llvm dev - Nov 2012 - [LLVMdev] [RFC] Passing Options to Different Parts of the Compiler Using Attributes

On Nov 19, 2012, at 1:49 PM, Eric Christopher <echristo at gmail.com>
wrote:
> 
> 
> Querying
> --------
> 
> The attributes are attached to the function. It's therefore trivial to
access
> the attributes within the middle- and the back-ends. Here's an example
of how
> attributes are queried:
> 
> Just had a thought, what about compile options that change
alignment/layout/section placement of globals etc? For example the -G
<num> option in gcc that the mips guys will want to support some day
(there are probably better options but this was the first the came to mind).
All of those can be directly represented in LLVM IR today, but if there were a
good reason to, I can see extending attributes to work on globals someday.

-Chris

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On Thu, Nov 22, 2012 at 11:24 AM, Chris Lattner <clattner at apple.com>
wrote:
>
> On Nov 19, 2012, at 1:49 PM, Eric Christopher <echristo at gmail.com>
wrote:
>
>
>
> Querying
>> --------
>>
>> The attributes are attached to the function. It's therefore trivial
to
>> access
>> the attributes within the middle- and the back-ends. Here's an
example of
>> how
>> attributes are queried:
>>
>
> Just had a thought, what about compile options that change
> alignment/layout/section placement of globals etc? For example the -G
<num>
> option in gcc that the mips guys will want to support some day (there are
> probably better options but this was the first the came to mind).
>
>
> All of those can be directly represented in LLVM IR today, but if there
> were a good reason to, I can see extending attributes to work on globals
> someday.
>
I'm a bit worried about this creating an arbitrary line between annotations
that are defined as attributes and annotations that are first-class
keywords in the IR language.  It may become a source of confusion for
people.  If attributes are only applied to functions, the obvious questions
for users is "why do I need to do things differently for functions vs.
globals?"  I'm not saying it's a big issue, but it does seem a bit
inconsistent.  If we're implementing these attributes anyway, why not unify
the handling of annotations on functions and global variables?


>
> -Chris
>
>
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>
>

-- 

Thanks,

Justin Holewinski
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On Nov 22, 2012, at 8:53 AM, Justin Holewinski <justin.holewinski at
gmail.com> wrote:
> On Thu, Nov 22, 2012 at 11:24 AM, Chris Lattner <clattner at
apple.com> wrote:
> 
> On Nov 19, 2012, at 1:49 PM, Eric Christopher <echristo at gmail.com>
wrote:
> 
>> 
>> 
>> Querying
>> --------
>> 
>> The attributes are attached to the function. It's therefore trivial
to access
>> the attributes within the middle- and the back-ends. Here's an
example of how
>> attributes are queried:
>> 
>> Just had a thought, what about compile options that change
alignment/layout/section placement of globals etc? For example the -G
<num> option in gcc that the mips guys will want to support some day
(there are probably better options but this was the first the came to mind).
> 
> All of those can be directly represented in LLVM IR today, but if there
were a good reason to, I can see extending attributes to work on globals
someday.
> 
> I'm a bit worried about this creating an arbitrary line between
annotations that are defined as attributes and annotations that are first-class
keywords in the IR language.  It may become a source of confusion for people. 
If attributes are only applied to functions, the obvious questions for users is
"why do I need to do things differently for functions vs. globals?" 
I'm not saying it's a big issue, but it does seem a bit inconsistent. 
If we're implementing these attributes anyway, why not unify the handling of
annotations on functions and global variables?
I'm not saying I'm opposed to it - I'm saying that it is a
completely different topic than what Bill is proposing.

-Chris

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>
>
> Querying
>> --------
>>
>> The attributes are attached to the function. It's therefore trivial
to
>> access
>> the attributes within the middle- and the back-ends. Here's an
example of
>> how
>> attributes are queried:
>>
>
> Just had a thought, what about compile options that change
> alignment/layout/section placement of globals etc? For example the -G
<num>
> option in gcc that the mips guys will want to support some day (there are
> probably better options but this was the first the came to mind).
>
>
> All of those can be directly represented in LLVM IR today, but if there
> were a good reason to, I can see extending attributes to work on globals
> someday.
>
>
Right, I couldn't think of anything that wasn't handled already, but I
wasn't sure if we wanted this to be a single way of encapsulating
information for globals. No opinion either way :)

-eric
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