llvm dev - Oct 2013 - [LLVMdev] [Debug Info PATCH] for support of ref_addr and removal of DIE duplication

On Tue, Oct 15, 2013 at 1:22 PM, Manman Ren <manman.ren at gmail.com>
wrote:
>
>
>
> On Tue, Oct 15, 2013 at 11:34 AM, David Blaikie <dblaikie at
gmail.com>wrote:
>
>>
>>
>>
>> On Tue, Oct 15, 2013 at 10:51 AM, Manman Ren <manman.ren at
gmail.com>wrote:
>>
>>>
>>>
>>>
>>> On Tue, Oct 15, 2013 at 10:10 AM, David Blaikie <dblaikie at
gmail.com>wrote:
>>>
>>>>
>>>>
>>>>
>>>> On Tue, Oct 15, 2013 at 10:05 AM, Manman Ren <manman.ren at
gmail.com>wrote:
>>>>
>>>>>
>>>>>
>>>>>
>>>>> On Wed, Oct 9, 2013 at 5:22 PM, Manman Ren <manman.ren
at gmail.com>wrote:
>>>>>
>>>>>>
>>>>>>
>>>>>>
>>>>>> On Wed, Oct 9, 2013 at 1:32 PM, Manman Ren
<manman.ren at gmail.com>wrote:
>>>>>>
>>>>>>>
>>>>>>> David,
>>>>>>>
>>>>>>> Thanks for reviewing!
>>>>>>>
>>>>>>> On Wed, Oct 9, 2013 at 11:36 AM, David Blaikie
<dblaikie at gmail.com>wrote:
>>>>>>>
>>>>>>>> Might be easier if these were on Phabricator,
but here are some
>>>>>>>> thoughts:
>>>>>>>>
>>>>>>>> 0001:
>>>>>>>>   This patch generally, while separated for
legibility, is untested
>>>>>>>> & difficult to discuss in isolation.
>>>>>>>>
>>>>>>> I agree, this patch adds the functionality but does
not use it, the
>>>>>>> 2nd patch uses ref_addr.
>>>>>>> If you think I should merge the two and commit as a
single patch,
>>>>>>> let me know.
>>>>>>>
>>>>>>>
>>>>>>>>  I may need to refer to the second patch in
reviewing this first
>>>>>>>> one.
>>>>>>>>   DwarfDebug.cpp:
>>>>>>>>     computeSizeAndOffsets:
>>>>>>>>       I believe this produces the wrong offset
for the 3rd CU and
>>>>>>>> onwards. computeSizeAndOffset returns the
EndOffset which is absolute, not
>>>>>>>> relative to the Offset passed in, so it should
be assigned to SecOffset,
>>>>>>>> not added to it. (eg: if you have CUs at 0, 42,
and 57 - the first pass
>>>>>>>> through SecOffset will be zero, then it'll
be 0 + 42, then on the 3rd it'll
>>>>>>>> be (0 + 42) + 57 which isn't right, it
should just be 57). Please add more
>>>>>>>> test coverage while fixing this issue.
>>>>>>>>
>>>>>>>
>>>>>>> computeSizeAndOffset takes an offset that is
relative to the start
>>>>>>> of the CU and returns the offset relative to the CU
after laying out the
>>>>>>> DIE.
>>>>>>> The initial offset before laying out the CU DIE is
the header size,
>>>>>>> EndOffset will be the offset relative to the CU
after laying out the whole
>>>>>>> CU DIE.
>>>>>>> We can think of EndOffset as the size of the whole
CU DIE. SecOffset
>>>>>>> is the offset from the Debug Info section, so we
can update it by adding
>>>>>>> the CU size.
>>>>>>>
>>>>>>>   // Offset from the beginning of debug info
section.
>>>>>>>   unsigned SecOffset = 0;
>>>>>>>   for (SmallVectorImpl<CompileUnit
*>::iterator I = CUs.begin(),
>>>>>>>          E = CUs.end(); I != E; ++I) {
>>>>>>>     (*I)->setDebugInfoOffset(SecOffset);
>>>>>>>      unsigned Offset >>>>>>>  
sizeof(int32_t) + // Length of Compilation Unit Info
>>>>>>>       sizeof(int16_t) + // DWARF version number
>>>>>>>       sizeof(int32_t) + // Offset Into Abbrev.
Section
>>>>>>>       sizeof(int8_t);   // Pointer Size (in bytes)
>>>>>>>
>>>>>>>     unsigned EndOffset =
computeSizeAndOffset((*I)->getCUDie(),
>>>>>>> Offset);
>>>>>>>     SecOffset += EndOffset;
>>>>>>>   }
>>>>>>>
>>>>>>
>>>>>> Added more comments in attached patch.
>>>>>>
>>>>>>
>>>>>>>
>>>>>>>
>>>>>>>> Eric/Manman: rough design question: compute the
absolute offset of
>>>>>>>> each CU within the debug_info section and
describe them all relative to a
>>>>>>>> single symbol at the start of the debug_info
section, or should we put a
>>>>>>>> label at the start of each CU?
>>>>>>>>
>>>>>>>
>>>>>>> Either way should work. But since we already have
the section offset
>>>>>>> for each CU, describing relative to the start of
debug_info section saves
>>>>>>> us a few symbols :)
>>>>>>>
>>>>>>>
>>>>>>>>
>>>>>>>> 0002:
>>>>>>>>   ref_addr_relocation.ll:
>>>>>>>>     seems a bit vague in terms of how you test
for the relocation.
>>>>>>>> I think it'd make more sense to test the
assembly, than the reafobj output,
>>>>>>>> that way you can test that the correct bytes
have the relocation rather
>>>>>>>> than just that there's "some"
.debug_info relocation in the file. For an
>>>>>>>> example, see test/DebugInfo/X86/tls.ll I wrote
- it has some "unannotated"
>>>>>>>> bytes because we still don't have a nice
way to annotate location bytes
>>>>>>>> that are DWARF expressions, but it's close
- I guess those should be
>>>>>>>> CHECK-NEXTs, though. In any case, you should be
able to check a few lines
>>>>>>>> of assembly with the # DW_AT/DW_TAG annotation
comments.
>>>>>>>>
>>>>>>>
>>>>>>> I can check for ".quad .Lsection_info+38
#DW_AT_type".
>>>>>>>
>>>>>> Done in attached patch.
>>>>>>
>>>>>>>
>>>>>>>
>>>>>>>>      You'd need to add the tu3.cpp from my
example if you want to
>>>>>>>> demonstrate that the relocation is actually
working as intended and
>>>>>>>> avoiding the bogus result I showed.
