[LLVMdev] [RFC] NoBuiltin Attribute

[Krzysztof Parzyszek]

On 2/19/2013 1:50 PM, Chris Lattner wrote:
>
> How is this not handled by handling fno-builtin by putting an attribute on the code being compiled?

Regardless of which solution you consider, it is always "putting an 
attribute on the code being compiled", the question is where exactly and 
what we do with it.  I'm opposed to putting the attribute on the 
definitions of the callers of functions indicated with 
-fno-builtin-<something>.

If the user says -fno-builtin-printf, then all callers of printf would 
need to be marked as "nobuiltin".  As your example demonstrates, we 
don't always know the exact set of callers of printf, since there can be 
indirect calls that may only later be resolved to direct calls.

Putting attributes on caller's bodies will pose difficulties during 
link-time inlining, which was also illustrated by your example from 
earlier in this branch of this thread.

If we implement it this way now, we may not be able to change it later, 
especially if we want to have backward compatibility of bitcode (i.e. 
future LLVMs compiling past bitcodes).

-Krzysztof

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