[llvm] r218041 - Always emit DW_AT_declaration attribute when the variable isn't a definition.

[David Blaikie]

On Thu, Sep 18, 2014 at 9:51 AM, Frédéric Riss <friss at apple.com> wrote:

> I pushed a partial revert in r218041 that should fix it.
>

Thanks - helps to get the bots green sooner rather than later.

Are you planning to investigate a deeper fix here? (at some point, at least
a test case would be good so we can catch this with the regression suite,
rather than waiting for the bot to pick it up)


>
> Fred
>
> On 18 Sep 2014, at 17:48, David Blaikie <dblaikie at gmail.com> wrote:
>
> Here's a simple example:
>
>   namespace x {
>     int i = 3;
>   }
>   int j = x::i;
>
> LLVM will emit a declaration for 'i' in namespace x and a definition at
> the CU scope referencing the declaration. With your change, we end up
> omitting the DW_AT_declaration on the declaration of 'i'. The debugger then
> thinks it's a definition without a location, so any attempt to use/print
> the variable produces "this value has been optimized away".
>
> A couple of side notes:
>
> 1) We should ideally not use "Verify()" for any debug info functionality -
> it should be enough to test "isBlah" methods. Any time isBlah is true but
> Verify fails is a bug we should fix at some point - I think that's a
> valid/useful invariant, but I could be wrong.
>
> 2) we don't actually need to separate declaration and definition in this
> way, just because the variable is inside a namespace - so if you happen to
> fix this by removing the separation of declaration from definition, that's
> OK too (& a minor win to reduce debug info size)
>
> On Thu, Sep 18, 2014 at 8:28 AM, Frédéric Riss <friss at apple.com> wrote:
>
>>
>> On 18 Sep 2014, at 17:23, David Blaikie <dblaikie at gmail.com> wrote:
>>
>> Looks like this might've regressed some debug scenarios:
>>
>> http://lab.llvm.org:8011/builders/clang-x86_64-ubuntu-gdb-75/builds/17377
>>
>> (could be r218040, but it seems like the less likely candidate of the two
>> on the blame list)
>>
>>
>> I’ve seen it. I sent a mail to the review thread asking for some help
>> from someone that can run the test suite.
>>
>> Fred
>>
>> On Thu, Sep 18, 2014 at 2:38 AM, Frederic Riss <friss at apple.com> wrote:
>>
>>> Author: friss
>>> Date: Thu Sep 18 04:38:23 2014
>>> New Revision: 218041
>>>
>>> URL: http://llvm.org/viewvc/llvm-project?rev=218041&view=rev
>>> Log:
>>> Always emit DW_AT_declaration attribute when the variable isn't a
>>> definition.
>>>
>>> Summary:
>>> This doesn't show up today as we don't emit decalration only variables.
>>> This
>>> will be tested when the followup patches implementing import of forward
>>> declared entities lands in clang.
>>>
>>> Reviewers: echristo, dblaikie, aprantl
>>>
>>> Subscribers: llvm-commits
>>>
>>> Differential Revision: http://reviews.llvm.org/D5382
>>>
>>> Modified:
>>>     llvm/trunk/lib/CodeGen/AsmPrinter/DwarfUnit.cpp
>>>
>>> Modified: llvm/trunk/lib/CodeGen/AsmPrinter/DwarfUnit.cpp
>>> URL:
>>> http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/CodeGen/AsmPrinter/DwarfUnit.cpp?rev=218041&r1=218040&r2=218041&view=diff
>>>
>>> ==============================================================================
>>> --- llvm/trunk/lib/CodeGen/AsmPrinter/DwarfUnit.cpp (original)
>>> +++ llvm/trunk/lib/CodeGen/AsmPrinter/DwarfUnit.cpp Thu Sep 18 04:38:23
>>> 2014
>>> @@ -1670,6 +1670,9 @@ void DwarfCompileUnit::createGlobalVaria
>>>        DD->addArangeLabel(SymbolCU(this, Sym));
>>>        addOpAddress(*Loc, Sym);
>>>      }
>>> +    // A static member's declaration is already flagged as such.
>>> +    if (!SDMDecl.Verify() && !GV.isDefinition())
>>> +      addFlag(*VariableDIE, dwarf::DW_AT_declaration);
>>>      // Do not create specification DIE if context is either compile unit
>>>      // or a subprogram.
>>>      if (GVContext && GV.isDefinition() && !GVContext.isCompileUnit() &&
>>> @@ -1678,9 +1681,6 @@ void DwarfCompileUnit::createGlobalVaria
>>>        VariableSpecDIE = &createAndAddDIE(dwarf::DW_TAG_variable,
>>> UnitDie);
>>>        addDIEEntry(*VariableSpecDIE, dwarf::DW_AT_specification,
>>> *VariableDIE);
>>>        addBlock(*VariableSpecDIE, dwarf::DW_AT_location, Loc);
>>> -      // A static member's declaration is already flagged as such.
>>> -      if (!SDMDecl.Verify())
>>> -        addFlag(*VariableDIE, dwarf::DW_AT_declaration);
>>>      } else {
>>>        addBlock(*VariableDIE, dwarf::DW_AT_location, Loc);
>>>      }
>>>
>>>
>>> _______________________________________________
>>> llvm-commits mailing list
>>> llvm-commits at cs.uiuc.edu
>>> http://lists.cs.uiuc.edu/mailman/listinfo/llvm-commits
>>>
>>
>>
>>
>
>
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