>>>>>>>>   type-unique-simple-a.ll
>>>>>>>>     While I agree that having common test cases
helps reduce the
>>>>>>>> number of separate invocations we have, this
test case seems like it might
>>>>>>>> be becoming a little hard to follow what's
under test. Just going from the
>>>>>>>> diff I'm not sure what's what. Could
you give a brief description of the
>>>>>>>> state of type-unique-simple2 files? What's
involved? What's it meant to
>>>>>>>> test? What's it actually testing?
>>>>>>>>
>>>>>>> I can add more comments. The source files are
included in the
>>>>>>> testing case. I am checking that llvm-link only
generates a single copy of
>>>>>>> the struct and the backend generates a single DIE
and uses ref_addr.
>>>>>>> The changes are to check "the backend
generates a single DIE and
>>>>>>> uses ref_addr".
>>>>>>>
>>>>>> Done in attached patch.
>>>>>>
>>>>>>>
>>>>>>>    DIE.h:
>>>>>>>>     checkCompileUnit could probably be called
>>>>>>>> "getCompileUnitOrNull", the name
"check*" seems to imply that it does some
>>>>>>>> checking, which isn't true.
>>>>>>>>
>>>>>>>  Will do.
>>>>>>>
>>>>>> Done in attached patch.
>>>>>>
>>>>>>>
>>>>>>>
>>>>>>>>   DwarfCompileUnit.cpp:
>>>>>>>>     the "istype || issubprogram"
check should probably be pulled
>>>>>>>> out into a separate function, something like
"isShareableAcrossCUs" or
>>>>>>>> something like that (please, that's not the
best name, let's discuss it
>>>>>>>> further before we settle on a name) so that
getDIE and insertDIE are sure
>>>>>>>> to use the same test at all times.
>>>>>>>>
>>>>>>> Yes, the condition is shared between getDIE and
insertDIE. I like
>>>>>>> isSharableAcrossCUs, because that is why the map is
in DwarfDebug instead
>>>>>>> of CompileUnit.
>>>>>>>
>>>>>> Done in attached patch.
>>>>>>
>>>>>>>
>>>>>>>
>>>>>>>>    Why does addDIEEntry take a form? When does
the caller get to
>>>>>>>> choose the form rather than the callee deciding
between ref4 and ref_addr
>>>>>>>> based on context?
>>>>>>>>
>>>>>>>
>>>>>>> addDIEEntry took a form before my change and I
didn't check why it
>>>>>>> did.
>>>>>>> I will check if all callers always use ref4, if it
it true, I will
>>>>>>> submit a cleanup patch first.
>>>>>>>
>>>>>> Done in attached patch.
>>>>>>
>>>>>>>
>>>>>>>   I'm still unsure about this worklist thing -
do your current tests
>>>>>>>> cover the need for the worklist? ie: if we
removed that logic, would tests
>>>>>>>> fail? Can you describe a specific sequence
where the worklist is necessary?
>>>>>>>>
>>>>>>>
>>>>>>> If we are sure that DIEs are always added to an
owner before calling
>>>>>>> addDIEEntry, we don't need the worklist.
>>>>>>> But I saw cases where that was not true, I will get
a reduced
>>>>>>> testing case.
>>>>>>>
>>>>>>
>>>>>> If we try to assert both DIEs have owner in
addDIEEntry, the
>>>>>> following testing cases will fail:
>>>>>>     LLVM :: DebugInfo/X86/multiple-aranges.ll
>>>>>>     LLVM :: DebugInfo/X86/ref_addr_relocation.ll
>>>>>>     LLVM ::
DebugInfo/X86/stmt-list-multiple-compile-units.ll
>>>>>>     LLVM :: DebugInfo/two-cus-from-same-file.ll
>>>>>>     LLVM :: Linker/type-unique-simple-a.ll
>>>>>>     LLVM :: Linker/type-unique-simple2.ll
>>>>>>
>>>>>> For ref_addr_relocation, it failed in
>>>>>> #5  0x0000000100b169ba in llvm::DwarfDebug::addDIEEntry
>>>>>> (this=0x103023600, Die=0x102e14090, Attribute=73,
Entry=0x10302a9d0) at
>>>>>>
/Users/manmanren/llvm_git/llvm/lib/CodeGen/AsmPrinter/DwarfDebug.cpp:3071
>>>>>> #6  0x0000000100b040e0 in llvm::CompileUnit::addType
>>>>>> (this=0x102e13ec0, Entity=0x102e14090,
Ty={<llvm::DIScope> >>>>>> {<llvm::DIDescriptor> =
{DbgNode = 0x102e05f30}, <No data fields>}, <No
>>>>>> data fields>}, Attribute=73) at
>>>>>>
/Users/manmanren/llvm_git/llvm/lib/CodeGen/AsmPrinter/DwarfCompileUnit.cpp:910
>>>>>> #7  0x0000000100b05bff in
llvm::CompileUnit::createGlobalVariableDIE
>>>>>> (this=0x102e13ec0, N=0x102e068c0) at
>>>>>>
/Users/manmanren/llvm_git/llvm/lib/CodeGen/AsmPrinter/DwarfCompileUnit.cpp:1505
>>>>>>
>>>>>> If we look at DwarfCompileUnit.cpp:
>>>>>>     VariableDIE = new DIE(GV.getTag());
>>>>>>     // Add to map.
>>>>>>     insertDIE(N, VariableDIE);
>>>>>>
>>>>>>     // Add name and type.
>>>>>>     addString(VariableDIE, dwarf::DW_AT_name,
GV.getDisplayName());
>>>>>>     addType(VariableDIE, GTy);
>>>>>>
>>>>>> The VariableDIE is not added to an owner yet when
calling addType.
>>>>>>
>>>>>
>>>>> I believe I have addressed all review comments, the patches
are
>>>>> re-attached here for convenience.
>>>>>
>>>>
>>>> So I'm still thinking about the work list work.
>>>>
>>>> If we don't know which CU a DIE is in - isn't it,
necessarily, going to
>>>> be in the current CU (& thus referenced by ref_data4 (using
a CU-local
>>>> offset), not ref_addr)?
>>>>
>>>
>>> That may be true. But can we prove that?
>>>
>>
>> We really shouldn't add extra complexity to the codebase just
because we
>> don't know how the codebase works - that's what leads to the
kind of
>> complexity we see in the debug info handling today.
>>
>
>>
>>>  There are two ways of handling this:
>>> 1> use a worklist to be conservative
>>> 2> do not use a worklist, but add an assertion when emitting a
DIE A,
>>> make sure the DIE referenced with ref4 is indeed in the same CU as
DIE A.
