[llvm] r203690 - When computing the size of a base type be conservative if the type

Wed Mar 12 14:01:20 PDT 2014

On Wed, Mar 12, 2014 at 1:48 PM, Eric Christopher <echristo at gmail.com> wrote:
> Realized some more elaboration may help here:
>
> Basically what was happening is that we were determining that the size
> of the base class was 0 as it was a declaration without size (with the
> vtable emission optimization for debug info) and so we were noticing
> that the size of the field wasn't the size of the base type for the
> field. This was because we didn't know the size of the field.

Sort of the other way around, right - we knew the size of the field
(represented by a DIDerivedType - for those following at home this
"derived" has nothing to do with C++ inheritance, we 'derive' one type
from another to represent things like member variables - so an int
member variable is derived from the int type) but not the size of the
underlying ("base" in this parlance) type because we only had a
declaration.

(for other readers: note in the example there is no inheritance -
there's a dynamic class and a non-dynamic class with the dynamic class
as a member. The LLVM IR metadata representation of this is to have a
DW_TAG_member "DIDerivedType" derived from the DICompositeType
representing 'foo' - but we only emit the declaration of 'foo' because
we'll emit the definition along with the vtable in some other TU (note
the declared-but-not-defined-here virtual dtor))

I'm somewhat inclined to rename some of the naming here to avoid the
use of the word "base" in favor of "underlying" - the "base"
terminology seems to just be here - it doesn't leak out into the
DIDerivedType itself at least.

>
> -eric
>
> On Wed, Mar 12, 2014 at 11:18 AM, Eric Christopher <echristo at gmail.com> wrote:
>> Author: echristo
>> Date: Wed Mar 12 13:18:05 2014
>> New Revision: 203690
>>
>> URL: http://llvm.org/viewvc/llvm-project?rev=203690&view=rev
>> Log:
>> When computing the size of a base type be conservative if the type
>> is a declaration and return the size of the type.
>>
>> Added:
>>     llvm/trunk/test/DebugInfo/decl-derived-member.ll
>> Modified:
>>     llvm/trunk/lib/CodeGen/AsmPrinter/DwarfUnit.cpp
>>
>> Modified: llvm/trunk/lib/CodeGen/AsmPrinter/DwarfUnit.cpp
>> URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/CodeGen/AsmPrinter/DwarfUnit.cpp?rev=203690&r1=203689&r2=203690&view=diff
>> ==============================================================================
>> --- llvm/trunk/lib/CodeGen/AsmPrinter/DwarfUnit.cpp (original)
>> +++ llvm/trunk/lib/CodeGen/AsmPrinter/DwarfUnit.cpp Wed Mar 12 13:18:05 2014
>> @@ -751,8 +751,9 @@ static uint64_t getBaseTypeSize(DwarfDeb
>>
>>    DIType BaseType = DD->resolve(Ty.getTypeDerivedFrom());
>>
>> -  // If this type is not derived from any type then take conservative approach.
>> -  if (!BaseType.isValid())
>> +  // If this type is not derived from any type or the type is a declaration then
>> +  // take conservative approach.
>> +  if (!BaseType.isValid() || BaseType.isForwardDecl())
>>      return Ty.getSizeInBits();
>>
>>    // If this is a derived type, go ahead and get the base type, unless it's a
>>
>> Added: llvm/trunk/test/DebugInfo/decl-derived-member.ll
>> URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/DebugInfo/decl-derived-member.ll?rev=203690&view=auto
>> ==============================================================================
>> --- llvm/trunk/test/DebugInfo/decl-derived-member.ll (added)
>> +++ llvm/trunk/test/DebugInfo/decl-derived-member.ll Wed Mar 12 13:18:05 2014
>> @@ -0,0 +1,142 @@
>> +; REQUIRES: object-emission
>> +
>> +; RUN: %llc_dwarf -O0 -filetype=obj %s -o %t
>> +; RUN: llvm-dwarfdump %t | FileCheck %s
>> +
>> +; Testcase from:
>> +; struct base {
>> +;  virtual ~base();
>> +; };
>> +; struct foo {
>> +;  base b;
>> +; };
>> +; foo f;
>> +
>> +; Where member b should be seen as a field at an offset and not a bitfield.
