[llvm] r202188 - Debug info: Support variadic functions.

[Adrian Prantl]

On Feb 25, 2014, at 13:54, Eric Christopher <echristo at gmail.com> wrote:

Thanks, Eric! I addressed everything unless explicitly stated in r202199.

On Tue, Feb 25, 2014 at 11:57 AM, Adrian Prantl <aprantl at apple.com> wrote:
>> Author: adrian
>> Date: Tue Feb 25 13:57:42 2014
>> New Revision: 202188
>> 
>> URL: http://llvm.org/viewvc/llvm-project?rev=202188&view=rev
>> Log:
>> Debug info: Support variadic functions.
>> Variadic functions have an unspecified parameter tag after the last
>> argument. In IR this is represented as an unspecified parameter in the
>> subroutine type.
>> 
>> Paired commit with CFE r202185.
>> 
>> rdar://problem/13690847
>> 
>> This re-applies r202184 + a bugfix in DwarfDebug's argument handling.
> 
> Would be nice to have more description what the bugfix is here. What
> was the difference? Did you add more to the testcase or a comment in
> some place?

With the refactoring in the follow-up commit the fix more or less became obsolete. All three places now use the canonical (and correct) implementation in DwarfUnit::constructSubprogramArguments().

> 
>> 
>> -    /// createUnspecifiedParameter - Create unspeicified type descriptor
>> +    /// createUnspecifiedParameter - Create unspecified type descriptor
>>     /// for a subroutine type.
>>     DIDescriptor createUnspecifiedParameter();
>> 
> 
> Could have been committed separately - especially since it's in a file
> by itself.
> 
>> 
>> Modified: llvm/trunk/lib/CodeGen/AsmPrinter/DwarfDebug.cpp
>> URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/CodeGen/AsmPrinter/DwarfDebug.cpp?rev=202188&r1=202187&r2=202188&view=diff
>> ==============================================================================
>> --- llvm/trunk/lib/CodeGen/AsmPrinter/DwarfDebug.cpp (original)
>> +++ llvm/trunk/lib/CodeGen/AsmPrinter/DwarfDebug.cpp Tue Feb 25 13:57:42 2014
>> @@ -403,15 +403,21 @@ DIE *DwarfDebug::updateSubprogramScopeDI
>>         DIArray Args = SPTy.getTypeArray();
>>         uint16_t SPTag = SPTy.getTag();
>>         if (SPTag == dwarf::DW_TAG_subroutine_type)
>> +          // FIXME: Use DwarfUnit::constructSubprogramArguments() here.
> 
> What's the problem here?

Code duplication in three places.

> 
>>           for (unsigned i = 1, N = Args.getNumElements(); i < N; ++i) {
>> -            DIE *Arg =
>> -                SPCU->createAndAddDIE(dwarf::DW_TAG_formal_parameter, *SPDie);
>>             DIType ATy(Args.getElement(i));
>> -            SPCU->addType(Arg, ATy);
>> -            if (ATy.isArtificial())
>> -              SPCU->addFlag(Arg, dwarf::DW_AT_artificial);
>> -            if (ATy.isObjectPointer())
>> -              SPCU->addDIEEntry(SPDie, dwarf::DW_AT_object_pointer, Arg);
>> +            if (ATy.isUnspecifiedParameter()) {
>> +              assert(i == N-1 && "ellipsis must be the last argument");
> 
> Reword this to avoid the use of ellipsis. Use unspecified parameter or
> something IR specific.
> The next line is over 80-columns as well.
> 
>>   // Collect arguments for current function.
>> -  if (LScopes.isCurrentFunctionScope(Scope))
>> +  if (LScopes.isCurrentFunctionScope(Scope)) {
>>     for (unsigned i = 0, N = CurrentFnArguments.size(); i < N; ++i)
>>       if (DbgVariable *ArgDV = CurrentFnArguments[i])
>>         if (DIE *Arg =
>> @@ -592,6 +598,16 @@ DIE *DwarfDebug::createScopeChildrenDIE(
>>             ObjectPointer = Arg;
>>         }
>> 
>> +    // Create the unspecified parameter that marks a function as variadic.
> 
> Might want to move this comment inside the conditional, or make it
> sound conditional.
> 
>> +    DISubprogram SP(Scope->getScopeNode());
>> +    assert(SP.Verify());
> 
> If this assert fires then something is really really wrong :) You
> might want to add some text here if it fails.
> 
>> +    DIArray FnArgs = SP.getType().getTypeArray();
>> +    if (FnArgs.getElement(FnArgs.getNumElements()-1).isUnspecifiedParameter()) {
>> +      DIE *Ellipsis = new DIE(dwarf::DW_TAG_unspecified_parameters);
>> +      Children.push_back(Ellipsis);
>> +    }
>> +  }
>> +
> 
> This feels awkward here. Thoughts?

