[Dwarf-discuss] Re: Dwarf2 Beginner's Question: Pointer variable...

Ron 603-884-2088 brender
Wed Jun 15 08:20:58 GMT 2005

>>>>Ron 603-884-2088 said:
> > 
> > The lack of a DW_AT_location attribute on the DIE for p_int
> > indicates that it has no address. That is, it was "optimized
> > away". In this example, value propagation might well move the
> > address of bbb directly into the point of use without ever
> > allocating a place specifically for p_int.
> > 
>Does this mean these two lines 
>  p_int = &bbb;
>  printf(..., p_int);
>can be optimized into the following one line?
>  printf(..., &bbb )

Absolutely possible, even likely if that is the only use of p_int.

>In this case, is it possible to determine the register of '&bbb'
>from the DWARF output?
>I was hoping that the DW_AT_location of 'p_int' would still be the register of 
>the '&bbb' even after this 'optimized away' step.

It is almost surely impossible to determine the register holding
'&bbb' from the DWARF info. That location would likely be a parameter
passing location, in this example, and unrelated to an user variable.
This is just like

   print(..., x+5 )

where the result of evaluating the expression 'x+5' will end up in
that same parameter passing location, which is not related to whatever
location might hold the value of x.


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