[llvm-dev] [DebugInfo]: Representing constants in debug-info

[Tomar, Sourabh Singh via llvm-dev]

[AMD Public Use]

Hi Everyone,

Is there a way of representing **constants** in LLVM debug-info ? Languages such as FORTRAN has constants

i.e, consider the following Fortran snippet
[...]
Module foo
Integer, parameter :: bar = 200 ! Constant
End module foo
[...]

A front-end may choose to emit as Global Constant in LLVM IR as:
[...]
@bar.. = internal constant i32 200

A naïve attempt to represent it as GlobalVariable(or constant) as
[...]
!7 = !DIGlobalVariableExpression(var: !8, expr: !DIExpression(DW_OP_consts, 200))
!8 = distinct !DIGlobalVariable(name: "bar", scope: !2, file: !3, line: 3, type: !9, isLocal: false, isDefinition: true)

This will materialize in DWARF as:
0x0000004a:     DW_TAG_variable
                  DW_AT_name    ("bar")
                  ...
                 DW_AT_location        (DW_OP_addr 0x2007d4, DW_OP_consts +200)  // This is incorrect, pointing to data section
[...]

Gfortran is representing this as: **DW_TAG_constant**
0x00000055:     **DW_TAG_constant**
                  DW_AT_name    ("bar")
                 ...
                  DW_AT_type    (0x0000006a "const integer(kind=4)")
                  DW_AT_external        (true)
                  DW_AT_const_value     (0xc8)

Do we have Metadata analog of (DW_TAG_constant) ? I think the primary question here is to how represent this ?

Any inputs appreciated!

Thanks.. much!
Sourabh.
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