[PATCH] DebugInfo: Allow CastInst instructions to show up around GlobalValues

Thu Aug 22 17:34:16 PDT 2013

On Thu, Aug 22, 2013 at 5:14 PM, David Blaikie <dblaikie at gmail.com> wrote:

> On Thu, Aug 22, 2013 at 5:08 PM, David Majnemer
> <david.majnemer at gmail.com> wrote:
> > On Thu, Aug 22, 2013 at 4:02 PM, David Blaikie <dblaikie at gmail.com>
> wrote:
> >>
> >>
> >> On Aug 22, 2013 3:02 PM, "David Majnemer" <david.majnemer at gmail.com>
> >> wrote:
> >> >
> >> > Hi dblaikie, echristo,
> >> >
> >> > We wouldn't emit DW_AT_location for DW_TAG_template_value_parameter if
> >> > the value the non-type template parameter had was casted.  This
> happens
> >> > even if there is no textual cast written.
> >> >
> >> > http://llvm-reviews.chandlerc.com/D1478
> >> >
> >> > Files:
> >> >   lib/CodeGen/AsmPrinter/DwarfCompileUnit.cpp
> >> >   test/DebugInfo/non-type-template-arg-cast.ll
> >> >
> >> > Index: lib/CodeGen/AsmPrinter/DwarfCompileUnit.cpp
> >> > ===================================================================
> >> > --- lib/CodeGen/AsmPrinter/DwarfCompileUnit.cpp
> >> > +++ lib/CodeGen/AsmPrinter/DwarfCompileUnit.cpp
> >> > @@ -1145,6 +1145,7 @@
> >> >    if (!VP.getName().empty())
> >> >      addString(ParamDIE, dwarf::DW_AT_name, VP.getName());
> >> >    if (Value *Val = VP.getValue()) {
> >> > +    Val = Val->stripPointerCasts();
> >>
> >> Should we strip the casts in the frontend instead? Perhaps there's some
> >> easy way to get the right/simple thing there?
> >
> > If by the "frontend" you mean CGDebugInfo::CollectTemplateParams, then we
> > could but I don't know if it would be better. For example, we would need
> to
> > fix this for Expression and Declaration.
>
> Fair enough, if there are two places that would need to be fixed in
> the frontend (well, they could presumably be adjusted to fall through
> to the same stripping code?) I can live with it here. Don't have a
> strong feeling.
>
> Do you know why these casts are introduced & whether there are any
> other things we might see here? (I prefer not to add fixes blindly
> without understanding why the fix is necessary)
>

The casts are introduced because of the padding.
- Y is struct Type but the ABI requires that we have padding at the end of
the struct. So instead, the object Y is an anonymous LLVM struct type with
the three padding bytes. The two fields are initialized with zeros and the
padding is filled with undefs.
- However, &Y's LLVM type is %struct.Type* and not of type "pointer to
anonymous struct type".

> >> >      if (ConstantInt *CI = dyn_cast<ConstantInt>(Val))
> >> >        addConstantValue(ParamDIE, CI,
> VP.getType().isUnsignedDIType());
> >> >      else if (GlobalValue *GV = dyn_cast<GlobalValue>(Val)) {
> >> > Index: test/DebugInfo/non-type-template-arg-cast.ll
> >> > ===================================================================
> >> > --- /dev/null
> >> > +++ test/DebugInfo/non-type-template-arg-cast.ll
> >> > @@ -0,0 +1,83 @@
> >> > +; REQUIRES: object-emission
> >> > +
> >> > +; RUN: llc -O0 -filetype=obj < %s > %t
> >> > +; RUN: llvm-dwarfdump %t | FileCheck %s
> >> > +
> >> > +; This was created from the following source:
> >> > +; struct Type {
> >> > +;   unsigned int Data1;
> >> > +;   unsigned short Data2, Data3;
> >> > +;   unsigned char Data4;
> >> > +; };
> >>
> >> Is this the simplest class that demonstrates the problem?
> >
> > No, I've simplified it a bit.
> >>
> >> > +; template<const Type *G>
> >> > +; const Type *func() {
> >> > +;   return G;
> >> > +; }
> >> > +
> >> > +; extern const Type Y;
> >>
> >> Do you need the extern declaration?
> >
> > If I don't declare it as extern, I get a warning about using a C++11
> > extension.
>
> Which extension would that be?
>

warning: non-type template argument referring to object 'Y' with internal
linkage is a C++11 extension [-Wc++11-extensions]

>
> > I guess we don't care about it here though. The patch is updated
> > to reflect this.
>
> Dropping the const might be nice too - just to keep it simple.
>
> Type Y;
> int main() {
>   func<&Y>();
> }
>

Will do.

