[LLVMdev] #APP/#NOAPP

[Eric Christopher]

On Thu, May 16, 2013 at 3:17 AM, reed kotler <rkotler at mips.com> wrote:
> On 05/15/2013 10:53 PM, Richard Smith wrote:
>
> On Mon, May 6, 2013 at 9:09 AM, reed kotler <rkotler at mips.com> wrote:
>>
>> On 05/06/2013 08:51 AM, Rafael Espíndola wrote:
>>>>
>>>> It's working fine just that it's ugly to see those APP/NOAPP markers.
>>>
>>> Inline assembly is inline assembly. It has the semantics defined in
>>> the IL documentation and should all be treated uniformly.
>>>
>>> I guess I would be OK with unconditionally removing those comments (I
>>> don't see a lot of value in them) or having different verbosity levels
>>> for the asm output.
>>>
>>> What we should never have is a "if (this asm was created by llvm
>>> itself)".
>>
>> I would like to see a method in asm printer which turns on/off these
>> comments.
>> It's trivial to add and use but I can't put back to this code without
>> permission so there is no point to write the patch if nobody will approve
>> it.
>>
>> Then I could call that method when I'm processing  compiler generated
>> stubs that have inline
>> assembly.
>>
>> Traditionally these comments are used in gcc so that when you look at
>> assembly code, you can tell which was generated by the compiler and which
>> was inline assembly the user created.
>
>
> This does not appear to be the case. As far as I can discern from the
> available documentation, #APP and #NOAPP are pragmas which inform the
> assembler's preprocessor whether it's in "application mode" (where it needs
> more expensive tokenization rules, including comment-stripping and the like)
> or whether it's in "processing compiler output mode" (where it can skip all
> that stuff).
>
> That these pragmas *also* mark where the user's inline asm ended up seems to
> just be a happy coincidence.
>
>
> I've read that too in the docs but I don't think it has any meaning here
> because I'm emitting the same kind of code that gcc emits; so I should not
> need them. Possible it slows down compilation by some
> tiny amount here.
>
> It does not hurt for me to have the APP/NO_APP markers; I just don't like to
> see them in the .s file.
> As Jim Grosbach and others have noted, if I move the inline asm generation
> to another place, I won't get those. It's just because the compiler is doing
> what I user would do that I'm getting them.
>

I would like to re-emphasize that you're not generating inline asm (or
well you shouldn't be) - you're generating a call stub and
interworking code between two ISAs. It's a very important distinction.

-eric