>>>
>>
>> Please just add this assertion. If it fires we'll have a test case
and a
>> concrete justification for this complexity such that should anyone
remove
>> it later because it looked unnecessary, they'll at least have a
failing
>> test to explain why it was there in the first plac .
>>
>
> The assertion fails even with a simple testing case when the referenced
> DIE has an owner and the DIE itself does not have an owner.
>
OK, sorry - I should've read your description of the assertion more
carefully. I believe the assertion you added wasn't the right thing to test
for.

I'm not sure there is a correct assertion to add here to detect the case
you're describing - perhaps a complex verification after-the-fact could be
done, but essentially if we have a DIE that's partially constructed/has no
parent we should assume it's in the current unit. If we can demonstrate a
case where this isn't true, then we should work to address that problem -
until we demonstrate that, we should not (though we might want to search
for such cases - but without type units I can't imagine how they could
occur - we build the DIE tree for one CU at a time, at no point do we have
DIEs under construction for multiple CUs).

So if we want to build a reference to a DIE, if the DIE is not in another
CU we should use ref4. (then the only other case is that it's either in
this CU or it's in no known CU at all - in which case it's under
construction and, without evidence to the contrary, will be added to the
current CU when it's done).

About the only assertion we could add would involve keeping a side-table of
"assumptions" ("we expect this DIE will be added to this
CU") and check
that those assumptions are fulfilled at some point.

> For that case, we can't assume ref4 should be used. I don't think
we can
> enforce that all DIEs must be added to a parent before calling addDIEEntry.
>
> For the specific testing case, when constructing children of a scope DIE,
> we call addDIEEntry on the children, after that, we add the children to the
> scope DIE.
> cat foo.cpp
>
> #include "a.hpp"
> void f(int a) {
>   Base t;
> }
> cat bar.cpp
>
> #include "a.hpp"
> void f(int);
> void g(int a) {
>   Base t;
> }
> int main() {
>   f(0);
>   g(1);
>   return 0;
> }
> cat a.hpp
> struct Base {
>   int a;
> };
>
> Let me know if I should investigate further.
>
> Thanks,
> Manman
>
>
>>
>>
>>>
>>> Let me know which one you prefer.
>>>
>>> Do you have any comments on the ref_addr patch (the 1st patch of
the
>>> two)?
>>>
>>
>> Nothing much - I wouldn't mind Eric taking a look (& would
rather you not
>> commit this until you're committing the second patch, since
it's otherwise
>> untested/unjustified code) on the label/offset related stuff since
I'm less
>> familiar with that.
>>
>> There's one or two cases of {} on single-statement blocks you could
fix
>> up.
>>
>> "DebugInfoOffset" (both the member and the functions to
set/get it) might
>> be more meaningfully named "SectionOffset" - but I'm not
sure. Eric? Other
>> names (DebugInfoSectionOffset?)?
>>
>> - David
>>
>
>
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On Tue, Oct 15, 2013 at 1:37 PM, David Blaikie <dblaikie at gmail.com>
wrote:
>
>
>
> On Tue, Oct 15, 2013 at 1:22 PM, Manman Ren <manman.ren at gmail.com>
wrote:
>
>>
>>
>>
>> On Tue, Oct 15, 2013 at 11:34 AM, David Blaikie <dblaikie at
gmail.com>wrote:
>>
>>>
>>>
>>>
>>> On Tue, Oct 15, 2013 at 10:51 AM, Manman Ren <manman.ren at
gmail.com>wrote:
>>>
>>>>
>>>>
>>>>
>>>> On Tue, Oct 15, 2013 at 10:10 AM, David Blaikie <dblaikie at
gmail.com>wrote:
>>>>
>>>>>
>>>>>
>>>>>
>>>>> On Tue, Oct 15, 2013 at 10:05 AM, Manman Ren <manman.ren
at gmail.com>wrote:
>>>>>
>>>>>>
>>>>>>
>>>>>>
>>>>>> On Wed, Oct 9, 2013 at 5:22 PM, Manman Ren
<manman.ren at gmail.com>wrote:
>>>>>>
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>> On Wed, Oct 9, 2013 at 1:32 PM, Manman Ren
<manman.ren at gmail.com>wrote:
>>>>>>>
>>>>>>>>
>>>>>>>> David,
>>>>>>>>
>>>>>>>> Thanks for reviewing!
>>>>>>>>
>>>>>>>> On Wed, Oct 9, 2013 at 11:36 AM, David Blaikie
<dblaikie at gmail.com>wrote:
>>>>>>>>
>>>>>>>>> Might be easier if these were on
Phabricator, but here are some
>>>>>>>>> thoughts:
>>>>>>>>>
>>>>>>>>> 0001:
>>>>>>>>>   This patch generally, while separated for
legibility, is
>>>>>>>>> untested & difficult to discuss in
isolation.
>>>>>>>>>
>>>>>>>> I agree, this patch adds the functionality but
does not use it, the
>>>>>>>> 2nd patch uses ref_addr.
>>>>>>>> If you think I should merge the two and commit
as a single patch,
>>>>>>>> let me know.
>>>>>>>>
>>>>>>>>
>>>>>>>>>  I may need to refer to the second patch in
reviewing this first
>>>>>>>>> one.
>>>>>>>>>   DwarfDebug.cpp:
>>>>>>>>>     computeSizeAndOffsets:
>>>>>>>>>       I believe this produces the wrong
offset for the 3rd CU and
>>>>>>>>> onwards. computeSizeAndOffset returns the
EndOffset which is absolute, not
>>>>>>>>> relative to the Offset passed in, so it
should be assigned to SecOffset,
>>>>>>>>> not added to it. (eg: if you have CUs at 0,
42, and 57 - the first pass
>>>>>>>>> through SecOffset will be zero, then
it'll be 0 + 42, then on the 3rd it'll
>>>>>>>>> be (0 + 42) + 57 which isn't right, it
should just be 57). Please add more
>>>>>>>>> test coverage while fixing this issue.
>>>>>>>>>
>>>>>>>>
>>>>>>>> computeSizeAndOffset takes an offset that is
relative to the start
>>>>>>>> of the CU and returns the offset relative to
the CU after laying out the
>>>>>>>> DIE.
>>>>>>>> The initial offset before laying out the CU DIE
is the header size,
>>>>>>>> EndOffset will be the offset relative to the CU
after laying out the whole
>>>>>>>> CU DIE.
>>>>>>>> We can think of EndOffset as the size of the
whole CU DIE.
>>>>>>>> SecOffset is the offset from the Debug Info
section, so we can update it by
>>>>>>>> adding the CU size.
>>>>>>>>
>>>>>>>>   // Offset from the beginning of debug info
section.
