[LLVMdev] Your commit 103140

[Duncan Sands]

Hi Chris,

On 13/03/12 21:11, Chris Lattner wrote:
>
> On Mar 13, 2012, at 8:26 AM, Duncan Sands wrote:
>
>> Hi Chris, your commit 103140 broke PR397 for llvm-gcc (in LLVM 2.9) and
>> dragonegg.
>
> Wow, this is an old patch :).
>
>> In the PR, asm renaming creates two linkonce functions with
>> the same asm name (in the IR they are @"\01lstat64" and "@lstat64".  What
>> used to happen is that they were both output to the assembler file, both
>> with the name lstat64, exactly like GCC does.  The assembler and linker
>> are perfectly happy about this, presumably because the functions have weak
>> linkage.  What happens now is that compilation fails with "label emitted
>> multiple times to assembly file".
>>
>> Do you agree that it is reasonable to support outputting multiple functions
>> with the same name, as long as they have weak linkage?
>
> No, I don't.  I think that an IR module should be required to be well defined and obey the rules.  For GCC/clang (and any other compilers that support things like asm renaming and USER_LABEL_PREFIX), I think it is best for the frontend to not use the "\01" prefix in a case that conflicts with the normal USER_LABEL_PREFIX.  For example, on an _'y system, if asm-renamed to "_foo", the IR name should be just @"foo", not "\01_foo".

I think I agree.  My agreement is helped by noticing that the assembler produced
by gcc for the testcase from PR397 doesn't assemble!  One of my side worries was
that the MC layer wouldn't be able to assemble the assembler produced by gcc if
it contained multiple functions with the same name, but since gas rejects it too
there is no compatibility issue there after all.

Ciao, Duncan.