[LLVMdev] [RFC] NoBuiltin Attribute

[Duncan Sands]

Hi Chris,

On 19/02/13 03:08, Chris Lattner wrote:
> On Feb 18, 2013, at 5:01 PM, Chandler Carruth <chandlerc at google.com
> <mailto:chandlerc at google.com>> wrote:
>>
>>     > In the context of LTO, it makes sense for the attribute to be on
>>     function bodies, not on prototypes.
>>     >
>>     Yeah, I noticed that after sending this patch. I modified it to check the
>>     function CI is in for that attribute. Once we have support for the
>>     `-fno-builtin-FUNCTION' flag, I expect the attribute to look something
>>     like this:
>>
>>             "no-builtin-functions" = "puts,foo,bar"
>>
>>
>> I wonder... why not attach the no-builtin attribute to the call instruction?
>> It seems like that would avoid the need of a string attribute altogether,
>> having the frontend match up calls to specific functions which should not be
>> considered calls to builtin functions?
>
> How does this work?  If I build with -fno-builtin-fputs, why would an attribute
> be added to a call to printf?

there are two parts to libcall simplification:

   (1) recognizing that a call is to a function we understand (eg: printf);
   (2) generating a new call to a library function (eg: synthesizing memcpy).

Plunking an attribute on a call to say "this isn't the printf function you know"
seems kind of useful to me, even if it only takes care of (1).

Ciao, Duncan.