Ricky Zhou 1522333c3c [ThinLTO][DebugInfo] Emit full type definitions when importing anonymous types. (#78461) ...

This fixes some cases of missing debuginfo caused by an interaction
between:


f0d66559ea,
which drops the identifier from a DICompositeType in the module
containing its
vtable.

and


a61f5e3796,
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.

2024-01-18 10:55:30 -08:00

89 KiB

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