Re: __builtin_* expansion to outcalls vs name space issues

[Roland McGrath <roland at hack dot frob dot com>]

> On Tue, 5 Feb 2013, Roland McGrath wrote:
> 
> > What should be the expectation of responsibility here?  On the one hand,
> > it seems vaguely reasonable that __builtin_foobar degenerates to calling
> > foobar.
> 
> Yes, that's expected.  (There is however a known GCC bug where calls may 
> be generated to functions that aren't reserved and without a corresponding 
> __builtin_* call: <http://gcc.gnu.org/bugzilla/show_bug.cgi?id=46926>.  
> But it's always expected that not all __builtin_* calls are expanded 
> inline.)

Certainly it's expected that not all __builtin_* calls are expanded to
instructions not involving a call.  That's a separate issue from whether
any calls the compiler generates implicitly in any fashion ought to be
using symbols outside the most constrained name space.

If any call to __builtin_foobar can be expected sometimes to generate a
call to foobar, then what's the point of having the __builtin_foobar names
in the first place?

> > So, are we wrong for using __builtin_mempcpy in a place where a call to
> > mempcpy is not kosher?
> 
> Yes.  Declaring mempcpy with __asm__ ("__mempcpy") should cause 
> __builtin_mempcpy to generate a call to __mempcpy.

I cannot figure out how to make that happen.  Can you post a patch that
accomplishes this?


Thanks,
Roland