We have to insert it immediately after the formal parameters and before the variables. There does not seem to be a more appropriate place than this one.

> 
>> +/// constructSubprogramArguments - Construct function argument DIEs.
>> +void DwarfUnit::constructSubprogramArguments(DIE &Buffer, DIArray Args) {
>> +    for (unsigned i = 1, N = Args.getNumElements(); i < N; ++i) {
>> +      DIDescriptor Ty = Args.getElement(i);
>> +      if (Ty.isUnspecifiedParameter()) {
>> +        assert(i == N-1 && "ellipsis must be the last argument");
> 
> Same comment as above about the text here.
> 
>>     // Add arguments. Do not add arguments for subprogram definition. They will
>>     // be handled while processing variables.
>> -    for (unsigned i = 1, N = Args.getNumElements(); i < N; ++i) {
>> -      DIE *Arg = createAndAddDIE(dwarf::DW_TAG_formal_parameter, *SPDie);
>> -      DIType ATy(Args.getElement(i));
>> -      addType(Arg, ATy);
>> -      if (ATy.isArtificial())
>> -        addFlag(Arg, dwarf::DW_AT_artificial);
>> -    }
>> +    constructSubprogramArguments(*SPDie, Args);
> 
> The comment here seems like it should go onto the function or change somewhat.
> 
>>   }
>> 
>>   if (SP.isArtificial())
>> 
>> Modified: llvm/trunk/lib/CodeGen/AsmPrinter/DwarfUnit.h
>> URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/CodeGen/AsmPrinter/DwarfUnit.h?rev=202188&r1=202187&r2=202188&view=diff
>> ==============================================================================
>> --- llvm/trunk/lib/CodeGen/AsmPrinter/DwarfUnit.h (original)
>> +++ llvm/trunk/lib/CodeGen/AsmPrinter/DwarfUnit.h Tue Feb 25 13:57:42 2014
>> @@ -476,6 +476,9 @@ protected:
>>   DIE *getOrCreateStaticMemberDIE(DIDerivedType DT);
>> 
>> private:
>> +  /// constructSubprogramArguments - Construct function argument DIEs.
>> +  void constructSubprogramArguments(DIE &Buffer, DIArray Args);
>> +
> 
> This refactoring could have been done in a separate patch.
> 
>>   /// constructTypeDIE - Construct basic type die from DIBasicType.
>>   void constructTypeDIE(DIE &Buffer, DIBasicType BTy);
>> 
>> 
>> Added: llvm/trunk/test/DebugInfo/X86/varargs.ll
>> URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/DebugInfo/X86/varargs.ll?rev=202188&view=auto
>> ==============================================================================
>> --- llvm/trunk/test/DebugInfo/X86/varargs.ll (added)
>> +++ llvm/trunk/test/DebugInfo/X86/varargs.ll Tue Feb 25 13:57:42 2014
>> @@ -0,0 +1,90 @@
>> +; RUN: llc -O0 -filetype=obj -o %t.o %s
>> +; RUN: llvm-dwarfdump -debug-dump=info %t.o | FileCheck %s
>> +;
>> +; Normal variadic function.
>> +;
>> +; CHECK: DW_TAG_subprogram
>> +; CHECK-NOT: DW_TAG
>> +; CHECK: DW_TAG_formal_parameter
>> +; CHECK-NOT: DW_TAG
>> +; CHECK: DW_TAG_unspecified_parameters
>> +;
>> +; Variadic C++ member function.
>> +;
>> +; CHECK: DW_TAG_subprogram
>> +; CHECK-NOT: DW_TAG
>> +; CHECK: DW_TAG_formal_parameter
>> +; CHECK-NOT: DW_TAG
>> +; CHECK: DW_TAG_formal_parameter
>> +; CHECK-NOT: DW_TAG
>> +; CHECK: DW_TAG_unspecified_parameters
>> +;
>> +; Variadic function pointer.
>> +;
>> +; CHECK: DW_TAG_subroutine_type
>> +; CHECK-NOT: DW_TAG
>> +; CHECK: DW_TAG_formal_parameter
>> +; CHECK-NOT: DW_TAG
>> +; CHECK: DW_TAG_unspecified_parameters
> 
> Please add more details (CHECK lines with names perhaps?) to what
> you're testing here and comments. The check and check-not lines are
> inscrutable. Also is there any reason that this is X86 only? You don't
> appear to be checking addresses or sizes.
> 
> -eric