Fixed by commit 4262a95979771a18d1030d3ed544af28442fea43 on
hjl/lto-mixed branch.

With ld.dk (ld.bfd with patch <http://gcc.gnu.org/ml/gcc/2011-02/msg00003.html>):

$ nm prog
[...]
080483a2 T bar
0804838e t bar.1988
[...]

`bar' is not needed.

ld.hjl --cref gives "symbol `...' missing from main hash table" errors and prints garbage to stdout.

(In reply to comment #2)
> With ld.dk (ld.bfd with patch
> <http://gcc.gnu.org/ml/gcc/2011-02/msg00003.html>):
> 
> $ nm prog
> [...]
> 080483a2 T bar
> 0804838e t bar.1988
> [...]
> 
> `bar' is not needed.

Yes, although note that it's just a symbol, not the actual function, and the program is correct.  There are left-over stray symbols from the LTO symtabs in the final exe, when ltrans decides to remove a function that was present in the IR object file.  I'll see if I can find a way to remove them, but as far as I know, the only potential harm they can do is that if they have non-default visibility, we get PR12277.

(In reply to comment #3)
> ld.hjl --cref gives "symbol `...' missing from main hash table" errors and
> prints garbage to stdout.

It is fixed by commit 9de3db977572464608623fe46cd7b39c66d4c1eb on
hjl/lto-mixed branch.

Works in 2.23 and tracked by "LTO 13" test.