenting with clang now to see how that looks).
>>>>>> 
>>>>>> - David
>>>>>> 
>>>>>> On Fri, Jun 13, 2014 at 11:08 PM, David Blaikie
<dblaikie at gmail.com> wrote:
>>>>>>> Yep, looks like a legit bug to me. I'll try to
reproduce it and reduce
>>>>>>> a test case, etc.
>>>>>>> 
>>>>>>> (the ODR doesn't require that the two copies of
the Test class
>>>>>>> template appear on the same line in the same file
in two distinct
>>>>>>> translation units, it only requires that the two
copies have the same
>>>>>>> sequence of tokens - which they do in your example)
>>>>>>> 
>>>>>>> On Fri, Jun 13, 2014 at 5:33 PM, Kevin Modzelewski
<kmod at dropbox.com> wrote:
>>>>>>>> Hi all, sorry to post to both lists, but
I'm running into an issue where
>>>>>>>> clang-generated debug info is deemed to be
invalid by LLVM tools (throws an
>>>>>>>> assertion error in both llc and mcjit), and
I'm not sure what the proper
>>>>>>>> resolution is.
>>>>>>>> 
>>>>>>>> Here's a test case; I last tested it on
revision r210953:
>>>>>>>> 
>>>>>>>> $ cat test1.cpp
>>>>>>>> #include "test.h"
>>>>>>>> test::Test<int> foo1() {
>>>>>>>> return test::Test<int>();
>>>>>>>> }
>>>>>>>> 
>>>>>>>> $ cat test2.cpp
>>>>>>>> namespace test {
>>>>>>>> }
>>>>>>>> #include "test.h"
>>>>>>>> test::Test<int> foo2() {
>>>>>>>> return test::Test<int>();
>>>>>>>> }
>>>>>>>> 
>>>>>>>> $ cat test.h
>>>>>>>> namespace test {
>>>>>>>> template <class T>
>>>>>>>> class Test {
>>>>>>>> };
>>>>>>>> }
>>>>>>>> 
>>>>>>>> $ clang++ -g -emit-llvm test1.cpp -S -o
test1.ll
>>>>>>>> $ clang++ -g -emit-llvm test2.cpp -S -o
test2.ll
>>>>>>>> $ llvm-link test1.ll test2.ll -S -o linked.ll
>>>>>>>> $ llc linked.ll
>>>>>>>> 
>>>>>>>> The last step raises an assertion error,
assuming you have assertions
>>>>>>>> enabled:
>>>>>>>> llc: lib/CodeGen/AsmPrinter/DwarfUnit.cpp:953:
llvm::DIE*
>>>>>>>> llvm::DwarfUnit::getOrCreateTypeDIE(const
llvm::MDNode*): Assertion `Ty =>>>>>>>>
resolve(Ty.getRef()) && "type was not uniqued, possible ODR
violation."'
>>>>>>>> failed
>>>>>>>> 
>>>>>>>> The initial introduction of the
"test" namespace in test2.cpp seems to
>>>>>>>> confuse clang -- test1.cpp and test2.cpp have
non-compatible debug
>>>>>>>> information for the test::Test type.  test1.cpp
says that test::Test's
>>>>>>>> namespace is defined in test.h, and test2.cpp
says that test::Test's
>>>>>>>> namespace is defined in test2.cpp (they both
say that the class itself is
>>>>>>>> defined in test.h).  Regardless of whether LLVM
tools should allow this,
>>>>>>>> this seems like the wrong output for these
files?
>>>>>>>> 
>>>>>>>> Another related example, is if we simply
defined the test::Test template in
>>>>>>>> both files (ie, manually executed the #include
"test.h") and got rid of the
>>>>>>>> test2.cpp "namespace test {}"
definition, we'd run into the same assertion,
>>>>>>>> without hitting the weird clang behavior with
the empty namespace
>>>>>>>> pre-declaration.
>>>>>>>> 
>>>>>>>> It's probably also worth noting that
compiling directly with clang, ie
>>>>>>>> adding a "int main() {}" function and
then doing
>>>>>>>> $ clang++ -g test1.cpp test2.cpp -o test
>>>>>>>> works fine.
>>>>>>>> 
>>>>>>>> I'm not a C++ expert and I don't know
if these template issues really are
>>>>>>>> violations of the ODR, but it feels like this
should be allowed, and
>>>>>>>> somewhere in the llvm toolchain (llvm-link?
DwarfUnit.cpp?) this should be
>>>>>>>> handled.  What do people think?
>>>>>>>> 
>>>>>>>> kmod
>>>>> 
>>> 
>>> 
>>> _______________________________________________
>>> LLVM Developers mailing list
>>> LLVMdev at cs.uiuc.edu         http://llvm.cs.uiuc.edu
>>> http://lists.cs.uiuc.edu/mailman/listinfo/llvmdev
> 
> 
> _______________________________________________
> LLVM Developers mailing list
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> http://lists.cs.uiuc.edu/mailman/listinfo/llvmdev