[llvm-commits] [llvm] r168704 - in /llvm/trunk: lib/CodeGen/AsmPrinter/AsmPrinter.cpp test/CodeGen/ARM/2010-12-15-elf-lcomm.ll test/CodeGen/ARM/elf-lcomm-align.ll

[Rafael Espíndola]

> What do you mean by "implement lcomm"?  There's two separate issues:

Correct.

> 1. How should the AsmParser interpret a ".lcomm" directive in an
>    assembler source file?
>
> 2. How should EmitLocalCommonSymbol be implemented, either in the
>    MCAsmStreamer or in the MCELFStreamer?
>
> As to 1., if we want to achieve full compatibility with gas, we'd have
> to implement the precise rules (platform-specific) default alignment
> rules gas uses.  This would be done in AsmParser::ParseDirectiveComm,
> I assume.  [ But this doesn't matter either way for the case I was
> fixing, which is generating code for a compiler-generated global
> variable via AsmPrinter::EmitGlobalVariable. ]

IMHO this is desirable. Switching to or from the integrated assembly
to the system external one should not change the meaning for the
program. In particular, it would probably make issues like this easier
to fix.

> As to 2., since EmitLocalCommonSymbol always gets a ByteAlignment
> argument, it is arguably correct to precisely honor that argument
> in the MCELFStreamer case.  The MCAsmStreamer case is the difficult
> one on platforms where the native assembler doesn't support an
> alignment argument with its .lcomm directive.  In this case, it is
> impossible to implement EmitLocalCommonSymbol precisely, except
> for very specific values of ByteAlignment.  This means that in
> almost all cases, it would still be incorrect for EmitGlobalVariable
> to call EmitLocalCommonSymbol, and since there is no particular
> advantage to doing so in the rare cases where it would be correct,
> the patch I checked in still seems the best solution ...

So it is the native assembler that was producing a broken binary? If
so your patch is correct, I had understood the other way: That codegen
was assuming the behavior of the external one and so the integrated
one was producing broken binaries.

> Bye,
> Ulrich
>

Cheers,
Rafael