>>>>>>>>   unsigned SecOffset = 0;
>>>>>>>>   for (SmallVectorImpl<CompileUnit
*>::iterator I = CUs.begin(),
>>>>>>>>          E = CUs.end(); I != E; ++I) {
>>>>>>>>     (*I)->setDebugInfoOffset(SecOffset);
>>>>>>>>      unsigned Offset
>>>>>>>>       sizeof(int32_t) + // Length of
Compilation Unit Info
>>>>>>>>       sizeof(int16_t) + // DWARF version number
>>>>>>>>       sizeof(int32_t) + // Offset Into Abbrev.
Section
>>>>>>>>       sizeof(int8_t);   // Pointer Size (in
bytes)
>>>>>>>>
>>>>>>>>     unsigned EndOffset =
computeSizeAndOffset((*I)->getCUDie(),
>>>>>>>> Offset);
>>>>>>>>     SecOffset += EndOffset;
>>>>>>>>   }
>>>>>>>>
>>>>>>>
>>>>>>> Added more comments in attached patch.
>>>>>>>
>>>>>>>
>>>>>>>>
>>>>>>>>
>>>>>>>>> Eric/Manman: rough design question: compute
the absolute offset of
>>>>>>>>> each CU within the debug_info section and
describe them all relative to a
>>>>>>>>> single symbol at the start of the
debug_info section, or should we put a
>>>>>>>>> label at the start of each CU?
>>>>>>>>>
>>>>>>>>
>>>>>>>> Either way should work. But since we already
have the section
>>>>>>>> offset for each CU, describing relative to the
start of debug_info section
>>>>>>>> saves us a few symbols :)
>>>>>>>>
>>>>>>>>
>>>>>>>>>
>>>>>>>>> 0002:
>>>>>>>>>   ref_addr_relocation.ll:
>>>>>>>>>     seems a bit vague in terms of how you
test for the relocation.
>>>>>>>>> I think it'd make more sense to test
the assembly, than the reafobj output,
>>>>>>>>> that way you can test that the correct
bytes have the relocation rather
>>>>>>>>> than just that there's "some"
.debug_info relocation in the file. For an
>>>>>>>>> example, see test/DebugInfo/X86/tls.ll I
wrote - it has some "unannotated"
>>>>>>>>> bytes because we still don't have a
nice way to annotate location bytes
>>>>>>>>> that are DWARF expressions, but it's
close - I guess those should be
>>>>>>>>> CHECK-NEXTs, though. In any case, you
should be able to check a few lines
>>>>>>>>> of assembly with the # DW_AT/DW_TAG
annotation comments.
>>>>>>>>>
>>>>>>>>
>>>>>>>> I can check for ".quad .Lsection_info+38
#DW_AT_type".
>>>>>>>>
>>>>>>> Done in attached patch.
>>>>>>>
>>>>>>>>
>>>>>>>>
>>>>>>>>>      You'd need to add the tu3.cpp from
my example if you want to
>>>>>>>>> demonstrate that the relocation is actually
working as intended and
>>>>>>>>> avoiding the bogus result I showed.
>>>>>>>>>   type-unique-simple-a.ll
>>>>>>>>>     While I agree that having common test
cases helps reduce the
>>>>>>>>> number of separate invocations we have,
this test case seems like it might
>>>>>>>>> be becoming a little hard to follow
what's under test. Just going from the
>>>>>>>>> diff I'm not sure what's what.
Could you give a brief description of the
>>>>>>>>> state of type-unique-simple2 files?
What's involved? What's it meant to
>>>>>>>>> test? What's it actually testing?
>>>>>>>>>
>>>>>>>> I can add more comments. The source files are
included in the
>>>>>>>> testing case. I am checking that llvm-link only
generates a single copy of
>>>>>>>> the struct and the backend generates a single
DIE and uses ref_addr.
>>>>>>>> The changes are to check "the backend
generates a single DIE and
>>>>>>>> uses ref_addr".
>>>>>>>>
>>>>>>> Done in attached patch.
>>>>>>>
>>>>>>>>
>>>>>>>>    DIE.h:
>>>>>>>>>     checkCompileUnit could probably be
called
>>>>>>>>> "getCompileUnitOrNull", the name
"check*" seems to imply that it does some
>>>>>>>>> checking, which isn't true.
>>>>>>>>>
>>>>>>>>  Will do.
>>>>>>>>
>>>>>>> Done in attached patch.
>>>>>>>
>>>>>>>>
>>>>>>>>
>>>>>>>>>   DwarfCompileUnit.cpp:
>>>>>>>>>     the "istype || issubprogram"
check should probably be pulled
>>>>>>>>> out into a separate function, something
like "isShareableAcrossCUs" or
>>>>>>>>> something like that (please, that's not
the best name, let's discuss it
>>>>>>>>> further before we settle on a name) so that
getDIE and insertDIE are sure
>>>>>>>>> to use the same test at all times.
>>>>>>>>>
>>>>>>>> Yes, the condition is shared between getDIE and
insertDIE. I like
>>>>>>>> isSharableAcrossCUs, because that is why the
map is in DwarfDebug instead
>>>>>>>> of CompileUnit.
>>>>>>>>
>>>>>>> Done in attached patch.
>>>>>>>
>>>>>>>>
>>>>>>>>
>>>>>>>>>    Why does addDIEEntry take a form? When
does the caller get to
>>>>>>>>> choose the form rather than the callee
deciding between ref4 and ref_addr
>>>>>>>>> based on context?
>>>>>>>>>
>>>>>>>>
>>>>>>>> addDIEEntry took a form before my change and I
didn't check why it
>>>>>>>> did.
>>>>>>>> I will check if all callers always use ref4, if
it it true, I will
>>>>>>>> submit a cleanup patch first.
>>>>>>>>
>>>>>>> Done in attached patch.
>>>>>>>
>>>>>>>>
>>>>>>>>   I'm still unsure about this worklist
thing - do your current
>>>>>>>>> tests cover the need for the worklist? ie:
if we removed that logic, would
>>>>>>>>> tests fail? Can you describe a specific
sequence where the worklist is
>>>>>>>>> necessary?
>>>>>>>>>
>>>>>>>>
>>>>>>>> If we are sure that DIEs are always added to an
owner before
>>>>>>>> calling addDIEEntry, we don't need the
worklist.
>>>>>>>> But I saw cases where that was not true, I will
get a reduced
>>>>>>>> testing case.
