[llvm] r200569 - DebugInfo: Flag type unit references as declarations

[David Blaikie]

On Fri, Jan 31, 2014 at 2:08 PM, Robinson, Paul <
Paul_Robinson at playstation.sony.com> wrote:

> This just seems wrong.


How so? (yeah, I'd sort of like it if the debugger assumed that a
DW_TAG_class/structure with a DW_AT_signature was assumed to be a
declaration (of sorts)) I can think of a few ways it seems wrong, but
curious what you've got in mind.


>  What prompted it?
>

Several failures in gdb.cp/m-static.exp in the GDB 7.5 test suite. (there's
still one more failure I'm investigating most likely due to missing
DW_AT_stmt_list on type units)

The story goes something like this:

* Type goes in a type unit.
* 'skeletal' type (DW_TAG_class with a DW_AT_signature) goes in the compile
unit.
* but now you want to reference one of the members of the type from within
the compile unit (in m-static's case, it's because you have an out-of-line
definition of a static member variable), so insert a declaration of that
particular member into the 'skeletal' type.

This freaks out GDB because it assumes the type with members (even though
it has DW_AT_signature) is a definition, it seems.

I can roll back the patch locally to show/demonstrate more specifically
what the failure mode is.


> --paulr
>
> > -----Original Message-----
> > From: llvm-commits-bounces at cs.uiuc.edu [mailto:llvm-commits-
> > bounces at cs.uiuc.edu] On Behalf Of David Blaikie
> > Sent: Friday, January 31, 2014 11:52 AM
> > To: llvm-commits at cs.uiuc.edu
> > Subject: [llvm] r200569 - DebugInfo: Flag type unit references as
> > declarations
> >
> > Author: dblaikie
> > Date: Fri Jan 31 13:52:26 2014
> > New Revision: 200569
> >
> > URL: http://llvm.org/viewvc/llvm-project?rev=200569&view=rev
> > Log:
> > DebugInfo: Flag type unit references as declarations
> >
> > This ensures DWARF consumers don't confuse these references for
> > definitions. I'd argue it might be nice to improve debuggers so we don't
> > need this, but it's just one field in an abbreviation anyway - so it
> > doesn't seem worth the fight.
> >
> > Modified:
> >     llvm/trunk/lib/CodeGen/AsmPrinter/DwarfDebug.cpp
> >     llvm/trunk/test/DebugInfo/X86/generate-odr-hash.ll
> >
> > Modified: llvm/trunk/lib/CodeGen/AsmPrinter/DwarfDebug.cpp
> > URL: http://llvm.org/viewvc/llvm-
> > project/llvm/trunk/lib/CodeGen/AsmPrinter/DwarfDebug.cpp?rev=200569&r1=2
> > 00568&r2=200569&view=diff
> > ========================================================================
> > ======
> > --- llvm/trunk/lib/CodeGen/AsmPrinter/DwarfDebug.cpp (original)
> > +++ llvm/trunk/lib/CodeGen/AsmPrinter/DwarfDebug.cpp Fri Jan 31 13:52:26
> > 2014
> > @@ -3016,6 +3016,11 @@ void DwarfDebug::emitDebugStrDWO() {
> >  void DwarfDebug::addDwarfTypeUnitType(DICompileUnit CUNode,
> >                                        StringRef Identifier, DIE
> > *RefDie,
> >                                        DICompositeType CTy) {
> > +  // Flag the type unit reference as a declaration so that if it
> > contains
> > +  // members (implicit special members, static data member definitions,
> > member
> > +  // declarations for definitions in this CU, etc) consumers don't get
> > confused
> > +  // and think this is a full definition.
> > +  CUMap.begin()->second->addFlag(RefDie, dwarf::DW_AT_declaration);
> >
> >    const DwarfTypeUnit *&TU = DwarfTypeUnits[CTy];
> >    if (TU) {
> >
> > Modified: llvm/trunk/test/DebugInfo/X86/generate-odr-hash.ll
> > URL: http://llvm.org/viewvc/llvm-
> > project/llvm/trunk/test/DebugInfo/X86/generate-odr-
> > hash.ll?rev=200569&r1=200568&r2=200569&view=diff
> > ========================================================================
> > ======
> > --- llvm/trunk/test/DebugInfo/X86/generate-odr-hash.ll (original)
> > +++ llvm/trunk/test/DebugInfo/X86/generate-odr-hash.ll Fri Jan 31
> > 13:52:26 2014
> > @@ -51,8 +51,10 @@
> >  ; CHECK: Compile Unit: length = [[CU_SIZE:[0-9a-f]+]]
> >
> >  ; CHECK: DW_TAG_structure_type
> > +; CHECK-NEXT: DW_AT_declaration
> >  ; CHECK-NEXT: DW_AT_signature
> >  ; CHECK: DW_TAG_class_type
> > +; CHECK-NEXT: DW_AT_declaration
> >  ; CHECK-NEXT: DW_AT_signature
> >
> >  ; Ensure the CU-local type 'walrus' is not placed in a type unit.
> >
> >
> > _______________________________________________
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>
>
>
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