>> +
>> +; CHECK: DW_AT_member
>> +; CHECK: DW_AT_name{{.*}}"b"
>> +; CHECK-NOT: DW_AT_bit_offset
>> +
>> + at f = global %struct.foo zeroinitializer, align 8
>> + at __dso_handle = external global i8
>> + at _ZTV4base = external unnamed_addr constant [4 x i8*]
>> + at llvm.global_ctors = appending global [1 x { i32, void ()* }] [{ i32, void ()* } { i32 65535, void ()* @_GLOBAL__I_a }]
>> +
>> +define internal void @__cxx_global_var_init() section ".text.startup" {
>> +entry:
>> +  call void @_ZN3fooC2Ev(%struct.foo* @f) #2, !dbg !35
>> +  %0 = call i32 @__cxa_atexit(void (i8*)* bitcast (void (%struct.foo*)* @_ZN3fooD2Ev to void (i8*)*), i8* bitcast (%struct.foo* @f to i8*), i8* @__dso_handle) #2, !dbg !35
>> +  ret void, !dbg !35
>> +}
>> +
>> +; Function Attrs: inlinehint nounwind uwtable
>> +define linkonce_odr void @_ZN3fooC2Ev(%struct.foo* %this) unnamed_addr #0 align 2 {
>> +entry:
>> +  %this.addr = alloca %struct.foo*, align 8
>> +  store %struct.foo* %this, %struct.foo** %this.addr, align 8
>> +  call void @llvm.dbg.declare(metadata !{%struct.foo** %this.addr}, metadata !36), !dbg !38
>> +  %this1 = load %struct.foo** %this.addr
>> +  %b = getelementptr inbounds %struct.foo* %this1, i32 0, i32 0, !dbg !39
>> +  call void @_ZN4baseC2Ev(%struct.base* %b) #2, !dbg !39
>> +  ret void, !dbg !39
>> +}
>> +
>> +; Function Attrs: inlinehint uwtable
>> +define linkonce_odr void @_ZN3fooD2Ev(%struct.foo* %this) unnamed_addr #1 align 2 {
>> +entry:
>> +  %this.addr = alloca %struct.foo*, align 8
>> +  store %struct.foo* %this, %struct.foo** %this.addr, align 8
>> +  call void @llvm.dbg.declare(metadata !{%struct.foo** %this.addr}, metadata !40), !dbg !41
>> +  %this1 = load %struct.foo** %this.addr
>> +  %b = getelementptr inbounds %struct.foo* %this1, i32 0, i32 0, !dbg !42
>> +  call void @_ZN4baseD1Ev(%struct.base* %b), !dbg !42
>> +  ret void, !dbg !44
>> +}
>> +
>> +; Function Attrs: nounwind
>> +declare i32 @__cxa_atexit(void (i8*)*, i8*, i8*) #2
>> +
>> +; Function Attrs: nounwind readnone
>> +declare void @llvm.dbg.declare(metadata, metadata) #3
>> +
>> +declare void @_ZN4baseD1Ev(%struct.base*) #4
>> +
>> +; Function Attrs: inlinehint nounwind uwtable
>> +define linkonce_odr void @_ZN4baseC2Ev(%struct.base* %this) unnamed_addr #0 align 2 {
>> +entry:
>> +  %this.addr = alloca %struct.base*, align 8
>> +  store %struct.base* %this, %struct.base** %this.addr, align 8
>> +  call void @llvm.dbg.declare(metadata !{%struct.base** %this.addr}, metadata !45), !dbg !47
>> +  %this1 = load %struct.base** %this.addr
>> +  %0 = bitcast %struct.base* %this1 to i8***, !dbg !48
>> +  store i8** getelementptr inbounds ([4 x i8*]* @_ZTV4base, i64 0, i64 2), i8*** %0, !dbg !48
>> +  ret void, !dbg !48
>> +}
>> +