>>>>>>>>
>>>>>>>
>>>>>>> If we try to assert both DIEs have owner in
addDIEEntry, the
>>>>>>> following testing cases will fail:
>>>>>>>     LLVM :: DebugInfo/X86/multiple-aranges.ll
>>>>>>>     LLVM :: DebugInfo/X86/ref_addr_relocation.ll
>>>>>>>     LLVM ::
DebugInfo/X86/stmt-list-multiple-compile-units.ll
>>>>>>>     LLVM :: DebugInfo/two-cus-from-same-file.ll
>>>>>>>     LLVM :: Linker/type-unique-simple-a.ll
>>>>>>>     LLVM :: Linker/type-unique-simple2.ll
>>>>>>>
>>>>>>> For ref_addr_relocation, it failed in
>>>>>>> #5  0x0000000100b169ba in
llvm::DwarfDebug::addDIEEntry
>>>>>>> (this=0x103023600, Die=0x102e14090, Attribute=73,
Entry=0x10302a9d0) at
>>>>>>>
/Users/manmanren/llvm_git/llvm/lib/CodeGen/AsmPrinter/DwarfDebug.cpp:3071
>>>>>>> #6  0x0000000100b040e0 in
llvm::CompileUnit::addType
>>>>>>> (this=0x102e13ec0, Entity=0x102e14090,
Ty={<llvm::DIScope> >>>>>>>
{<llvm::DIDescriptor> = {DbgNode = 0x102e05f30}, <No data fields>},
<No
>>>>>>> data fields>}, Attribute=73) at
>>>>>>>
/Users/manmanren/llvm_git/llvm/lib/CodeGen/AsmPrinter/DwarfCompileUnit.cpp:910
>>>>>>> #7  0x0000000100b05bff in
llvm::CompileUnit::createGlobalVariableDIE
>>>>>>> (this=0x102e13ec0, N=0x102e068c0) at
>>>>>>>
/Users/manmanren/llvm_git/llvm/lib/CodeGen/AsmPrinter/DwarfCompileUnit.cpp:1505
>>>>>>>
>>>>>>> If we look at DwarfCompileUnit.cpp:
>>>>>>>     VariableDIE = new DIE(GV.getTag());
>>>>>>>     // Add to map.
>>>>>>>     insertDIE(N, VariableDIE);
>>>>>>>
>>>>>>>     // Add name and type.
>>>>>>>     addString(VariableDIE, dwarf::DW_AT_name,
GV.getDisplayName());
>>>>>>>     addType(VariableDIE, GTy);
>>>>>>>
>>>>>>> The VariableDIE is not added to an owner yet when
calling addType.
>>>>>>>
>>>>>>
>>>>>> I believe I have addressed all review comments, the
patches are
>>>>>> re-attached here for convenience.
>>>>>>
>>>>>
>>>>> So I'm still thinking about the work list work.
>>>>>
>>>>> If we don't know which CU a DIE is in - isn't it,
necessarily, going
>>>>> to be in the current CU (& thus referenced by ref_data4
(using a CU-local
>>>>> offset), not ref_addr)?
>>>>>
>>>>
>>>> That may be true. But can we prove that?
>>>>
>>>
>>> We really shouldn't add extra complexity to the codebase just
because we
>>> don't know how the codebase works - that's what leads to
the kind of
>>> complexity we see in the debug info handling today.
>>>
>>
>>>
>>>>  There are two ways of handling this:
>>>> 1> use a worklist to be conservative
>>>> 2> do not use a worklist, but add an assertion when emitting
a DIE A,
>>>> make sure the DIE referenced with ref4 is indeed in the same CU
as DIE A.
>>>>
>>>
>>> Please just add this assertion. If it fires we'll have a test
case and a
>>> concrete justification for this complexity such that should anyone
remove
>>> it later because it looked unnecessary, they'll at least have a
failing
>>> test to explain why it was there in the first plac .
>>>
>>
>> The assertion fails even with a simple testing case when the referenced
>> DIE has an owner and the DIE itself does not have an owner.
>>
>
> OK, sorry - I should've read your description of the assertion more
> carefully. I believe the assertion you added wasn't the right thing to
test
> for.
>
> I'm not sure there is a correct assertion to add here to detect the
case
> you're describing - perhaps a complex verification after-the-fact could
be
> done, but essentially if we have a DIE that's partially constructed/has
no
> parent we should assume it's in the current unit.
>
Why should we make the assumption that a DIE without a parent at some point
should belong to the CU that is constructing the DIE?
The CU constructing a DIE will add the DIE to the context owner, which may
not belong to the CU itself.
In the case that a DIE is added to an owner in DwarfDebug, I don't think we
should try to enforce that DwarfDebug will add the DIE to the CU that
constructed the DIE earlier.

> If we can demonstrate a case where this isn't true, then we should work
to
> address that problem - until we demonstrate that, we should not (though we
> might want to search for such cases - but without type units I can't
> imagine how they could occur - we build the DIE tree for one CU at a time,
> at no point do we have DIEs under construction for multiple CUs).
>
> So if we want to build a reference to a DIE, if the DIE is not in another
> CU we should use ref4. (then the only other case is that it's either in
> this CU or it's in no known CU at all - in which case it's under
> construction and, without evidence to the contrary, will be added to the
> current CU when it's done).
>
> About the only assertion we could add would involve keeping a side-table
> of "assumptions" ("we expect this DIE will be added to this
CU") and check
> that those assumptions are fulfilled at some point.
>
In my opinion, if we can't verify the assumption with a reasonable amount
of effort, then we should not make the assumption.

Manman

>
>> For that case, we can't assume ref4 should be used. I don't
think we can
>> enforce that all DIEs must be added to a parent before calling
addDIEEntry.
>>
>> For the specific testing case, when constructing children of a scope
DIE,
>> we call addDIEEntry on the children, after that, we add the children to
the
>> scope DIE.
>> cat foo.cpp
>>
>> #include "a.hpp"
>> void f(int a) {
>>   Base t;
>> }
>> cat bar.cpp
>>
>> #include "a.hpp"
>> void f(int);
>> void g(int a) {
>>   Base t;
>> }
>> int main() {
>>   f(0);
>>   g(1);
>>   return 0;
>> }
>> cat a.hpp
>> struct Base {
>>   int a;
>> };
>>
>> Let me know if I should investigate further.
>>
>> Thanks,
>> Manman
>>
>>
>>>
>>>
>>>>
>>>> Let me know which one you prefer.
>>>>
>>>> Do you have any comments on the ref_addr patch (the 1st patch
of the
>>>> two)?
>>>>
>>>
>>> Nothing much - I wouldn't mind Eric taking a look (& would
rather you
>>> not commit this until you're committing the second patch, since
it's
>>> otherwise untested/unjustified code) on the label/offset related
stuff
>>> since I'm less familiar with that.
>>>
>>> There's one or two cases of {} on single-statement blocks you
could fix
>>> up.
