COFF Debug info shows variable at the wrong lexical scope.

[CarlosAlbertoEnciso]

Bugzilla Link	43860
Version	trunk
OS	All
CC	@dwblaikie,@gregbedwell,@JDevlieghere,@jmorse,@walkerkd,@pogo59,@rnk

Extended Description

Given the following test case:

//------------------------------------------------------------
// inlined.cpp
//------------------------------------------------------------

int inlineFunction(int Param) __attribute__((always_inline));
int inlineFunction(int Param) {
  int Var_1 = Param;
  {
    int Var_2 = Param + Var_1;
    Var_1 = Var_2;
  }
  return Var_1;
}

int testInlined(int Param_1, int Param_2) {
  int A = Param_1;
  A += inlineFunction(Param_2);
  return A;
}

//------------------------------------------------------------

Using the following command line options to generate debug info
(DWARF) and (COFF):

clang -c -g -O0 inlined.cpp -o inlined-dwarf.o
clang -c -g -O0 inlined.cpp -o inlined-coff.o -gcodeview --target=x86_64-windows

Looking at the output generated by llvm-dwarfdump and llvm-readobj,
the COFF debug info shows the variable 'Var_2' at the same lexical
scope as the variable 'Var_1' in the 'testInlined' as results of the
function 'inlineFunction' being inlined.

llvm-dwarfdump --debug-info inlined-dwarf.o

[CarlosAlbertoEnciso]

This is the reduced output generated by llvm-dwarfdump:

---

inlined-dwarf.o: file format ELF64-x86-64

.debug_info contents:

DW_TAG_compile_unit

DW_TAG_subprogram
DW_TAG_formal_parameter
DW_AT_abstract_origin (0x00000074 "Param")
DW_TAG_variable
DW_AT_abstract_origin (0x0000007f "Var_1")
DW_TAG_lexical_block
DW_TAG_variable
DW_AT_abstract_origin (0x0000008b "Var_2")

DW_TAG_subprogram
DW_AT_name ("InlineFunction")
DW_TAG_formal_parameter
DW_AT_name ("Param")
DW_TAG_variable
DW_AT_name ("Var_1")
DW_TAG_lexical_block
DW_TAG_variable
DW_AT_name ("Var_2")

DW_TAG_subprogram
DW_AT_name ("testInlined")
DW_TAG_formal_parameter
DW_AT_name ("Param_1")
DW_TAG_formal_parameter
DW_AT_name ("Param_2")
DW_TAG_variable
DW_AT_name ("A")

DW_TAG_inlined_subroutine
  DW_TAG_formal_parameter
    DW_AT_abstract_origin	(0x00000074 "Param")
  DW_TAG_variable
    DW_AT_abstract_origin	(0x0000007f "Var_1") <------ (*)
  DW_TAG_lexical_block
    DW_TAG_variable
      DW_AT_abstract_origin	(0x0000008b "Var_2") <------ (*)

---

(*) Var_1 and Var_2 are at different lexical scopes.

[CarlosAlbertoEnciso]

This is the reduced output generated by llvm-readobj:

outline copy (inlineFunction)

Subsection [
...
GlobalProcIdSym {
Kind: S_GPROC32_ID (0x1147)
...
DisplayName: inlineFunction
LinkageName: ?inlineFunction@@yahh@Z
}
FrameProcSym {
Kind: S_FRAMEPROC (0x1012)
...
}
LocalSym {
Kind: S_LOCAL (0x113E)
...
VarName: Param
}
DefRangeFramePointerRelSym {
...
}
LocalSym {
Kind: S_LOCAL (0x113E)
...
VarName: Var_1 <-- Var_1 ()
}
DefRangeFramePointerRelSym {
Kind: S_DEFRANGE_FRAMEPOINTER_REL (0x1142)
...
}
BlockSym {
Kind: S_BLOCK32 (0x1103) <-- Lexical scope
...
}
LocalSym {
Kind: S_LOCAL (0x113E)
...
VarName: Var_2 <-- Var_2()
}
DefRangeFramePointerRelSym {
Kind: S_DEFRANGE_FRAMEPOINTER_REL (0x1142)
...
}
ScopeEndSym {
Kind: S_END (0x6) <-- End lexical scope
}
ProcEnd {
Kind: S_PROC_ID_END (0x114F)
}
]

(*) Var_1 and Var_2 at different lexical scopes.

[CarlosAlbertoEnciso]

This is the reduced output generated by llvm-readobj:

caller (testInlined)