>> +define internal void @_GLOBAL__I_a() section ".text.startup" {
>> +entry:
>> +  call void @__cxx_global_var_init(), !dbg !49
>> +  ret void, !dbg !49
>> +}
>> +
>> +attributes #0 = { inlinehint nounwind uwtable "less-precise-fpmad"="false" "no-frame-pointer-elim"="true" "no-frame-pointer-elim-non-leaf" "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 = { inlinehint uwtable "less-precise-fpmad"="false" "no-frame-pointer-elim"="true" "no-frame-pointer-elim-non-leaf" "no-infs-fp-math"="false" "no-nans-fp-math"="false" "stack-protector-buffer-size"="8" "unsafe-fp-math"="false" "use-soft-float"="false" }
>> +attributes #2 = { nounwind }
>> +attributes #3 = { nounwind readnone }
>> +attributes #4 = { "less-precise-fpmad"="false" "no-frame-pointer-elim"="true" "no-frame-pointer-elim-non-leaf" "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 = !{!32, !33}
>> +!llvm.ident = !{!34}
>> +
>> +!0 = metadata !{i32 786449, metadata !1, i32 4, metadata !"clang version 3.5.0 (trunk 203673) (llvm/trunk 203681)", i1 false, metadata !"", i32 0, metadata !2, metadata !3, metadata !8, metadata !30, metadata !2, metadata !"", i32 1} ; [ DW_TAG_compile_unit ] [/usr/local/google/home/echristo/foo.cc] [DW_LANG_C_plus_plus]
>> +!1 = metadata !{metadata !"foo.cc", metadata !"/usr/local/google/home/echristo"}
>> +!2 = metadata !{}
>> +!3 = metadata !{metadata !4, metadata !7}
>> +!4 = metadata !{i32 786451, metadata !1, null, metadata !"foo", i32 5, i64 64, i64 64, i32 0, i32 0, null, metadata !5, i32 0, null, null, metadata !"_ZTS3foo"} ; [ DW_TAG_structure_type ] [foo] [line 5, size 64, align 64, offset 0] [def] [from ]
>> +!5 = metadata !{metadata !6}
>> +!6 = metadata !{i32 786445, metadata !1, metadata !"_ZTS3foo", metadata !"b", i32 6, i64 64, i64 64, i64 0, i32 0, metadata !"_ZTS4base"} ; [ DW_TAG_member ] [b] [line 6, size 64, align 64, offset 0] [from _ZTS4base]
>> +!7 = metadata !{i32 786451, metadata !1, null, metadata !"base", i32 1, i64 0, i64 0, i32 0, i32 4, null, null, i32 0, null, null, metadata !"_ZTS4base"} ; [ DW_TAG_structure_type ] [base] [line 1, size 0, align 0, offset 0] [decl] [from ]
>> +!8 = metadata !{metadata !9, metadata !13, metadata !19, metadata !22, metadata !28}
>> +!9 = metadata !{i32 786478, metadata !1, metadata !10, metadata !"__cxx_global_var_init", metadata !"__cxx_global_var_init", metadata !"", i32 9, metadata !11, i1 true, i1 true, i32 0, i32 0, null, i32 256, i1 false, void ()* @__cxx_global_var_init, null, null, metadata !2, i32 9} ; [ DW_TAG_subprogram ] [line 9] [local] [def] [__cxx_global_var_init]
>> +!10 = metadata !{i32 786473, metadata !1}         ; [ DW_TAG_file_type ] [/usr/local/google/home/echristo/foo.cc]