>>>
>>> "DebugInfoOffset" (both the member and the functions to
set/get it)
>>> might be more meaningfully named "SectionOffset" - but
I'm not sure. Eric?
>>> Other names (DebugInfoSectionOffset?)?
>>>
>>> - David
>>>
>>
>>
>
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On Tue, Oct 15, 2013 at 1:56 PM, Manman Ren <manman.ren at gmail.com>
wrote:
>
>
>
> On Tue, Oct 15, 2013 at 1:37 PM, David Blaikie <dblaikie at
gmail.com> wrote:
>
>>
>>
>>
>> On Tue, Oct 15, 2013 at 1:22 PM, Manman Ren <manman.ren at
gmail.com> wrote:
>>
>>>
>>>
>>>
>>> On Tue, Oct 15, 2013 at 11:34 AM, David Blaikie <dblaikie at
gmail.com>wrote:
>>>
>>>>
>>>>
>>>>
>>>> On Tue, Oct 15, 2013 at 10:51 AM, Manman Ren <manman.ren at
gmail.com>wrote:
>>>>
>>>>>
>>>>>
>>>>>
>>>>> On Tue, Oct 15, 2013 at 10:10 AM, David Blaikie
<dblaikie at gmail.com>wrote:
>>>>>
>>>>>>
>>>>>>
>>>>>>
>>>>>> On Tue, Oct 15, 2013 at 10:05 AM, Manman Ren
<manman.ren at gmail.com>wrote:
>>>>>>
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>> On Wed, Oct 9, 2013 at 5:22 PM, Manman Ren
<manman.ren at gmail.com>wrote:
>>>>>>>
>>>>>>>>
>>>>>>>>
>>>>>>>>
>>>>>>>> On Wed, Oct 9, 2013 at 1:32 PM, Manman Ren
<manman.ren at gmail.com>wrote:
>>>>>>>>
>>>>>>>>>
>>>>>>>>> David,
>>>>>>>>>
>>>>>>>>> Thanks for reviewing!
>>>>>>>>>
>>>>>>>>> On Wed, Oct 9, 2013 at 11:36 AM, David
Blaikie <dblaikie at gmail.com
>>>>>>>>> > wrote:
>>>>>>>>>
>>>>>>>>>> Might be easier if these were on
Phabricator, but here are some
>>>>>>>>>> thoughts:
>>>>>>>>>>
>>>>>>>>>> 0001:
>>>>>>>>>>   This patch generally, while separated
for legibility, is
>>>>>>>>>> untested & difficult to discuss in
isolation.
>>>>>>>>>>
>>>>>>>>> I agree, this patch adds the functionality
but does not use it,
>>>>>>>>> the 2nd patch uses ref_addr.
>>>>>>>>> If you think I should merge the two and
commit as a single patch,
>>>>>>>>> let me know.
>>>>>>>>>
>>>>>>>>>
>>>>>>>>>>  I may need to refer to the second
patch in reviewing this first
>>>>>>>>>> one.
>>>>>>>>>>   DwarfDebug.cpp:
>>>>>>>>>>     computeSizeAndOffsets:
>>>>>>>>>>       I believe this produces the wrong
offset for the 3rd CU and
>>>>>>>>>> onwards. computeSizeAndOffset returns
the EndOffset which is absolute, not
>>>>>>>>>> relative to the Offset passed in, so it
should be assigned to SecOffset,
>>>>>>>>>> not added to it. (eg: if you have CUs
at 0, 42, and 57 - the first pass
>>>>>>>>>> through SecOffset will be zero, then
it'll be 0 + 42, then on the 3rd it'll
>>>>>>>>>> be (0 + 42) + 57 which isn't right,
it should just be 57). Please add more
>>>>>>>>>> test coverage while fixing this issue.
>>>>>>>>>>
>>>>>>>>>
>>>>>>>>> computeSizeAndOffset takes an offset that
is relative to the start
>>>>>>>>> of the CU and returns the offset relative
to the CU after laying out the
>>>>>>>>> DIE.
>>>>>>>>> The initial offset before laying out the CU
DIE is the header
>>>>>>>>> size, EndOffset will be the offset relative
to the CU after laying out the
>>>>>>>>> whole CU DIE.
>>>>>>>>> We can think of EndOffset as the size of
the whole CU DIE.
>>>>>>>>> SecOffset is the offset from the Debug Info
section, so we can update it by
>>>>>>>>> adding the CU size.
>>>>>>>>>
>>>>>>>>>   // Offset from the beginning of debug
info section.
>>>>>>>>>   unsigned SecOffset = 0;
>>>>>>>>>   for (SmallVectorImpl<CompileUnit
*>::iterator I = CUs.begin(),
>>>>>>>>>          E = CUs.end(); I != E; ++I) {
>>>>>>>>>     (*I)->setDebugInfoOffset(SecOffset);
>>>>>>>>>      unsigned Offset
>>>>>>>>>       sizeof(int32_t) + // Length of
Compilation Unit Info
>>>>>>>>>       sizeof(int16_t) + // DWARF version
number
>>>>>>>>>       sizeof(int32_t) + // Offset Into
Abbrev. Section
>>>>>>>>>       sizeof(int8_t);   // Pointer Size (in
bytes)
>>>>>>>>>
>>>>>>>>>     unsigned EndOffset =
computeSizeAndOffset((*I)->getCUDie(),
>>>>>>>>> Offset);
>>>>>>>>>     SecOffset += EndOffset;
>>>>>>>>>   }
>>>>>>>>>
>>>>>>>>
>>>>>>>> Added more comments in attached patch.
>>>>>>>>
>>>>>>>>
>>>>>>>>>
>>>>>>>>>
>>>>>>>>>> Eric/Manman: rough design question:
compute the absolute offset
>>>>>>>>>> of each CU within the debug_info
section and describe them all relative to
>>>>>>>>>> a single symbol at the start of the
debug_info section, or should we put a
>>>>>>>>>> label at the start of each CU?
>>>>>>>>>>
>>>>>>>>>
>>>>>>>>> Either way should work. But since we
already have the section
>>>>>>>>> offset for each CU, describing relative to
the start of debug_info section
>>>>>>>>> saves us a few symbols :)
>>>>>>>>>
>>>>>>>>>
>>>>>>>>>>
>>>>>>>>>> 0002:
>>>>>>>>>>   ref_addr_relocation.ll:
>>>>>>>>>>     seems a bit vague in terms of how
you test for the
>>>>>>>>>> relocation. I think it'd make more
sense to test the assembly, than the
>>>>>>>>>> reafobj output, that way you can test
that the correct bytes have the
>>>>>>>>>> relocation rather than just that
there's "some" .debug_info relocation in
>>>>>>>>>> the file. For an example, see
test/DebugInfo/X86/tls.ll I wrote - it has
>>>>>>>>>> some "unannotated" bytes
because we still don't have a nice way to annotate
>>>>>>>>>> location bytes that are DWARF
expressions, but it's close - I guess those
>>>>>>>>>> should be CHECK-NEXTs, though. In any
case, you should be able to check a
>>>>>>>>>> few lines of assembly with the #
DW_AT/DW_TAG annotation comments.
