[PATCH] analysis of global statics and removal associated vdefs and vuses

[Paolo Bonzini]

> However, once we get the aliasing really working, we may find that this 
> is a significant performance problem in real (i.e. non bench marking) 
> code. In real code, significant number of functions have calls to printf 
> and because of this extension a call to any function that calls printf, 
> must clobber every static variable.  Without the extension, the calls to 
> printf (assuming we could properly annotate them,) would not effect the 
> clobber sets at all. 

I wonder, how many application have inner loops that call printf or 
sprintf?!?  And even if there were, I doubt that not clobbering all 
static variables around printf is going to give any real advantage.  So 
this glibc extension is not a problem.

Most examples of functions that are amenable to this optimization *and* 
are used in inner loops, will already be pure; and it is true even 
without taking glibc extensions into account, that callbacks will hinder 
this optimization by not allowing to make the function pure (think bsearch).

Paolo