>> +!11 = metadata !{i32 786453, i32 0, null, metadata !"", i32 0, i64 0, i64 0, i64 0, i32 0, null, metadata !12, i32 0, null, null, null} ; [ DW_TAG_subroutine_type ] [line 0, size 0, align 0, offset 0] [from ]
>> +!12 = metadata !{null}
>> +!13 = metadata !{i32 786478, metadata !1, metadata !"_ZTS3foo", metadata !"~foo", metadata !"~foo", metadata !"_ZN3fooD2Ev", i32 5, metadata !14, i1 false, i1 true, i32 0, i32 0, null, i32 320, i1 false, void (%struct.foo*)* @_ZN3fooD2Ev, null, metadata !17, metadata !2, i32 5} ; [ DW_TAG_subprogram ] [line 5] [def] [~foo]
>> +!14 = metadata !{i32 786453, i32 0, null, metadata !"", i32 0, i64 0, i64 0, i64 0, i32 0, null, metadata !15, i32 0, null, null, null} ; [ DW_TAG_subroutine_type ] [line 0, size 0, align 0, offset 0] [from ]
>> +!15 = metadata !{null, metadata !16}
>> +!16 = metadata !{i32 786447, null, null, metadata !"", i32 0, i64 64, i64 64, i64 0, i32 1088, metadata !"_ZTS3foo"} ; [ DW_TAG_pointer_type ] [line 0, size 64, align 64, offset 0] [artificial] [from _ZTS3foo]
>> +!17 = metadata !{i32 786478, null, metadata !"_ZTS3foo", metadata !"~foo", metadata !"~foo", metadata !"", i32 0, metadata !14, i1 false, i1 false, i32 0, i32 0, null, i32 320, i1 false, null, null, i32 0, metadata !18, i32 0} ; [ DW_TAG_subprogram ] [line 0] [~foo]
>> +!18 = metadata !{i32 786468}
>> +!19 = metadata !{i32 786478, metadata !1, metadata !"_ZTS3foo", metadata !"foo", metadata !"foo", metadata !"_ZN3fooC2Ev", i32 5, metadata !14, i1 false, i1 true, i32 0, i32 0, null, i32 320, i1 false, void (%struct.foo*)* @_ZN3fooC2Ev, null, metadata !20, metadata !2, i32 5} ; [ DW_TAG_subprogram ] [line 5] [def] [foo]
>> +!20 = metadata !{i32 786478, null, metadata !"_ZTS3foo", metadata !"foo", metadata !"foo", metadata !"", i32 0, metadata !14, i1 false, i1 false, i32 0, i32 0, null, i32 320, i1 false, null, null, i32 0, metadata !21, i32 0} ; [ DW_TAG_subprogram ] [line 0] [foo]
>> +!21 = metadata !{i32 786468}
>> +!22 = metadata !{i32 786478, metadata !1, metadata !"_ZTS4base", metadata !"base", metadata !"base", metadata !"_ZN4baseC2Ev", i32 1, metadata !23, i1 false, i1 true, i32 0, i32 0, null, i32 320, i1 false, void (%struct.base*)* @_ZN4baseC2Ev, null, metadata !26, metadata !2, i32 1} ; [ DW_TAG_subprogram ] [line 1] [def] [base]
>> +!23 = metadata !{i32 786453, i32 0, null, metadata !"", i32 0, i64 0, i64 0, i64 0, i32 0, null, metadata !24, i32 0, null, null, null} ; [ DW_TAG_subroutine_type ] [line 0, size 0, align 0, offset 0] [from ]
>> +!24 = metadata !{null, metadata !25}
>> +!25 = metadata !{i32 786447, null, null, metadata !"", i32 0, i64 64, i64 64, i64 0, i32 1088, metadata !"_ZTS4base"} ; [ DW_TAG_pointer_type ] [line 0, size 64, align 64, offset 0] [artificial] [from _ZTS4base]
