Extra implicit 'this' parameter entry when emitting a DW_TAG_subprogram with an explicit object parameter

[Michael137]

struct Foo {                      
    template <class Self>         
    void func(this Self&& self) {}
};                                
                                  
int main() {                      
    Foo{}.func();                 
}                                 

The above will currently produce following DWARF:

DW_TAG_structure_type
  DW_AT_name      ("Foo")
  DW_TAG_subprogram
    DW_AT_name    ("func<Foo>")
    DW_AT_declaration     (true)
    DW_AT_external        (true)
    DW_TAG_template_type_parameter
      DW_AT_type  (0x0000000000000034 "Foo")
      DW_AT_name  ("Self")
    DW_TAG_formal_parameter
      DW_AT_type  (0x0000000000000051 "Foo *")
      DW_AT_artificial    (true)
    DW_TAG_formal_parameter
      DW_AT_type  (0x0000000000000056 "Foo &&")
    NULL
  NULL

DW_TAG_subprogram
  DW_AT_specification     (0x000000000000003a "_ZNH3Foo4funcIS_EEvOT_")
  DW_TAG_formal_parameter
    DW_AT_location        (DW_OP_fbreg +8)
    DW_AT_name    ("self")
    DW_AT_type    (0x0000000000000056 "Foo &&")
  DW_TAG_template_type_parameter
    DW_AT_type    (0x0000000000000034 "Foo")
    DW_AT_name    ("Self")

Note how the declaration of func has 2 DW_TAG_formal_parameter entries, one for the explicit object parameter self and (erroneously) another for the implicit object parameter this. The definition only has the explicit object parameter.

Looks like CGDebugInfo::getOrCreateInstanceMethodType would need to account for the fact that an explicit object parameter may exist, in which case we don't want to create the implicit artificial this parameter.

[llvmbot]

@llvm/issue-subscribers-clang-codegen

Author: Michael Buch (Michael137)

``` struct Foo { template <class Self> void func(this Self&& self) {} };

int main() {
Foo{}.func();
}

The above will currently produce following DWARF:

DW_TAG_structure_type
DW_AT_name ("Foo")
DW_TAG_subprogram
DW_AT_name ("func<Foo>")
DW_AT_declaration (true)
DW_AT_external (true)
DW_TAG_template_type_parameter
DW_AT_type (0x0000000000000034 "Foo")
DW_AT_name ("Self")
DW_TAG_formal_parameter
DW_AT_type (0x0000000000000051 "Foo *")
DW_AT_artificial (true)
DW_TAG_formal_parameter
DW_AT_type (0x0000000000000056 "Foo &&")
NULL
NULL

DW_TAG_subprogram
DW_AT_specification (0x000000000000003a "ZNH3Foo4funcIS_EEvOT")
DW_TAG_formal_parameter
DW_AT_location (DW_OP_fbreg +8)
DW_AT_name ("self")
DW_AT_type (0x0000000000000056 "Foo &&")
DW_TAG_template_type_parameter
DW_AT_type (0x0000000000000034 "Foo")
DW_AT_name ("Self")

Note how the declaration of `func` has 2 `DW_TAG_formal_parameter` entries, one for the explicit object parameter `self` and (erroneously) another for the `implicit` object parameter `this`. The definition only has the explicit object parameter.

Looks like `CGDebugInfo::getOrCreateInstanceMethodType` would need to account for the fact that an explicit object parameter may exist, in which case we don't want to create the implicit artificial `this` parameter.
</details>

[llvmbot]

@llvm/issue-subscribers-debuginfo

Author: Michael Buch (Michael137)

``` struct Foo { template <class Self> void func(this Self&& self) {} };

int main() {
Foo{}.func();
}

The above will currently produce following DWARF:

DW_TAG_structure_type
DW_AT_name ("Foo")
DW_TAG_subprogram
DW_AT_name ("func<Foo>")
DW_AT_declaration (true)
DW_AT_external (true)
DW_TAG_template_type_parameter
DW_AT_type (0x0000000000000034 "Foo")
DW_AT_name ("Self")
DW_TAG_formal_parameter
DW_AT_type (0x0000000000000051 "Foo *")
DW_AT_artificial (true)
DW_TAG_formal_parameter
DW_AT_type (0x0000000000000056 "Foo &&")
NULL
NULL

DW_TAG_subprogram
DW_AT_specification (0x000000000000003a "ZNH3Foo4funcIS_EEvOT")
DW_TAG_formal_parameter
DW_AT_location (DW_OP_fbreg +8)
DW_AT_name ("self")
DW_AT_type (0x0000000000000056 "Foo &&")
DW_TAG_template_type_parameter
DW_AT_type (0x0000000000000034 "Foo")
DW_AT_name ("Self")

Note how the declaration of `func` has 2 `DW_TAG_formal_parameter` entries, one for the explicit object parameter `self` and (erroneously) another for the `implicit` object parameter `this`. The definition only has the explicit object parameter.

Looks like `CGDebugInfo::getOrCreateInstanceMethodType` would need to account for the fact that an explicit object parameter may exist, in which case we don't want to create the implicit artificial `this` parameter.
</details>