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

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)?

Even in the not-too-distant type unit future, we'd essentially have a stack
of units (this CU lead us to produce this TU which lead us to produce this
other TU, etc) but the creation of one (compile or type) unit wouldn't ever
cause us to insert new DIEs into previous/earlier units) so far as I can
think of...
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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? 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.

Let me know which one you prefer.

Do you have any comments on the ref_addr patch (the 1st patch of the two)?

Thanks,
Manman

> Even in the not-too-distant type unit future, we'd essentially have a
> stack of units (this CU lead us to produce this TU which lead us to produce
> this other TU, etc) but the creation of one (compile or type) unit
wouldn't
> ever cause us to insert new DIEs into previous/earlier units) so far as I
> can think of...
>
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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 place.

>
> 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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