>> +!26 = metadata !{i32 786478, null, metadata !"_ZTS4base", metadata !"base", metadata !"base", metadata !"", i32 0, metadata !23, i1 false, i1 false, i32 0, i32 0, null, i32 320, i1 false, null, null, i32 0, metadata !27, i32 0} ; [ DW_TAG_subprogram ] [line 0] [base]
>> +!27 = metadata !{i32 786468}
>> +!28 = metadata !{i32 786478, metadata !1, metadata !10, metadata !"", metadata !"", metadata !"_GLOBAL__I_a", i32 1, metadata !29, i1 true, i1 true, i32 0, i32 0, null, i32 64, i1 false, void ()* @_GLOBAL__I_a, null, null, metadata !2, i32 1} ; [ DW_TAG_subprogram ] [line 1] [local] [def]
>> +!29 = metadata !{i32 786453, i32 0, null, metadata !"", i32 0, i64 0, i64 0, i64 0, i32 0, null, metadata !2, i32 0, null, null, null} ; [ DW_TAG_subroutine_type ] [line 0, size 0, align 0, offset 0] [from ]
>> +!30 = metadata !{metadata !31}
>> +!31 = metadata !{i32 786484, i32 0, null, metadata !"f", metadata !"f", metadata !"", metadata !10, i32 9, metadata !4, i32 0, i32 1, %struct.foo* @f, null} ; [ DW_TAG_variable ] [f] [line 9] [def]
>> +!32 = metadata !{i32 2, metadata !"Dwarf Version", i32 4}
>> +!33 = metadata !{i32 1, metadata !"Debug Info Version", i32 1}
>> +!34 = metadata !{metadata !"clang version 3.5.0 (trunk 203673) (llvm/trunk 203681)"}
>> +!35 = metadata !{i32 9, i32 0, metadata !9, null}
>> +!36 = metadata !{i32 786689, metadata !19, metadata !"this", null, i32 16777216, metadata !37, i32 1088, i32 0} ; [ DW_TAG_arg_variable ] [this] [line 0]
>> +!37 = metadata !{i32 786447, null, null, metadata !"", i32 0, i64 64, i64 64, i64 0, i32 0, metadata !"_ZTS3foo"} ; [ DW_TAG_pointer_type ] [line 0, size 64, align 64, offset 0] [from _ZTS3foo]
>> +!38 = metadata !{i32 0, i32 0, metadata !19, null}
>> +!39 = metadata !{i32 5, i32 0, metadata !19, null}
>> +!40 = metadata !{i32 786689, metadata !13, metadata !"this", null, i32 16777216, metadata !37, i32 1088, i32 0} ; [ DW_TAG_arg_variable ] [this] [line 0]
>> +!41 = metadata !{i32 0, i32 0, metadata !13, null}
>> +!42 = metadata !{i32 5, i32 0, metadata !43, null}
>> +!43 = metadata !{i32 786443, metadata !1, metadata !13, i32 5, i32 0, i32 0, i32 0} ; [ DW_TAG_lexical_block ] [/usr/local/google/home/echristo/foo.cc]
>> +!44 = metadata !{i32 5, i32 0, metadata !13, null}
>> +!45 = metadata !{i32 786689, metadata !22, metadata !"this", null, i32 16777216, metadata !46, i32 1088, i32 0} ; [ DW_TAG_arg_variable ] [this] [line 0]
>> +!46 = metadata !{i32 786447, null, null, metadata !"", i32 0, i64 64, i64 64, i64 0, i32 0, metadata !"_ZTS4base"} ; [ DW_TAG_pointer_type ] [line 0, size 64, align 64, offset 0] [from _ZTS4base]
>> +!47 = metadata !{i32 0, i32 0, metadata !22, null}
>> +!48 = metadata !{i32 1, i32 0, metadata !22, null}
>> +!49 = metadata !{i32 1, i32 0, metadata !28, null}
>>
>>
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