>
> Also - I think we have an existing test case for non-type template
> parameters (test/DebugInfo/X86/templates.ll, probably?) - would this
> be reasonable to add there instead of adding a new test file?
>
> >>
> >> > +; const Type Y = {};
> >> > +; int main() {
> >> > +;   func<&Y>();
> >> > +; }
> >> > +
> >> > +; CHECK: DW_TAG_template_value_parameter
> >> > +; CHECK-NEXT: DW_AT_type
> >> > +; CHECK-NEXT: DW_AT_name
> >> > +; CHECK-NEXT: DW_AT_location
> >> > +; CHECK: NULL
> >> > +
> >> > +%struct.Type = type { i32, i16, i16, i8 }
> >> > +
> >> > + at Y = constant { i32, i16, i16, i8, [3 x i8] } { i32 0, i16 0, i16 0,
> i8
> >> > 0, [3 x i8] undef }, align 4
> >> > +
> >> > +; Function Attrs: uwtable
> >> > +define i32 @main() #0 {
> >> > +entry:
> >> > +  %call = call %struct.Type* @_Z4funcIXadL_Z1YEEEPK4Typev(), !dbg !28
> >> > +  ret i32 0, !dbg !29
> >> > +}
> >> > +
> >> > +; Function Attrs: nounwind uwtable
> >> > +define linkonce_odr %struct.Type* @_Z4funcIXadL_Z1YEEEPK4Typev() #1 {
> >> > +entry:
> >> > +  ret %struct.Type* bitcast ({ i32, i16, i16, i8, [3 x i8] }* @Y to
> >> > %struct.Type*), !dbg !30
> >> > +}
> >> > +
> >> > +attributes #0 = { uwtable "less-precise-fpmad"="false"
> >> > "no-frame-pointer-elim"="true" "no-frame-pointer-elim-non-leaf"="true"
> >> > "no-infs-fp-math"="false" "no-nans-fp-math"="false"
> >> > "stack-protector-buffer-size"="8" "unsafe-fp-math"="false"
> >> > "use-soft-float"="false" }
> >> > +attributes #1 = { nounwind uwtable "less-precise-fpmad"="false"
> >> > "no-frame-pointer-elim"="true" "no-frame-pointer-elim-non-leaf"="true"
> >> > "no-infs-fp-math"="false" "no-nans-fp-math"="false"
> >> > "stack-protector-buffer-size"="8" "unsafe-fp-math"="false"
> >> > "use-soft-float"="false" }
> >> > +
> >> > +!llvm.dbg.cu = !{!0}
> >> > +!llvm.module.flags = !{!27}
> >> > +
> >> > +!0 = metadata !{i32 786449, metadata !1, i32 4, metadata !"clang
> >> > version 3.4 ", i1 false, metadata !"", i32 0, metadata !2, metadata
> !2,
> >> > metadata !3, metadata !25, metadata !2, metadata !""} ; [
> >> > DW_TAG_compile_unit ]
> >> > [/usr/local/google/home/majnemer/llvm/build//var/tmp/dlb.cpp]
> >> > [DW_LANG_C_plus_plus]
> >> > +!1 = metadata !{metadata !"/var/tmp/dlb.cpp", metadata
> >> > !"/usr/local/google/home/majnemer/llvm/build"}
> >> > +!2 = metadata !{i32 0}
> >> > +!3 = metadata !{metadata !4, metadata !9}
> >> > +!4 = metadata !{i32 786478, metadata !1, metadata !5, metadata
> !"main",
> >> > metadata !"main", metadata !"", i32 14, metadata !6, i1 false, i1
> true, i32
> >> > 0, i32 0, null, i32 256, i1 false, i32 ()* @main, null, null,
> metadata !2,
> >> > i32 14} ; [ DW_TAG_subprogram ] [line 14] [def] [main]
> >> > +!5 = metadata !{i32 786473, metadata !1}          ; [
> DW_TAG_file_type
> >> > ] [/usr/local/google/home/majnemer/llvm/build//var/tmp/dlb.cpp]
> >> > +!6 = metadata !{i32 786453, i32 0, i32 0, metadata !"", i32 0, i64 0,
> >> > i64 0, i64 0, i32 0, null, metadata !7, i32 0, i32 0} ; [
> >> > DW_TAG_subroutine_type ] [line 0, size 0, align 0, offset 0] [from ]
> >> > +!7 = metadata !{metadata !8}
> >> > +!8 = metadata !{i32 786468, null, null, metadata !"int", i32 0, i64
> 32,
> >> > i64 32, i64 0, i32 0, i32 5} ; [ DW_TAG_base_type ] [int] [line 0,
> size 32,
> >> > align 32, offset 0, enc DW_ATE_signed]
> >> > +!9 = metadata !{i32 786478, metadata !1, metadata !5, metadata
> >> > !"func<&Y>", metadata !"func<&Y>", metadata
> !"_Z4funcIXadL_Z1YEEEPK4Typev",
> >> > i32 8, metadata !10, i1 false, i1 true, i32 0, i32 0, null, i32 256,
> i1
> >> > false, %struct.Type* ()* @_Z4funcIXadL_Z1YEEEPK4Typev, metadata !23,
