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

Thu Aug 22 17:41:19 PDT 2013

On Thu, Aug 22, 2013 at 5:34 PM, David Majnemer
<david.majnemer at gmail.com> wrote:
> 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".

OK - thanks for the explanation. Yeah, that sort of feels like a
frontend concern & thus a frontend issue to translate this back into a
pointer to struct.Type...

I'm tossing this up. Might discuss it with you & Eric tomorrow - it's
not important, I'm just indecisive.

>
>>
>> >> >      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'm guessing that was because it was 'const. Without the const it
seems to go away.

Please drop the {} initialization too.

>
>>
>>
>> > 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}
>> >
>> >
>
>