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

Thu Aug 22 17:14:53 PDT 2013

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)

>> >      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?

> 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>();
}

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}
>
>