[DebugInfo] -fno-eliminate-unused-debug-types doesn't apply to nested enums

[pogo59]

Given the following source (from issue 63999):

struct Type {
    enum { Unused };
    int value = 0;
};
int main() {
    Type t;
    return t.value;
}

The enumeration type isn't used anywhere, so by default the DWARF doesn't contain a description of the unused enum, which is fine.

Normally, an unused type can be emitted by adding -fno-eliminate-unused-debug-types however that seems not to apply to unused enums. It should.

[llvmbot]

@llvm/issue-subscribers-debuginfo

[dwblaikie]

Seems to work with non-nested enums, at least:

$ cat enum.cpp
enum E { A };
enum { B };
struct t1 { enum C { X }; };
void f1() { }
$ clang++-tot -fno-eliminate-unused-debug-types enum.cpp -g -c && llvm-dwarfdump-tot enum.o | grep "DW_TAG\|DW_AT_name"
0x0000000c: DW_TAG_compile_unit
              DW_AT_name        ("enum.cpp")
0x00000023:   DW_TAG_enumeration_type
                DW_AT_name      ("E")
0x0000002c:     DW_TAG_enumerator
                  DW_AT_name    ("A")
0x00000030:   DW_TAG_base_type
                DW_AT_name      ("unsigned int")
0x00000034:   DW_TAG_enumeration_type
0x0000003c:     DW_TAG_enumerator
                  DW_AT_name    ("B")
0x00000040:   DW_TAG_structure_type
                DW_AT_name      ("t1")
0x00000046:   DW_TAG_subprogram
                DW_AT_name      ("f1")