r275040 - [CodeGen] Treat imported static local variables as declarations

Tue Jul 12 15:50:22 PDT 2016

On Tue, Jul 12, 2016 at 2:55 PM, Robinson, Paul <paul.robinson at sony.com>
wrote:

> A declaration that gets used within the CU generally does get a debug-info
> description.
>

It does except if it is a static data member:
$ cat t.cpp
struct S {
  static int i;
};
int &gv = &S::i;
$ ~/llvm/Debug+Asserts/bin/clang t.cpp -target x86_64-gnu-linux -g -S
-emit-llvm -o -
; ModuleID = 't.cpp'
source_filename = "t.cpp"
target datalayout = "e-m:e-i64:64-f80:128-n8:16:32:64-S128"
target triple = "x86_64--linux-gnu"

@_ZN1S1iE = external global i32, align 4
@gv = global i32* @_ZN1S1iE, align 8

!llvm.dbg.cu = !{!0}
!llvm.module.flags = !{!7, !8}
!llvm.ident = !{!9}

!0 = distinct !DICompileUnit(language: DW_LANG_C_plus_plus, file: !1,
producer: "clang version 3.9.0 (trunk 275169) (llvm/trunk 275188)",
isOptimized: false, runtimeVersion: 0, emissionKind: FullDebug, enums: !2,
globals: !3)
!1 = !DIFile(filename: "t.cpp", directory:
"/usr/local/google/home/majnemer")
!2 = !{}
!3 = !{!4}
!4 = distinct !DIGlobalVariable(name: "gv", scope: !0, file: !1, line: 4,
type: !5, isLocal: false, isDefinition: true, variable: i32** @gv)
!5 = !DIDerivedType(tag: DW_TAG_pointer_type, baseType: !6, size: 64,
align: 64)
!6 = !DIBasicType(name: "int", size: 32, align: 32, encoding: DW_ATE_signed)
!7 = !{i32 2, !"Dwarf Version", i32 4}
!8 = !{i32 2, !"Debug Info Version", i32 3}
!9 = !{!"clang version 3.9.0 (trunk 275169) (llvm/trunk 275188)"}

Note that there is no DIGlobalVariable for S::i.  I agree that this is not
great behavior.  I merely changed a dllimport'd template instantiation of a
static data member to behave the same way, poor, way a declaration is
treated.