>>>>>>>>>>
>>>>>>>>>
>>>>>>>>> I can check for ".quad
.Lsection_info+38 #DW_AT_type".
>>>>>>>>>
>>>>>>>> Done in attached patch.
>>>>>>>>
>>>>>>>>>
>>>>>>>>>
>>>>>>>>>>      You'd need to add the tu3.cpp
from my example if you want to
>>>>>>>>>> demonstrate that the relocation is
actually working as intended and
>>>>>>>>>> avoiding the bogus result I showed.
>>>>>>>>>>   type-unique-simple-a.ll
>>>>>>>>>>     While I agree that having common
test cases helps reduce the
>>>>>>>>>> number of separate invocations we have,
this test case seems like it might
>>>>>>>>>> be becoming a little hard to follow
what's under test. Just going from the
>>>>>>>>>> diff I'm not sure what's what.
Could you give a brief description of the
>>>>>>>>>> state of type-unique-simple2 files?
What's involved? What's it meant to
>>>>>>>>>> test? What's it actually testing?
>>>>>>>>>>
>>>>>>>>> I can add more comments. The source files
are included in the
>>>>>>>>> testing case. I am checking that llvm-link
only generates a single copy of
>>>>>>>>> the struct and the backend generates a
single DIE and uses ref_addr.
>>>>>>>>> The changes are to check "the backend
generates a single DIE and
>>>>>>>>> uses ref_addr".
>>>>>>>>>
>>>>>>>> Done in attached patch.
>>>>>>>>
>>>>>>>>>
>>>>>>>>>    DIE.h:
>>>>>>>>>>     checkCompileUnit could probably be
called
>>>>>>>>>> "getCompileUnitOrNull", the
name "check*" seems to imply that it does some
>>>>>>>>>> checking, which isn't true.
>>>>>>>>>>
>>>>>>>>>  Will do.
>>>>>>>>>
>>>>>>>> Done in attached patch.
>>>>>>>>
>>>>>>>>>
>>>>>>>>>
>>>>>>>>>>   DwarfCompileUnit.cpp:
>>>>>>>>>>     the "istype ||
issubprogram" check should probably be pulled
>>>>>>>>>> out into a separate function, something
like "isShareableAcrossCUs" or
>>>>>>>>>> something like that (please, that's
not the best name, let's discuss it
>>>>>>>>>> further before we settle on a name) so
that getDIE and insertDIE are sure
>>>>>>>>>> to use the same test at all times.
>>>>>>>>>>
>>>>>>>>> Yes, the condition is shared between getDIE
and insertDIE. I like
>>>>>>>>> isSharableAcrossCUs, because that is why
the map is in DwarfDebug instead
>>>>>>>>> of CompileUnit.
>>>>>>>>>
>>>>>>>> Done in attached patch.
>>>>>>>>
>>>>>>>>>
>>>>>>>>>
>>>>>>>>>>    Why does addDIEEntry take a form?
When does the caller get to
>>>>>>>>>> choose the form rather than the callee
deciding between ref4 and ref_addr
>>>>>>>>>> based on context?
>>>>>>>>>>
>>>>>>>>>
>>>>>>>>> addDIEEntry took a form before my change
and I didn't check why it
>>>>>>>>> did.
>>>>>>>>> I will check if all callers always use
ref4, if it it true, I will
>>>>>>>>> submit a cleanup patch first.
>>>>>>>>>
>>>>>>>> Done in attached patch.
>>>>>>>>
>>>>>>>>>
>>>>>>>>>   I'm still unsure about this worklist
thing - do your current
>>>>>>>>>> tests cover the need for the worklist?
ie: if we removed that logic, would
>>>>>>>>>> tests fail? Can you describe a specific
sequence where the worklist is
>>>>>>>>>> necessary?
>>>>>>>>>>
>>>>>>>>>
>>>>>>>>> If we are sure that DIEs are always added
to an owner before
>>>>>>>>> calling addDIEEntry, we don't need the
worklist.
>>>>>>>>> But I saw cases where that was not true, I
will get a reduced
>>>>>>>>> testing case.
>>>>>>>>>
>>>>>>>>
>>>>>>>> If we try to assert both DIEs have owner in
addDIEEntry, the
>>>>>>>> following testing cases will fail:
>>>>>>>>     LLVM :: DebugInfo/X86/multiple-aranges.ll
>>>>>>>>     LLVM ::
DebugInfo/X86/ref_addr_relocation.ll
>>>>>>>>     LLVM ::
DebugInfo/X86/stmt-list-multiple-compile-units.ll
>>>>>>>>     LLVM :: DebugInfo/two-cus-from-same-file.ll
>>>>>>>>     LLVM :: Linker/type-unique-simple-a.ll
>>>>>>>>     LLVM :: Linker/type-unique-simple2.ll
>>>>>>>>
>>>>>>>> For ref_addr_relocation, it failed in
>>>>>>>> #5  0x0000000100b169ba in
llvm::DwarfDebug::addDIEEntry
>>>>>>>> (this=0x103023600, Die=0x102e14090,
Attribute=73, Entry=0x10302a9d0) at
>>>>>>>>
/Users/manmanren/llvm_git/llvm/lib/CodeGen/AsmPrinter/DwarfDebug.cpp:3071
>>>>>>>> #6  0x0000000100b040e0 in
llvm::CompileUnit::addType
>>>>>>>> (this=0x102e13ec0, Entity=0x102e14090,
Ty={<llvm::DIScope> >>>>>>>>
{<llvm::DIDescriptor> = {DbgNode = 0x102e05f30}, <No data fields>},
<No
>>>>>>>> data fields>}, Attribute=73) at
>>>>>>>>
/Users/manmanren/llvm_git/llvm/lib/CodeGen/AsmPrinter/DwarfCompileUnit.cpp:910
>>>>>>>> #7  0x0000000100b05bff in
>>>>>>>> llvm::CompileUnit::createGlobalVariableDIE
(this=0x102e13ec0,
>>>>>>>> N=0x102e068c0) at
>>>>>>>>
/Users/manmanren/llvm_git/llvm/lib/CodeGen/AsmPrinter/DwarfCompileUnit.cpp:1505
>>>>>>>>
>>>>>>>> If we look at DwarfCompileUnit.cpp:
>>>>>>>>     VariableDIE = new DIE(GV.getTag());
>>>>>>>>     // Add to map.