Subsection [
...
GlobalProcIdSym {
Kind: S_GPROC32_ID (0x1147)
...
DisplayName: testInlined
LinkageName: ?testInlined@@yahhh@Z
}
FrameProcSym {
Kind: S_FRAMEPROC (0x1012)
...
}
LocalSym {
Kind: S_LOCAL (0x113E)
...
VarName: Param_1
}
DefRangeFramePointerRelSym {
...
}
LocalSym {
Kind: S_LOCAL (0x113E)
...
VarName: Param_2
}
DefRangeFramePointerRelSym {
...
}
LocalSym {
Kind: S_LOCAL (0x113E)
...
VarName: A
}
DefRangeFramePointerRelSym {
Kind: S_DEFRANGE_FRAMEPOINTER_REL (0x1142)
...
}
InlineSiteSym {
Kind: S_INLINESITE (0x114D) <-- Lexical scope for inlined function
...
}
LocalSym {
Kind: S_LOCAL (0x113E)
...
VarName: Param
}
DefRangeFramePointerRelSym {
Kind: S_DEFRANGE_FRAMEPOINTER_REL (0x1142)
...
}
LocalSym {
Kind: S_LOCAL (0x113E)
...
VarName: Var_1 <-- Var_1 ()
}
DefRangeFramePointerRelSym {
Kind: S_DEFRANGE_FRAMEPOINTER_REL (0x1142)
...
}
LocalSym {
Kind: S_LOCAL (0x113E)
...
VarName: Var_2 <-- Var_2 ()
}
DefRangeFramePointerRelSym {
Kind: S_DEFRANGE_FRAMEPOINTER_REL (0x1142)
...
}
InlineSiteEnd {
Kind: S_INLINESITE_END (0x114E) <-- End lexical scope inlined function
}
ProcEnd {
Kind: S_PROC_ID_END (0x114F)
}
]
]

(*) Var_1 and Var_2 at the same lexical scope.

[CarlosAlbertoEnciso]

This is the ouput from llvm-diva (tool under development).

llvm-diva --print=scopes,symbols,types inlined-dwarf.o inlined-coff.o --attribute=level,format

Logical View:
[000] {File} 'inlined-dwarf.o' -> ELF64-x86-64

[001] {CompileUnit} 'inlined.cpp'
[002] 2 {Function} inlined 'inlineFunction' -> 'int'
[003] {Block}
[004] 5 {Variable} 'Var_2' -> 'int'
[003] 2 {Parameter} 'Param' -> 'int'
[003] 3 {Variable} 'Var_1' -> 'int'
[002] 2 {Function} extern inlined 'inlineFunction' -> 'int'
[003] {Block}
[004] 5 {Variable} 'Var_2' -> 'int'
[003] 2 {Parameter} 'Param' -> 'int'
[003] 3 {Variable} 'Var_1' -> 'int'
[002] 11 {Function} extern not_inlined 'testInlined' -> 'int'
[003] 13 {InlinedFunction} inlined 'inlineFunction' -> 'int'
[004] {Block}
[005] 5 {Variable} 'Var_2' -> 'int' <-- Var_2 ()
[004] 2 {Parameter} 'Param' -> 'int'
[004] 3 {Variable} 'Var_1' -> 'int' <-- Var_1 ()
[003] 11 {Parameter} 'Param_1' -> 'int'
[003] 11 {Parameter} 'Param_2' -> 'int'
[003] 12 {Variable} 'A' -> 'int'

Logical View:
[000] {File} 'inlined-coff.o' -> COFF-x86-64

[001] {CompileUnit} 'inlined.cpp'
[002] {Function} not_inlined 'inlineFunction' -> 'int'
[003] {Block}
[004] {Variable} 'Var_2' -> 'int'
[003] {Parameter} 'Param' -> 'int'
[003] {Variable} 'Var_1' -> 'int'
[002] {Function} not_inlined 'testInlined' -> 'int'
[003] {Variable} 'A' -> 'int'
[003] {Parameter} 'Param_1' -> 'int'
[003] {Parameter} 'Param_2' -> 'int'
[003] {InlinedFunction} inlined 'inlineFunction' -> 'int'
[004] {Parameter} 'Param' -> 'int'
[004] {Variable} 'Var_1' -> 'int' <-- () Var_1
[004] {Variable} 'Var_2' -> 'int' <-- () Var_2

The logical view for the DWARF debug info, shows 'Var_1' and 'Var_2'
at different lexical scopes:

() Var_1, scope [004]
() Var_2, scope [005]

The logical view for the COFF debug-info, shows 'Var_1' and 'Var_2'
at the same lexical scopes.

() Var_1, scope [004]
() Var_2, scope [004]

[rnk]

Would it be correct to say that the bug is: lexical scopes disappear from codeview after inlining?

There are some conditions under which lexical scopes may be ignored:
https://github.com/llvm/llvm-project/blob/master/llvm/lib/CodeGen/AsmPrinter/CodeViewDebug.cpp#L2754

Perhaps this example hits one of those cases.

[CarlosAlbertoEnciso]

There are some conditions under which lexical scopes may be ignored:
https://github.com/llvm/llvm-project/blob/master/llvm/lib/CodeGen/AsmPrinter/
CodeViewDebug.cpp#L2754

Thanks very much for the link.

For the given case,

https://github.com/llvm/llvm-project/blob/master/llvm/lib/CodeGen/AsmPrinter/CodeViewDebug.cpp#L2769

const DILexicalBlock *DILB = dyn_cast(Scope.getScopeNode());

DILB is null.

From my understanding, the lexical blocks created due to the inlining
are not treated as standard ones and they have been ignored.

[CarlosAlbertoEnciso]

Would it be correct to say that the bug is: lexical scopes disappear from
codeview after inlining?

Yes. That would be a better description for the bug.

[CarlosAlbertoEnciso]

I am just starting to get familiar with the CodeView format and the
main question I have now is: Why the lexical scopes created during
inlining are treated in a different way as in DWARF?