> I think no DWARF-using target has dllimport (yet) so you are actually
> handling a new situation here.  Being unable to find the entity in the
> dllimport-using CU is not a friendly debugging experience.
>
> --paulr
>
>
>
> *From:* David Majnemer [mailto:david.majnemer at gmail.com]
> *Sent:* Tuesday, July 12, 2016 2:07 PM
>
> *To:* Robinson, Paul
> *Cc:* cfe-commits (cfe-commits at lists.llvm.org)
> *Subject:* Re: r275040 - [CodeGen] Treat imported static local variables
> as declarations
>
>
>
>
>
>
>
> On Tue, Jul 12, 2016 at 2:02 PM, Robinson, Paul <paul.robinson at sony.com>
> wrote:
>
> I was asking for the debug info to describe the entity as a declaration,
> rather than a definition.
>
> Instead you eliminated the debug-info description entirely.  These are
> pretty different things.
>
>
>
> I treated the dllimported entity the same way we currently treat
> declarations: ignore them.
>
> I don't have the bandwidth to generically improve debug info beyond what
> we can do for DWARF/GDB targets.
>
>
>
> --paulr
>
>
>
> *From:* David Majnemer [mailto:david.majnemer at gmail.com]
> *Sent:* Monday, July 11, 2016 12:27 PM
>
>
> *To:* Robinson, Paul
> *Cc:* cfe-commits (cfe-commits at lists.llvm.org)
> *Subject:* Re: r275040 - [CodeGen] Treat imported static local variables
> as declarations
>
>
>
>
>
>
>
> On Mon, Jul 11, 2016 at 11:45 AM, Robinson, Paul <paul.robinson at sony.com>
> wrote:
>
> It was not particularly obvious that by "static local variables" you
> actually meant "template static data members."
>
> Now I can tell that this is not addressing what I was asking about in the
> comment on r274986.
>
>
>
> I'm not sure I understand.  How is this not addressing what you are asking
> for?  We will no longer emit a DIGlobalVariable for the imported static
> data member.
>
>
>
> --paulr
>
>
>
> *From:* David Majnemer [mailto:david.majnemer at gmail.com]
> *Sent:* Monday, July 11, 2016 9:53 AM
> *To:* Robinson, Paul
> *Cc:* cfe-commits (cfe-commits at lists.llvm.org)
> *Subject:* Re: r275040 - [CodeGen] Treat imported static local variables
> as declarations
>
>
>
>
>
>
>
> On Mon, Jul 11, 2016 at 9:48 AM, Robinson, Paul <paul.robinson at sony.com>
> wrote:
>
> This changes the IR but not the debug-info metadata?
> --paulr
>
>
>
> The net effect is that the debug-info metadata is not generated for such
> static members.
>
>
>
>
> > -----Original Message-----
> > From: cfe-commits [mailto:cfe-commits-bounces at lists.llvm.org] On Behalf
> Of
> > David Majnemer via cfe-commits
> > Sent: Sunday, July 10, 2016 9:28 PM
> > To: cfe-commits at lists.llvm.org
> > Subject: r275040 - [CodeGen] Treat imported static local variables as
> > declarations
> >
> > Author: majnemer
> > Date: Sun Jul 10 23:28:21 2016
> > New Revision: 275040
> >
> > URL: http://llvm.org/viewvc/llvm-project?rev=275040&view=rev
> > Log:
> > [CodeGen] Treat imported static local variables as declarations
> >
> > Imported variables cannot really be definitions for the purposes of
> > IR generation.
> >
> > Modified:
> >     cfe/trunk/lib/CodeGen/CGDeclCXX.cpp
> >     cfe/trunk/lib/CodeGen/CodeGenModule.cpp
> >     cfe/trunk/test/CodeGenCXX/dllimport.cpp
> >
> > Modified: cfe/trunk/lib/CodeGen/CGDeclCXX.cpp
> > URL: http://llvm.org/viewvc/llvm-
> >
> project/cfe/trunk/lib/CodeGen/CGDeclCXX.cpp?rev=275040&r1=275039&r2=275040
> > &view=diff
> >
> ==========================================================================
> > ====
> > --- cfe/trunk/lib/CodeGen/CGDeclCXX.cpp (original)
> > +++ cfe/trunk/lib/CodeGen/CGDeclCXX.cpp Sun Jul 10 23:28:21 2016
> > @@ -323,10 +323,6 @@ CodeGenModule::EmitCXXGlobalVarDeclInitF
> >         D->hasAttr<CUDASharedAttr>()))
> >      return;
> >
> > -  // DLL imported variables will be initialized by the export side.
> > -  if (D->hasAttr<DLLImportAttr>())
> > -    return;
> > -
> >    // Check if we've already initialized this decl.
> >    auto I = DelayedCXXInitPosition.find(D);
> >    if (I != DelayedCXXInitPosition.end() && I->second == ~0U)
> >
> > Modified: cfe/trunk/lib/CodeGen/CodeGenModule.cpp
> > URL: http://llvm.org/viewvc/llvm-
> >
> project/cfe/trunk/lib/CodeGen/CodeGenModule.cpp?rev=275040&r1=275039&r2=27
> > 5040&view=diff
> >
> ==========================================================================
> > ====
> > --- cfe/trunk/lib/CodeGen/CodeGenModule.cpp (original)
> > +++ cfe/trunk/lib/CodeGen/CodeGenModule.cpp Sun Jul 10 23:28:21 2016
> > @@ -2851,6 +2851,10 @@ static void ReplaceUsesOfNonProtoTypeWit
> >  }
> >
> >  void CodeGenModule::HandleCXXStaticMemberVarInstantiation(VarDecl *VD) {
> > +  auto DK = VD->isThisDeclarationADefinition();
> > +  if (DK == VarDecl::Definition && VD->hasAttr<DLLImportAttr>())
> > +    return;
> > +
> >    TemplateSpecializationKind TSK = VD->getTemplateSpecializationKind();
> >    // If we have a definition, this might be a deferred decl. If the
> >    // instantiation is explicit, make sure we emit it at the end.
> >
> > Modified: cfe/trunk/test/CodeGenCXX/dllimport.cpp
> > URL: http://llvm.org/viewvc/llvm-
> >
> project/cfe/trunk/test/CodeGenCXX/dllimport.cpp?rev=275040&r1=275039&r2=27
> > 5040&view=diff
> >
> ==========================================================================
> > ====
> > --- cfe/trunk/test/CodeGenCXX/dllimport.cpp (original)
> > +++ cfe/trunk/test/CodeGenCXX/dllimport.cpp Sun Jul 10 23:28:21 2016
> > @@ -676,7 +676,7 @@ namespace ClassTemplateStaticDef {
> >      static int x;
> >    };
> >    template <typename T> int S<T>::x;
> > -  // MSC-DAG: @"\01?x@?$S at H@ClassTemplateStaticDef@@2HA" =
> > available_externally dllimport global i32 0
> > +  // MSC-DAG: @"\01?x@?$S at H@ClassTemplateStaticDef@@2HA" = external
> > dllimport global i32
> >    int f() { return S<int>::x; }
> >
> >    // Partial class template specialization static field:
> > @@ -685,7 +685,7 @@ namespace ClassTemplateStaticDef {
> >      static int x;
> >    };
> >    template <typename A> int T<A*>::x;
> > -  // GNU-DAG: @_ZN22ClassTemplateStaticDef1TIPvE1xE =
> > available_externally dllimport global i32 0
> > +  // GNU-DAG: @_ZN22ClassTemplateStaticDef1TIPvE1xE = external dllimport
> > global i32
> >    int g() { return T<void*>::x; }
> >  }
> >
> >
> >
> > _______________________________________________
> > cfe-commits mailing list
> > cfe-commits at lists.llvm.org
> > http://lists.llvm.org/cgi-bin/mailman/listinfo/cfe-commits
>
>
>
>
>
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