>>>>>>>>     insertDIE(N, VariableDIE);
>>>>>>>>
>>>>>>>>     // Add name and type.
>>>>>>>>     addString(VariableDIE, dwarf::DW_AT_name,
GV.getDisplayName());
>>>>>>>>     addType(VariableDIE, GTy);
>>>>>>>>
>>>>>>>> The VariableDIE is not added to an owner yet
when calling addType.
>>>>>>>>
>>>>>>>
>>>>>>> I believe I have addressed all review comments, the
patches are
>>>>>>> re-attached here for convenience.
>>>>>>>
>>>>>>
>>>>>> So I'm still thinking about the work list work.
>>>>>>
>>>>>> If we don't know which CU a DIE is in - isn't
it, necessarily, going
>>>>>> to be in the current CU (& thus referenced by
ref_data4 (using a CU-local
>>>>>> offset), not ref_addr)?
>>>>>>
>>>>>
>>>>> That may be true. But can we prove that?
>>>>>
>>>>
>>>> We really shouldn't add extra complexity to the codebase
just because
>>>> we don't know how the codebase works - that's what
leads to the kind of
>>>> complexity we see in the debug info handling today.
>>>>
>>>
>>>>
>>>>>  There are two ways of handling this:
>>>>> 1> use a worklist to be conservative
>>>>> 2> do not use a worklist, but add an assertion when
emitting a DIE A,
>>>>> make sure the DIE referenced with ref4 is indeed in the
same CU as DIE A.
>>>>>
>>>>
>>>> Please just add this assertion. If it fires we'll have a
test case and
>>>> a concrete justification for this complexity such that should
anyone remove
>>>> it later because it looked unnecessary, they'll at least
have a failing
>>>> test to explain why it was there in the first plac .
>>>>
>>>
>>> The assertion fails even with a simple testing case when the
referenced
>>> DIE has an owner and the DIE itself does not have an owner.
>>>
>>
>> OK, sorry - I should've read your description of the assertion more
>> carefully. I believe the assertion you added wasn't the right thing
to test
>> for.
>>
>> I'm not sure there is a correct assertion to add here to detect the
case
>> you're describing - perhaps a complex verification after-the-fact
could be
>> done, but essentially if we have a DIE that's partially
constructed/has no
>> parent we should assume it's in the current unit.
>>
>
> Why should we make the assumption that a DIE without a parent at some
> point should belong to the CU that is constructing the DIE?
>
Because the code we have today only constructs one CU at a time. I know of
no code that adds anything to prior CUs. Indeed this may become an
invariant one day when we do CU-at-a-time DWARF emission to reduce memory
overhead. There's nothing in the design today that I know of that would
make CU-at-a-time DWARF emission anything other than trivial. We build all
the DIEs for a CU in one go, then move on to the next CU - the CU_Nodes
loop in beginModule does this.

> The CU constructing a DIE will add the DIE to the context owner, which may
> not belong to the CU itself.
>
That's the question, isn't it? When is it ever /not/ the current CU
under
construction?

> In the case that a DIE is added to an owner in DwarfDebug, I don't
think
> we should try to enforce that DwarfDebug will add the DIE to the CU that
> constructed the DIE earlier.
>
My claim is that this is already an invariant. That the code you are adding
is never needed and thus is additional, unjustified/unused complexity that
comes at a cost to all future developers/development. This codebase needs
/much/ less of this than it already has, let alone adding more of it.
Though I wouldn't mind an assertion, I suspect it'll be more code than
is
really worth it to keep track of this information/state.

I think if we more to CU-at-a-time DWARF emission it'll be more obvious
that this invariant is true and cannot be violated.

>
>
>>  If we can demonstrate a case where this isn't true, then we should
work
>> to address that problem - until we demonstrate that, we should not
(though
>> we might want to search for such cases - but without type units I
can't
>> imagine how they could occur - we build the DIE tree for one CU at a
time,
>> at no point do we have DIEs under construction for multiple CUs).
>>
>> So if we want to build a reference to a DIE, if the DIE is not in
another
>> CU we should use ref4. (then the only other case is that it's
either in
>> this CU or it's in no known CU at all - in which case it's
under
>> construction and, without evidence to the contrary, will be added to
the
>> current CU when it's done).
>>
>> About the only assertion we could add would involve keeping a
side-table
>> of "assumptions" ("we expect this DIE will be added to
this CU") and check
>> that those assumptions are fulfilled at some point.
>>
> In my opinion, if we can't verify the assumption with a reasonable
amount
> of effort, then we should not make the assumption.
>
This leads to unbounded, unjustified complexity that makes the codebase
impossible to maintain. It just cannot be an acceptable method of
development.

- David

>
> Manman
>
>
>>
>>> For that case, we can't assume ref4 should be used. I don't
think we can
>>> enforce that all DIEs must be added to a parent before calling
addDIEEntry.
>>>
>>> For the specific testing case, when constructing children of a
scope
>>> DIE, we call addDIEEntry on the children, after that, we add the
children
>>> to the scope DIE.
>>> cat foo.cpp
>>>
>>> #include "a.hpp"
>>> void f(int a) {
>>>   Base t;
>>> }
>>> cat bar.cpp
>>>
>>> #include "a.hpp"
>>> void f(int);
>>> void g(int a) {
>>>   Base t;
>>> }
>>> int main() {
>>>   f(0);
>>>   g(1);
>>>   return 0;
>>> }
>>> cat a.hpp
>>> struct Base {
>>>   int a;
>>> };
>>>
>>> Let me know if I should investigate further.
>>>
>>> Thanks,
>>> Manman
>>>
>>>
>>>>
>>>>
>>>>>
>>>>> Let me know which one you prefer.
>>>>>
>>>>> Do you have any comments on the ref_addr patch (the 1st
patch of the
>>>>> two)?
>>>>>
>>>>
>>>> Nothing much - I wouldn't mind Eric taking a look (&
would rather you
>>>> not commit this until you're committing the second patch,
since it's
>>>> otherwise untested/unjustified code) on the label/offset
related stuff
>>>> since I'm less familiar with that.
>>>>
>>>> There's one or two cases of {} on single-statement blocks
you could fix
>>>> up.
>>>>
>>>> "DebugInfoOffset" (both the member and the functions
to set/get it)
>>>> might be more meaningfully named "SectionOffset" -
but I'm not sure. Eric?
>>>> Other names (DebugInfoSectionOffset?)?
>>>>
>>>> - David
>>>>
>>>
>>>
>>
>
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