[ThinLTO][DebugInfo] Emit full type definitions when importing anonymous types. (#78461)
This fixes some cases of missing debuginfo caused by an interaction
between:
https://github.com/llvm/llvm-project/commit/f0d66559ea345db4b2116cae044aaf3399d7e829,
which drops the identifier from a DICompositeType in the module
containing its
vtable.
and
https://github.com/llvm/llvm-project/commit/a61f5e379675732666744bcba25efbc9922e016a,
which causes ThinLTO to import composite types as declarations when they
have
an identifier.
If a virtual class's DICompositeType has no identifier due to the first
change,
and contains a nested anonymous type which does have an identifier, then
the
second change can cause ThinLTO to output the classes's DICompositeType
as a
type definition that links to a non-defining declaration for the nested
type.
Since the nested anonyous type does not have a name, debuggers are
unable to
find the definition for the declaration.
Repro case:
```
cat > a.h <<EOF
class A {
public:
A();
virtual ~A();
private:
union {
int val;
};
};
EOF
cat > a.cc <<EOF
#include "a.h"
A::A() { asm(""); }
A::~A() {}
EOF
cat > main.cc <<EOF
#include "a.h"
int main(int argc, char **argv) {
A a;
return 0;
}
EOF
clang++ -O2 -g -flto=thin -mllvm -force-import-all main.cc a.cc
gdb ./a.out -batch -ex 'pt /rmt A'
```
The gdb command outputs:
```
type = class A {
private:
union {
<incomplete type>
};
}
```
and dwarfdump -i a.out shows a DW_TAG_class_type for A with an
incomplete union
type (note that there is also a duplicate entry with the full union type
that
comes after).
```
< 1><0x0000001e> DW_TAG_class_type
DW_AT_containing_type <0x0000001e>
DW_AT_calling_convention DW_CC_pass_by_reference
DW_AT_name (indexed string: 0x00000007)A
DW_AT_byte_size 0x00000010
DW_AT_decl_file 0x00000001 /path/to/./a.h
DW_AT_decl_line 0x00000001
...
< 2><0x0000002f> DW_TAG_member
DW_AT_type <0x00000037>
DW_AT_decl_file 0x00000001 /path/to/./a.h
DW_AT_decl_line 0x00000007
DW_AT_data_member_location 8
< 2><0x00000037> DW_TAG_union_type
DW_AT_export_symbols yes(1)
DW_AT_calling_convention DW_CC_pass_by_value
DW_AT_declaration yes(1)
```
This change works around this by making ThinLTO always import full
definitions
for anonymous types.
llvm-project
1522333c - [ThinLTO][DebugInfo] Emit full type definitions when importing anonymous types. (#78461)