> null,
> >> > metadata !2, i32 8} ; [ DW_TAG_subprogram ] [line 8] [def] [func<&Y>]
> >> > +!10 = metadata !{i32 786453, i32 0, i32 0, metadata !"", i32 0, i64
> 0,
> >> > i64 0, i64 0, i32 0, null, metadata !11, i32 0, i32 0} ; [
> >> > DW_TAG_subroutine_type ] [line 0, size 0, align 0, offset 0] [from ]
> >> > +!11 = metadata !{metadata !12}
> >> > +!12 = metadata !{i32 786447, null, null, metadata !"", i32 0, i64 64,
> >> > i64 64, i64 0, i32 0, metadata !13} ; [ DW_TAG_pointer_type ] [line
> 0, size
> >> > 64, align 64, offset 0] [from ]
> >> > +!13 = metadata !{i32 786470, null, null, metadata !"", i32 0, i64 0,
> >> > i64 0, i64 0, i32 0, metadata !14} ; [ DW_TAG_const_type ] [line 0,
> size 0,
> >> > align 0, offset 0] [from Type]
> >> > +!14 = metadata !{i32 786451, metadata !1, null, metadata !"Type", i32
> >> > 1, i64 96, i64 32, i32 0, i32 0, null, metadata !15, i32 0, null,
> null} ; [
> >> > DW_TAG_structure_type ] [Type] [line 1, size 96, align 32, offset 0]
> [def]
> >> > [from ]
> >> > +!15 = metadata !{metadata !16, metadata !18, metadata !20, metadata
> >> > !21}
> >> > +!16 = metadata !{i32 786445, metadata !1, metadata !14, metadata
> >> > !"Data1", i32 2, i64 32, i64 32, i64 0, i32 0, metadata !17} ; [
> >> > DW_TAG_member ] [Data1] [line 2, size 32, align 32, offset 0] [from
> unsigned
> >> > int]
> >> > +!17 = metadata !{i32 786468, null, null, metadata !"unsigned int",
> i32
> >> > 0, i64 32, i64 32, i64 0, i32 0, i32 7} ; [ DW_TAG_base_type ]
> [unsigned
> >> > int] [line 0, size 32, align 32, offset 0, enc DW_ATE_unsigned]
> >> > +!18 = metadata !{i32 786445, metadata !1, metadata !14, metadata
> >> > !"Data2", i32 3, i64 16, i64 16, i64 32, i32 0, metadata !19} ; [
> >> > DW_TAG_member ] [Data2] [line 3, size 16, align 16, offset 32] [from
> >> > unsigned short]
> >> > +!19 = metadata !{i32 786468, null, null, metadata !"unsigned short",
> >> > i32 0, i64 16, i64 16, i64 0, i32 0, i32 7} ; [ DW_TAG_base_type ]
> [unsigned
> >> > short] [line 0, size 16, align 16, offset 0, enc DW_ATE_unsigned]
> >> > +!20 = metadata !{i32 786445, metadata !1, metadata !14, metadata
> >> > !"Data3", i32 3, i64 16, i64 16, i64 48, i32 0, metadata !19} ; [
> >> > DW_TAG_member ] [Data3] [line 3, size 16, align 16, offset 48] [from
> >> > unsigned short]
> >> > +!21 = metadata !{i32 786445, metadata !1, metadata !14, metadata
> >> > !"Data4", i32 4, i64 8, i64 8, i64 64, i32 0, metadata !22} ; [
> >> > DW_TAG_member ] [Data4] [line 4, size 8, align 8, offset 64] [from
> unsigned
> >> > char]
> >> > +!22 = metadata !{i32 786468, null, null, metadata !"unsigned char",
> i32
> >> > 0, i64 8, i64 8, i64 0, i32 0, i32 8} ; [ DW_TAG_base_type ]
> [unsigned char]
> >> > [line 0, size 8, align 8, offset 0, enc DW_ATE_unsigned_char]
> >> > +!23 = metadata !{metadata !24}
> >> > +!24 = metadata !{i32 786480, null, metadata !"G", metadata !12,
> >> > %struct.Type* bitcast ({ i32, i16, i16, i8, [3 x i8] }* @Y to
> >> > %struct.Type*), null, i32 0, i32 0} ; [
> DW_TAG_template_value_parameter ]
> >> > +!25 = metadata !{metadata !26}
> >> > +!26 = metadata !{i32 786484, i32 0, null, metadata !"Y", metadata
> !"Y",
> >> > metadata !"", metadata !5, i32 13, metadata !13, i32 0, i32 1, { i32,
> i16,
> >> > i16, i8, [3 x i8] }* @Y, null} ; [ DW_TAG_variable ] [Y] [line 13]
> [def]
> >> > +!27 = metadata !{i32 2, metadata !"Dwarf Version", i32 3}
> >> > +!28 = metadata !{i32 15, i32 0, metadata !4, null}
> >> > +!29 = metadata !{i32 16, i32 0, metadata !4, null}
> >> > +!30 = metadata !{i32 9, i32 0, metadata !9, null}
> >
> >
>
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